1995 Movement & Dispersal Research

Black Cutworm, Agrotis ipsilon (Hufnagel), Moth Captures at Selected Texas and Missouri Sites, 1995

A. J. Keaster, R. D. Parker, K. Ensey, A. Knutson, C. Patrick, J. R. Raulston, C. Sansone, K. E. Schwindt, G. Cronholm, and C. Sorenson

A spring and autumn migration of black cutworm, Agrotis ipsilon (Hufnagel) in the U. S. has been documented (Carey and Beegle 1975, Clement et al. 1985, Domino et al. 1983, Hutchins et al. 1988, Kaster and Showers 1982, Showers et al. 1986; Showers et al. 1989a, 1989b; Showers et al. 1993, Williams 1926, Williams et al. 1942). However, the sources for spring migratory populations have not been delineated. Showers et al. (1986) have suggested that possible areas of source populations include a triangular region from the southeastern tip of Missouri to southeastern Georgia and westward to the Rio Grande Valley. The most likely sources within the confines of the U.S. appear to be areas within the state of Texas (Keaster et al., accepted by Southwestern Entomologist).

Materials and Methods

In 1995, Texas 70-50-cm cone traps (Hartstack et al. 1979) were operated for the third year in seven major regions of Texas. Traps were monitored at least three times each week and daily when possible from early January through May. All traps were baited with a rubber septum (Scentry Inc.) impregnated with black cutworm sex pheromone (3:1 ratio of Z-7 dodecenyl acetate and Z-9-tetradecenyl acetate). In 1995, cone traps were monitored at two Missouri locations (Boone and Pemiscot Counties) from early March through June. In addition, wing-style traps (26 x 20 x 11 cm [Scentry Inc., Buckeye, Arizona]) were monitored March-June at nine other sites in Missouri, including most of the regions where corn is produced.

Results and Discussion

Texas

Figures 1 through 5 provide a summary of black cutworm captures in Texas as weekly totals for January through May 1995. Figures 6 through 9 are summaries of cone trap captures at two Missouri sites (Boone and Pemiscot Counties) and wing trap captures at the nine other Missouri sites. Weekly totals are highlighted when 10 or more black cutworm moths were captured. Ten moths is an arbitrary number selected to indicate black cutworm activity and is the number of moths normally used to signify an intensive cone trap capture over a three-day period for IPM decisions.

It is apparent from the weekly summary for January presented in Figure 1 that moth activity was greatest for the Weslaco trapping site. During weeks 3 and 4, moths were also captured at Corpus Christi and Austwell.

During February, captures of 10 or more moths were recorded at Weslaco (10 moths) during week 1 and at Dallas (32 moths) and Plainview (11 moths) during week 4. During March, 20 moths were recorded from Corpus Christi during week 1; however, during weeks 2 through 4 the majority of the captured moths were from the trapping sites in the northern part of the state. In April and May, the greatest moth captures were still recorded for the northern portion of the state, and very high captures were reported from the Dallas site during weeks 1 and 4 in April, and 103 moths were recorded from Plainview during week 2 in April. Moth catches in the Dallas area remained relatively high during May.

It is interesting to note that 11 moths were captured at the Amarillo site during week 2 of May in 1994, and 14 moths were recorded from this site in 1995 during week 4 of May in 1995.

Missouri

In Missouri, the Pemiscot and Boone County sites were monitored with cone traps, and the remaining nine sites were monitored with wing traps. Traps were not operational until the second week of March. Captures in March were low until week 4 when intense captures (10 or more moths) were recorded from three sites. In April, captures were recorded from all of the reporting locations, but the highest captures occurred during weeks 2 and 3. In May, the greatest statewide captures occurred during week 2. High captures were recorded from Boone County (cone trap) during all 4 weeks in May and continued through June.

In general, the initial captures of moths in Missouri were associated with the first intense captures of moths in northern Texas. This association of captures in Missouri and northern Texas continued through the cessation of trap monitoring in Texas (May 31).

Data collected during the three years of this study (1993 through 1995) suggest that black cutworm moths in Texas migrate beginning in February from the southern regions to the north-central area. These limited data also suggest that this north-central area may be the "loading dock" and "launching pad" for moths that migrate into the Midwest during the spring months.

Acknowledgment

The authors wish to acknowledge the assistance of Ms. Maureen O'Day, Don Huckla, and Missouri extension personnel in providing the Missouri wing-trap data.

Literature Cited

Carey, J. R. and C. C. Beegle. 1975. Black cutworm overwintering investigations in infested screenhouses. Entomol. Soc. Amer., No. Cent. Br. Proc. 30:59-65.

Clement, S. L., L. V. Kaster, W. B. Showers and R. S. Schmidt. 1985. Seasonal changes in the reproductive condition of female black cutworm moths (Lepidoptera: Noctuidae). J. Kansas Entomol. Soc. 58:62-68.

Domino, R. P., W. B. Showers, S. E. Taylor and R. H. Shaw. 1983. Spring weather pattern associated with suspected black cutworm moth (Lepidoptera: Noctuidae) introduction to Iowa. Environ. Entomol. 12:1863-1871.

Hartstack, A. W., J. A. Witz and D. R. Buck. 1979. Moth traps for the tobacco budworm. J. Econ. Entomol. 72:519-522.

Hutchins, S. H., R. B. Smelser and L. P. Pedigo. 1988. Insect migration: atmospheric modeling and industrial application of an ecological phenomenon. Bull. Entomol. Soc. Amer. 34:9-15.

Kaster, L. V. and W. B. Showers. 1982. Evidence of spring immigration and autumn reproductive diapause of the adult black cutworm in Iowa. Environ. Entomol. 11:306-312.

Keaster, A. J., J. A. Grundler, M. A. Jackson, M. D. McCorcle, W. B. Showers, M. O. Way, R. D. Parker, J. B. Giezentanner, K. Schwindt and J. R. Raulston. Occurrence and winter activity of black cutworm moths along the Texas Gulf Coast. Accepted by Southwestern Entomologist.

Showers, W. B., J. J. Keaster, J. F. Robinson, and T. J. Riley. 1986. Evidence of migration of the black cutworm adult into the U.S. Corn Belt. USDA ARS-43:10-24.

Showers, W. B., R. B. Smelser, A. J. Keaster, F. Whitford, J. F. Robinson, J. D. Lopez and S. E. Taylor. 1989a. Recapture of marked black cutworm black cutworm (Lepidoptera: Noctuidae) males after long-range transport. Environ. Entomol. 18:447-458.

Showers, W. B., F. Whitford, R. B. Smelser, A. J. Keaster, J. F. Robinson, J. D. Lopez and S. E. Taylor. 1989b. Direct evidence for meteorologically driven long-range dispersal of an economically important moth. Ecology 70:987-992.

Showers, W. B., A. J. Keaster, F. R. Raulston, W. H. Hendrix III, M. E. Derrick, M. D. McCorcle, J. F. Robinson, M. O. Way, M. J. Wallendorf, and J. L. Goodenough. 1993. Mechanism of southward migration of a noctuid moth (Agrotis ipsilon [Hufnagel]): A complete migrant. Ecology 74: 2303-2314.

Williams, C. B. 1926. Further records of insect migration. Trans. R. Entomol. Soc. London 74:193-202.

Williams, C. B., F. Cockbill, M. E. Gibbs and J. A. Downes. 1942. Studies in the migration of Lepidoptera. Trans. R. Entomol. Soc. London 92:101-283.

Publications

Keaster, A. J.,. J. A. Grundler, M. A. Jackson, M. D. McCorcle, W. B. Showers, M. O. Way, R. D. Parker, J. B. Giezentanner, K. Schwindt, and J. R. Raulston. 1995. Occurrence and winter activity of black cutworm moths along the Texas Gulf Coast, 1987-1991. Southwestern Entomologist, Suppl. No. 18, Sept. 1995: 135-154.

Showers, W. B., A. J. Keaster, J. R. Raulston, J. L. Goodenough, W. H. Hendrix, III, M. O. Way, and J. F. Robinson. 1995. Seasonal migration of the black cutworm. Southwestern Entomologist, Suppl. No. 18, Sept. 1995: 119-134.

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Wheat Curl Mite Dynamics and Wheat Streak Mosaic Epidemiology in Volunteer Wheat

Gary L. Hein and Talat Mahmood

University of Nebraska, Panhandle Res. & Ext. Center Scottsbluff, NE

Wheat streak mosaic is the most damaging disease in wheat in the Central High Plains. Over the last several years regional epiphytotics have developed in Nebraska, Kansas, Colorado, Montana and North and South Dakota. In addition, infections occur on a smaller scale nearly every year. The disease seems to be increasing in occurrence over the last decade. This disease situation is complicated by the recent occurrence of a new disease, High Plains disease, which has just recently been found to be transmitted by the wheat curl mite. Wheat streak mosaic virus is a persistent virus that is transmitted by the wheat curl mite, an eriophyid mite, Aceria tosichella Keifer. The virus becomes a problem when the mite is able to over-summer on volunteer or other alternate hosts and move into fall planted wheat as it emerges in the fall. The mite because of its small size relies on wind to move it from plant to plant or field to field. Current recommendations to eliminate volunteer wheat and delay planting date reduce the potential for wheat streak mosaic, but do not always prevent the occurrence of severe infections. These recommendations in being straight forward and simple reflect the current state of knowledge of wheat streak mosaic virus and its eriophyid vector. These simple recommendations are no longer adequate for today's growers to make complicated decisions that will help reduce the risk of losses from wheat streak mosaic. Little is known about the factors that influence mite movement. Important factors may include the dynamics of mite populations on volunteer wheat and other alternate hosts, condition of the host plants, weather factors and perhaps several others. Mites show a non- preference to certain wheat varieties (e.g. TAM 107), but the impact of this "resistance" on mite dynamics is not known. The goal of this research is to increase the knowledge base about the wheat curl mite dynamics and wheat streak mosaic virus epidemiology so that improved management decisions can be made concerning the need to control secondary volunteer wheat and/or delay winter wheat planting time. We are trying to address the following objectives through our research:

1. Determine the effect of resistant and susceptible varieties on wheat curl mite dynamics and wheat streak mosaic epidemiology in volunteer wheat. In 1994 and 1995 plantings of a resistant (mite non-preference) and a susceptible variety were made at 2, 4, and 6 weeks post harvest to simulate volunteer emerging at various times. These planting were monitored for wheat curl mites through the summer and fall. In both years of this study mite populations were very slow to build through the hot part of summer (August), but as temperatures began to moderate and rainfall was slightly more common, the populations of mites began to build. Populations in the two varieties differed with up to 10-20 times more mites in the susceptible variety than the resistant variety. Also, mite populations in the earlier emerged wheat built to much higher levels than those emerging later in the summer. Populations in 1994 were quite low and monitoring of adjacent winter wheat did not show significant infections of wheat streak mosaic. Populations in 1995 were higher than in 1994, but remain low throughout August due to the very hot and dry weather. Currently samples are being evaluated for virus infection rates. It appears that under adverse environmental conditions mite populations are slow to build through the later part of summer. We plan to continue this study to hopefully observe mite buildup under more favorable conditions.
2. Determine wheat curl mite survival and wheat streak risk from chemical and mechanical volunteer control. A study was conducted in 1994 to determine the impact of herbicides (Roundup and Cyclone) and tillage (disc and blade plow) on mite populations and subsequent ability to transmit virus to adjacent wheat planting. Plots were established in areas of moderate mite populations, and on the date that the volunteer was controlled wheat was planted adjacent to the plots. Mite populations were monitored in the volunteer plots and in the adjacent wheat. Virus infection levels were monitored in the adjacent wheat plantings. The tillage treatments rapidly reduced the mite populations to very low levels and also reduced the infection levels in adjacent wheat to 4% (blade plow) and 8% (disk). Because the volunteer was stressed by hot and dry conditions at the time of treatment, the plants were slow to respond to the herbicide treatments. Cyclone, a rapid acting burn-down herbicide, did not reduce mite populations for about 2 weeks. This reduction did not result in a reduced incidence of virus infection (18%) compared to the untreated check (24%). The Roundup treatment stressed the plants but did not kill them. In addition, it did not reduce the mite populations at any sampling date when compared to the check. However, the virus infection rate did increase to 38% for the Roundup treatments. This indicated that the mites were responding to the Roundup treatments and more likely to move off the plants even though the plants were not dying. This study was repeated in 1995 and the results are being summarized. The results indicate that the movement levels of the mites may be in part a response to the condition of the host plant. Attempts to control volunteer with Roundup should only be made well ahead of the emergence of the subsequent crop.
3. Establish the level of isolate variability of wheat streak mosaic across Nebraska. The amount of isolate variability through a large region may provide clues to the ability of the mite to move over longer distances. If virus isolates are isolated geographically it is not likely that extensive mite movement occurs. However, if major isolates are common in all areas, longer range movement of the mite is more likely. Sampling in 1994 and 1995 along with PCR analysis indicated that there were 3 main isolates found in all areas sampled. This indicates a good deal of mixing of the populations of mites and the viruses that they carry. However, an additional 33 other types were identified based on banding patterns. Many of these types were found only at one or two locations, but their incidence at any one location was also very low. The data from this study is inconclusive, but indicates the possibility of long range movement of the mites and mixing of the virus populations. Additional isolate sampling will need to be done to further delineate the occurrence of these less common isolates. Further study as to the virulence and plant response to the various isolates needs to be done.

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The 1995 Tobacco Blue Mold Epidemic in the U.S.

C.E. Main, J.M. Davis, Thomas Keever and T.A. Melton

Departments of Plant Pathology and Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, NC, 27695-7616,USA.

Blue mold is a foliar disease of tobacco caused by the obligately parasitic fungus Peronospora tabacina. The pathogen does not overwinter in the U.S. and must be introduced each year from the Caribbean and Latin America. A widescale and serious epidemic of blue mold started on March 31, 1995 with the first report in Alachua County, Florida. This was the most serious epidemic of blue mold since the infamous epidemic of 1979. The epidemic developed slowly in the southern flue-cured production area of Florida and Georgia in late April and May. A general shortage of tobacco transplants in the southeast resulted in illegal movement of infested plants from the infected areas of Georgia to the mid-Atlantic burley and flue-cured areas. Both windborne and transplant-borne dissemination resulted in sporadic outbreaks of blue mold in the more northern tobacco areas. A protracted period of cloudy, wet weather in June resulted in a general epidemic. The epidemic in burley was most serious, but slowed in July and August as a result of dry weather. Localized epidemics occurred in burley through mid-August as scattered rains occurred in western Kentucky and southern Indiana. Adding to the problem was the early occurrence and continuing presence of a metalaxyl-insensitive strain of P. tabacina. Blue mold was reported late in the season on tobacco in Maryland, Pennsylvania and Ontario, Canada. Missouri, Wisconsin and Connecticut did not report blue mold during 1995.

Meteorological Conditions Associated with the 1995 Epidemic

The weather situation during the spring and summer of 1995 greatly influenced the spread and severity of blue mold. The mid-Atlantic and southeast states were mostly dry in the spring with the exception of southern Georgia and Florida, where heavy amounts of rain occurred. May rainfall in the southern states region was also below average. A number of frontal systems passed through the area, bringing showers to various locales, but there were no persistent events of note. However, in late May the situation changed dramatically. The steering currents of the jet stream became located far north and south of the southeast U.S. A large area of low pressure in the upper levels settled over the region and began drifting, first hovering over the Southeast in late May through mid-June, then meandering farther north over the mid-Atlantic states in late June and early July. This pool of cool air aloft created a regime of general instability over the entire region. Surface systems that came into the area from the west or north often slowed down and gradually dissipated rather than passing through quickly. The result was one of the wettest June's on record in the Southeast. There was at least a chance of showers or storms every day for weeks. Conditions were persistently warm and humid. Cloudiness and afternoon or evening showers were common. This general weather pattern remained until the second week of July, after which a much drier situation evolved.

The correlation of these weather events with the spread and development of blue mold is striking. Blue mold established itself in Florida and Georgia in late April and May where rainfall provided adequate moisture. During most of May there was some slight incursions of the disease into the flue-cured and burley production areas. The airborne introductions were associated with the favorable weather conditions near the approaching frontal systems. However, as it was mostly sunny and dry, infection and disease spread was limited. Late May and June presented a near best-case scenario for the spread and development and worst-case scenario of blue mold damage. Warm, humid days with frequent showers or storms provided a rich environment in which the pathogen could flourish. Rain-soaked soils and standing water helped keep ground-level humidities high, aiding sporulation and infection. Fog contributed to favorable conditions, especially in the burley production regions in the mountains. As the upper-level low drifted north into the mid-Atlantic states towards the latter half of June, heavy precipitation occurred in the Virginias and adjacent states. Areas such as Maryland, Ohio, and Pennsylvania, which had previously been at somewhat lower risk, reported blue mold in July as favorable disease conditions evolved in that region. After the first week of July the steering currents finally changed, and drier weather moved into the region. This resulted in a dramatic slowdown in the disease spread. Only smaller-scale outbreaks were observed from mid-July and beyond.

For the latest information see: http://www.ces.ncsu.edu/depts/pp/bluemold/

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Airborne Spores of Wheat Pathogens

Leonard Francl

Department of Plant Pathology, North Dakota State University, 701/231-7079 Fax 701/231-7851

Airborne spores of wheat pathogens were monitored with a Burkhard spore sampler during growth of a hard red spring wheat crop. Pathogen spores were sparse during the vegetative stage. After heading, Phaeosphearia nodorum ascospores were very abundant during rainy periods and Fusarium species occurred coincidentally but in lower numbers. Dreschlera tritici-repentis conidia were commonly found on dry days following wet periods. Wheat disease bioassays were conducted daily during the wheat season. Pathogenic Fusarium spores (101 to 103) were recovered from head washings. The Septoria leaf blotch complex and tan spot were the most commonly occurring diseases on leaves. Conidia of Septoria tritici were collected on sticky slides placed 100 m from a hectare of spring wheat being harvested.

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Airborne ascospores of Sclerotinia sclerotiorum

J. R. Venette and R. L. Lamppa

Department of Plant Pathology, NDSU

Sclerotinia sclerotiorum causes an important and sometimes yield limiting disease, white mold, on dry edible beans. Grower surveys have indicated that white mold is the most important disease of beans in the growing area of North Dakota-Minnesota. Nearly 300,000 ha of beans are produced in this area. Ascospores dispersed from apothecia are the primary inoculum units. Chemical control measures have been directed at protecting the blossoms from colonization. Chemical control has not been very effective because applications are difficult to time, coverage is difficult, and sometimes protective chemicals are not applied when apothecia do not appear within bean fields; hence the danger is perceived as low. Most of the inoculum may be introduced into bean fields from nearby crops. In 1995, counts of apothecia in small grains following Sclerotinia-infected beans averaged 33 m-2. In a nearby field two years out of beans, counts were nearly 3 m-2 and in an adjacent bean field not planted to a susceptible crop for three years, apothecial numbers averaged 0.3 m-2. Eighteen paired air samples (Andersen Samplers, 500 L total sample, selective media in glass plates in Stages 1-4) were collected midday at canopy height with the infested small grain fields and at distances from 10 to 30 m downwind on four different dates in late July. Colony counts showed propagule populations of >2000 m-3 within the field and exponential decline in ascospore populations with distance. Spores were detected at all sampler stages but most were in stages two and three. Paired samples collected upwind and downwind from an infested grain field in early August showed high "background" populations of 4.5 m-3, but populations were 5 times greater downwind. Paired samples collected at canopy height and 7 m above the canopy at the downwind margin of an infested grain field showed nearly equal numbers of airborne propagules. The data suggests that ascospores readily escape small grain canopies and that Sclerotinia-infested grain fields are an important source of inoculum for Sclerotinia diseases.

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Aster Leafhopper Dispersal

C. W. Hoy , L. R. Nault, & S. A. Miller

We are developing a mathematical model of aster yellows epidemiology to explore strategies for managing this important disease of vegetable crops. The model simulates yellows epidemics in lettuce, celery, and carrots grown in a mixed vegetable (muck) cropping system. Epidemics are initiated by migrating inoculative aster leafhoppers, Macrosteles quadrilineatus Forbes, and are dependent on subsequent population dynamics and transmission. Part of the project is to refine a PCR assay to quickly detect the phytoplasma in migrating leafhoppers. Leafhopper movement after arrival in the vegetable growing area influences two critical rates in the epidemiological model: the rate at which uninfected leafhoppers acquire the phytoplasma and the rate at which inoculative leafhoppers transmit the phytoplasma to uninfected plants. Both rates depend on two scales of movement, interplant and interfield. In a USDA-funded project initiated during 1995, we plan to estimate rates of interplant and interfield aster leafhopper movement by three methods: measuring distributions of plant residence times in the laboratory and field, mark-recapture experiments, and trapping flying leafhoppers between plants within fields and between fields. Preliminary work this year included a comparison of different trapping methods, mark-recapture experiments in small field plots, and preliminary direct observations of leafhopper residence times on lettuce plants.

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Insect Behavioral Response to Toxins

C. W. Hoy, G. P. Head & F. R. Hall

Planting random mixtures of transgenic and nontransgenic seed has been proposed as a means of providing a refuge from intense selection for resistance to transgenic crops. We had previously measured a positive genetic correlation between behavioral avoidance and physiological tolerance of Bt d-endotoxin in Colorado potato beetle larvae. More behaviorally responsive second instars, those moving away from leaves with high endotoxin concentration, tend to be more physiologically resistant. The implications for use of seed mixtures to manage resistance are that larvae moving onto transgenic foliage in a mixture are more likely to return to the nontransgenic foliage if they are more resistant; indirect selection for physiological resistance could result. Because the seed mixture strategy has not gained acceptance for most transgenic crops, resistance management will still require refugia at a greater spatial scale and would benefit from an understanding of and ability to manipulate adult dispersal.

We are currently measuring behavioral responses of fourth instars and adult beetles to the endotoxin. Using an image analysis system, we record the position of insects at 10 second intervals during two different time periods after ingestion of a standard dose. The dose is administered by providing a single leaflet of a potato line expressing the endotoxin at a known concentration. Dose is estimated by monitoring the leaf area eaten and removing the beetle when a standard area has been consumed. Movement monitoring takes place in large petri dishes with no food. Changes in coordinates over the 10 second intervals are then analyzed to estimate velocity and turning patterns. For genetic analysis of locomotion parameters, beetles are being reared in full-sib families from individual mated pairs. We plan to provide additional beetles from each family to David Ferro, Univ. of Massachusetts, who plans further analysis of adult flight behavior, measured with flight mills, in response to endotoxin.

Publications

J. R. S. Lopes, L. R. Nault & P. L. Phelan. Periodicity of diel activity of Graminella nigrifrons (Homoptera: Cicadellidae) and implications for leafhopper dispersal. Ann Entomol. Soc. Am. 88: 227-233.

Head, G., C. W. Hoy, and F. R. Hall. 1995. The quantitative genetics of behavioral and physiological response to a pyrethroid in diamondback moth. J. Econ. Entomol. 88: 447-453.

Head, G., C. W. Hoy, and F. R. Hall. 1995. Effects of direct and indirect selection on behavioral response to permethrin in larval diamondback moths. J. Econ. Entomol. 88: 461-469.

Hoy, C. W. and G. Head. 1995. Correlation between behavioral and physiological responses to transgenic potatoes containing Bacillus thuringiensis d-endotoxin in Leptinotarsa dedemlineata Say (Coleoptera: Chrysomelidae) J. Econ. Entomol. 88: 480-486.

Head, G., C. W. Hoy, and F. R. Hall. Permethrin droplets influence larval Plutella xylostella (Lepidoptera: Plutellidae) movement. Pestic. Sci. In Press.

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Oklahoma News Clips

Alfalfa weevil

Oklahoma struggles trying to manage the alfalfa weevil because of variant fall and winter weather patterns. A dissertation was completed that used discriminate analysis to tie together to movement and reproduction of alfalfa weevil into a multivariate model that predicts peak abundance and spray date. This model was 90% correct when compared to 20 years of data and was field validated the past 2 years. Contact: G. Cuperus

Anthracnose

Anthracnose diseases annually cause significant reduction in yield and require fungicide applications. A new predictive model developed and validated by Jim Duthie and John Damicone predicts outbreaks based on weather-based schedules. Number of fungicide applications was significantly reduced in field validated demonstrations across Oklahoma. Fungicide applications were often reduced from 5 to 2 integrating these predictive systems into management programs. Contact: Jim Duthie 405-889-7343.

Stored product insects:

Historically management recommendations have ignored migration of stored product insects. Studies were undertaken in farm and commercial grain storage facilities the past 4 years to investigate the importance of insect immigration into facilities. Results indicate: I. short and long term movement into facilities in very important in developing a stored grain management program in both farm and commercial facilities. Short range (<100 yards) movement is critical to minimizing populations development. In farm (8 m) and large (20 m) storage facilities the max. catch was a the eaves where air moves and the insects follow that air movement. Results have already made significant changes in stored grain management recommendations.

Publications

Levetin, E., R. Shaughnessy, E. Fisher, B. Ligman, J. Harrison, T. Brennan. 1995. Indoor air quality in schools: exposure to fungal allergens. Aerobiologia 11: 27-34.

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Understanding the Physiology of Migratory Noctuid Moths

H.W. Fescemyer

Strong migratory capabilities and a highly efficient reproductive system make the noctuids and other migratory insects important agricultural pests. We are interested in understanding the endocrine and molecular mechanisms coordinating migration and reproduction. Vitellogenins are a unique group of female-specific reproductive proteins in insects. Oogenesis can not occur without the vitellogenins, which are produced by the fat body. Understanding the endocrine and molecular mechanisms regulating vitellogenin gene expression and oogenesis are important to elucidating the reproductive-flight syndrome physiology of migratory noctuids.

One of our research projects involves the developmental biology of vitellogenin expression and oogenesis in the fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae). The second project investigates molecular biology of the vitellogenin gene in the fall armyworm and gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae). Our continued research on these two projects has produced the complete sequence for vitellogenin mRNA from the gypsy moth. We have also made progress on elucidating the endocrine regulation of vitellogenin expression in the fall armyworm. Ongoing research is described below on reproductive and genetic differences between plant-host strains of the fall armyworm and on the effects of nematode infection on flight potential in the fall armyworm.

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Effects of Noctuidonema guyanense on Flight of the Fall Armyworm.

H.W. Fescemyer and C.E. Rogers

Noctuidonema guyanense Remillet and Silvain (Nematoda: Aphlenchoididae) is an external parasitic nematode found on fall armyworm moths and other closely related noctuid moths (Remillet and Silvain 1988; Rogers et al. 1990a,b). This ectoparasite can be found on moths in their tropical overwintering areas and on moths derived from immigrant populations such as those occurring in Tift County, Georgia (Marti et al. 1990; Simmons & Rogers 1990; Rogers & Marti 1992). It is possible that moths infested with N. guyanense are poor fliers and not capable of making long-duration migratory flights. Moths observed in overwintering, source habitats have significantly more nematodes on them than moths observed in migratory habitats (Rogers & Marti 1992). The objective of this project is to determine how the behavioral characteristics associated with dispersal-like and long-duration flight behaviors are influenced by N. guyanense infestation.

Support for this project, which started October 1994, is provided by a USDA, ARS Cooperative Agreement. Over the past year a computer based roundabout actograph system for remote monitoring of tethered moth flight behavior has been constructed. The actograph system incorporates the platform system of Cooter and Armes (1993) and is housed in an environmentally controlled incubator with dusk and dawn simulation. Preliminary behavioral studies of fall armyworm flight are just beginning.

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Developmental Biology of Vitellogenin Expression and Oogenesis in the Fall Armyworm.

H.W. Fescemyer

Noctuid moths, such as the fall armyworm, initiate vitellogenin expression and oogenesis after adult eclosion. The role of juvenile hormone in regulating vitellogenin expression in the fall armyworm was tested. Pharate adult females were neck-ligated 12 h before eclosion. This ligation prevents juvenile hormone produced in the head from reaching the fat body located in the abdomen. These females were then treated with the juvenile hormone analog, methoprene. Neck- ligated females treated with ethanol served as the controls. Hemolymph was collected from these ligated adults 3 days after hormone treatment. Proteins in the hemolymph were separated using sodium dodescylsulfate polyacrylamide gel electrophoresis (SDS-PAGE). This technique detected none of the 185 kD apovitellogenin in the hemolymph of the ethanol controls. The 185 kD apovitellogenin was abundant in the hemolymph of the methoprene treated adults.

Methoprene stimulated vitellogenin expression in the absence of in vivo juvenile hormone. Stimulation of vitellogenin expression by juvenile hormone or its analogs has been shown to occur in the adults of two other noctuids, the corn earworm (Satyanarayana et al., 1992, 1994), Helicoverpa zea (Boddie), and the true armyworm (Cusson et al., 1994), Pseudaletia unipuncta Haworth. Apparently, it is the increase in the juvenile hormone titer after adult emergence that activates vitellogenin expression.

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Molecular Biology of the Vitellogenin Gene in the Fall Armyworm and Gypsy Moth.

H.W. Fescemyer, J.J. Adamczyk, Jr., D.G. Heckel, L.J. Gahan, R.E. Davis, and T.J. Kelly

Techniques involving reverse transcriptase-polymerase chain reaction (RT-PCR) were used to obtain the entire nucleotide sequence for high molecular weight vitellogeinin mRNA in the gypsy moth. This sequence has 55% nucleotide sequence and 38% amino acid sequence (deduced) similarities with high molecular weight vitellogenin in the silkworm, Bombyx mori (L.) (Lepidoptera: Bombycidae) (Yano et al., 1994). Other sequence alignments indicate that gypsy moth vitellogenin is a member of the nematode-vertebrate-insect family of large vitellogenin genes. This research along with that reported last year on this project are in press (Adamczyk et al., 1995).

Nucleotide sequence similarities between the vitellogenin mRNAs of the gypsy moth and silkworm were used to design polymerase chain reaction (PCR) primers. These primers amplify a ca. 366 bp DNA product out of genomic DNA from the fall armyworm. The size of this product is the same as DNA amplified by these primers out of genomic DNA from the gypsy moth and silkworm. Sequencing and northern blot analyses are being conducted to determine if the 366 bp DNA product codes for a portion of the vitellogenin gene in the fall armyworm.

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Genetic Differences Between Plant Host-Strains of the Fall Armyworm.

H.W. Fescemyer, J.J. Adamczyk, Jr., Y.-T. Ma, and D.G. Heckel

The fall armyworm is composed of two strains, one of which feeds on corn and the other on rice and grasses. An investigation was begun to determine the developmental and host-strain specific aspects of reproduction in the fall armyworm. In the process of setting up colonies of the fall armyworm host strains, the genetic relationships were elucidated for enzyme loci associated with differentiation of the host strains as rice or corn. Pashley (1986) reported allozyme markers in adults that enable nearly complete discrimination of the host strains. These enzymes are hydroxybutyrate dehydrogenase (Hbdh), Peptidase-F (PepF), and Esterase-3 (Est3) which is a much better marker for host strain than the other enzyme loci. However, the genetic linkage relationships of these allozyme markers has not been investigated. Although we were unable to establish colonies of the host strains, the single-pair matings of insects we collected from peanut were very useful in determining the genetic relationships of the allozyme markers for host-strain differentiation.

Alleles of Hbdh in the parents of informative matings are shown in Table 1. These alleles segregated in the progeny in ratios not significantly different from the 1:1 ratio expected for an autosomal gene (Table 1). Alleles of PepF in the parents of informative matings are shown in Table 2. These alleles segregated in the progeny in ratios not significantly different from the 1:1 ratio expected for an autosomal gene (Table 2). Although Hbdh and PepF are autosomal genes, it is often not possible to use these enzymes to discriminate the host strains.

Like Pashley (1986), four alleles designated C-F were observed for Est3, but they did not segregate in a pattern expected for an autosomal gene. In some crosses, unexpected and unpredicted genotypes, such as DD (Table 3), were observed. Alleles that were not even in the parents, such as E (Table 4), were observed. Yet in other crosses, unpredicted genotypes, such as CC and FF (Table 5), were observed along with alleles that were not even in the parents, such as D (Table 5). It was obvious that Est3 alleles were segregating into the progeny in an unusual manner. However, it was not possible to use the colony established from insects collected off of peanut to determine the segregation mechanism. This colony did not consist of any pure corn or rice individuals.

In January 1994, pure corn and rice strains were obtained from Jeremy N. McNeil at Laval University in Canada. Esterase-3 alleles C and D are only observed in the corn strain while alleles E and F are only observed in the rice strain (Table 6). However, sexual dimorphism of the Est3 alleles was also observed within a strain (Table 6). Corn females have both C and D alleles, but corn males only have the C allele. Rice females have the F allele, but some rice males have only the E allele while others have both E and F alleles. This sexual dimorphism suggested that segregation of Est3 might be sex-linked.

Several matings with the F1 generation from a corn male x rice female cross were made because these backcross matings can provide information about sex-linkage. Only matings between the F1 males and corn or rice females produced progeny. Of the matings set up among the corn and rice strains, the corn females would not mate with rice males as shown by Pashley and Martin (1987). The progeny of the backcross shown in Table 7 gave a segregation ratio of 1:1:2 instead of the 1:1 expected if Est3 was an autosomal gene. In Lepidoptera, the Y chromosome is in the female not the male like humans for example. If Est3 is sex-linked, then the expected genotype of the parents in an F1 x rice backcross would be CE for males and EY for the females (Table 8). Likewise, the expected genotype of the progeny from this backcross would be CE and EE for males in a 1:1 ratio, and CY and EY for females in a 1:1 ratio. The expected phenotypes of the progeny from this backcross would be CE, C, and E in a ratio of 1:1:2 (Table 8).

The Est3 alleles segregated as expected for sex-linkage when tested using the F1 x rice backcross (Table 9). Genotypes CE and EE were in a 1:1 ratio for male progeny while genotypes CY and EY were in a 1:1 ratio for female progeny. The phenotypes for all progeny were CE, C, and E in a ratio of 1:1:2. Thus, the Est3 allozyme is sex-linked in the fall armyworm. This discovery is consistent with those for a number of Lepidoptera, such as the European corn borer, that have sex-linked differences in traits involved in reproductive isolation Sperling (1994).

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Reproductive Differences Between Plant Host-Strains of the Fall Armyworm

H.W. Fescemyer

An investigation was conducted to determine if the fall armyworm host strains differed in their reproductive-flight syndrome physiology. Both the rice and corn strains were reared during the larval stage at 27°C, a 14:10 L:D photoperiod, and 70-80% relative humidity. One-day-old pupae of both strains were placed at 20°C, a 14:10 L:D photoperiod, and 70-80% relative humidity. Adults emerging from these pupae were held under the same conditions as the pupae. These unmated adults were sampled at ages ranging from 1-10 ± 0.25 days after emergence (n = 5 per age). Hemolymph was collected from each adult and used for the analysis of vitellogenin using SDS-PAGE. An ovary from each hemolymph drained moth was dissected, weighed, and homogenized in phosphate buffered saline containing 1% phenylthiourea (PTU). The supernatant of this homogenate was used to determine total soluble protein as an estimate of the protein content of the ovary. Tissue remaining after ovary dissection was used for analysis of the Est3 allozyme alleles.

Vitellogenin was first detected in hemolymph from corn strain adults two days before it was detected in hemolymph from rice strain adults. Hemolymph vitellogenin was first detected in the corn strain on the second day after emergence. Ovary development of corn strain adults was much faster than that of the rice strain. Peak wet weight and protein content of ovaries from the corn strain was observed on the fourth day after emergence. Ovaries from the rice strain did not reach their peak wet weight and protein content until the seventh day after emergence.

These finding suggests that host strain differences exist in the development of reproductive capability. The rice strain delays reproduction longer than the corn strain. This delay is particularly noticeable at cool temperatures. No strain differences in the development of reproductive capability occur at 27°C. The rice strain appears to be more sensitive to cool temperatures than the corn strain. This sensitivity is demonstrated by the observation that the proportion of the rice strain emerging from pupae was ca. 40% lower than that for the corn strain.

These findings would be especially exciting if Jeremy N. McNeil's findings at Laval University in Canada were not opposite those of this study. He found the corn strain to delay oogenesis longer than the rice strain at cool temperatures. A mix-up in the colonies can be ruled out because the insects used in our experiment were derived from McNeil's colonies. In addition, the Est3 allozyme alleles typed true for the rice and corn insects used in our study. The rice strain is particularly hard to rear. Our rice colony went through two bottle necks before this experiment was conducted. The laboratory environment has been shown to alter genetic composition and behavior of the fall armyworm (Mason et al. 1987). It is possible that these bottle necks altered the composition of genes directing reproductive development.

Acknowledgments.

We are grateful for the technical assistance from D.A. Jenkins, D.R. Lewis, E. Malico, M. Mitchell, O. Onifade, M.I. Smathers, L.J. Snipes, and A.E. Thorne. Financial support was provided by HATCH project 66-1437 allocated to the South Carolina Agricultural Experiment Station, by USDA, ARS Cooperative Agreement (58-6602-4-020), by the USDA Cooperative State Research Service Research Apprenticeship Program for Minority Students (94-COOP-2- 0255, 95-COOP-2-1527), which supported the summer salaries of M.M. and O.O., by the SCUREF Summer Scholars Program (SCUREF/U.S. Department of Energy Cooperative Agreement DE-FC09-93SR18262) which also supported the summer salaries of M.M. and O.O., and by a National Science Foundation EPSCoR grant to the State of South Carolina.

Publications.

Adamczyk J.J., Jr., Fescemyer H.W., Heckel D.G., Gahan L.J., Davis R.E. and Kelly T.J. 1995. Sex-specific and hormone-controlled expression of a vitellogenin-encoding gene in the gypsy moth. Arch. Insect Biochem. Physiol. In Press.

DuRant J.A., Fescemyer H.W. and Mason C.E. 1995. Effectiveness of four blends of European corn borer (Lepidoptera: Pyralidae) sex pheromone isomers at three locations in South Carolina. J. Agric. Entomol. In Press.

Sappington T.W., Fescemyer H.W. and Showers W.B. 1995. Lipid and carbohydrate utilization during flight of the migratory moth, Agrotis ipsilon (Lepidoptera: Noctuidae). Arch. Insect Biochem. Physiol. 29, 397-414.

Fescemyer H.W., Masler E.P., Kelly T.J. and Lusby W.R. 1995. Influence of development and prothoracicotropic hormone on the ecdysteroids produced in vitro by the prothoracic glands of female gypsy moth (Lymantria dispar) pupae and pharate adults. J. Insect Physiol. 41, 489-500.

Fescemyer, H.W. In Press. Pheromones. In J.J. Lagowski [ed.], Encyclopedia of Chemistry, Macmillan, New York.

References.

Adamczyk J.J., Jr., Fescemyer H.W., Heckel D.G., Gahan L.J., Davis R.E. and Kelly T.J. 1995. Sex-specific and hormone-controlled expression of a vitellogenin-encoding gene in the gypsy moth. Arch. Insect Biochem. Physiol. In Press.

Cooter R.J. and Armes N.J. 1993. Tethered flight technique for monitoring the flight performance of Helicoverpa armigera (Lepidoptera: Noctuidae). Environ. Entomol. 22, 339-345.

Cusson M., Yu C.G., Carruthers K., Wyatt G.R., Tobe S.S. and McNeil J.N. 1994. Regulation of vitellogenin production in armyworm moths, Pseudaletia unipuncta. J. Insect Physiol. 40, 129-136.

Marti O.G., Jr., Rogers C.E., Silvain J.F. and Simmons A.M. 1990. Pathological effects of an ectoparasitic nematode Noctuidonema guyanense (Nematoda: Aphlenchoididae) on adults of the fall armyworm (Lepidoptera: Noctuidae). Ann. Entomol. Soc. Am. 83, 956-960.

Mason L.J., Pashley D.P. and Johnson S.J. 1987. The laboratory as an altered habitat: Phenotypic and genetic consequences of colonization. Fla. Entomol. 70, 49-58.

Pashley D.P. 1986. Host-associated genetic differentiation in fall armyworm (Lepidoptera: Noctuidae): a sibling species complex? Ann. Entomol. Soc. Am. 79, 898-904.

Pashley D.P. and Martin J.A. 1987. Reproductive incompatibility between host strains of the fall armyworm (Lepidoptera: Noctuidae). Ann. Entomol. Soc. Am. 80, 731-733.

Remillet M. and Silvain J.F. 1988. Noctuidonema guyanense n.g., n. sp. (Nematoda: Aphlenchoididae) ectoparasite de noctuelles du genre Spodoptera (Lepidoptera: Noctuidae). Rev. Nematol. 11, 21-24.

Rogers C.E. and Marti O.G., Jr. 1992. Infestation and dispersal of Noctuidonema guyanense (Nematoda: Aphlenchoididae) on Spodoptera frugiperda (Lepidoptera: Noctuidae). Environ. Entomol. 21, 417-421.

Rogers C.E., Marti O.G., Jr., Simmons A.M. and Silvain J.F. 1990a. Host range of Noctuidonema guyanense (Nematoda: Aphlenchoididae): an ectoparasite of moths in French Guiana. Environ. Entomol. 19, 795-798.

Rogers C.E., Simmons A.M. and Marti O.G., Jr. 1990a. Parasitism of Lepidoptera adults by Noctuidonema guyanense Remillet and Silvain (Nematoda: Aphlenchoididae) in southeastern United States. J. Agric. Entomol. 7, 241-245.

Satyanarayana K., Bhaskaran G., Dahm K.H., and Meola R. 1992. Regulation of vitellogenin synthesis by juvenile hormone in the corn earworm, Helicoverpa zea. Invert. Reprod. Devel. 21, 169-178.

Satyanarayana K., Bradfield J.Y., Bhaskaran G. and Dahm K.H. 1994. Stimulation of vitellogenin production by methoprene in prepupae and pupae of Manduca sexta. Arch. Insect Biochem. Physiol. 25, 21-37.

Simmons A.M. and Rogers C.E. 1990. Distribution and prevalence of an ectoparasitic nematode, Noctuidonema guyanense, on moths of the fall armyworm (Lepidoptera: Noctuidae) in the tropical Americas. J. Entomol. Sci. 25, 510-518.

Sperling F.A.H. 1994. Sex-linked genes and species differences in Lepidoptera. Can. Entomol. 126, 807-818.

Yano K.-I., Sakurai M.T., Watabe S., Izumi S. and Tomino S. 1994. Structure and expression of mRNA for vitellogenin in Bombyx mori. Biochim. Biophys. Acta 1218, 1-10.

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The Texas-based research cited below involves primary researchers (J.K. Westbrook, W.W. Wolf, J.D. López, J.R. Coppedge, G.D. Jones, J. F. Esquivel, R.S. Eyster and P.G. Schleider) from the USDA, ARS, Areawide Pest Management Research Unit, College Station, TX 77845 and the following collaborators:
J.R. Raulston and D. Spurgeon, USDA, ARS, Cotton Insects Research Unit, Weslaco, TX
S.J. Johnson, A.M. Hammond and L. Luo, Louisiana State University, Baton Rouge, LA
J.H. Matis, Texas A&M University, College Station, TX
S. Allen, National Weather Service, League City, TX
J. Snyder, National Weather Service, Brownsville, TX
J. Ward, National Weather Service, New Braunfels, TX

Entomopalynology

Gretchen Jones

Adults of numerous insect species feed on pollen, nectar, and other plant exudates that are frequently associated with flowers. As a result of this feeding activity, these adults become contaminated with pollen. Identification of this pollen is useful in the study of adult insect feeding and migratory activities for several reasons. First, most pollen grains are very distinctive, easily recognizable, and identifiable to the family, genus, and often species rank. Thus, very specific information can be obtained about the plants that serve as adult host plants. Second, pollen is composed of sporopollenin that is very durable and does not easily decay. Therefore, pollen remains as a durable natural marker on or in an insect. Third, from the identification of this pollen, the geographical origin of the plant from which the pollen came can often be determined, especially when there is temporal and geographical variation in the distribution of the identified plant.

This year several new techniques in preparing corn earworm (CEW) moths and boll weevils (BW) for pollen analyses were developed. From these techniques new natural markers were found. In addition, these techniques have added new data to the foraging resources of these two insect pests. Although initially designed to obtain a better array of natural markers for adult CEW and BW, these new techniques can be applied to other insect species.

Summer and early-fall 1994 populations of CEW adults from Texas, Oklahoma, Iowa, and Minnesota were examined for pollen. Fifty-two percent of the moths from Texas were contaminated with pollen, in Iowa 100%, in Oklahoma 70% and in Minnesota 34%. Most of the pollen found on the moths was from the plant family Asteraceae.

Adult CEW were collected through direct capture in selected blooming citrus groves in the Lower Rio Grande Valley (LRGV) of Texas to evaluate citrus pollen contamination, behavioral activities, and population dynamics. These aspects are fundamental for understanding the migratory activity of corn earworm from a documented source zone. Preliminary electron microscopy observations indicate 71% of direct captured corn earworm possessed citrus pollen. Dissections show that 61% of captured females had been mated. However, only 6% were mating at the time of capture. A transect of pheromone traps through the citrus growing region will yield additional data regarding citrus pollen contamination and population dynamics of corn earworm field populations. These data can be used to identify peak population activity and citrus pollen contamination of field populations throughout the LRGV. Direct captures resulted in identification of twenty additional noctuid species active in citrus groves.

Studies were initiated to evaluate pollen cross-contamination of corn earworm adults. Placing citrus-contaminated insects with laboratory reared insects showed occurrence of cross-contamination. Likewise, placing laboratory-reared insects in pheromone trap tops at dusk resulted in pollen cross-contamination of laboratory insects by field insects attracted to the trap.

BW from three locations in Texas are being examined for pollen. Also, BW from 17 sites in the state of Tamaulipas, Mexico, are being examined for pollen in a collaborative agreement with J. Raulston (USDA, ARS). Migratory activities between locations will be evaluated from pollen found on these boll weevils.

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Early-season Insect Migration

Adult corn earworms (CEW) have been captured north of their overwintering range before local emergence, indicating that migration was required. Adult CEW feed on nectar from citrus and other flowering plants in February and March before migrating. Pollen from the citrus and other plants contaminates the proboscis, eyes and other body parts of the adult CEW. Such pollen provide unique natural markers that can be used to determine the migratory range and host variety of the CEW.

Corn earworm pheromone traps were monitored in and away from the LRGV. Traps were placed throughout northeastern Mexico to evaluate activity in the region. The downwind trapping scheme used during the 1994 campaign was expanded to include 26 additional locations throughout Texas and New Mexico to monitor migratory movement from the LRGV. Combining downwind trapping data with meteorological, radar, and direct capture data will provide a basis for determining implementation of areawide pest management strategies. Pheromone traps were operated daily to determine the distribution of the adult CEW throughout northeastern Tamaulipas, Mexico, and southern Texas from February - March. Captured specimens were frozen and later analyzed for the presence of pollen by scanning electron microscopy.

A vertical-pointing radar and a scanning radar were operated in the LRGV near citrus orchards. A scanning radar and a tracking radar were operated about 100 km north-northwest of the LRGV. Tetroons (i.e., large tetrahedral-shaped balloons made of mylar) were released nightly from the LRGV and tracked to determine the nocturnal wind transport available to migrating CEW.

We attempted to capture migrating CEW in blacklight traps that were attached to tetroons. The 0.5 m x 0.25 m traps were constructed of balsa wood vanes covered with white monocote. An 8-watt blacklight in the center of the trap was powered by 4 alkaline AA batteries. TangleTrap® adhesive was applied to the trap vanes for capturing insects on contact. No CEW were captured in the traps during several hours of aerial deployment. Modifications to the traps will be made, including consideration of other modes of insect attraction, before the traps are deployed next year.

As part of the Unit's cooperative research with S. Johnson, A. Hammond and L. Luo (LSU) on the migration of the true armyworm, sex pheromone and blacklight traps were operated in an agricultural area close to College Station, Texas, to monitor adult activity and response and to collect moth samples for reproductive, physiological and flight analyses. Field populations were also sampled at night in ergot-infected ryegrass. Large numbers of moths representing several migratory species were observed feeding on the ergot honeydew. It appears that the honeydew from ergot-infected ryegrass may be an important food source for early-season migration and other adult activities. More intensive evaluation or ergot-infected ryegrass as a source of food for migratory insect pest species and of feeding attractants / stimulants for use in developing adult control technology is planned for the Spring of 1996.

Contact John Westbrook for additional information.

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Mid-season Insect Migration

A pheromone trap network similar to that used in February and March was deployed in June. Cooperators monitored traps daily. Spatial resolution was emphasized more than identification of the migratory / nonmigratory status of captured specimens.

Tetroons were launched nightly from the LRGV. Blacklight insect traps were attached to some of the tetroons. No adhesive was applied to the trap vanes, but a fabric sock was attached to the bottom of the trap to collect insects in good condition.

Three entomological radars were located along a line north-northwest from the LRGV to detect migratory insect flight along the mean wind trajectory. A vertical-pointing radar was located in the LRGV; a tracking radar was located 100 km north-northwest of the LRGV; and a scanning radar was located 200 km north-northwest of the LRGV. The tracking radar was used to determine insect air speed, heading, and rates of ascent and descent.

Doppler radar data from NEXRAD facilities at Del Rio (Laughlin AFB), New Braunfels, Brownsville and League City were acquired for use in analysis of reflectivity (i.e., concentration of targets) and speed (i.e., wind speed plus target speed). NEXRAD facilities at New Braunfels and Del Rio were recently commissioned for service, and Brownsville began 24-hour operations about one week before the start of the June field study.

During the course of the field project, NEXRAD reflectivity images were reviewed and discussed with Jim Raulston and Dale Spurgeon of the USDA-ARS at Weslaco, TX. An anomalous cluster of high reflectivity originated from Lyford, TX, and moved downwind on the night of 5 June 1995. This cluster of high reflectivity was hypothesized to be beet armyworms which had already devastated the cotton production in the LRGV. Level II data will be analyzed with respect to winds and entomological field survey data to evaluate the hypothesis. In any event, beet armyworms became a new target of interest for migration studies.

A field study of beet armyworm migration was conducted in an area of mature cotton fields from 31 August 1995 - 4 September 1995 near San Angelo, TX. The Ralph Hoelscher farm location was situated within an area where beet armyworm infestations had devastated cotton production. The study period was during the time of estimated peak emergence of the beet armyworm. A scanning radar was operated throughout the night to monitor insect migratory flight. Tetroons were launched nightly and tracked by the Argos satellite system. Pilot balloons and radiosondes were tracked to measure vertical profiles of wind velocity, air temperature, relative humidity and barometric pressure.

Scientists studying the abundance and behavior of the Mexican free-tailed bat population in central Texas have discussed opportunities for future collaborative research. Dr. McCracken, of the Univ. of Tennessee, conducts physiological analyses of bats to determine dietary patterns. He reports that the bats change their primary food source during the night, with bats consuming a larger proportion of moths in the late-night / early-morning. Coincidentally, noctuids from the LRGV would be arriving in central Texas at this time. Because the Mexican free-tailed bats and the corn earworm migrate during the same time of the year, knowledge of the dietary proportion of particular insect species, particularly marked specimens, would aid in our understanding of long-distance insect migration. Dr. McCracken is also interested in attaching a microphone / radio transmitter to a tetroon, and recording bat audio signals that indicate the bats' feeding behavior along the approximate trajectory of noctuids migrating from the LRGV. Plans are also underway to instrument the U.S. Drug Enforcement Agency Aerostat surveillance radar near Rio Grande City, TX, with insect traps and microphone / radio transmitters.

Contact John Westbrook for additional information.

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Ground-truth of NEXRAD Doppler Radar Measurements

A scanning radar and a tracking radar were operated in an area of mature corn fields about 30 km east of the NEXRAD doppler radar facility at New Braunfels to provide ground truth of target reflectivity and speed. Pilot balloons and radiosondes were tracked to independently measure vertical profiles of wind velocity, air temperature, relative humidity and barometric pressure. Tetroons with attached blacklight insect traps were tracked for two hours per night to capture insects along wind trajectories. NEXRAD Level IV archive data have been examined for preliminary evaluations with respect to the ARS field measurements. NEXRAD Level II data will be analyzed for more precise analyses.

Contact Wayne Wolf for additional information.

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Publications

Beerwinkle, K. R., J. D. Lopez, Jr., D. Cheng, P. D. Lingren, and R. W. Meola. 1995. Flight potential of feral Helicoverpa zea (Lepidoptera: Noctuidae) males measured with a 32-channel, computer-monitored, flight-mill system. Environ. Entomol. 24: 1122-1130.

Lingren, P. D., J. R. Raulston, T. W. Popham, W. W. Wolf, P. S. Lingren, and J. F. Esquivel. 1995. Flight behavior of corn earworm (Lepidoptera: Noctuidae) moths under low wind speed conditions. Environ. Entomol. 24: 851-860.

Showers, W. B., A. J. Keaster, J. R. Raulston, J. L. Goodenough, W. H. Hendrix, III, M. O. Way, and J. F. Robinson. 1995. Seasonal migration of the black cutworm. Southwestern Entomologist, Suppl. No. 18, Sept. 1995: 119-134.

Westbrook, J. K., R. S. Eyster, W. W. Wolf, P. D. Lingren and J. R. Raulston. 1995. Migration pathways of corn earworm (Lepidoptera: Noctuidae) indicated by tetroon trajectories. Agric. Forest Meteorol. 73: 67-87.

Westbrook, J. K., J. R. Raulston, W. W. Wolf, S. D. Pair, R. S. Eyster, and P. D. Lingren. 1995. Field observations and simulations of atmospheric transport of noctuids from northeastern Mexico and the south-central U.S. Southwestern Entomologist, Suppl. No. 18: 25-44.

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Trapping Survey of Boll Weevil Populations in Northeastern Mexico

D. W. Spurgeon and J. R. Raulston

USDA, ARS, SARL, Crop Insects Research Unit, Weslaco, TX

Knowledge of spatial and temporal movement patterns of boll weevils in northeastern Mexico is critically needed in support of recently initiated eradication programs in Texas. Because existing data are not extensive enough to predict the potential impacts of Mexican boll weevil populations on control programs in Texas, we initiated a trapping study in northeastern Mexico to obtain this information. Our objectives were to define seasonal boll weevil pheromone trap capture profiles throughout cotton- and non-cotton-producing regions of northeastern Mexico, determine seasonal reproductive morphology of captured weevils, define spatial and temporal foraging patterns of weevils through analysis of gut contents, and attempt to integrate these data in an assessment of interregional movement patterns.

Eighteen trapping sites were established in mid-February, 1995. Sites were selected with particular reference to major geographical features and cotton production areas. The study area is bordered on the west and south by the Sierra Madre Orientals and on the east by the Gulf of Mexico. Primary northern cotton producing areas (planted in February, harvested in July and August) lie north and east of Valle Hermoso, and east of San Fernando. The primary southern cotton producing region (planted in June, harvested in December) lies in an area roughly bordered by El Limon, Cuauhtemoc, and Ebano. In addition, a small hectarage of dryland cotton was located near Mendez, and we received reports of a small hectarage near Soto la Marina (agronomically similar to northern production areas).

Traps are not directly associated with cotton except at Gonzalez. Three pheromone traps separated by >50 m were placed at each site. Traps are maintained twice weekly on consecutive days, resulting in one 6-d and one 1-d trapping period each week. Weevils captured during the 6-d period are sexed and counted to determine trap capture patterns. Weevils captured during the 1-d period are sexed, counted, and dissected to determine mating status, degree of reproductive development, gut and fat body conditions, and to obtain gut sections for pollen analysis.

Only preliminary results regarding the 6-d trap captures are currently available. Weevils were captured at all sites regardless of the distance from cotton, including General Teran, which is situated approximately 115 km from the nearest cotton to the east (Mendez) and 270 km from the nearest cotton to the south (El Limon). Trap captures were generally very low until June at sites within about 50 km of northern cotton production areas (Valle Hermoso, San Fernando, Mendez, Abasolo; Casas, Soto la Marina, La Pesca). Trap captures were very low at two of the sites >50 km from cotton producing regions (General Teran, Ciudad Victoria), but substantial numbers of weevils were caught at two other sites (Villagran, Llera). Captures at sites within about 50 km of southern cotton production areas tended to be highest immediately after trap establishment, and captures at most sites increased again during July. Trap captures tended to be lowest in May, regardless of trapping site. At this time no conclusions can be drawn from these data except that we were unable to identify any sites where weevils could not be captured.

Because it is unlikely that boll weevil interregional movement patterns will be understood through the use trap captures alone, our supporting research involves boll weevil reproductive biology and morphology, biotic and abiotic factors influencing overwintering strategies and success, and boll weevil trap response. This information will improve our ability to interpret trap capture patterns and enhance the usefulness of associated information from dissections of captured weevils.

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