Flight Activity of the Bollworm, Mexican Corn Rootworm & Boll Weevil in Texas John Westbrook (state rep to NCR-148) USDA/ARS, College Station, TX Field studies were conducted to investigate the flight activity of three important crop insect pests in Texas: bollworm, Helicoverpa zea (Boddie), Mexican corn rootworm, Diabrotica virgifera zeae, and boll weevil, Anthonomus grandis (Boheman). Boll Weevil A field study was conducted in collaboration with ARS colleagues, K.R. Beerwinkle and J.R. Coppedge, to investigate the influence of wind on the dispersal of boll weevils from senescent cotton fields. A 64-ha dryland cotton production area near Caldwell, Texas, served as the source of boll weevils for the dispersal study. The cotton fields represented the only dryland cotton produced in Burleson County, and were at least 9 km from the nearest cotton (irrigated) which was grown in the Brazos Valley. Pheromone traps (67) were deployed around the perimeter, in concentric rings at a 2- and 4-km range, and at a 5-, 6-, 7-, 8- and 9-km range along a line emanating northeast, from the approximate center of the dryland cotton production area. The traps were checked daily, except for weekends, from 5 Aug through 2 Sep. A Campbell CR21X weather station at the center of the dryland cotton production area recorded hourly values of air temperature, soil temperature, relative humidity, precipitation, barometric pressure, solar radiation, wind speed, and wind direction. Pheromone traps captured 43,580 boll weevils during the 30-d sampling period. Daily capture averaged 21.4 weevils/trap at the perimeter of the cotton fields, 25.5 weevils/trap at the 2-mile range, 22.9 weevils/trap at the 4-mile range, 8.5 weevils/trap from a 5- to 9- mile range, and 21.7 weevils/trap overall. Mean daily capture was maximum (55.9 weevils/trap) in the northern octant, representing 19.2% of the total capture. Mean daily capture was minimum (25.7 weevils/trap) in the southwestern octant, representing 8.9% of the total capture. A cold front passage brought northeasterly wind and a large influx of weevils from the Brazos Valley on 24-26 Aug; captures after 23 Aug were excluded from subsequent logistic analysis. Logistic regression of daily mean captures by octants from 7-22 Aug revealed a significant positive relationship between the daily relative percentage occurrence of wind heading and the proportion of daily mean capture by octant (c2. = 26.19, p < 0.05). At a critical probability level of 0.5, the logistic regression equation had an overall accuracy of 75%: 44% for higher-than-expected capture events, and 92% for lower-than-expected capture events. Also, the error rate of the logistic regression equation was 25% for false positives and false negatives. Fig. 1 Daily capture of boll weevils near Caldwell, Texas from 5 Aug to 2 Sept. 1997 Mexican Corn Rootworm A trapping study of corn rootworm dispersal from mature corn fields was conducted at two locations in Bell County, Texas, in the summer of 1997. One location was near an untreated corn field (Field 26B) where adult Mexican corn rootworms (MCRW) populations were expected to be relatively high. A second location was between a corn field (Field 2A) and a sorghum field (Field 3A). Traps were checked two to three times per week during the period when the corn silks were drying down, and becoming unsuitable as a food source for MCRW. Beetles were removed from the traps and brought to the laboratory for identification of species, gender, and mating status. Eight pheromone traps were deployed at 50-m intervals from the southeastern corner to the mid-eastern side of Field 26B. An automated weather station was set up in the center of Field 26B to measure the soil, air and canopy environment. A 4-meter blimp and a 0.5-m2 kite towed a 1-m2 insect net and a 0.25-m2 net to about 25 m above ground level (AGL), respectively, for a total of 15 hours. A total of 196 MCRW and 111 SCRW were captured in pheromone traps from 13 June to 18 July. Total capture of CRW increased from the southeastern corner to the east-central side of Field 26B. MCRW outnumbered SCRW in most of the pheromone traps. Daily mean capture attained a maximum value of 6.63 beetles per trap on 2 July, and remained less than 0.5 beetles per trap after 3 July. The proportion of gravid female MCRW was highly variable due to the low number of captured beetles. No CRW were captured in nets at 25 m AGL during approximately 15 hours of daytime operation (two days). Daily mean air temperature at 1.5 m AGL averaged 27.6 C, or 0.1 C higher than the air temperature at 3.0 m AGL; infrared thermometric measurements recorded a daily mean temperature of 29.5 C for the top of the canopy. Daily mean relative humidity averaged 78% at 1.5 m AGL and 3.0 m AGL. Daily mean wind speed averaged 1.7 m/s. Mean daily capture of male MCRW in pheromone traps was significantly correlated only with barometric pressure (r = -0.43, N = 35). Figure 2. Mean daily capture of Mexican Corn Rootworms (MCRW) in pheromone traps vs. mean daily minimum and maximum air temperature at Field 26B (Corn) \|in Bell County, TX in 1997. Ten 0.76-m x 0.76-m screen traps were coated with TangleTrap® and placed at a height of 2.06 m at 50-m intervals along the northern side of Field 2A (and southern side of Field 3). An automated weather station was set up between Field 2A and Field 3A to measure the atmospheric environment. Sticky traps were also deployed at heights of 2.3 m, 7.6 m, and 11.4 m AGL on a telescoping mast. A total of 176 MCRW and 22 SCRW were captured on sticky traps from 24 June to 24 July. The traps captured 126 (28 gravid) female MCRW and 50 male MCRW. However, the temporal pattern of capture of male MCRW and female MCRW was well synchronized. The mean daily capture of MCRW reached a maximum of 1.76 MCRW per trap on 25-27 June, the first sampling date. Minimum capture (0.1 MCRW per trap) occurred on 2 July. A secondary capture maximum (1.03 MCRW per trap) was observed on 7 July. Captures decreased rapidly after 7 July. SCRW captures remained consistently low throughout the observation period. No CRW were captured on the mast-mounted sticky traps during the single date (25 June) of observation. Daily mean air temperature at 1.5 m above ground level (AGL) averaged 27.4 C. Daily mean relative humidity averaged 78% at 1.5 m AGL and 3.0 m AGL. Daily mean wind speed averaged 1.9 m/s. Mean daily capture of MCRW was significantly correlated with only air temperature (r = -0.58, N=17) and relative humidity (r = 0.53, N = 17). Figure 3. Mean daily capture of Mexican Corn Rootworms (MCRW) on sticky traps and daily minimum and maximum air temperature between corn & sorghum fields (Fields 2A and 3A) in Bell County, TX in 1997 Bollworm Radar field studies of bollworm migration have generally been conducted near monoculture habitats during peak emergence in order to increase the probability that the radar targets are primarily bollworms. However, new approaches are needed to confirm the identity of the radar targets. One field study, in collaboration with G.F. McCracken of the Univ. of Tennessee and M. Tuttle of Bat Conservation Intl., was conducted from 16-18 June near Pearsall and Uvalde, Texas, using a drifting hot-air balloon as a measurement platform for the investigation of high-altitude bollworm immigration flight and predation by Mexican free-tail bats, Tadarida brasiliensis, during pre-dawn hours. Night-vision intensified videography was used in an attempt to visually identify insects and bats. However, light which emanated from the balloon's propane burner and station lights deactivated the night-vision intensifying scope. No insects were captured in either a small pheromone trap or an 8W/12VDC blacklight trap. However, one bat and three moths were observed 20-50 m below the balloon basket between 4:20 and 4:40 CST on 18 June using an unfiltered, million-candle-power spot light. A radiomicrophone detected infrequent bat echolocation calls and feeding buzzes. The apparently sparse aerial density of bats and bollworm moths may have resulted from smaller populations emigrating from a 90%-smaller acreage of irrigated corn in the Lower Rio Grande Valley. Further, crop consultants reported only minor bollworm infestations near Uvalde in mid-June. A second field study was conducted near Uvalde from 10-18 July, in collaboration with G.F. McCracken of the Univ. of Tennessee, B. Balsley of the Univ. of Colorado, and M. Tuttle of Bat Conservation Intl., to investigate high-altitude bollworm emigration flight and predation by Mexican free-tail bats using an 8-m2 kite as a measurement platform. Pupal excavations in field corn and captures of bollworms in a pheromone trap indicated that peak bollworm emergence was underway. Radiomicrophones attached to the kite tether line recorded frequent bat echolocation calls and feeding buzzes which exhibited time- and altitude-dependence. No bollworms were captured in a 1-m2 insect net or in an 8W/12VDC blacklight trap attached to the tether line for less than 10 hours of operation. On 18 July, however, the insect net captured three female green lacewings, Chrysopa rufilabris, the larvae of which prey on bollworm larvae. A third field study was conducted in June and July to investigate the relative proportion of bollworms making local and distant flights from field corn in the Brazos Valley near College Station, Texas. Larval surveys and pupal excavations were conducted to determine infestation rates and predicted emergence cycles in field corn. Scanning radar displays were recorded for 10 elevation angles every 15 minutes from sunset to sunrise. Targets within a 0.5- to 0.6-mile annulus for each elevation scan are being counted to determine target concentration; vertical profiles of target concentration are being constructed using all elevation scans. The aerial concentration of targets will be compared with the capture of bollworms in pheromone and blacklight traps and the estimated emergence cycle. [ 1997 Research Index ]
Last updated 1 June, 2007 This page was constructed by Gail Kampmeier at gkamp[at]uiuc.edu Please direct questions of content and prospects of collaborative research to respective scientists. Research reports do not constitute publication and results may be preliminary. They are included here for informational purposes only. You should contact the authors for further information. Any references to commercial products do not constitute endorsement. [ NCR-148 \| Movement & Dispersal Index \| News Index ]

Flight Activity of the Bollworm,

Mexican Corn Rootworm &

Boll Weevil in Texas

John Westbrook (state rep to NCR-148)
USDA/ARS, College Station, TX

Field studies were conducted to investigate the flight activity of three important crop insect pests in Texas: bollworm, Helicoverpa zea (Boddie), Mexican corn rootworm, Diabrotica virgifera zeae, and boll weevil, Anthonomus grandis (Boheman).

Boll Weevil
A field study was conducted in collaboration with ARS colleagues, K.R. Beerwinkle and J.R. Coppedge, to investigate the influence of wind on the dispersal of boll weevils from senescent cotton fields. A 64-ha dryland cotton production area near Caldwell, Texas, served as the source of boll weevils for the dispersal study. The cotton fields represented the only dryland cotton produced in Burleson County, and were at least 9 km from the nearest cotton (irrigated) which was grown in the Brazos Valley. Pheromone traps (67) were deployed around the perimeter, in concentric rings at a 2- and 4-km range, and at a 5-, 6-, 7-, 8- and 9-km range along a line emanating northeast, from the approximate center of the dryland cotton production area. The traps were checked daily, except for weekends, from 5 Aug through 2 Sep. A Campbell CR21X weather station at the center of the dryland cotton production area recorded hourly values of air temperature, soil temperature, relative humidity, precipitation, barometric pressure, solar radiation, wind speed, and wind direction.

Pheromone traps captured 43,580 boll weevils during the 30-d sampling period. Daily capture averaged 21.4 weevils/trap at the perimeter of the cotton fields, 25.5 weevils/trap at the 2-mile range, 22.9 weevils/trap at the 4-mile range, 8.5 weevils/trap from a 5- to 9- mile range, and 21.7 weevils/trap overall. Mean daily capture was maximum (55.9 weevils/trap) in the northern octant, representing 19.2% of the total capture. Mean daily capture was minimum (25.7 weevils/trap) in the southwestern octant, representing 8.9% of the total capture. A cold front passage brought northeasterly wind and a large influx of weevils from the Brazos Valley on 24-26 Aug; captures after 23 Aug were excluded from subsequent logistic analysis. Logistic regression of daily mean captures by octants from 7-22 Aug revealed a significant positive relationship between the daily relative percentage occurrence of wind heading and the proportion of daily mean capture by octant (c2. = 26.19, p < 0.05). At a critical probability level of 0.5, the logistic regression equation had an overall accuracy of 75%: 44% for higher-than-expected capture events, and 92% for lower-than-expected capture events. Also, the error rate of the logistic regression equation was 25% for false positives and false negatives.

Fig. 1 Daily capture of boll weevils near Caldwell, Texas from 5 Aug to 2 Sept. 1997

Mexican Corn Rootworm

A trapping study of corn rootworm dispersal from mature corn fields was conducted at two locations in Bell County, Texas, in the summer of 1997. One location was near an untreated corn field (Field 26B) where adult Mexican corn rootworms (MCRW) populations were expected to be relatively high. A second location was between a corn field (Field 2A) and a sorghum field (Field 3A). Traps were checked two to three times per week during the period when the corn silks were drying down, and becoming unsuitable as a food source for MCRW. Beetles were removed from the traps and brought to the laboratory for identification of species, gender, and mating status.

Eight pheromone traps were deployed at 50-m intervals from the southeastern corner to the mid-eastern side of Field 26B. An automated weather station was set up in the center of Field 26B to measure the soil, air and canopy environment. A 4-meter blimp and a 0.5-m2 kite towed a 1-m2 insect net and a 0.25-m2 net to about 25 m above ground level (AGL), respectively, for a total of 15 hours.

A total of 196 MCRW and 111 SCRW were captured in pheromone traps from 13 June to 18 July. Total capture of CRW increased from the southeastern corner to the east-central side of Field 26B. MCRW outnumbered SCRW in most of the pheromone traps. Daily mean capture attained a maximum value of 6.63 beetles per trap on 2 July, and remained less than 0.5 beetles per trap after 3 July. The proportion of gravid female MCRW was highly variable due to the low number of captured beetles. No CRW were captured in nets at 25 m AGL during approximately 15 hours of daytime operation (two days). Daily mean air temperature at 1.5 m AGL averaged 27.6 C, or 0.1 C higher than the air temperature at 3.0 m AGL; infrared thermometric measurements recorded a daily mean temperature of 29.5 C for the top of the canopy. Daily mean relative humidity averaged 78% at 1.5 m AGL and 3.0 m AGL. Daily mean wind speed averaged 1.7 m/s. Mean daily capture of male MCRW in pheromone traps was significantly correlated only with barometric pressure (r = -0.43, N = 35).

Figure 2. Mean daily capture of Mexican Corn Rootworms (MCRW) in pheromone
traps vs. mean daily minimum and maximum air temperature at Field 26B (Corn)
|in Bell County, TX in 1997.

Ten 0.76-m x 0.76-m screen traps were coated with TangleTrap® and placed at a height of 2.06 m at 50-m intervals along the northern side of Field 2A (and southern side of Field 3). An automated weather station was set up between Field 2A and Field 3A to measure the atmospheric environment. Sticky traps were also deployed at heights of 2.3 m, 7.6 m, and 11.4 m AGL on a telescoping mast.

A total of 176 MCRW and 22 SCRW were captured on sticky traps from 24 June to 24 July. The traps captured 126 (28 gravid) female MCRW and 50 male MCRW. However, the temporal pattern of capture of male MCRW and female MCRW was well synchronized. The mean daily capture of MCRW reached a maximum of 1.76 MCRW per trap on 25-27 June, the first sampling date. Minimum capture (0.1 MCRW per trap) occurred on 2 July. A secondary capture maximum (1.03 MCRW per trap) was observed on 7 July. Captures decreased rapidly after 7 July. SCRW captures remained consistently low throughout the observation period. No CRW were captured on the mast-mounted sticky traps during the single date (25 June) of observation. Daily mean air temperature at 1.5 m above ground level (AGL) averaged 27.4 C. Daily mean relative humidity averaged 78% at 1.5 m AGL and 3.0 m AGL. Daily mean wind speed averaged 1.9 m/s. Mean daily capture of MCRW was significantly correlated with only air temperature (r = -0.58, N=17) and relative humidity (r = 0.53, N = 17).

Figure 3. Mean daily capture of Mexican Corn Rootworms (MCRW) on sticky traps and
daily minimum and maximum air temperature between corn & sorghum fields (Fields 2A and 3A)
in Bell County, TX in 1997

Bollworm

Radar field studies of bollworm migration have generally been conducted near monoculture habitats during peak emergence in order to increase the probability that the radar targets are primarily bollworms. However, new approaches are needed to confirm the identity of the radar targets.

One field study, in collaboration with G.F. McCracken of the Univ. of Tennessee and M. Tuttle of Bat Conservation Intl., was conducted from 16-18 June near Pearsall and Uvalde, Texas, using a drifting hot-air balloon as a measurement platform for the investigation of high-altitude bollworm immigration flight and predation by Mexican free-tail bats, Tadarida brasiliensis, during pre-dawn hours. Night-vision intensified videography was used in an attempt to visually identify insects and bats. However, light which emanated from the balloon's propane burner and station lights deactivated the night-vision intensifying scope. No insects were captured in either a small pheromone trap or an 8W/12VDC blacklight trap. However, one bat and three moths were observed 20-50 m below the balloon basket between 4:20 and 4:40 CST on 18 June using an unfiltered, million-candle-power spot light. A radiomicrophone detected infrequent bat echolocation calls and feeding buzzes. The apparently sparse aerial density of bats and bollworm moths may have resulted from smaller populations emigrating from a 90%-smaller acreage of irrigated corn in the Lower Rio Grande Valley. Further, crop consultants reported only minor bollworm infestations near Uvalde in mid-June.

A second field study was conducted near Uvalde from 10-18 July, in collaboration with G.F. McCracken of the Univ. of Tennessee, B. Balsley of the Univ. of Colorado, and M. Tuttle of Bat Conservation Intl., to investigate high-altitude bollworm emigration flight and predation by Mexican free-tail bats using an 8-m2 kite as a measurement platform. Pupal excavations in field corn and captures of bollworms in a pheromone trap indicated that peak bollworm emergence was underway. Radiomicrophones attached to the kite tether line recorded frequent bat echolocation calls and feeding buzzes which exhibited time- and altitude-dependence. No bollworms were captured in a 1-m2 insect net or in an 8W/12VDC blacklight trap attached to the tether line for less than 10 hours of operation. On 18 July, however, the insect net captured three female green lacewings, Chrysopa rufilabris, the larvae of which prey on bollworm larvae.

A third field study was conducted in June and July to investigate the relative proportion of bollworms making local and distant flights from field corn in the Brazos Valley near College Station, Texas. Larval surveys and pupal excavations were conducted to determine infestation rates and predicted emergence cycles in field corn. Scanning radar displays were recorded for 10 elevation angles every 15 minutes from sunset to sunrise. Targets within a 0.5- to 0.6-mile annulus for each elevation scan are being counted to determine target concentration; vertical profiles of target concentration are being constructed using all elevation scans. The aerial concentration of targets will be compared with the capture of bollworms in pheromone and blacklight traps and the estimated emergence cycle.

[ 1997 Research Index ]