Colorado Potato Beetles,
Aster Leafhoppers, Japanese Beetles,
& Gypsy Moths on the Move
Department of Entomology
Ohio Agricultural Research and Development Center
Wooster, OH
Colorado potato beetle locomotion after Bt ingestion
Casey W. Hoy & Xianjin Liu
Dr. Liu visited C. W. Hoy's laboratory for 8 months from the National IPM on Food & Economic Plants Technology Engineering Research Centre, Institute of Plant Protection, Jiangsu Academy of Agricultural Sciences, Nanjing, China. During this time he compared the electrophysiological recordings from the midgut and leg neuromuscular systems of adult Colorado potato beetles to their behavioral changes in locomotory activity after Bt treatments.
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Movement rate and spontaneous action potentials in the midgut and leg muscles were recorded with an image analysis and a waveform recording system, respectively. Bt treatments were administered by injecting purified endotoxin in buffer solution into the foregut. After approximately 60 min, locomotory activity of the beetles treated with a high dose of Cry3Ac toxin was reduced whereas that of beetles treated with a low dose was increased relative to controls (Fig. 1), consistent with previous results. The action potentials recorded from the midgut (Fig. 2) of the Cry3Ac toxin treated beetles help to explain the locomotion data. The high dose treatment quickly led to much greater firing frequency than that of the buffer treated and much longer interspike intervals of resting, followed by generally lower levels of firing frequency. |
| The low dose treatment resulted in higher frequency and shorter duration of firing than that of the high dose treatment and buffer control, but these effects did not begin until more than 30 minutes after administration of the Bt treatment. The inhibitory and excitement activities of different doses on the leg neuromuscular system also were obvious, but differences among treatments were not as large as that of the gut action potentials. The early high firing frequency in the midgut of high dose treated beetles did not lead to greater firing frequency in the leg muscle relative to controls. Rather firing frequency gradually declined in the leg muscle in high dose treated beetles during the period from 30-90 minutes after treatment. In contrast, high firing frequency beginning 30 minutes after treatment in the midgut of low dose treated beetles was associated with higher firing frequency in the leg muscles. |  |
Our results on locomotion provide an interesting contrast with those of Alyokhin et al. (1999) on beetle flight after Bt ingestion. In the flight study, ingestion of even very low doses of Bt reduced flight propensity in Colorado potato beetle. Central nervous system processing of gut responses may lead to different effects in the leg and flight muscles. The two sets of results together suggest that we may be able to identify ranges of Bt doses that affect neither flight nor locomotion, ranges that would decrease flight and increase locomotion, and ranges that would decrease both flight and locomotion. Manipulation of dispersal is central to the objectives of NCR-148 and, particularly once combined with the additional effects of Bt on beetle development, fecundity and survival, could be central to sustainable use of the Bt endotoxin.
Colorado potato beetle population dynamics in seed mixtures
Casey W. Hoy
When spatial variation in toxin concentrations within plants is present, insect movement governs the dose accumulated over time and the selective pressure placed on either behavioral or physiological mechanisms of adaptation by the insect population. Colorado potato beetle is known to move frequently among potato plants within fields, both by flight and walking. We have observed severe impacts on potato beetle populations, essentially local extinction, of 50:50 and 70:30 ratios of NewLeaf:standard potatoes in the field. To test the hypothesis that a threshold percentage of toxin expressing plants, lower than 50:50, would be required to have a significant effect on Colorado potato beetle population growth, we established mixtures in a greenhouse cage experiment. Lines expressing lower and lines expressing higher concentrations of Bt endotoxin were used in mixtures of 10, 20, 30, 40, and 50% transgenic plants compared with a 100% standard potato control. Adults less than 7-10 days old that had been fed standard potato foliage were released into the cages. Eggs, larvae, and emerging adults in the following generation were counted. The amount of feeding and egg development taking place on standard potato foliage before release into the mixture cages influenced oviposition and subsequent numbers of larvae and adults (note rep 3 in particular). Even 10% transgenic plants, however, resulted in significant reductions in population growth (Fig. 3).
When dispersal rates among plants are large, as in Colorado potato beetle and many other agricultural pests, even low percentages of plants possessing a particular resistance trait can exert a significant effect on the pest population. An ability to design distributions of toxins according to the pattern of dispersal of pests could result in more efficient and sustainable use of crop protection agents. Furthermore, results demonstrate that selection on naturally occurring plant populations for resistance traits with an associated cost by herbivores with high dispersal rates is likely to result in heterogeneous distributions of the trait.
Aster Leafhopper Dispersal
C. W. Hoy, S. A. Miller, L. R. Nault, J. Zhang
A postdoctoral research associate, Dr. Liyang Zhou of the Institute of Zoology, Chinese Academy of Sciences (laboratory of Prof. Li Dianmo) has been hired recently to complete the project. Dr. Zhou will be linking our spatially explicit simulation model of aster leafhopper population dynamics and yellows epidemiology to a GIS describing an Ohio diversified vegetable production area to simulate and compare season long control strategies.
Predicting Pest Populations on Terceira Island, The Azores
R.A.J. Taylor
We have built a GIS-based model of Japanese beetle distribution and abundance on the island of Terceira in the Azores. This model combines the spatial dynamics of the Japanese beetle on Terceira with a climatological model (developed by Dr. Eduardo Brito Azevado, Azores Agricultural University). Weather in the Azores is entirely orographic, that is to say it is dominated by the interaction of moisture-bearing wind and elevation of the terrain over which it passes. The climatological model, which is programmed in the language of the GIS ARC/INFO, is driven by monthly data from a meteorological station on Terceira. Japanese beetle pheromone trap data for the years 1977 to 1998 and larval data from 1991 to 1998 are combined with the climatological data and geophysical data (elevation, slope, aspect, and landuse) in a neural net model that predicts the next year's map of adult trap catch. Predictions of this model will be tested against the actual data for 1999 which will become available late in 1999. The closed system represented by Terceira provides a simpler and smaller system in which to develop the methodology. This approach will be applied in the "open" system of Gypsy moth in Ohio.
Predicting Insect Pest Populations
at Synoptic and Local Scales:
A Pilot Study with Gypsy Moth in Ohio
R.A.J. Taylor, D. Sydnor, J. Nichols
This project, which has just been funded, will use the nearly 30 years of gypsy moth distribution data collected by the Ohio Department of Agriculture to develop a predictive model of GM distribution and abundance using the pattern recognition abilities of neural nets. A GIS will be used to create, store and manage maps of GM distribution and the neural net will be used to predict future maps. This is the same technology developed to predict Japanese beetle distribution and abundance in Terceira, the Azores. Output from the model will be provided to ODA, ODNR, USDA, and local authorities charged with moth management to help improve the planning and execution of gypsy moth management in Ohio. The gypsy moth problems facing Ohio are likely to differ from those encountered in the Appalachian Mountain system (from which the USDA-FS' Slow the Spread program was developed) because of differences in the moth's biology in Ohio's harlequin landscape. It is intended that the model will also be used to investigate the impact of the degree of environmental fragmentation on gypsy moth population dynamics and to investigate fundamental questions of insect population and migration dynamics in a harlequin (fragmented) environment. Questions of scale in population dynamics will also be investigated by comparing model predictions with those from the "closed" Japanese beetle system in Terceira. It should be noted that both species are introduced to North America and have proved impossible to eradicate: Japanese beetle was introduced to Terceira ca. 1970.
Bibliography
Hoy, C. W., G. Head, and F. R. Hall. 1998. Spatial heterogeneity and insect adaptation to toxins. Ann. Rev. Entomol. 43: 571-594.
Alyokhin, A., D. N. Ferro, C. W. Hoy, and G. Head. 1999. Laboratory assessment of flight activity displayed by Colorado potato beetles (Coleoptera : Chrysomelidae) fed on transgenic and Cry3A toxin-treated potato foliage. J. Econ. Entomol. 92: 115-120.
Hoy, C. W. , X. Zhou, L. R. Nault, S. A. Miller, and J. Styer. 1999. Host plant, phytoplasma, reproductive status, and aster leafhopper (Homoptera: Cicadellidae) flight behavior. Annals Entomol. Soc. Am. 92: 523-528.
Hoy, C. W. 1999. Colorado potato beetle resistance management strategies for transgenic potatoes. Am. J. Pot. Res. 76: 215-219.
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