PREDATOR-PREY RELATIONSHIPS BETWEEN ORIUS INSIDIOSUS (SAY) AND THE SOYBEAN THRIPS, SERICOTHRIPS VARIABILIS (BEACH), ON SOYBEANS IN KENTUCKY

The objectives of this study were to: (1) determine the degree of stratification of Orius insidiosus (Say) and Sericothrips variabilis (Beach) on individual soybean plants; (2) assess the effect of crop phenology on populations of O. insidiosus and its most common prey species, S. variabilis; (3) evaluate the effectiveness of O. insidiosus as a predator of S. variabilis under laboratory conditions, and (4) observe behavioral interactions between O. insidiosus and S. variabilis on soybeans.; Populations of O. insidiosus and S. variabilis were monitored in adjacent early and late June planted soybeans, Glycine max (L.). A modified plant sampling technique was used to determine the degree of stratification on individual soybean plants, while the shake-cloth method was used to measure the seasonal cycles of O. insidiosus and soybean thrips. Direct visual counts were made for O. insidiosus in corn, Zea mays L., planted adjacent to the soybean plots.; Both O. insidiosus and S. variabilis were found to occur predominately in the uppermost trifoliolates and terminal bud. Distribution of S. variabilis, on individual plants, was also found to be stratified on the basis of development stage.; Adult O. insidiosus abundance increased significantly in both plantings as the soybeans began flowering. The population of O. insidiosus in the early June planted soybeans was greater during the vegetative and early reproductive stages (R1-R2) than in the late June planting for this same phenological period. The reverse was found to be true for the latter phenological stages (R5-R6) in the respective plantings.; Adult S. variabilis densities peaked in both plantings when the soybeans were at the full bloom stage (R2). Soybean thrips numbers then declined at a gradual rate in the early June planted soybeans; however, a more stable population was found to have been present in the late June planting during the later reproductive stages (R5-R7).; Adult and nymphal O. insidiosus on corn appeared to exhibit a definite preference for the leaf axils during pollen shed and also were numerous on fresh corn silks. Populations of O. insidiosus declined sharply in corn when pollen shed ceased and once the silks had dried.; Predation studies in the laboratory revealed that female and male O. insidiosus both exhibited a type-II functional response for the number of adult soybean thrips killed at varying prey densities.; First, third, and fifth instar nymphs, and adult female and male O. insidiosus all were able to capture and kill all three of the active stages of S. variabilis under laboratory conditions. The number of soybean thrips killed increased significantly with development for each of the nymphal stages of O. insidiosus tested, and females killed significantly more soybean thrips than males.; Observations made on the searching strategy of O. insidiosus indicated the predator was killing a much higher percentage of soybean thrips at certain regions of the trifoliolate, particularly the petiolule junction and the upper leaflet midrib.; Adult O. insidiosus were observed to have ca. 50 percent capture success in their encounters with adult soybean thrips.