|Elliott, Norman - Norm|
Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2007
Publication Date: 6/15/2007
Citation: Jones, D.B., Giles, K.L., Elliott, N.C., Payton, M.E. 2007. Parasitism of greenbug, Schizaphis graminum, by the parasitoid Lysiphlebus testaceipes, at winter temperatures. Environmental Entomology. 36:1-8. Interpretive Summary: The functional response of a parasitoid or predator of a pest insect is important because it is one of the main factors that determine how well the natural enemy can biologically control the pest. The functional response measures the rate of increase in the number of prey killed by a natural enemy as the density of the prey increases. Functional responses by the common parasitoid of cereal aphids, Lysiphlebus testaceipes, on the greenbug, a key aphid pest of winter wheat, were measured at seven temperatures. At temperatures below 4°C the parasitoid was observed to kill greenbugs. This temperature is below the temperature at which the aphid can mature and reproduce. The ability to kill greenbugs at such low temperatures enables the parasitoid to increase the percentage of greenbugs that are killed while the greenbugs are unable to reproduce. The importance of this finding is that the parasitoid may be able to reduce greenbug infestations during winter in Oklahoma and other southern states and thereby circumvent greenbug outbreaks in winter wheat during spring.
Technical Abstract: Functional responses by Lysiphlebus testaceipes (Cresson), a common parasitoid of small grain aphids, on greenbug, Schizaphis graminum (Rondani), were measured at seven temperatures (14, 12, 10, 8, 6, 4, and 2°C) during a 24 hour period (12 h Light: 12 h Dark). Oviposition by L. testaceipes ceased at temperatures below 4°C. At all experimental temperatures, a type I, rather than a type II or type III functional response, was determined to be the best fit based upon coefficient of determination (r2) values. Lysiphlebus testaceipes was observed to oviposit in greenbugs at temperatures below the developmental temperature of both the greenbug host (5.8°C) and the parasitoid itself (6.6°C). This ability to oviposit at sub-developmental temperatures enables the parasitoid to increase the percentage of greenbugs that are parasitized while the greenbugs are unable to reproduce. The implications of these findings regarding population suppression of greenbugs are discussed.