|Elliott, Norman - Norm|
Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2003
Publication Date: 4/15/2003
Citation: JONES, D.B., GILES, K.L., BERBERET, R.C., ROYER, T.A., ELLIOTT, N.C., PAYTON, M.E. FUNCTIONAL RESPONSES OF AN INTRODUCED PARASITOID AND AN INDIGENOUS PARASITOID ON GREENBUG AT FOUR TEMPERATURES. ENVIRONMENTAL ENTOMOLOGY. 2003. V. 32. P. 425-432. Interpretive Summary: The greenbug is a serious insect pest of wheat that causes extensive monetary losses to wheat growers. Certain parasitic wasps lay their eggs in greenbugs, which subsequently hatch into larvae that kill the host greenbug. The parasitic wasp Lysiphlebus testaceipes is an important biological control agent of greenbugs in wheat in the United States, whereas the parasite Aphidius colemani is an important biological control agent of cereal aphids in the Old World that warrants evaluation as a candidate for release in the United States as a biological control agent of the greenbug. We studied two behaviors, which partially determine how good a wasp will be at controlling a particular host species, for L. testaceipes and A. colemani with the greenbug as the host. The first behavior is called the functional response, whereby a wasp lays an egg in more hosts when the host is at high density than when it is at low density. The second behavior is called superparasitism, whereby the wasp lays more eggs in each host when host density is low than when it is high. The first behavior promotes effective biological control, whereas the second can reduce the effectiveness of biological control. The functional response of L. testaceipes and A. colemani were very similar at moderate and high temperatures typical of those encountered in wheat fields during autumn and spring. However, the functional response of L. testaceipes was reduced at low temperatures compared to that of A. colemani. Superparasitism for both wasps was often less than expected if superparasitism were a random occurrence, suggesting that these wasps are able to sense when a greenbug has been previously parasitized. Aphidius colemani achieved higher parasitism rates than L. testaceipes at lower temperatures. These observations suggest that A. colemani may be an effective addition to the parasite fauna for biological control of the greenbug during cool seasons in the Southern Great Plains.
Technical Abstract: Functional responses and superparasitism by the indigenous parasitoid wasp Lysiphlebus testaceipes Cresson and the introduced parasitoid Aphidius colemani Viereck on the greenbug, Schizaphis graminum Rondani were measured at four temperatures (14, 18, 22, and 26°C) during a 24-hour period (12:12 L:D). At each temperature, from 5 to 75 greenbugs were exposed to individual wasp mating pairs for 24 hours. At all experimental temperatures, functional responses for both wasps most closely fit the Type III model. Instantaneous attack rates for Aphidius colemani were not significantly different among experimental temperatures. However, for L. testaceipes, the estimate for the instantaneous attack rate at 14°C was significantly lower than estimates at 22 and 26°C when data were fit to a Type II functional response model. When data were fit to a Type III functional response model for L. testaceipes, the estimate for the instantaneous attack rate at 14°C was significantly lower than estimates at 18, 22 and 26°C. Superparasitism for both wasps was often less than expected if superparasitism were a random occurrence, suggesting that these parasitoids may be able to sense when the host has been previously parasitized. Aphidius colemani achieved higher parasitism rates than L. testaceipes at lower temperatures. This observations suggests that A. colemani may be an effective addition to the parasitoid guild for biological control of greenbug during cooler periods in the Southern Great Plains.