|Elliott, Norman - Norm|
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/3/2006
Publication Date: 10/9/2007
Citation: Phoofolo, M., Giles, K.L., Elliott, N.C. 2007. Quantitative evaluation of suitability of the greenbug, Schizaphis graminum, and the bird cherry-oat aphid, Rhopalosiphum padi, as prey for Hippodamia convergens (Coleoptera: Coccinellidae). Biological Control. 41(1):25-32. Interpretive Summary: The nutritional health of ladybeetles, such as Hippodamia convergens, impacts how effective they are as biological control agents of pest aphids in crops. We studied the effects of different amounts of two species of aphid, the greenbug and bird cherry-oat aphid, on development and survival of immature H. convergens. There was no effect of the different diets on the sex ratio of individuals that developed to adulthood. Only the development time of fourth instar larvae was significantly influenced by diet. Fourth instars fed ad libitum aphids had shorter development times that did not vary between aphid species. However, among the suboptimal aphid levels, fourth instars that fed on higher proportions of bird cherry-oat aphid had longer development times. Both diet and gender of developing larvae had effects on the body size of adult H. convergens. Our results suggest that both the greenbug and bird cherry-oat aphid are essential prey for H. convergens, and the amounts of these aphids available to immature beetles as they develop can have a significant effect on the survival and development of the beetles, and presumably on their effectiveness in biological control of the pest aphids.
Technical Abstract: The nutritive value of two cereal aphid species, Schizaphis graminum and Rhopalosiphum padi, for Hippodamia convergens development was compared as pure- and mixed-species diets and as suboptimum and ad libitum quantities. Comparisons were based on the following daily aphid quantities and combinations: 4 mg R. padi, 4 mg S. graminum, 3:1 mg mixture of R. padi and S. graminum, 2:2 mg mixture of R. padi and S. graminum, 1:3 mg mixture of R. padi and S. graminum, ad libitum R. padi, and ad libitum S. graminum. Preimaginal survival levels of H. convergens were high across all treatments and were neither influenced by aphid species, daily amounts of aphids, nor the mixtures supplied to the larvae. There was no diet effect on the sex ratio of individuals that developed to adulthood. Only the development time of fourth instars was significantly influenced by the larval prey regimes. Fourth instars fed ad libitum aphids had shorter development times that did not vary between aphid species. However, among the suboptimal aphid levels, fourth instars that fed on higher proportions of R. padi had longer development times. Both diet and gender of developing larvae had individual and interactive effects on the body size of adult H. convergens. Under ad libitum aphids feeding on R. padi resulted in smaller females whereas males showed no diverence. Our results suggest that both R. padi and S. graminum are essential prey for H. convergens development with S. graminum being relatively more suitable than R. padi.