Survival and development of Chrysoperla rufilabris (Neuroptera : chrysopidae) supplied with pea aphids (Homoptera : aphididae) reared on alfalfa and faba bean

The importance of host plant effects on aphids, and their natural enemies, has been well documented. However, few studies have isolated the mechanisms that determine suitability of insect prey among host plants for the surviv al and development of predators. We evaluated the nutritional interactions among alfalfa, Medicago sativa L. 'OKO8', and faba bean, Vicia faba L. Wind sor', host plants, pea aphid herbivores, Acyrthosiphon pisum (Harris), and a lacewing predator, Chrysoperla rufilabris Burmeister. The survival and de velopment of lacewing larvae supplied with five daily levels (1.2-16.4 mg) of pea aphids reared on either alfalfa or faba bean mere documented. Compar ed with aphids reared on faba bean, those reared on alfalfa stored 6.3 time s greater levels of myristic acid resulting in a 2.7 fold increase in total fatty acid content (micrograms per milligram of aphid weight). This increa se in total fatty. acids equated to an approximate to 1.3-fold increase in available calories for C. rufilabris provided with pea aphids reared on alf alfa. There were no statistical differences among treatments in the ratio o f lacewing individuals surviving to the pupal or adult stage. The ratio of deformed lacewing adults increased with decreasing daily prey levels. and t his increase was greatest for C. rufilabris supplied with pea aphids reared on faba beans. Lacewing larvae supplied with pea aphids reared on alfalfa had faster developmental rates (1/d) than C. rufilabris larvae supplied wit h pea aphids reared on faba beans. Interestingly, these differences in deve lopmental rates between host plants continued to occur after the rates plat eaued at the highest daily prey level. The separation of C. rufilabris deve lopmental rates between host plants at low and high daily pea aphid levels does not support the hypothesis that quantitative differences in the nutrit ional value of pea aphids, as influenced by differences in fatty acids and calculated nutrition levels (calories) between pea aphids Feared on separat e plant hosts, were responsible for differences in C. rufilabris developmen tal rates. Rather, separation of developmental rates at low and high daily prey levels, and no statistical interactions between daily prey levels and host plants, suggest qualitative differences in the nutritional value of pe a aphids between host plants.