Host pubescence and the behavior and performance of the butterfly Papilio troilus (Lepidoptera: Papilionidae)

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 survival and development of predators. We evaluated the nutritional interactions among alfalfa, Medicago sativa L. 'OKO8', and faba bean, Vicia faba L. 'Windsor', host plants, pea aphid herbivores, Acyrthosiphon pisum (Harris), and a lacewing predator, Chrysoperla rufilabris Burmeister. The survival and development of lacewing larvae supplied with five daily levels (1.2-16.4 mg) of pea aphids reared on either alfalfa or faba bean were documented. Compared with aphids reared on faba bean, those reared on alfalfa stored 6.3 times greater levels of myristic acid resulting in a 2.7-fold increase in total fatty acid content (micrograms per milligram of aphid weight). This increase in total fatty acids equated to an approximately 1.3-fold increase in available calories for C. rufilabris provided with pea aphids reared on alfalfa. There were no statistical differences among treatments in the ratio of lacewing individuals surviving to the pupal or adult stage. The ratio of deformed lacewing adults increased with decreasing daily prey levels, and this 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 with pea aphids reared on faba beans. Interestingly, these differences in developmental rates between host plants continued to occur after the rates plateaued at the highest daily prey level. The separation of C. rufilabris developmental rates between host plants at low and high daily pea aphid levels does not support the hypothesis that quantitative differences in the nutritional value of pea aphids, as influenced by differences in fatty acids and calculated nutrition levels (calories) between pea aphids reared on separate plant hosts, were responsible for differences in C. rufilabris developmental 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 pea aphids between host plants.