Host plants affect predator fitness via the nutritional value of herbivore prey: Investigation of a plant-aphid-ladybeetle system

The interactions among host plants (Medicago sativa L., cv. 'OKO8' and Vicia faba L., cv. 'Windsor'), aphid prey (Acyrthosiphon pisum Harris, Homoptera: Aphididae), and Coccinella septempunctata L. (Coleoptera: Coccinellidae) preimaginal biology were evaluated. Interactions were measured over a range of limiting daily prey levels (1.2 mg-16.4 mg) from each host plant colony. Compared with A. pisum reared on V. faba, A. pisum reared on M. sativa stored significantly more fatty acids which resulted in a 1.17-fold increase in available calories for developing C. septempunctata. The increased survival, decreased developmental times, and larger size of C. septempunctata supplied with A. pisum reared on M. sativa clearly demonstrate host plant effects at the third trophic level. At low very limiting daily prey levels, A. pisum reared on M. sativa were more suitable prey for C. septempunctata survival, development, and adult size than A. pisum reared on V. faba. Coccinella septempunctata survival ratios (larval), developmental times, and adult size converged (were not statistically different) between host plants at higher daily A. pisum levels. These convergence's support the hypothesis that there were quantitative differences in the nutritional value of aphids, as influenced by differences in fatty acids and subsequent nutritional levels (calories), between aphids reared on separate plant hosts. The observed tritrophic interactions appear to be modulated by the biochemical response of A. pisum to host plants.