Chemically mediated intraguild predator avoidance by aphid parasitoids: interspecific variability in sensitivity to semiochemical trails of ladybird predators.

The avoidance responses of aphid parasitoids with varying host ranges (Aphidius eadyi, Aphidius ervi, and Praon volucre) to chemical trails deposited by intraguild predatory ladybirds, Coccinella septempunctata and Adalia bipunctata, were investigated. Females of all three parasitoid species avoided leaves previously visited by C. septempunctata or A. bipunctata adults. The avoidance responses shown by the two Aphidius species were stronger to trails of C. septempunctata than to those of A. bipunctata. However, P. volucre avoided trails of both ladybird species to a similar degree. Dose responses of these three parasitoid species to the hydrocarbons n-tricosane (C23H48), n-pentacosane (C25H52), and n-heptacosane (C27H56), which are components of the trails of both C. septempunctata and A. bipunctata, were evaluated. Dual-choice bioassays indicated the following: (1) A. eadyi showed more sensitive avoidance responses to n-tricosane than did the other two parasitoid species, (2) all three species showed similar responses to n-pentacosane across a range of doses, and (3) only P. volucre showed avoidance responses to n-heptacosane. Quantitative analyses of each hydrocarbon in the trails of the two ladybird species showed that n-pentacosane and n-heptacosane occur in significantly greater amounts in C. septempunctata trails than in those of A. bipunctata. The trails of the two species also differ qualitatively in the other hydrocarbons present.