Effects of dietary nicotine on the development of an insect herbivore, its parasitoid and secondary hyperparasitoid over four trophic levels

Abstract

Abstract 1. Allelochemicals in herbivore diet are known to affect the development of higher trophic levels, such as parasitoids and predators.2. This study examines how differing levels of nicotine affects the development of a herbivore, its parasitoid and secondary hyperparasitoid over four trophic levels. Separate cohorts of the herbivore, Manduca sexta, were fed on artificial diets containing 0.0, 0.1, and 0.5% wet weights of nicotine. Some of the larvae in each cohort were separately parasitised in the first (L1) and third (L3) instars by the gregarious endoparasitoid, Cotesia congregata. Newly emerged parasitoid cocoons were, in turn, parasitised by the hyperparasitoid, Lysibia nana.3. Pupal mass in M. sexta was negatively correlated with nicotine concentrations in the artificial diet, although larval development time was unaffected.4. Hyperparasitoid survival was highest when there were low levels of nicotine in the diet of M. sexta. Cocoon mass in C. congregata and adult mass in L. nana were mostly affected by nicotine levels in host diet when L1 M. sexta larvae were parasitised. The effects were slightly stronger on L. nana than on C. congregata, indicating the presence of both qualitative and quantitative effects of nicotine concentration on both species.5. The results suggest that allelochemicals in herbivore diet can have both direct and indirect effects on the performance of higher trophic levels. However, in multitrophic interactions these effects can vary with the stage of the herbivore attacked by the primary parasitoid, as well as with the strategy employed by the herbivore to deal with plant phytotoxins.