Arbuscular mycorrhizal fungi influence life history traits of a lepidopteran herbivore

Results from pot and microcosm studies in the greenhouse have shown that pl ant growth and foliar chemistry is altered by the presence and species comp osition of arbuscular mycorrhizal fungi (AMF). The growth and survival of h erbivores which feed on plants could, as a consequence, also be affected by these mutualistic soil fungi. Consequently, interactions between AMF, plan ts and herbivores could occur. To test this, larvae of the common blue butt erfly, Polyommatus icarus (Lycaenidae), were fed with sprigs of Lotus corni culatus (Fabaceae) plants which were inoculated with one of two different A MF species, with a mixture of these AMF species or with sprigs of plants wh ich were not inoculated with AMF Survival and larval weight of third instar larvae fed with plants colonised by AMF were greater than those of larvae fed with non-mycorrhizal plants. Survival of larvae feeding on non-mycorrhi zal plants was 1.6 times lower than that of larvae feeding on plants inocul ated with a mixture of AMF species and 3.8 times lower than that of larvae feeding on plants inoculated with single AMF species. Furthermore, larvae f ed with non-mycorrhizal plants attained only about half the weight of larva e fed with mycorrhizal plants after 11 days of growth. These differences in larval performance might be explained by differences in leaf chemistry, si nce mycorrhizal plants had a 3 times higher leaf P concentration and a high er C/N-ratio. Our results, thus, show that the presence of belowground mutu alistic soil fungi influences the performance of aboveground herbivores by altering their food quality. Larval consumption, larval food use and adult lipid concentrations of the common blue butterfly differed between larvae w hich were fed with plants inoculated with different AMF species. This sugge sts that the performance of herbivores is not only influenced by the presen ce of AMF but also depends on the identity of the AMF species colonising th e host plants. Moreover, a significant interaction term between AMF species and maternal identity of the larvae occurred for adult dry weight, indicat ing that the performance of offspring from different females was differentl y influenced by AMF species composition. To our knowledge, these results sh ow for the first time that the species composition of AMF communities can i nfluence life-history traits of butterfly larvae and possibly herbivores in general.