Parasitoids of European butterflies

Parasitoids are insects (mainly Hymenoptera and Diptera) whose larvae develop by feeding on the bodies of other arthropods (mainly immature insects) and the adults are free living. They are of immense importance in practically all terrestrial ecosystems because of their impact on the population levels of their hosts. In contrast to the considerable attention paid to European butterflies their parasitoids have received very little scrutiny, and the recognition that some reared parasitoids are in fact hyperparasitoids (parasitoids of parasitoids) has often been lacking in published records. A review of the biology and taxonomy of European butterfly parasitoids is presented, including a simple key to the various parasitoid families that include relevant species, followed by a brief discussion of the authors’ current knowledge of their use of butterfly hosts. Quantitative case studies on the butterfly taxa Iphiclides podalirius, Pieris spp., Maculinea rebeli, Aglais urticae, Melitaea and Euphydryas spp. and Thymelicus lineola illustrate the range of parasitoid assemblages and the extent to which parasitoids account for butterfly mortality. The needs and difficulties inherent in moving from a simple understanding of what parasitoids are using a host population to a more sophisticated assessment of the impact they may have on the host’s population dynamics are outlined. Parasitoids can be expected to have many important effects on the ecology of butterfly species and, on the evolutionary timescale, defence against parasitoids has shaped aspects of the physiology of the immature stages and the behaviour of both larval and adult butterflies. Butterfly researchers are encouraged to help build better knowledge about the host relations and effects of parasitoids. To better understand the place of parasitoids in the lives of butterflies there is still much to be gained from close attention to natural history, careful experimentation and thorough taxonomic investigation.