Large-scale diversity patterns of parasitoid insects

Parasitoids, which mainly include taxa belonging to the Hymenoptera, play an important role in the maintenance of other arthropod populations, acting as regulators of host densities. However, the large-scale patterns of these insects and the factors that shape them are still not well established. In this review we focus on several aspects of the biology and macroecological patterns of parasitoids that have received some attention in the past, including recent studies on island parasitoid faunas. Parasitoid latitudinal gradients have been widely analyzed, with most studies apparently showing the anomalous pattern of species richness decreasing towards the tropics, particularly in the Ichneumonidae. This pattern has been proposed to be related to host feeding niche and parasitoid attack strategy. However, it is quite possible that these latitudinal gradients might be artifacts of sampling or description biases. Island parasitoid faunas also show latitudinal gradients in species richness, with the proportion of generalist species increasing towards the tropics. Island communities are in fact biased towards generalist species, being highly influenced by the communities of the surrounding territories and by the existence of rainforests. We conclude by briefly discussing the need for the development of future studies on parasitoid large scale diversity patterns, and proposing new research lines.