Microhabitat selection of Aporia crataegi (Lepidoptera: Pieridae) larvae in a traditionally managed landscape

Abstract

In this study we assessed microhabitat and host plant preferences of Aporia crataegi (Linne 1758) larvae in the field. The study was conducted in the submediterranean part of Slovenia, at the edge of the limestone region Kraški rob, where this species is widespread. The larvae were most abundant on blackthorn (Prunus spinosa L.) and the common hawthorn (Crataegus monogyna Jacq.), and infrequent on the rosehip (Rosa sp.) and rock cherry (Prunus mahaleb L.). Smaller shrubs with greater exposure to sun appeared to be preferred and larvae constructed their nests on outer branches of plants. The thermophilic nature of larvae was evident by the low and sheltered position of the nests, although in P. spinosa, which is more thermophilic than C. monogyna, they were positioned somewhat higher. As the nests and larvae occur mostly on plants growing in warmer microhabitats, larvae that had overwintered can take advantage of the quicker development of buds and leaves in early spring. The rocky ground below and around the occupied plants was often covered with grass, suggesting the need for cooler and warmer microclimate during hot summers and cold winters with strong winds, respectively. Densities of larvae and nests were positively but non-significantly correlated to density of host plants; however, in later successional stages, where host plants are most abundant, open and sunny microhabitats that can provide opportunities for larvae to warm up are lacking. The revival of the traditional management practices with extensive grazing with late and only occasional mowing may slow down the overgrowing process, leaving spiny host plants abundant and in close proximity to the nectaring sources for the adults.