Microclimate-based oviposition site selection in butterflies and moths

The sites herbivorous insects select to deposit eggs determine to a variable degree the environment their larvae will experience during development. Therefore, oviposition site selection should be seen as a significant life-history trait affecting the survival of the offspring. While searching for suitable sites, egg-laying terrestrial insects are predicted to respond to environmental factors that function as indicators for larval development and survival. In herbivorous insects, such as butterflies and moths, microclimate may be of significance for the selection of a suitable host plant or specific host plant parts. Although the preference-performance hypothesis attracted much interest in insects to address host plant species generalism versus specialism, a synthetic review on the diversity and functional relevance of microclimate-based oviposition site selection (MBOSS) is lacking for the Lepidoptera (butterflies and moths). Temperature and humidity are of ecological significance throughout their life cycle, but the role of oviposition site selection for larval development and survival may vary considerably. In this review, we conducted a literature survey of studies on the Lepidoptera that analysed oviposition site selection in the field and that tested for MBOSS relationships in natural habitats. We focused on the following questions: (i) how common is MBOSS in butterflies and moths; (ii) to what extent does the preference-performance hypothesis apply for MBOSS in this group of insects; and (iii) what is the relevance of MBOSS relationships for conservation principles and conservation management? In 89% of the tested cases, evidence for MBOSS was found, although there was a strong bias towards studies on temperate-zone butterfly species. By contrast, moths and tropical butterflies were understudied. Several moth studies did not provide support for the MBOSS hypothesis. Whether MBOSS occurred relative to warmer, cooler or thermally more buffered sites depended on: (i) the spatial scale at which MBOSS was tested; and (ii) regional climatic conditions. Vegetation type (i.e. forest versus non-forest habitats) was not significantly predictive for the type of MBOSS. However, when analysed in a case-by-case manner, vegetation type often clarified the ecological circumstances under which MBOSS was observed. There was a high prevalence of oviposition site selection for warmer microclimates than the thermal conditions of the surrounding environment. Understanding microclimate-mediated behavioural interactions with the environment is a key component for understanding resource-centred functional habitat and movement patterns to spread eggs in herbivorous insects. This small-scale component of habitat heterogeneity (including post-disturbed early-successional microhabitats) is key for understanding functional habitat use in butterflies and moths and is of high relevance for conservation and restoration management of their habitats in natural and anthropogenic landscapes. We identify outstanding questions and discuss new perspectives for the ecology and evolution of oviposition site selection, as well as for species conservation under human-induced rapid environmental change.