Effect of habitat type and soil moisture on pupal stage of a Mediterranean forest pest (Thaumetopoea pityocampa)

Abstract

Habitat selection is especially important for pupae of holometabolous insects because this stage is usually immobile and to a certain extent unable to react to environmental changes. In the present study, we analyze how habitat and soil moisture determine the fate of pupae of the pine processionary moth Thaumetopoea pityocampa, a defoliator pest in pine woodlands of Europe and the Circunmediterranean region. The pine processionary moth pupates buried in the soil and can spend up to 9 years in an extra-long diapause. We considered the impact that different habitats, as well as the manipulation of soil water conditions in the preferred habitat (i.e. in bare ground with null or sparse herbaceous vegetation), can exert on pupation. Less than half of the buried larvae successfully pupated, even in the most favourable habitats and soil water conditions, whereas, on average, 2.5% underwent extra-long pupae diapause (2 years after pupation). Although habitat influenced mainly pupation success and pupal survival, changing moisture conditions in the preferred habitat affected primarily the phenology of emergence, whereas pupal survival remained unaffected. The results of the present study reveal the importance of both habitat and soil moisture on the pupal stage, providing valuable information with respect to adequately forecasting the effects of changes in climate or land use on the population dynamic of this important forest pest.