Plant phenotype affects oviposition behaviour of pine processionary moth and egg survival at the southern edge of its range

Abstract

Morphological traits of Aleppo pine (Pinus halepensis) needles in native and planted stands at the southern edge of its range influence oviposition behaviour of the pine processionary moth (Thaumetopoea pityocampa). Extreme environmental conditions result in a reduction in needle size of the host plant which corresponds to a lower rate of fecundity in the moth. Our results showed that egg batches were laid closer to the needle buds, especially on native trees with short needles, and this resulted in increased egg mortality. Number of eggs laid by the female moths did not vary between native and planted stands, nor did the number of parasitized eggs of the two common Hymenopteran parasitoids, Baryscapus servadeii and Ooencyrtus pityocampae. The observed differences in egg mortality are likely due to abiotic factors associated with the position of the egg batch on the needles. Thaumetopoea pityocampa eggs require a thermal niche for optimal development, and further measurements are required to determine the thermal threshold of these eggs. Understanding the role of climate in T. pityocampa populations will be an important factor for the survival of the Aleppo pine forests and protecting it from desertification.