Determining the edge effect of pine processionary moth (Thaumetopoea pityocampa) in its horizontal distribution in the stand

Pine processionary moth is one of the most important forest pests in the Mediterranean Basin. There is need to explore its distribution behaviour to undertake effective control and determine the edge effect of its horizontal distribution in the stand. Five trial sites damaged by the insect were selected and traps installed in all trees in the sites. The number of nests and larvae was counted and diameter increment cores were taken. The distance to the edge of the stand revealed that there was no statistical difference in the number of nests and larvae up to 25 m while there was a statistically significant difference(0.5%)at [25 m. There was a 2-fold difference in the density of nests between 0 and 25 m and [25 meters, and a 3.8-fold difference in the number of larvae. The effect of pine processionary moth on tree diameter was not significant between trees at the edge of the stand and those in the stand.

Is the expansion of the pine processionary moth, due to global warming, impacting the endangered Spanish moon moth through an induced change in food quality?

Recent climate change is known to affect the distribution of a number of insect species,resulting in a modifica­tion of their range boundaries.In newly colonized areas,novel interactions become apparent between expanding and endemic species sharing the same host.The pine processionary moth is a highly damaging pine defoliator,extending its range northwards and upwards in response to winter warming.Its expansion in the Alps has result­ed in an invasion into the range of the Spanish moon moth,a red listed species developing on Scots pine.Pine processionary moth larvae develop during winter,preceding those of the moon moth,which hatch in late spring.Using pine trees planted in a clonal design,we experimentally tested the effect of previous winter defoliation by pine processionary moth larvae upon the survival and development of moon moth larvae.Feeding on foliage of heavily defoliated trees(>50%)resulted in a significant increase in the development time of moon moth larvae and a decrease in relative growth rate compared to feeding on foliage of undefoliated trees.Dry weight of pupae also decreased when larvae were fed with foliage of defoliated trees,and might,therefore,affect imago perfor­mances.However,lower defoliation degrees did not result in significant differences in larval performances com­pared to the control.Because a high degree of defoliation by pine processionary moth is to be expected during the colonization phase,its arrival in subalpine pine stands might affect the populations of the endangered moon moth .