Environmental factors impact and incidence of parasitism of psyllaephagus bliteus riek (Hymenoptera Encyrtidae) on populations of glycaspis brimblecombei moore (Hemiptera Aphalaridae) in mediterranean climatic areas

Abstract

The red gum lerp psyllid, Glycaspis brimblecombei Moore (Hemiptera, Aphalaridae), is an Australian native sap-sucking insect pest of eucalypts that has been first reported for the West Palaearctic Region in 2008 and, in 2010, it has been found also in Italy. Subsequently its primary parasitoid, Psyllaephagus bliteus Riek (Hymenoptera: Encyrtidae), was also detected within the main European and North African infested areas, where no release of the parasitoid was ever performed. This study, carried out in 30 Eucalyptus camaldulensis plantations located along the coast, on the hills and the mountains in Mediterranean climatic areas of Sicily (Italy), aimed to determine the influence of environmental parameters on the incidence of both, the psyllid infestation level and the parasitization activity. P. bliteus reached highest average levels in summer samplings and resulted widespread in Sicily at all detected altitudes without statistically significant differences. P. bliteus parasitization is the main factor lowering G. brimblecombei infestation; this result, together with the accidental and contemporaneous arrival of the host and its parasitoid, could explain the absence of high damage level on eucalypts in Sicily. The most significant metric factors positively influencing G. brimblecombei infestation are the percentage of daily hours above 80% of relative humidity and the average maximum temperature, obviously related to other, but less significant climatic factors. The altitude affects both infestation and parasitization, but single sites could explain significantly more, so that the local conditions where the samplings were carried out have to be considered as the main responsibles for the variability in the obtained results. In any sampled Sicilian site, from sea level to 540 m a.s.l., both the psyllid and its parasitoids show a good adaptation to climatic conditions, confirming that areas fitting for E. camaldulensis growth fit also for P. bliteus activity, and proving that Mediterranean climate, differently from some inland areas of California, does not obstacle its parasitic activity.