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 brimblecombeiMoore (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 hasbeen 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 everperformed. This study, carried out in 30 Eucalyptus camaldulensis plantations located along the coast, on the hills andthe mountains in Mediterranean climatic areas of Sicily (Italy), aimed to determine the influence of environmentalparameters on the incidence of both, the psyllid infestation level and the parasitization activity. P. bliteusreached high-est average levels in summer samplings and resulted widespread in Sicily at all detected altitudes without statisticallysignificant 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 highdamage level on eucalypts in Sicily. The most significant metric factors positively influencing G. brimblecombei infes-tation are the percentage of daily hours above 80% of relative humidity and the average maximum temperature, obvi-ously related to other, but less significant climatic factors. The altitude affects both infestation and parasitization, but sin-gle sites could explain significantly more, so that the local conditions where the samplings were carried out have to beconsidered as the main responsibles for the variability in the obtained results. In any sampled Sicilian site, from sea levelto 540 m a.s.l., both the psyllid and its parasitoids show a good adaptation to climatic conditions, confirming that areasfitting for E. camaldulensisgrowth fit also for P. bliteus activity, and proving that Mediterranean climate, differently fromsome inland areas of California, does not obstacle its parasitic activity.