Using life-history parameters and a degree-day model to predict climate suitability in England for the Japanese knotweed psyllid Aphalara itadori Shinji (Hemiptera: Psyllidae)

Japanese knotweed, Fallopia japonica, is an invasive weed that is spreading rapidly in large parts of Europe and North America. To reduce knotweed density, the knotweed psyllid Aphalara itadori was recently introduced from Mt. Aso, Kyushu Island of Japan into southeastern England as a classical weed biological control agent. To determine whether climate differences between the areas of origin and introduction might impede A. itadori, the effects of temperature on the development, survival, longevity and fecundity of Kyushu Island population of A. itadori were investigated to predict what the phenology and voltinism of the insects should be in southeastern England. The intrinsic rates of natural increase, survival rates and fecundity rates of A. itadori were significantly higher at 20 and 25 °C than at 15 and 30 °C, indicating that the psyllid is adapted for July and August temperatures found in both Mt. Aso and a representative site of southeastern England. The survival rate of A. itadori was significantly lower at 15 °C than at 20 and 25 °C, but there was still positive population growth at 15 °C. The estimated numbers of generation per year were also similar between Mt. Aso and the southeastern England for A. itadori. For these reasons, we believe that A. itadori population from Mt. Aso should be able to thrive in at least some parts of southeastern England.