This thesis focuses on a recently approved biological control agent, the psyllid Aphalara itadori for biological control of invasive knotweeds. Two different populations of A. itadori are available for field releases that have differential performance on three knotweed species and have distinct climate adaptations. A southern population from the island of Kyushu in Japan is recommended for release on Japanese and Bohemian knotweeds (Fallopia spp.) while the northern population from Hokkaido develops best on giant knotweed. In the first chapter, different release approaches are evaluated including the importance of release frequency and the genetic composition of released populations for establishment success in southern Michigan. Kyushu psyllids were released on Japanese knotweeds and a mix of Kyushu and Hokkaido psyllids were released on Bohemian knotweeds either as part of a single release or two introduction events. Signs of a phenological mismatch were seen for Kyushu psyllids and limited overwintering success. Release frequency appeared to be more important at smaller release sizes.In the second chapter the effects of hybridization between Kyushu and Hokkaido psyllids are investigated on host preference and performance. Parental and reciprocal hybrid psyllids showed largely indiscriminate host choice behavior and laid eggs on all three knotweed species offered. This behavior was maladaptive for Hokkaido psyllids that were not able to develop on Japanese and Bohemian knotweeds. Hybridization had a neutral effect on reproductive potential and a neutral to positive effect on development success. These results indicate that intentional hybridization may help to increase establishment success and control of different knotweed species in different climatic regions.
Read
