Multi-generational impacts of the psyllid Arytinnis hakani (Hemiptera: Psyllidae) on growth and survival of the invasive weed Genista monspessulana

Abstract

Pre-release efficacy assessments of biological control agents can identify species with the most potential to impact the target weed. Experiments typically occur within a single generation of the agent, however, and strong impacts on target weeds may take longer to emerge. This study examined the effects of the prospective agent Arytinnis hakani (Hemiptera: Psyllidae) on the invasive weed French broom, Genista monspessulana, over three generations of the psyllid (∼150days) under quarantine conditions. All of the psyllid-free control plants survived to the end of the experiment, whereas 23 out of 28 (82.1%) of the plants infested with psyllids died. Only three plants with psyllids died during the first psyllid generation; plant mortality rate peaked at the transition between the second and third psyllid generations. Plant growth was also reduced on plants with psyllids. Impacts on proportional increases in plant height and total stem length were evident by the end of the first psyllid generation, but effects on proportional change in leaf number were not apparent until the end of the third psyllid generation. By the end of the experiment, average proportional increases in height, total stem length and leaf number were 65.7%, 60.7% and 53.2% lower, respectively, on surviving psyllid-infested plants than controls. Final above-ground biomass of surviving psyllid-infested plants was 66.4% lower on average compared to the psyllid-free control plants. The results of this study highlight the need for pre-release efficacy assessments that allow effects on target weeds to develop over time.