Prerelease efficacy test of the psyllid,Arytinnis hakani,a prospective biological control agent of the invasive weed Genista monspessulana

In weed biological control, conducting a prerelease efficacy test can help ascertain if prospective biological control agents will be capable of controlling the target plant. Currently, the phloem-feeding psyllid, Arytinnis hakani, is being evaluated as a prospective agent for the exotic invasive weed, Genista monspessulana, in the USA. Small potted plants were exposed to 0, 4, 8, 12 or 16 A. hakani second-instar nymphs which were allowed to develop on the plants for six weeks in an incubator at 18°C. Increasing A. hakani densities had a significant negative impact on the number of leaflets grown, per cent change in plant height and the final number of leaflets per centimeter of plant height. Increase in plant height and the number of leaflets relative to uninfested plants were reduced by 16 and 29%, respectively, at the highest infestation levels. Psyllids did not increase leaf senescence. One of the 10 plants that was exposed to 16 psyllids died, whereas none of the others died. Weekly nymphal mortality was 10–18% at the lowest density (four psyllids), but was at least 40% at the three highest densities. Although dead nymphs were replaced weekly, insect mortality may have reduced impact on the plants, especially at the higher densities. This insect is multivoltine, so prolongation of the infestation period may have a greater impact on the plant.