Location: Exotic and Invasive Weeds Research
Title: Pre-release efficacy test of the prospective biological control agent Arytinnis hakani on the invasive weed Genista monspessulana Authors
Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 15, 2014
Publication Date: June 1, 2014
Citation: Cook, B.S., Smith, L. 2014. Pre-release efficacy test of the prospective biological control agent Arytinnis hakani on the invasive weed Genista monspessulana. Biocontrol Science and Technology. 24(6):641-651. Interpretive Summary: French broom (Genista monspessulana) is a leguminous shrub from western Europe that has invaded rangeland, woodlands and rights-of-way in the Pacific western USA. The plant produces thickets that displace native species and increase the risk and intensity of wildfire. Large quantities of seeds are produced which remain dormant until the soil is disturbed, which makes restoration extremely difficult. The plant contains quinolizidine alkaloids which are toxic to many animals including livestock. The plant is a target of biological control in the USA, Australia and New Zealand. Foreign exploration studies ranked the psyllid, Arytinnis hakani, as the prospective agent with the highest potential as a prospective biological control agent. It is important to evaluate the potential for a prospective agent to control the target weed before investing heavily in host specificity evaluations. We conducted laboratory experiments exposing small plants to various numbers of psyllids to determine how much they affect the growth and survival of its host plant. High densities of psyllids reduced production of leaflets by up to 16% and of plant height by up to 29% during a 45-day period. The psyllid may have much more effect in the field where French broom has to compete with other plants and the psyllid has many generations per year. The results indicate that the psyllid is worthy of further host plant specificity testing.
Technical Abstract: In weed biological control, conducting a pre-release 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 U.S.A. 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, percent change in plant height and the final number of leaflets per cm of plant height. 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 to 18% at the lowest density (4 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. Increase in plant height and the number of leaflets relative to uninfested plants was reduced by 16% and 29%, respectively, at the highest infestation levels. This insect is multivoltine, so prolongation of the infestation period may have greater impact on the plant.