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

Authors: Hogg, Brian; Moran, Patrick; Smith, Lincoln

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2016
Publication Date: 6/1/2016
Citation: Hogg, B.N., Moran, P.J., Smith, L. 2016. Multi-generational impacts of the psyllid Arytinnis hakani (Hemiptera: Psyllidae) on growth and survival of the invasive weed Genista monspessulana. Biological Control. 100(1):87-93. doi: 10.1016/j.biocontrol.2016.05.015.

Interpretive Summary: French broom, Genista monspessulana, is an invasive shrub from the Mediterranean area of Europe that is widespread in California and southern Oregon, and is also problematic in Australia, New Zealand and Chile. It grows up to 3-5 m tall and can live 10-15 years. It was originally brought to California as an ornamental plant, and now infests at least 40,000 hectares (about 100,000 acres) in the state. Mature French broom plants often produce thousands of seeds that can lie dormant in the soil for years. The weed outgrows and outcompetes native plant species, and increases the risk of wild fire. The psyllid Arytinnis hakani is under consideration as a potential agent for control of French broom in California. This insect pierces the plant tissue and feeds on plant fluids. It was accidentally introduced to Australia, where it has been reported to kill plants in many locations. This study examined whether this psyllid is capable of reducing the growth and survival of French broom. The experiment took place over three generations of the psyllid (about 150 days), which is longer than most studies of this type. Plants were put in cages in a quarantine greenhouse and either received or did not receive psyllids. All of the plants without psyllids survived to the end of the experiment, whereas over 80% of the plants with psyllids died. Most plants died during the second and third psyllid generations, and negative effects on plant growth intensified as time went on. These results show that the psyllid has clear potential to help control French broom in California.

Technical Abstract: Pre-release efficacy assessments can identify agents 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 psyllid generations (~150 days). 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.