Location: Invasive Species and Pollinator HealthTitle: Relative performance and impacts of the psyllid Arytinnis hakani on non-target plants and the target weed Genista monspessulana Author
Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2019
Publication Date: N/A
Interpretive Summary: The introduction of natural enemies from the native range can help improve the control of invasive weeds. Before a natural enemy is released in the weed’s invaded range, tests must be conducted in quarantine facilities to determine whether it will attack native plants. These tests are very conservative, and may exclude natural enemies that would be effective and safe in the field. It is usually assumed that the natural enemy would harm any plant that it is able to feed and develop on in quarantine tests. However, the actual amount of damage to native plants often goes unstudied. Furthermore, tests are often short in duration, and usually are conducted over only one generation of the natural enemy. This study focused on a natural enemy that is under consideration for release in California to help control the invasive shrub French broom. We examined whether the natural enemy could develop on seven lupine species, which are the closest relatives of French broom in California. The natural enemy laid eggs on all seven lupines. It developed to adulthood on six lupines and completed two generations on five, although its numbers were consistently higher on French broom. In another experiment, the natural enemy did not reduce the growth or survival of one lupine species on which it developed, although it killed all the French broom plants that received it. Taken together, these results indicate that the natural enemy is not likely to affect lupines in the field.
Technical Abstract: No-choice tests can help select weed biological control agents with a high degree of host specificity, but may exclude potentially effective agents that can develop on non-target plants under laboratory conditions. Agents are usually considered to be harmful to non-target plant species that support development in no-choice tests. However, the actual amount of damage to non-target plants often goes unstudied, even though agents may exploit non-target plants without inflicting significant harm. Furthermore, tests typically assess whether prospective agents can complete one generation on non-target plants, and rarely examine whether agents are likely to persist on the non-target plants over the long term. Pre-release damage assessments that occur over multiple generations of the agent could help determine whether prospective agents pose a threat to non-target plants under field conditions. This study focused on the psyllid Arytinnis hakani, which is under consideration in California for release against the invasive shrub French broom, Genista monspessulana. We examined the host suitability of seven non-target Lupinus spp. for the psyllid using no-choice tests, and assessed psyllid impacts on Lupinus arboreus, which consistently supported psyllid oviposition and development. The psyllid oviposited on all of the tested Lupinus spp., and completed two generations on five of the Lupinus spp., although numbers of psyllids were highest on French broom. In additional tests, A. hakani did not affect growth or survival of L. arboreus, but dramatically reduced survival of French broom; all French broom plants that received psyllids died. Taken together, these results indicate that Lupinus spp. are suboptimal hosts for the psyllid and were not significantly impacted by its development.