Ecological host range and potential non-target impacts of Pseudophilothrips ichini (Thysanoptera: Phlaeothripidae) on plants native to Australia and the United States

Pre-release quarantine testing of weed biological control agents is frequently done using simple no-choice tests. However, these fundamental host range tests are very conservative and do not realistically depict how potential biological control agents might interact with surrounding non-target plant species in the field. This can cause the rejection of a safe agent. Ecological host range studies in areas where the biological control agent is native or already present can test the validity of laboratory findings with the advantage of allowing the agent to use host-seeking behaviors or other cues. A weed biological control program targeting Schinus terebinthifolia Raddi (Anacardiaceae) was given permission to release Pseudophilothrips ichini (Hood) (Thysanoptera: Phlaeothripidae) in Florida, USA in 2019. Information from Florida’s program has provided insight for other countries with invasive Brazilian peppertree, such as Australia, which has several culturally and ecologically important non-target species that are closely related to S. terebinthifolia. To evaluate the risk for non-target attack by P. ichini on these non-target species, we performed an open field experiment to simulate the spillover risk of these insects in both the presence and absence of their preferred host, S. terebinthifolia. The results suggest that P. ichini populations may spill over onto two non-target plants in the absence of their preferred host and could pose a risk to non-targets in Australia.