Assessing emigration of the biocontrol agent, Pseudophilothrips ichini, from herbicide-treated Brazilian peppertree

Invasive plant management costs the state of Florida about $45 million, annually. Expenses include a variety of control tactics such as mechanical and chemical. Previous studies have shown that integrating multiple management strategies may help to maximize control of invasive plants, and when combined with biological control may help achieve the same level of control at a lower cost. Pseudophilothrips ichini (Thysanoptera: Phlaeothripidae) was released in Florida in June of 2019 as a biological control agent for Brazilian peppertree, Schinus terebinthifolia, one of the worst invasive plants in Florida. Recent direct toxicity studies have shown that herbicides and biological control were compatible for this system. Over 70% of thrips survived five days after being sprayed with or fed plant material treated with label rate herbicides commonly used to control Brazilian peppertree, except in the case of triclopyr. Only 50% of thrips survived feeding on triclopyr-treated plant material, but thrips demonstrated some aversive behaviors toward triclopyr-treated plant material. In this experiment, we assessed emigration of thrips from plants treated with triclopyr by basal bark application and foliar application of imazapyr, since imazapyr resulted in the greatest survival of thrips in previous direct toxicity experiments. Preliminary results showed that thrips emigrated from herbicide-treated plants to untreated plants and are able to produce offspring, suggesting that under field conditions thrips are capable of escaping from herbicide-treated to untreated plants (refugia). These data provide insight into thrips movement in large scale field trials and demonstrate the need for refugia in integrated management programs.