Interaction between a naturalized stem galling fungus and an introduced agent, <i>Pseudophilothrips ichini</i> (Thysanoptera: Phlaeothripidae), on the biological control of <i>Schinus terebinthifolia</i> (Sapindales: Anacardiaceae)

Abstract Cophinforma spp. are gall-inducing fungi that can infect the highly invasive Brazilian peppertree ( Schinus terebinthifolia Raddi), in its introduced range in southern Florida, USA. A classical biological control agent, the thrips Pseudophilothrips ichini , has been released to mitigate the invasive potential of S. terebinthifolia. We investigated the synergistic potential of thrips feeding damage and gall formation on S. terebinthifolia management program success. A group of potted S. terebinthifolia saplings were inoculated with Cophinforma. Galled, symptomatic and ungalled, asymptomatic saplings were then paired in laboratory cages for a two-choice test with 40 P. ichini adults. Galled and ungalled plants were assessed for dead stem tips and necrotic stem tissue, with and without thrips present. Larval F 1 thrips were also counted on each plant. Thrips feeding damage significantly increased the number of dead tips and extent of stem necrosis. Regardless of thrips presence, stem tip mortality and extent of necrosis were not significantly different between galled and ungalled plant pairs. Additionally, the maximum number of F 1 larvae counted on stems did not differ between those on galled versus ungalled plants. Gall growth on heavily thrips-damaged plants nearly stopped, while galls continued to grow on plants with little thrips damage. While our results suggest the Cophinforma galls do not impact damage potential or plant preference from P. ichini , more work is needed to understand other factors that may contribute to at least additive impacts on S. terebinthifolia in the field, such as more advanced stages of the fungal infection on mature plants and prolonged thrips feeding damage.