Interaction between a naturalized stem galling fungus and an introduced agent, Pseudophilothrips ichini (Thysanoptera: Phlaeothripidae), on the biological control of Brazilian peppertree

Authors: Halbritter, Dale; RAYAMAJHI, MIN - Retired ARS Employee; MEDEIRA, PAUL - Retired ARS Employee; Leidi, Jorge; TELMADARREHEI, TELMAH - University Of Florida; MINTEER, CAREY - University Of Florida

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Galls are abnormal plant growths often caused by the infection of a microorganism and galls can change how nutritious plants are to herbivores. We have discovered that the plant we are trying to manage, Brazilian peppertree (BP), using an insect biological control agent, a species of thrips, will occasionally have galls on its stems caused by a naturally-occurring fungus identified in a previous study. The problem here is that we do not know whether the galls may help or hinder the effectiveness of the biological control agent in the field or whether galled food plants will be more or less nutritious to agents mass produced in the laboratory. To solve this problem, we compared the damage the thrips agents caused to galled and ungalled plants and the number of thrips agents we saw feeding on stems of galled and ungalled plants in a laboratory study. We showed that plants with thrips feeding damage had significantly more dead stem tips and more dead tissue than plants without thrips feeding damage. However, the amount of damage and dead stem tissue on galled plants was no different than amounts on ungalled plants, and thrips were equally abundant on both. Our accomplishment is that we now understand how the fungus and thrips may interact at early stages of infection and under short term thrips feeding damage. This has set the stage for the next step which is to find out if advanced stages of infection and prolonged thrips damage can combine to enhance damage to BP.

Technical Abstract: Cophinforma sp. are gall-inducing fungi that can infect the highly invasive Brazilian peppertree (BP), Schinus terebinthifolia, in its introduced range in southern Florida. A classical biological control agent, the thrips Pseudophilothrips ichini, has been released to mitigate the invasive potential of BP. We investigated the synergistic potential of thrips feeding damage and gall formation on BP management program success. A group of potted BP saplings was inoculated with Cophinforma and galled, symptomatic and ungalled, asymptomatic saplings were 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 F1 thrips were also counted on each galled and ungalled 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 F1 larvae counted on stems did not differ between those on galled versus ungalled plants. While our results suggest that damage from Cophinforma galls does not impact damage potential from P. ichini or plant preference, other factors may contribute to at least additive impacts on S. terebinthifolia in the field, such as during more advanced stages of the fungal infection and with prolonged thrips feeding damage. More work is needed to explore agent impacts within the context of the broader environment.