Herbivore priority effects and impacts on the Brazilian peppertree biological control agent Pseudophilothrips ichini (Thysanoptera: Phlaeothripidae)

Brazilian peppertree (BP) is a woody shrub that is highly invasive in Florida, Texas, Hawaii, South Africa, and Australia. Since 2019, a flush-damaging biological control agent, Pseudophilothrips ichini Hood (Thysanoptera: Phlaeothripidae), has been released at over 900 sites across Florida. At many sites, we noted damage to flushing leaves caused by native or naturalized Paectes sp. (Lepidoptera: Euteliidae) caterpillars. Our goal was to investigate the possibility of interspecific competition affecting thrips efficacy. We conducted a laboratory study comparing first generation (F₁) thrips numbers with respect to herbivore priority: (1) thrips before Paectes (n=4), (2) Paectes before thrips (n=4), and (3) thrips alone (control) (n=4). Each replicate arena consisted of a potted BP plant housed in a vented acrylic box. For treatment 1, plants were inoculated with 30 adult thrips. Two weeks later, five Paectes larvae were added when F₁ thrips larvae were observed. For treatment 2, plants were first inoculated with five Paectes larvae and 30 adult thrips were added 1 week later. For treatment 3, plants were inoculated with 30 adult thrips. Results suggested thrips performance may be negatively impacted when Paectes are present before thrips, but there was high variability. We repeated treatments 2 and 3 each with six more replicates and results continued to suggest a negative impact of Paectes on P. ichini numbers. The application of this study is to develop protocols to identify thrips release sites at which thrips populations and damage to the target weed would be maximized.