Location: Invasive Plant Research Laboratory
Project Number: 6032-22000-013-139-A
Project Type: Cooperative Agreement
Start Date: Jun 1, 2024
End Date: Apr 30, 2025
Objective:
The primary purpose of this project is to reduce populations of the aggressive invasive weed, Brazilian peppertree by the deployment of an approved biological control agent. This environmentally safe, cost-effective, and sustainable means of weed control will be accomplished with the mass production, distribution, and evaluation of the approved thrips, Pseudophilothrips ichini. Established methods will be implemented and improved as needed to mass produce, release, detect, evaluate the safety and impact of the thrips on the target weed.
Approach:
After 4 years of releases across the state, thrips have become established at numerous release sites and survey data and research suggests the goals and objectives described herein can be achieved. Preliminary results suggest, but additional field data needs to confirm, that release strategies with large numbers of individuals (over 1000 individuals), several repeated releases, releases in diverse habitats, and manipulation of plant phenologies will assist in agent establishment. Natural enemies of the thrips may include generalist predators though parasitoid natural enemies have not been found attacking the thrips P. ichini after releases. Further work is needed to identify other potential natural enemies and the impacts they may have.
After completing quarantine host range tests, the continued success of a classical biological control program depends on the mass production, redistribution, and examination of the potential of the approved agent and their limitations to develop outbreak populations. Improvements in the ongoing mass rearing of the thrips continue. For example, different substrates for rearing thrips were tested and organic mulch increased pupal survival compared to other materials. When the thrips are fed previously damaged foliage with low levels of nutrients, they were able to mitigate the decreased plant quality by modifying their life cycle. We continue to optimize plant nutrition to maximize thrips fecundity. The potential for control of the target weed by small populations of thrips was demonstrated pre-release in quarantine cages where one generation of adult thrips reduced sapling tip number and plant growth by 80%. These results were confirmed under field conditions, where we are beginning to see field sites with damage levels comparable to those seen in captive studies.
The proposed research described here builds upon the previous discoveries. Objective 1, “Maintain lab colonies of the Brazilian peppertree biological control agent” builds upon the previous research documenting the benefit of pupation substrates and plant fertilizer in thrips survival. Previous research showed the thrips is a flush feeder that exploits seasonably available, actively growing tips. Objective 2 “Field site selection and release of the agent” builds on field survey data and will continue to ensure coverage of agents across the state; Objective 3 ‘Determine environmental variables affecting agent establishment and efficacy’ will investigate impacts of predators, plant chemistry and genetics, and site-specific variables, building on observed trends in previous field surveys; Objective 4 “Determine the impact of the agent on seedling recruitment” will help predict how ongoing damage from agents translates to weed population reduction; and Objective 5 “Integrate Brazilian peppertree biological control with herbicides” will assist land managers reduce pesticide applications by combining with biological control.
