Location: Invasive Plant Research Laboratory
Project Number: 6032-22000-013-138-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.
Brazilian pepper is one of the most invasive weeds in Florida covering over 280,000 hectares in the peninsula alone. To limit the Brazilian peppertree invasion, public land managers in the state of Florida spend nearly $3 million annually on chemical and mechanical controls. However, these controls are often ineffective or problematic due to the weed’s ability to regrow from cut stumps and the inaccessibility of many remote stands. Because of these difficulties, the lack of effective controls, and their high cost, classical biological control has been developed for the sustainable management of Brazilian peppertree. Numerous phytophagous insects have been tested as potential agents but most exhibited broad host ranges and were rejected. However, a thrips Pseudophilothrips ichini is very specific and damaging to the target weed. In July 2019, a permit was issued by USDA/APHIS and this thrips was released in Florida for biological control of Brazilian peppertree. Biological control agents in general may fail to establish in the introduced area or may exert less than satisfactory control of the target weed. These problems may be mitigated by allocation of resources to produce abundant numbers of agents for release, frequent releases of agent at a range of densities and locations, and avoidance of potential factors that exert biotic resistance. The relationship between the target weed and agent may not be well understood, and releases may occur during a period when it’s unable to exploit the weed. This proposal seeks support to conduct research that mitigates these potential obstacles.
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.
