Location: Invasive Plant Research Laboratory
Project Number: 6032-22000-013-119-A
Project Type: Cooperative Agreement
Start Date: Sep 1, 2023
End Date: Apr 28, 2024
The primary purpose of this project is to reduce populations of the aggressive invasive weed, Brazilian peppertree by the development of a newly 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. Methods will be developed 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. Recently, July 2019, a permit was issued by USDA/APHIS and this thrips was released in Florida for biological control of Brazilian peppertree. A second insect, Calophya latiforceps, a leaf-galling psyllid has also been approved for release in Florida. Calophya latiforceps is completely host specific and will only feed and reproduce on 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 its unable to exploit the weed. This proposal seeks support to conduct research that mitigates these potential obstacles.
After two years the thrips appears to be persisting in numerous release sites and research suggests these goals and objectives described herein can be achieved. Preliminary results suggest, but further study needs to confirm, that release strategies with large numbers of individuals (over 1000 individuals), frequent releases, in diverse habitats and manipulation of plant phenologies will assist in agent establishment. Grooming of field populations of Brazilian pepper can increase the production of flush tips, the preferred feeding site of thrips. Natural enemies of the thrips may include generalist predators though parasitoid natural enemies have not been found attacking the thrips P. ichini after releases. Research initiated to determine safety of the agent suggests the field specificity of the thrips will match the results from quarantine host range tests. Research suggests the thrips will respond to Brazilian pepper foliage odors in olfactometer bioassays. Behavioral responses were found with colored sticky traps suggesting that these will assist in field monitoring. Safety of the thrips P. ichini, toward non target species was examined during quarantine host range tests and overseas surveys. These studies conducted from 2007 to 2016 showed that the thrips had a narrow host range and was restricted to the target weed Brazilian pepper and an invasive congener, S. molle. 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 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. 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. The proposed research described here builds upon the previous discoveries. Objective 1, ‘maintains lab colonies’ 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 release of the Brazilian pepper thrips throughout the invaded range; Objective 3 develop standard operating procedure to mass produce the thrips; Objective 4 determine the impact of flowering on thrips follows up on observations that the thrips may be directly impacting the target weed reproduction; and Objective 5 integrate Brazilian pepper biological controls with herbicides will assist land managers reduce pesticide applications by combining with biological control.