Location: Invasive Plant Research Laboratory
Project Number: 6032-22000-013-157-A
Project Type: Cooperative Agreement
Start Date: Sep 22, 2025
End Date: May 31, 2026
Objective:
The primary objective of this project is to reduce the competitive advantage of the highly invasive weed, Brazilian peppertree, through the mass production and field release of one or more biological control agents. 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. One of the APHIS-approved biological control agents, the thrips Pseudophilothrips ichini, has been shown to reduce the weed’s competitive advantage by causing damage directly to individual plants and may potentially reduce seedling survival, thereby reducing weed populations over time. However, 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 conducting studies to better understand and avoid ecological factors that exert biotic resistance. The relationship between the target weed and its agents may not be well understood in the weed’s introduced area, and hence the need for research that both increases agent releases and contributes to understanding ecological interactions and variables affecting agent success. When optimized, this environmentally safe, cost-effective, and sustainable means of weed control can be accomplished with the mass production and distribution of insect agents, surveys of agent populations, and surveys of target plant damage and native plant community responses. This work requires the combined efforts of cooperators across the state focusing on the following aims:
Aim 1: Maintain lab colonies of the Brazilian peppertree biological control agent, the thrips Pseudophilothrips ichini
Aim 2: Field site selection and release of the agent
a) Increase agent releases in mangrove habitats
Aim 3: Investigate the potential of other species of biological control agents
Aim 4: Model agent probability of establishment, efficacy, and/or range expansion
Aim 5: Improved survey data collection/consolidation and long-term agent performance/impact assessments at well-established sites
a) Improve efficiency of data collection and exchange
b) Evaluate thrips dispersal
c) Establish BP canopy extent, density, and damage as baseline for future site-scale impact monitoring
Approach:
Data from lab assays and observations from field surveys provide insights to the remaining knowledge gaps in this weed-agent system and evidence suggests our objective and its aims described herein can be achieved and build upon these earlier findings. Since releases began in May 2019, thrips have established at multiple release sites, and many of the older sites have succumbed to heavy damage. Data suggests that release strategies with large numbers of individuals (~4,000 to 6,000) spread across several smaller releases in diverse habitats aids in agent establishment, but thrips don't establish at all sites. Further research is needed to understand the long-term impacts of established agents on mature Brazilian peppertree vigor as well as impacts on plant populations given plants are large woody perennials and can live for decades. Site specific environmental conditions may impact thrips success and preliminary data suggest sites with more organic soils and sheltered microclimates may benefit the thrips. Variations in plant genetics may also impact plant resistance to agent damage. These variables collected in FY 24 will be incorporated into models to help predict site suitability for agent success.