Location: Invasive Plant Research Laboratory
Project Number: 6032-22000-013-133-I
Project Type: Interagency Reimbursable Agreement
Start Date: Jun 1, 2024
End Date: May 31, 2025
Objective:
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. The biological control agents include the APHIS-approved thrips, Pseudophilothrips ichini, and a leaf-galling psyllid relative, Calophya latiforceps, both of which can reduce the weed’s competitive advantage by causing damage directly to individual plants and the thrips 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 avoidance of potential 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.
Approach:
There are preliminary data from lab assays and observations from field surveys that provide some insights to the remaining knowledge gaps in this weed-agent system and early evidence suggests our objective and its aims described herein can be achieved and build upon these. Since releases began in May 2019, thrips have established at several release sites, some of which have succumbed to heavy damage. Preliminary results suggest, but further study needs to confirm, that release strategies with large numbers of individuals (ca. 4,000) spread across several smaller releases in diverse habitats will assist in agent establishment. Further research is needed to understand the long-term impacts of the agents on mature Brazilian peppertree vigor as well as impacts on plant populations given plants are large woody perennials and can live for decades. Natural enemies of the thrips may include generalist predators such as ants and spiders and potentially specialists of thrips such as an introduced pirate bug, Montandoniola confusa. It is unclear whether these predators are impacting thrips populations in the wild, but the pirate bug has been shown to impact lab populations. Site specific environmental conditions may impact thrips success and preliminary data suggest sites with more organic soils and sheltered microclimates may benefit thrips. Shortly after herbicide treatment, thrips may be indirectly impacted as they have been shown in the prior funding year to avoid recently treated plants, but more work is needed to understand how the thrips respond to plants recovering from herbicide. In the prior funding year, we demonstrated that thrips could feed on reproductive plant tissues when their preferred vegetative tissues are not flushing. Thrips can cause significant damage and even mortality to seedlings in the laboratory, and there is anecdotal evidence for thrips impacting seedlings in the field, but a replicated study is needed to confirm impacts on seedlings when mature plants are available.
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 its limitations to develop damaging populations. The proposed research described here builds upon the previous discoveries and field observations. To accomplish our objective, we will work collaboratively to address five aims outlined below. The geographic scope will cover field sites across the state and work conducted will consist of field surveys, field experiments, laboratory rearing operations, and laboratory analysis of plant and insect samples.
Aim 1: maintain lab colonies of the thrips biological control agent, Pseudophilothrips ichini
Aim 2: release of the thrips biological control agent and field site selection
Aim 3: determine environmental variables affecting thrips establishment and efficacy
Aim 4: determine the impact of thrips on understory seedling recruitment
Aim 5: integrate Brazilian peppertree biological control with herbicides
