Pruning Brazilian pepper trees to augment field populations of the biological control agent Pseudophilothrips Ichini

Authors: Wheeler, Gregory; MINTEER, CAREY - University Of Florida; Palacios, Jean; Halbritter, Dale; DAVID, AARON - Archbold Biological Station

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/3/2024
Publication Date: 8/1/2024
Citation: Wheeler, G.S., Minteer, C., Palacios, J.N., Halbritter, D.A., David, . 2024. Pruning Brazilian pepper trees to augment field populations of the biological control agent Pseudophilothrips Ichini. Biological Control. 105550. https://doi.org/10.1016/j.biocontrol.2024.105550.
DOI: https://doi.org/10.1016/j.biocontrol.2024.105550

Interpretive Summary: Brazilian peppertree is a perennial ornamental tree has become one of the worst invasive species of southern Florida. In the USA, Brazilian pepper is invasive in California, Florida, Hawaii, and Texas. To limit the invasion, land managers in the state of Florida spend nearly $3 million annually on Brazilian pepper chemical and mechanical control. These herbicidal controls have many limitations such as damage to non-target vegetation, are prohibitively expensive in many situations, and they typically require annual retreatments. A sap-feeding biological control agent, a thrips, was introduced in Florida in 2019. In laboratory colonies the thrips preferred to feed and often would kill the seasonal flushing leaves and stem tips. To produce sufficient thrips for field releases, they have been mass produced on hundreds of potted weed plants in laboratories and screenhouses at several research facilities. To increase thrips survival, development and reproduction, plants were fertilized and pruned to produce flushing leaves. Periodically, thrips were collected from these production facilities and transported for release at field sites. We developed a method presented herein that mass produces the biological control agents in gardens using existing populations of the weed at field sites. This method employees period pruning of the weed which stimulates flush regrowth. This flush regrowth is highly attractive and nutritious to the biological control agent. Agents fed this regrowth had 4 times greater fecundity compared with agents fed normal leaves. This method should assist land managers produce biological control agents on their properties to distribute to their highest priority infestations.

Technical Abstract: Brazilian peppertree, Schinus terebinthifolia (Anacardiaceae) is an invasive weed of natural and agricultural areas of California, Florida, Hawaii, and Texas, USA. A thrips, Pseudophilothrips ichini, is being mass produced and released as an approved agent for biological control of this invasive weed. The P. ichini thrips are flush feeders, especially the larvae, that exploit seasonal new plant growth. Adult P. ichini thrips selected pruned, re-flushing Brazilian pepper plants, and produced 4-fold more F1 thrips than those that chose unpruned, non-flushing plants. To determine if pruning increased the abundance of foliar flush production, field populations of Brazilian peppertree in the invaded range were pruned every 3 months for 14 months. The pruned Brazilian pepper plants produced more flush leaves, that continued to be produced for longer periods, compared with seasonal unpruned plants. Following pruning, re-flushed Brazilian peppertree leaves had greater percent moisture (65.0% vs 60.0%) and nitrogen (1.6 % vs 1.3%) compared with non-flushing leaves. Several terpenoid constituents had greater concentrations in the re-flushed leaves compared with the non-flushing leaves including Germacrene D, Caryophyllene, Bicyclogermacrene, and Sabinene. These results suggest that routine pruning of Brazilian pepper plants at field sites can improve plant quality and may increase the production of thrips. This management approach can be implemented at field nurseries for the mass production of agents.