Temporal optimization of abamectin use on Schinus terebinthifolia used to rear Pseudophilothrips ichini (Thysanoptera: Phlaeothripidae), its biological control agent

Authors: Halbritter, Dale; Leidi, Jorge; Rayamajhi, Min

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2022
Publication Date: 6/26/2022
Citation: Halbritter, D.A., Leidi, J.G., Rayamajhi, M.B. 2022. Temporal optimization of abamectin use on Schinus terebinthifolia used to rear Pseudophilothrips ichini (Thysanoptera: Phlaeothripidae), its biological control agent. Biocontrol Science and Technology. 1-9. https://doi.org/10.1080/09583157.2022.2085661.
DOI: https://doi.org/10.1080/09583157.2022.2085661

Interpretive Summary: When growing invasive plants (Brazilian peppertree) to mass rear biological control insects (thrips), unwanted local pests such as mites can infest and reduce plant quality, causing problems for the thrips colonies. Using pesticides can help minimize the unwanted pest damage but the plants will also be toxic to the thrips colonies until enough time has passed for the pesticide to break down and be non-toxic for thrips. Herein, we determined the amount of time needed for abamectin (a pesticide commonly used to control mites) to break down in Brazilian peppertree before the plants could be fed to the thrips colonies mass reared for field releases. Groups of three plants each sprayed with Avid (2% abamectin) were infested with 40 adult thrips as founding populations after 1, 3, 7, 10, and 14 day waiting periods post-spray, and thrips were allowed to feed for 10 days after which the surviving adults were recovered. The experiment was terminated after the collection of last adult offspring from each plant. At least 75% of each founding population was recovered after 10 days. However, the number of offspring produced by founding adults was different with respect to the delay of infestation with founding adults after abamectin application. Only 50 thrips were produced when infestation of founding adults was carried out after 1-day, 250 to 364 produced for the intermediate days, and 688 produced after the 14-day waiting period. We conclude waiting at least 7 days after abamectin application would be a reasonable balance between maintaining timely production operations and a healthy thrips colony.

Technical Abstract: Mass rearing herbivorous insects used as biological control agents requires a steady supply of optimal host plant material. This often necessitates the use of pesticides to minimize infestations and damage from generalist herbivores. Knowing the efficacy persistence of the pesticide is critical to prevent non-target effects on reared agent populations. We determined the amount of time necessary for an abamectin-based miticide to degrade such that there were minimal impacts on the mass rearing of Pseudophilothrips ichini (Hood), a biological control agent for Brazilian peppertree, Schinus terebinthifolia Raddi, in Florida. The miticide was applied to plants at the label rate (0.31 ml ai L-1) for controlling mites. Groups of three plants were brought into a quarantine facility 1, 3, 7, 10, and 14 d after application and were then each infested with 40 founding adult thrips for 10 d. The experiment was concluded after the last F1 adults were collected from each plant. Founding adult survival was not impacted by delaying infestation after abamectin treatment, with at least 75% recovered alive. However, delaying infestation after abamectin treatment had a significant effect on the number of F1 thrips produced, with, on average, only 50 produced when waiting 1 d, between 250 and 364 for the intermediate wait times (with greater variability), and 688 produced when waiting 14 d. We conclude that waiting 14 d after treatment would achieve optimal colony yields but waiting as little as 7 d may still be a reasonable balance between timely production operations and colony yields.