UC Riverside

Citrus thrips, Scirtothrips citri (Moulton), is a plant-feeding pest most widely recognized for damage caused to citrus and mango fruits. Citrus thrips have also become a significant pest in California's blueberries. Avocado thrips, Scirtothrips perseae Nakahara, is a pest of avocados (Persea americana Mill. [Lauraceae]) in California. Pesticides are often used to manage these two species of thrips and therefore, the likelihood of resistance development is high. There is increasing pressure in the United States to move away from broad-spectrum insecticides and focus on alternative methods of control, e.g., genetically modified crop plants expressing Bt (Bacillus thuringiensis) toxins, use of biorational insecticides such as toxic Bt protein sprays and entomopathogens (such as various strains of Beauveria bassiana Balsamo, and other agents). Integrated pest management programs are essential for any agricultural commodity. The goal of the work described here is to add to the foundation of knowledge to improve the integrated pest management of citrus thrips and avocado thrips. The research conducted for this disseration 1) examined alternatives to traditional insecticides (Bt protein sprays and several strains of B. bassiana) to control both avocado and citrus thrips in the laboratory and resulted in no efficacy of the Bts tested but one strain of fungus, the commercially available strain was able to infect citrus thrips at field obtainable levels, 2) tested the commercially available strain in different formulations and water regimes against citrus thrips in blueberry fields which resulted in some control but not enough to strongly recommend this as an alternative to traditional pesticides, 3) evaluated the impact of some of the insecticides registered for avocado thrips management on the beneficial native predaceous mite Euseius hibisci Chant in avocado orchards and found that each of the pesticides harmed the mite but at varying levels and durations, 4) assessed citrus thrips oviposition on blueberry varieties with choice and no-choice tests and it was determined that citrus thrips likely oviposit to differing degrees in some plants over others, and finally 5) determined that citrus thrips in the Americas was actually a complex of species that were nearly morphologically identical but molecularly quite distinct.