Efficacy of pesticide mixtures on the western flower thrips (Frankliniella occidentalis)

Western flower thrips, Franklinella occidentalis Pergande, is one of the most important insect pests of greenhouses. Greenhouse producers typically apply pesticides as mixtures to mitigate western flower thrips populations; however, there is limited information available on the efficacy of pesticide mixtures. This study assessed nine two-way pesticide mixtures commonly used in greenhouses with products containing abamectin, acephate, azadirachtin, bifenazate, bifenthrin, fenpropathrin, novaluron, pymetrozine, and spinosad. Pesticide mixture compatibility was determined using jar tests. Applications of the mixtures were made to chrysanthemum, begonia, and petunia to determine phytotoxicity; with effects assessed 7 days after treatment application. Bean-dip bioassays were performed in a laboratory using green bean, Phaseolus vulgaris to determine LC₅₀ values for each individual pesticide and the mixtures to establish whether the mixtures were synergistic, antagonistic, or there was no effect. Pesticides were mixed using the formulated products. Concentrations were prepared by developing five serial dilutions, the control was distilled water. Each green bean was excised into 2 mm sections and then dipped into the mixture for 10 seconds. After drying, the beans were placed into 5.0 ml glass vials and approximately 15 ten day old female western flower thrips were added to each vial. Vials were covered with parafilm with 40 holes perforated in the top and placed in a growth chamber. Mortality was assessed after 24 hours, and LC₅₀ values were calculated. Results from the jar tests indicated that all the mixtures were compatible and none of the mixtures were phytotoxic to any of the plant species evaluated.