Evaluation of Insecticides against Onion Thrips and Crop Phenology Based Population Fluctuates

Abstract

Onion (Allium cepa L.) is one of the most important vegetable crops commercially grown in Ethiopia. However, its productivity in Ethiopia is far below the world average. Among constraints of onion productivity in Ethiopia, high infestations of thrips are the most important ones. This field experiment was conducted to evaluate the efficacy of insecticides in controlling onion thrips and to analyze the population dynamics of thrips in relation to crop phenology in the Central Rift Valley of Ethiopia in 2022. The experiment evaluated four insecticides (lambda-cyhalothrin, profenofos, spinetoram and imidacloprid), which were laid out in a randomized complete block design with four replications. Two thrips species (Thrips tabaci and Frankliniella occidentalis) which belong to the Thripidae family were observed. Thrips tabaci accounted for 91.90%, while Frankliniella occidentalis accounted for 8.10% of the thrips collected with yellow water traps in the study area. The overall thrips population was higher at the vegetative growth stage, and the levels of the population decreased when the plants approached physiological maturity. Among the four evaluated insecticides against onion thrips, the yield increased by 48.88% and 43.78% for spinoteram and imidacloprid treatments, respectively, compared to the control. The lowest mean marketable bulb yield among the insecticide treatments was obtained from lambda-cyhalothrin, which suggests a loss in its efficacy and the development of resistance. Future studies ought to focus on the evaluation of different chemistries of insecticides, schemes of insecticide application, and integration of non-pesticide methods in to the current pesticide-dependent onion pest management method.