Short and long term effects of some bio-insecticides on Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) and its coexisting generalist predators in tomato fields

Abstract

Tomato leaf miner, Tuta absoluta Meyrick (Lepidoptera: Gelechiidae), is one of the most destructive pests of tomato in many parts of the world including Iran. Field studies were conducted to determine the short and long term effects of Bacillus thuringiensis var Kurstaki (Bt), azadirachtin (AZ), a mix of AZ + Bt, and indoxacarb, as a current chemical insecticide, on T. absoluta larvae. Also, effects of the insecticides were studied on the coexisting generalist predators, Coccinella septempunctata L., Chrysoperla carnea Stephens and Syritta sp. Sampling of T. absoluta and its coexisting generalist predators were performed 1 day before treatment (DBT) and one, 5, 8, 14 and 19 days after treatment (DAT). The results indicated significant short term effect of indoxacarb on the pest larvae. Indoxacarb reduced T. absoluta density and damages. Bt, AZ and mixture of them significantly suppressed the larval density at 19 DAT and caused significant reduction in leaf, stem and fruit damage. The highest long term effect on the pest abundance and damage were observed in Az + Bt caused 100% reduction in fruit and foliage damage compared to the control. The highest and lowest adverse effects on C. carnea, C. septempunctat and Serrita sp. were observed in indoxacarb and Bt treatments, respectively. Findings of this study imply that the mixture of Az + Bt has the highest selective toxicity on the pest and the lowest effect on its coexisting generalist predators.

Keywords

• tomato
• leafminer
• bt
• azadirachtin
• indoxacarb
• toxicity