Comparative Toxicity of Synthetic Insecticides and Bacillus thuringiensis var. kurstaki and Bacillus thuringiensis var. aizawai against the Fall Armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae)

Abstract

The fall armyworm, Spodoptera frugiperda (J.E. Smith) is an important pest of corn. It was first reported to have spread into Thailand in late 2018, with significant outbreaks in the provinces of Mae Hong Son, Tak, Kanchanaburi, and Nakhon Sawan. The fall armyworm starts damaging corn from 7 days after planting until the corn reaches the ear stage by feeding on the leaves, shoots, and ears, causing severe damage. There are several methods of controlling S. frugiperda larvae with the most common being the use of insecticides. The objective of this study was to determine the toxicity levels of insecticides and biopesticides (Bacillus thuringiensis) to fall armyworm. The experiment was conducted using the leaf-dipping method, where corn leaves were dipped into insecticides and then fed to the larvae.  The results showed that after 24 hours, the insecticide Lambda-cyhalothrin had the lowest toxicity, with an LC50 value as high as 49.344 ppm, while the insecticide Emamectin benzoate had the highest toxicity, with an LC50 value as low as 2.578 ppm. The bioinsecticides Bt. var. kurstaki and Bt. var. aizawai were found to be less toxic than Emamectin benzoate, with LC50 values of 2.521×10¹¹ and 3.011´1011 CFU/ml, respectively.  These findings can be used as a guideline for selecting effective insecticides available in the market for controlling fall armyworm. Additionally, to prevent resistance development in pests, it is recommended to implement an integrated resistance. management (IRM) strategy, which is part of integrated pest management (IPM), when making decisions on insecticide use.