Contact Toxicity of Selective Insecticides for Non-Target Predaceous Hemipterans in Soybeans

Abstract

New insecticides with selectivity for lepidopterous pests are currently being registered for use in soybeans throughout the mid-south. The effect of these products on important hemipteran beneficials found in Louisiana soybean agroecosystems was tested in the laboratory and the field. In the laboratory, adult and nymphal hemipteran predators were exposed to foliage treated with selective insecticides (methoxyfenozide and indoxacarb) or broad-spectrum pyrethroid and organophosphate insecticides, and survival between these two groups was compared using contingency table analysis. Survival of Geocoris punctipes (Say), Tropiconabis capsiformis (Germar), or Podisus maculiventris (Say) adults and nymphs exposed to a rate of 0.12 kg Al/ha of indoxacarb or a rate of 0.22 kg Al/ha of methoxyfenozide was consistently higher than their survival when exposed to 0.03 kg Al/ha of lambda-cyhalothrin or 0.84 kg Al/ha of acephate. At the rates tested, indoxacarb reduced the survival of P. maculiventris adults and nymphs more than methoxyfenozide. In the field, indoxacarb at 0.05 and 0.07 kg Al/ha significantly reduced G. punctipes populations at 2 and 7 days after treatment compared to the untreated check. Methomyl or thiodicarb, both at 0.5 kg Al/ha, also significantly reduced populations of T. capsiformis and Nabis rosiepennis (Reuter) 2 days after treatment. None of the other treatments tested in the field (methoxyfenozide, spinosad, and permethrin) significantly reduced predator populations. The results from this study indicate that both methoxyfenozide and indoxacarb will affect hemipteran predator populations less than pyrethroid, organophosphorus, or carbamate insecticides. Of the two, however, indoxacarb may affect predators more than methoxyfenozide.