Effect of biological and chemical insecticides on Spodoptera species (Lep., Noctuidae) and marketable yields of tomatoes

Abstract

Various biological and chemical insecticide treatments were evaluated against beet armyworm Spodoptera exigua (Hübner), yellowstriped armyworm Spodoptera ornithogalli (Guenée) and southern armyworm Spodoptera eridania (Cramer) to determine their effects on Spodoptera species, fruit quality and marketable yields of tomatoes Lycopersicon esculentum Mill. Biological insecticides included several Bacillus thuringiensis (Berliner) products including Condor® OF, Dipel® 2X, Javelin® WG, Bactec® III, Biobit® FC, Cutlass® WP and Lepinox® G. Other biological treatments included a baculovirus, SeNPV isolated from S. exigma, and an entomophagous nematode, Steinernema carpocapsae Weiser. Chemical treatments consisted of several insecticides from various classes including a carbamate (methomyl), pyrethroid (fenpropathrin) and an organophosphate (chlorpyrifos). A natural extract from the neem tree azadirachtin and an untreated control were also included in the evaluation studies. Population densities of S. exigua were below the economic threshold level in control plots and there were no significant differences for small, medium and large larvae. Densities of S. ornithogalli and S. eridania larvae exceeded the threshold level and significant treatment differences were observed in their populations. Fruit injuries were significantly higher in nonefficacious treatments that included S. carpocapsae, SeNPVs and untreated controls. Average weight per fruit was not significantly affected by treatment rates of applications, but total marketable yields were significantly higher in efficacious biological, chemical and combination treatments compared with the control.