A field trial of the entomogenous fungus Metarhizium anisopliae for control of onion thrips, Thrips tabaci

In Kenya, Thrips tabaci Lind., is an important constraint to onion production. The current strategy to use synthetic pesticides is inadequate and unsustainable. An isolate of Metarhizium anisopliae (Metsch.) Sorok. with high pathogenicity to legume thrips, Megalurothrips sjostedti, and western flower thrips, Frankliniella occidentalis, was tested in field trials as a potential alternative for control of onion thrips. Weekly and bi-weekly applications of the fungus M. anisopliae and bi-weekly spray of the chemical insecticide dimethoate (Rogor((R)) 50) were compared for 3 seasons. M. anisopliae was applied at the rate of 1 x 10(11) conidia ha(-1) and dimethoate was applied at the recommended rate of 17.5 g a.i. ha(-1). In all the trials, thrips density and damage were significantly lower in the fungal and chemical insecticide treatments compared with the untreated control. Onion bulb yield did not differ significantly among the treatments during the first season trial. However, in the second season trial, dimethoate-treated plots provided the greatest bulb yield (17 metric tons ha(-1)) and in the third season trial, M. anisopliae applied weekly recorded the highest yield (24 metric tons ha(-1)). With the exception of spiders, densities of nontarget organisms were higher in plots treated with M. anisopliae than in dimethoate-treated plots. The results indicate the potential of using M. anisopliae for the control of T. tabaci while protecting biodiversity in the onion agroecosystem. (C) 2003 Elsevier Science Ltd. All rights reserved.