Biorational control strategies for Scirtothrips aurantii that minimize non-target effects on arboreal and edaphic predatory mites
Grout TG
Citrus Research International, PO Box 28, Nelspruit, 1200 South Africa.
Correspondence: tg@cri.co.za
South African citrus thrips (SACT), Scirtothrips aurantii Faure (Thripidae), is an indigenous pest of citrus in southern Africa and is often responsible for cosmetic damage to fruit that prevents the fruit from meeting export quality standards. Although the population density of SACT is largely determined by the availability of new, tender foliage (Gilbert MJ, Bedford ECG. 1998. In: Bedford ECG et al. editors. Citrus Pests in the Republic of South Africa. Second edition. 164¨C170. Republic of South Africa: Agricultural Research Council.), a complex of natural enemies helps to suppress the pest population. Some insect predators such as anthocorids, chrysopids and Thysanoptera are seldom abundant and levels of parasitism by Goetheana incerta Annecke are generally low. Predatory mites, and to a lesser extent, spiders, seem to be the most consistently abundant natural enemies both in the trees and in the soil below trees where SACT pupates. Little research has been conducted on non-target effects on spiders but recent research on the soil mite Androlaelaps sp. (Laelapidae) and earlier research on arboreal Euseius spp. (Phytoseiidae) (Grout TG, Richards GI.1992. Experimental & Applied Acarology 15: 199¨C204.; Grout TG et al. 1997. Experimental & Applied Acarology 21: 171¨C177) has enabled the selection of thripicides that are the least detrimental to these natural enemies. The efficacies of these and other biorational treatments were compared in the field with a view to finding the most effective but least disruptive thripicide. Application of insecticides via drip irrigation was also evaluated as a means of reducing non-target effects. Foliar treatments showing reasonable efficacy against SACT coupled with reduced mortality of predatory mites were: abamectin (0.00036% a.i.) plus oil (0.15%), spinosad (0.0072% a.i.) plus oil (0.3%), tartar emetic (0.199% a.i.) plus sugar (0.2%) and thiacloprid (0.0144% a.i.) plus oil (0.25%). Both dimethoate (36 g a.i./tree) and imidacloprid (2.1 g a.i./tree) showed promise as chemigation treatments.
