Effects of a plant activator and insecticides on tobacco thrips (Thysanoptera : Thripidae) feeding and survival

摘要

Tomato spotted wilt tospovirus (TSWV) remains a major threat to several cropping systems in the southeastern United States. The tobacco thrips, Fran-kliniella fusca (Hinds), is one of the most common thrips infesting hosts of TSWV in Georgia and is also the most abundant vector of TSWV in Georgia's peanut, Arachis hypogaea L., and flue-cured tobacco, Nicotiana tabacum L., crops. Attempts at managing viral diseases in agronomic and horticultural crops through chemical control of insect vectors have been largely unsuccessful or uneconomical (Todd et al. 1994). One insecticide, phorate (BASF, Research Triangle Park, North Carolina), has demonstrated consistent, low-level suppression of TSWV in peanut (Todd et al. 1996). Although the actual mechanism responsible for this suppression remains unknown, it has been previously postulated that phorate may activate the plant's immune system (Todd et al. 1996). Mechanical inoculation of TSWV to phorate-treated plants in the greenhouse has demonstrated no reduction in TSWV incidence with use of this chemical (B. Mandal, personal communication, The University of Georgia, Coastal Plain Experiment Station). Therefore, it would seem that the effect of phorate on TSWV might be a result of interference with thrips feeding, survival, behavior, or reproduction. Phorate is currently recommended for use in Georgia peanut production practices by the tomato spotted wilt risk assessment index (Brown et al. 2000). Recently, successful suppression of TSWV has been attained in tobacco through the use of aciben-zolar-S-methyl (Novartis, Greensboro, North Carolina) and imidacloprid. Aciben-zolar-S-methyl is a plant activator that activates the defense mechanisms of the plant (Pappu et al. 2000), whereas imidacloprid is an insecticide used primarily for the control of aphids and flea beetles (Jones & McPherson 1999). These two chemicals have led to reductions in TSWV symptomatic plants when applied alone; however, the percentage of symptomatic plants was significantly reduced when acibenzolar-S-methyl and imidacloprid were used in combination (Pappu et al. 2000). The treatment of a host plant with insecticidal or plant-activating materials can directly affect thrips behavior and feeding. As a result, virus transmission may be affected as well.