Effects of Acephate on the Distribution of Tarnished Plant Bugs within the Cotton Plant Profile
The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is a primary pest of cotton in the mid-southern United States. Chemical control strategies are the primary integrated pest management tool used to manage this pest in cotton. A better understanding of tarnished plant bug behavior and distribution on cotton plants is needed to improve the scouting and monitoring protocols used to estimate population and crop injury levels needed to initiate treatments. This pest frequently re-infests fields after insecticide treatments. Sampling protocols should consider the sub-lethal effects of insecticides on migrating populations or on survivors that remain on insecticide-treated plants. Studies were performed during 2007-2008 to evaluate the effects of acephate on tarnished plant bug nymph age-classes, preference for selected fruiting structures, and vertical distribution within the cotton canopy. The test sites included flowering stage cotton plants that were infested with native populations of nymphs (>1 insect / row ft). Non-treated and acephate-treated (Orthene 90SP 0.8 lb AI/acre) cotton plants were evaluated at 0 (pre-treatment) to 120 hours after treatment (HAT). Numbers of small (1st ¨C 3rd instars) nymphs were significantly greater than large (¡Ý4th instars) on non-treated plants, but no differences between age-classes were detected on acephate-treated plants. Regardless of insecticide treatment, nymphs were significantly greater on flower buds (squares) compared to bolls or white flowers. Nymphs were greater on sympodial branches of plant main stem nodes 1-5 (top five) and 6-10 compared to those on main stem nodes 11-15 for both treatments. On non-treated plants, the numbers of nymphs found on nodes 1-5 compared to those on 6-10 were not significantly different. However, on acephate-treated plants from 24 to 72 HAT, more nymphs were found on sympodial branches 6-10 compared to sympodial branches 1-5. The results of this study showed that acephate influenced tarnished plant bug nymph age-class, short-term vertical distribution on cotton plants, but did not change the preference for squares. Whole-plant sampling protocols that measure infestations throughout a cotton plant¡¯s entire profile or examination of squares for injury should provide the best estimate of tarnished plant bugs on non-treated and insecticide (acephate)-treated cotton plants.
Advisor:James A. Griffin; B. Rogers Leonard; Jeffrey A. Davis; Boyd Padgett
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Date of Publication:06/11/2009