Influence of Imidacloprid and Jasmonic Acid on Cotton Phytohormone Expression and Spider Mite Population Growth

Cotton responds to insect injury by eliciting signal pathways that result in the production of metabolites that have been demonstrated to deter insect feeding, reduce insect fitness, and attract predators. Furthermore, neonicotinoid seed treatments have been shown to suppress some of these natural secondary metabolites increasing the prevalence of phytophagous arthropods on seedling cotton.  Therefore, we investigated the effects of selected elicitors on the production of plant defenses using phytohormone analysis and measuring population growth of two-spotted spider mite, Tetranychus urticae, (TSSM) on cotton plants grown in a growth chamber after foliar applications of Jasmonic Acid (JA) and seed applied imidacloprid. Our research indicates neonicotinoid seed treatments may alter naturally occurring secondary plant metabolites resulting in significantly more adult spider mites as compared JA treated cotton. However, eggs, motiles and total mites were not affected by the addition of a neonicotinoid seed treatment or exogenous applications of JA.  Concentrations of JA were determined to be significantly greater in plots where JA was applied compared to plots that had no JA applications. Jasmonate-isoleucine (JA-Ile) was also determined to be significantly greater in plots sprayed with JA compared to plots that were not sprayed. Concentrations of 12-oxo-phytodienoic acid (OPDA), salicylic acid (SA), abscisic acid (ABA) were not found to be significantly different in sprayed compared to non-sprayed plots.  Finally, neonicotinoid seed treatments appeared to have little effect on the population growth or health of TSSM populations in this study.