Effects of irrigation regime on interactions between Lygus hesperus, insecticides and predators in cotton

Authors: ASIIMWE, PETER - University Of Arizona; Naranjo, Steven; ELLSWORTH, PETER - University Of Arizona

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/20/2013
Publication Date: 4/30/2014
Publication URL: http://handle.nal.usda.gov/10113/58830
Citation: Asiimwe, P., Naranjo, S.E., Ellsworth, P. 2014. Effects of irrigation regime on interactions between Lygus hesperus, insecticides and predators in cotton. Environmental Entomology. 43:263-273.

Interpretive Summary: Lygus hesperus is a key pest of cotton and other crops in the western region of the US and basic information about factors influencing its population dynamics and that of its natural enemies could be important in developing better management strategies. The variation in plant quality and natural enemy abundance plays an important role in insect population dynamics. In manipulative field studies, we evaluated the impact of plant quality on densities of Lygus and the arthropod predator community in cotton. We also evaluated how the insect responses to plant quality might be mediated by two important insecticides, acephate and flonicamid, used in the control of Lygus. Plant quality was manipulated using differential irrigation while insect populations were manipulated using the broad-spectrum insecticide acephate, the selective insecticide flonicamid, and an untreated check. Lygus populations were significantly influenced by plant quality with lower densities in the deficit-irrigated cotton; however, the generalist predators known to prey on Lygus in cotton were unaffected. The predator guild was significantly reduced in the broad spectrum spray conditions. Given these patterns, predator:prey ratios were highest under low quality conditions (deficit-irrigated plants) and where selective insecticides were used. Predator function, as inferred from a predation index, was not affected by plant quality, but it was significantly reduced under broad-spectrum spray conditions. Plant quality is an important factor in seasonal dynamics of Lygus in cotton, but predator density and function is not mediated by plant quality and is instead dependent on the efficacy and selectivity of the compounds used to control the pest. This knowledge suggests that management of water stress and choice of insecticides are important components of an overall management system.

Technical Abstract: The variation in plant quality and natural enemy abundance plays an important role in insect population dynamics. In manipulative field studies, we evaluated the impact of plant quality on densities of Lygus hesperus Knight and the arthropod predator community in cotton. We also evaluated how the insect responses to plant quality might be mediated by two important insecticides, acephate and flonicamid, used in the control of L. hesperus. Plant quality was manipulated using differential irrigation to achieve 20%, 40% or 60% soil water depletion (SWD), while insect populations were manipulated using the broad spectrum insecticide acephate, the selective insecticide flonicamid, and an untreated check. L. hesperus populations were significantly influenced by plant quality with lower densities in the deficit-irrigated cotton; however, the generalist predators known to prey on L. hesperus in cotton were unaffected. The predator guild was significantly reduced in the broad spectrum spray conditions. Specifically, Misumenops celer Hentz and Geocoris punctipes Say were the most abundant predators and most significantly reduced by acephate applications. Given these patterns, predator:prey ratios were highest under low quality conditions (deficit-irrigated plants) and where selective insecticides were used. Predator function, as inferred from a predation index, was not affected by plant quality, but it was significantly reduced under broad-spectrum spray conditions. Plant quality is an important factor in seasonal dynamics of L. hesperus in cotton, but predator density and function is not mediated by plant quality and is instead dependent on the efficacy and selectivity of the compounds used to control L. hesperus. The implications of these findings on L. hesperus management, yield and the overall ecology of insect-plant dynamics in cotton are discussed.