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Title: CONSERVATION OF PREDATORY ARTHROPODS IN COTTON: ROLE OF ACTION THRESHOLDS FOR BEMISIA TABACI

Author
item Naranjo, Steven
item ELLSWORTH, PETER - U OF AZ, MARICOPA, AZ
item Chu, Chang Chi
item Henneberry, Thomas

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2002
Publication Date: 7/1/2002
Citation: NARANJO, S.E., ELLSWORTH, P.C., CHU, C., HENNEBERRY, T.J. CONSERVATION OF PREDATORY ARTHROPODS IN COTTON: ROLE OF ACTION THRESHOLDS FOR BEMISIA TABACI. JOURNAL OF ECONOMIC ENTOMOLOGY. 2002. 95:682-691

Interpretive Summary: A diverse array of natural enemies species inhabit cotton fields in the western US and they are generally crediting with being important in the natural control of pest insects. Heavy use of insecticides in most cotton systems is a severe constraint in efforts to conserve these natural enemies. Sweetpotato whitefly is a key pest of cotton in Arizona and southern California and action thresholds have been established for management of this pest with broad-spectrum insecticides. This study examines the relationship between a range of potential thresholds levels and conservation of predatory arthropods in replicated experimental arenas in central AZ and southern CA. We found that higher thresholds have a smaller impact on predator abundance through the season than lower thresholds. Further analyses indicated that this pattern was strongly affected by the timing of the first application but not the total number of fapplications. That is, later applications have a smaller impact than earlier applications. These findings suggest that simply raising the threshold for initial application could enhance conservation by temporally delaying the first spray. Prior research suggests that higher thresholds may not compromise pest control or resulting net returns to producers, but further research is needed to more fully explore this option and to begin explicitly incorporating natural enemy abundance into the decision-making process.

Technical Abstract: Studies were conducted in 1994 and 1995 to measure the effects of prescriptive insecticide use for Bemisia tabaci in cotton on populations of arthropod predators in Imperial Valley, California and Maricopa, Arizona. Replicated plots were sprayed with a pyrethroid + organophosphate mix when densities of adult B. tabaci exceeded 2.5, 5, 10, or 20 per leaf. Untreated dplots served as controls. Application of insecticides significantly reduce population densities of most predator species and groups in one or both years and sites compared to untreated controls. Use of higher thresholds conserved some species and groups relative to lower thresholds. Stepwise regression analyses indicated that reductions in predator populations were influenced more strongly by the timing of the first insecticide application than by the total number of sprays necessary to maintain suppression of the pest below any given action threshold. A predation index, which weights the eimportance of predator species based on their known frequency of predation on B. tabaci and another key pest, Pectinophora gossypiella, was developed and analyzed. General patterns were similar to results based on changes in abundance alone, but the index generally revealed less severe effects of insecticides on overall predator function. Results suggest that predator conservation may be enhanced by raising the initial threshold to delay the first application or initially using more selective materials such as insect growth regulators.