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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 A MARICOPA AZ
item Chu, Chang Chi
item Henneberry, Thomas

Submitted to: Sweetpotato Whitefly Progress Review Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/1/2002
Publication Date: 6/1/2002
Citation: N/A

Interpretive Summary:

Technical Abstract: Studies were conducted in 1994 and 1995 to measure the effects of prescriptive insecticide use for Bemisia tabaci (SPW) in cotton on populations of arthropod predators in Imperial Valley, California and Maricopa, AZ. Replicated plots were sprayed with a pyrethroid + organophosphate mixture when densities of adult SPW exceeded 2.5, 5, 10, or 20/leaf. Untreated plots served as controls. Application of insecticides significantly reduced population densities of spiders, Geocoris punctipes (Say), G. pallens (Stål), Orius tristicolor (White), Nabis alternatus Parshley, Zelus renardii Kolenati, Hippodamia convergens Guérin-Méneville, Spanogonicus albofasciatus (Reuter), Drapetis sp., and Chrysoperla carnea Stephens in one or both years and sites compared to untreated controls. Use of higher SPW thresholds conserved some species and groups relative to lower thresholds. Stepwise regression analyses indicated that reductions in predator populations were generally 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 importance of predator species based on their known frequency of predation on SPW and another key pest, pink bollworm, 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. The current action threshold for conventional insecticidal control of SPW in AZ and southern CA is 5 adults/leaf. Results here 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.