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Title: CONSERVATION OF NATURAL ENEMIES IN COTTON: ROLE OF INSECT GROWTH REGULATORS FOR MANAGEMENT OF BEMISIA TABACI

Author
item Naranjo, Steven
item ELLSWORTH, PETER - UNIV OF AZ MARICOPA AGIC
item Hagler, James

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2003
Publication Date: 1/1/2004
Citation: Naranjo, S.E., Ellsworth, P.C., Hagler, J.R. 2004. Conservation of natural enemies in cotton: role of insect growth regulators for management of bemisia tabaci. Biological Control. 30:52-72.

Interpretive Summary: Insecticides remain an important tactic for the control of sweetpotato whitefly in cotton. However, many conventional insecticides are toxic to natural enemies, leading to disruption of potential biological control. In 1996 the state of Arizona was granted an EPA emergency exemption for two new insecticides, both of them insect growth regulators (IGRs), for whitefly control. These IGRs have a narrower spectrum of activity; however published laboratory studies suggested that they can be toxic to various species of parasitoids and insect predators. This 3-year field study was initiated to evaluate the impact of these IGRs on natural enemies. Replicated field plots examined management regimes based on the use of the two IGRs and compared them to an existing regime based on the rotation of conventional insecticides and an untreated control. IGR-based regimes reduced populations of 8 of 20 predator taxa in at least one year. Conversely, the use of conventional insecticides reduced populations of nearly all the predatory taxa examined in most years, including those affected by IGRs, with the impact being greater in all cases. Further analyses of the IGR regimes suggest that factors other than direct toxic effects, such as reduction in prey availability, may be involved. Results demonstrate the selective action of these two IGRs and suggest that their use may enhance opportunities for conservation biological control in cotton systems affected by B. tabaci.

Technical Abstract: Field studies were conducted from 1997-1999 to contrast the effects of two insect growth regulators (IGRs) and conventional insecticides on natural enemy conservation in cotton within the context of alternative management strategies for Bemisia tabaci. Insecticide regimes based on the IGR buprofezin or pyriproxyfen reduced densities of eight predators out of 20 examined in at least one year, including common species such as Geocoris punctipes, Nabis alternatus, Chrysoperla carnea, and Drapetis nr. divergens. In comparison, the use of conventional insecticides reduced populations of nearly all the predatory taxa examined in most years, including those affected by IGRs, with the impact being greater in all cases. Patterns of predator and pest population change relative to IGR application dates suggest that factors other than direct toxic effects, such as reduction in prey availability, may be involved. Nonetheless, predator:prey ratios were significantly increased by the use of IGRs compared with both the untreated control and a conventional insecticide regime in most instances. These same overall patterns were observed for the entire predator community over the growing season based on principal response curves analysis, a time-dependent multivariate method. Rates of parasitism by aphelinid parasitoids were generally low and did not vary consistently due to insecticide regimes. The use of these IGRs should enhance opportunities for conservation biological control in cotton production systems.