Field Evaluations of Augmentative Releases of Delphastus catalinae (Horn) (Coleoptera: Coccinellidae) for Suppression of Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae) Infesting Cotton Kevin M. Heinz,* James R. Brazzle,† Michael P. Parrella,‡ and Charles H. Pickett§ *Biological Control Laboratory, Department of Entomology, Texas A&M University, College Station, Texas 77843-2475; †University of California, Cooperative Extension, Kern County, Bakersfield, California 93307; ‡Department of Entomology, University of California, Davis, California 95616; and §Biological Control Program, California Department of Food and Agriculture, Sacramento, California 95832 Received September 30, 1998; accepted May 20, 1999 In 1992 and 1993, field evaluations were conducted to determine the efficacy of Delphastus catalinae (Horn) releases for the suppression of Bemisia argentifolii Bellows & Perring infesting cotton in the Imperial Valley of California. Augmentative releases of adult beetles, totaling 3.5 and 5.5 beetles per plant for 1992 and 1993, respectively, were made into four 0.2-hectare cotton plots and four exclusion cages covering 40 cotton plants. Equal numbers of field plots and cages served as controls for the D. catalinae releases. Open field evaluations revealed no significant difference in the whitefly densities between the release and the nonrelease fields. In addition, no differences in plant growth measures were detected in the year that these data were collected. Releases of D. catalinae into whitefly exclusion cages resulted in a 55% and a 67% decrease in whitefly densities in 1992 and 1993, respec- tively. Observational data suggested that intraguild predation on D. catalinae by the existing predator fauna may have limited the potential for D. catalinae to provide biological whitefly control in open field plots relative to the levels observed within the cages. Releases of D. catalinae did not adversely affect popu- lation densities of indigenous parasitoids, suggesting an absence of statistically significant, antagonistic predator–parasitoid interactions.  1999 Academic Press Key Words: augmentation; biological control; migra- tion; interspecific interactions; silverleaf whitefly. INTRODUCTION A key pest of many crops grown in the southern third of the United States is the silverleaf whitefly (Perring et al., 1993), Bemisia argentifolii Bellows & Perring (Ho- moptera: Aleyrodidae) (= strain B of Bemisia tabaci [Bellows et al., 1994]) (Brazzle et al., 1997; Toscano et al., 1998). In Florida, Texas, Arizona, and California, damage to crops in 1991 and 1992 was estimated at $200 and $500 million, respectively (Henneberry and Toscano, 1996). Growers have adjusted agricultural practices to cope with the whitefly but costs for insecti- cides to control the pest remain high. Whitefly control costs for 1993 were estimated to exceed the $18.9 million 1992 costs (Henneberry and Toscano, 1994). Growers in California’s Imperial County spent roughly $12 million in 1996 to protect 49,442 acres of melons from silverleaf whitefly (White, 1998). In addition to its economic costs, reliance on periodic applications of insecticides for management of Bemisia spp. cause other problems. One problem is the develop- ment of widespread resistance and cross-resistance of whiteflies to many commonly used conventional insecti- cides, particularly organophosphates and synthetic py- rethroids (Prabhaker et al., 1985; Horowitz et al., 1988; Dittrich et al., 1990; Bloch and Wool, 1994). Resistance to the insect growth regulators buprofezin and pyri- proxyfen has also been reported (Horowitz and Ishaaya, 1994). Resistance to insecticides, concerns about envi- ronmental toxicity (Bascietto et al., 1990), and danger to worker safety (Maddy et al., 1985; Hock, 1987) mandate the development of alternatives to conven- tional chemical control of whitefly. Biological control has great potential for use against silverleaf whitefly, based on successes of biological control against other introduced whitefly species and the abundance of potential biological control agents. In California, there are at least 8 species of exotic white- flies, of which 4 are managed with the help of biological control (DeBach and Rose, 1976; Rose and DeBach, 1981; Miklasiewicz and Walker, 1990; Bellows et al., 1992; Gould et al., 1992; Metcalf and Metcalf, 1993). As for the Bemisia complex, many potential natural en- emies have been identified, including 37 parasitoid species, mainly in the genera Eretmocerus (Howard) and Encarsia Fo ¨rster, and 34 predators, in the families Coccinellidae and Phytoseiidae (Cock, 1986, 1993; Ger- ling, 1986, 1990). Biological Control 16, 241–251 (1999) Article ID bcon.1999.0750, available online at http://www.idealibrary.com on 241 1049-9644/99 $30.00 Copyright  1999 by Academic Press All rights of reproduction in any form reserved.