Field Evaluations of Augmentative Releases of Delphastus catalinae (Horn) (Coleoptera: Coccinellidae) for Suppression of Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae) Infesting Cotton

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, respectively. 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 population densities of indigenous parasitoids, suggesting an absence of statistically significant, antagonistic predator–parasitoid interactions.