Effects of lambda-cyhalothrin and Beauveria bassiana spores on abundance of Chilean soil surface predators, especially spiders and carabid beetles

Abstract

Summary The effects on generalist predators of the insecticide lambda-cyhalothrin and a new biopesticide based on Beauveria bassiana spores were studied in the 2003 growing season (October to December, Southern spring) in Valdivia, Chile. Both pesticides target larvae of Dalaca spp. (Lepidoptera: Hepialidae), a complex formed by Dalaca chiliensis, Dalaca pallens and Dalaca variabilis. Lambda-cyhalothrin, B. bassiana spores and water (control) were sprayed once. Pitfall traps were used to sample predators one day before spraying as well as 1, 30 and 60 days after spraying. Sampling revealed an assemblage of 11 carabid species and two spider families (Lycosidae and Gnaphosidae). In order of abundance, the carabid species found were Ferionomorpha nebroides (45%), Allendia chilensis (20%), Argutoridius chilensis (13%), Ferionomorpha aerea (11%) and Ceroglossus chilensis (6%). Metius flavipes, Mimodromites cyaneus, Parhypates sp., Trechisibus angularis, Calosoma vagans and Trirammatus unistriatus accounted for less than 1% each. Spider families were almost equally represented. Activity of predators increased over time and negative effects of lambda-cyhalothrin were detected for F. nebroides, F. aerea, Lycosidae and Gnaphosidae. Differences vanished by day 60, except for F. aerea. Inundative release of B. bassiana spores affected only F. aerea at the last sampling date. Therefore, B. bassiana isolate B-931 is a good potential alternative to the broad-spectrum insecticide lambda-cyhalothrin, which disrupted the generalist predator assemblage more severely.