An Evaluation of Some Natural Enemies of Cabbage Looper 1 on Cotton in California 3

Abstract

A comparative life-table analysis of Trichoplusia ni (Hubner) populations on cotton in California revealed that, where predators were suppressed with properly timed applications of dimethoate insecticide, increases in larval survival of T. ni occurred. When the populations of predators were allowed to reach density levels comparable to those in the nontreated control, survival rates for T. ni larvae did not differ significantly between nontreated plots and previously treated plots. The results suggest that predators, particularly adults and nymphs of Orius tristicolor (White), Geoeoris pallens Stal, Nabis americoferus Carayon, and larvae of Chrysopa carnea Stephens, inflict a major intrageneration mortality on T. ni larvae on cotton, and that, when these natural enemies are suppressed, a secondary pest outbreak of T. ni can occur. Rates of parasitization and polyhedrosis of T. ni developmental stages were not, in general, adversely affected by the dimethoate sprays. A nuclear polyhedrosis virus and an egg-larval parasite, Copidosoma truncatellum (Dalman), appeared to cause mortality which was density related. Two apparently new parasite records for T. ni are recorded: Chelonus texanus Cresson and Patrocloides montanus (Cresson).