Suppression of Peris rapae1 Using A New Control System: Mass Releases of Both the Pest and its Parasites

Abstract

Populations of the imported cabbageworm, Pieris rapae (L.), were controlled by mass releases of fertile hosts and parasites. Releases of hosts alone did not increase the natural populations of parasites to an effective level, and mass releases of parasites alone were effective only after the host's generations overlapped. Highest mortalities of hosts occurred in plots where inoculative releases of parasites were made and where hosts were supplied continuously. The low natural population of Trichogramma evanescens Westwood in cabbage fields in the spring was the result of mortalities within the overwintering population and lack of sufficient hosts to sustain the population emerging from diapause. The number of hosts needed to establish an effective level of parasites was determined to be ca. 100,000 laboratory-reared or 12,000–36,000 field-reared adults per day per acre. Natural populations of Apanteles rubecula Marshall were not effective in reducing hosts in the spring; control with this parasite was not obtained until the 4th generation. The number of these parasites needed to control the host was 5000 adults/acre per host's generation. When both larval parasites parasitized the same host, only A. rubecula survived, and A. glomeralus (L.) never became an effective parasite in the presence of A. rubecula.