Parasitization of Imported Cabbageworm and Cabbage Looper Eggs on Cabbage in Southern California, with Notes on the Colonization of Trichogramma evanescens

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Abstract
Parasitization of eggs of imported cabbageworm, Pieris rapae (L.), and cabbage looper, Trichoplusia ni (Hübner), was studied on successive cabbage plantings in Orange County, California, from April 1963 through October 1967 by collecting eggs from field plants and holding them individually in the laboratory for larval or parasite emergence. Trichogramma evanescens Westwood, obtained from Europe, was released in study plots during 1965, 1966, and 1967 for establishment on imported cabbageworm eggs. Host eggs were collected during 4 periods, April 1963 to April 1965; August 24 to October 26, 1965; August 30 to December 2, 1966; and June 6 to November 14. 1967. The number collected during each period varied from 834 to 3313. Of the imported cabbageworm eggs collected, 0, 0, 2.9, and 17.8%, respectively, were parasitized; 12.4, 10.2, 18.9, and 18.9% failed to hatch or produce parasites; and 87.6, 89.8. 78.8, and 66.7% hatched. Of the cabbage looper eggs collected 7.8, 15.8, 18.5, and 40.6%, respectively, were parasitized; 4.8, 4.6, and 4.7% of eggs collected during the 1st, 3rd, and 4th periods, respectively, failed to hatch or produce parasites; and 87.7, 77.7, and 56.6% of those collected during the same periods hatched. Only T. evanescens was reared from the imported cabbageworm eggs in 1966 and 1967. Prior to 1967. only T. pretiosum Riley was reared from the cabbage looper eggs, whereas in 1967 both T. evanescens and T. pretiosum was obtained. Parasitization of imported cabbageworm eggs by T. evanescens increased from 0 on September 16 to 21.1% on October 4, 1966. and 73.9% on August 8, 1967. Cabbage looper eggs were parasitized by this species in 1967. Parasitization of cabbage looper eggs (73.8%) by T. pretiosum reached its highest peak on October 10, 1967. The number of T. pretiosurn averaged 2.3 per cabbage looper egg in 1966 and 1967. The number of T. evanescens averaged 2.3 and 2.5 per imported cabbageworm egg in 1966 and 1967, respectively. and 1.9 per cabbage looper egg in 1967. The male: female sex ratio for T. pretiosum and T. evanescens reared from cabbage looper eggs was 1:1.97 and 1:2.27, respectively, in 1967. That for T. evanescens on imported cabbageworm eggs was 1:1.96 in 1966 and 1:2.32 in 1967.