An Ecological Study of Cabbage Looper and Imported Cabbageworm Populations on Cruciferous Crops in Southern California1

Abstract

Ecological studies of the cabbage looper, Trichoplusia ni (Hübner), and imported cabbageworm, Pieris rapae (L.), on cruciferous crops were conducted in southern California during 1963-64. Eggs, larvae, and pupae were collected at random from consecutive plantings for I hour at weekly intervals for I year, and held for completion of delvelopment and/or parasite emergence. Totals of 566 cabbage looper eggs and 2439 imported cabbageworm eggs were collected, of which 93.5% and 92.0% hatched, 5.6% and 7.5% failed to hatch, and 0.9% and 0.4% were parasitized for total egg mortalities of 6.5% and 7.9% respectively. The imported cabbageworm egg population reached a peak of 179 eggs per 1 hour search on July 30 and 72 eggs for the cabbage looper on August 6. Trichogramma pretiosum Riley was the only parasite reared from the egg stage. Totals of 1737 larvae and 68 pupae of the cabbage looper, and 960 larvae and 181 pupae of the imported cabbageworm were collected. Six generations of each species occurred during the year, with the imported cabbageworm reaching a peak of 78 larvae per 1 hour search on July 24, and 130 for the cabbage looper on September 26. Twenty-six percent of the cabbage looper larvae were parasitized, of which 90% were by tachinids and 10% by hymenopterous parasites. Pupae were not parasitized. Twenty-three percent of the imported cabbageworm larvae and 51% of the pupae were parasitized for a total of 7470 parasitization. Tachinids accounted for 57% of the total larval and 5%of the pupal parasitization, and hymenopterous parasites 43% and 46%, respectively. Voria ruralis (Fallén) and Copidosoma truncatellum (Dalman) were the principal tachinid and hymenopterous parasites, respectively, on cabbage looper larvae, and Madremyia saundersii (Williston) and Apanteles glomeralus (L.) on imported cabbageworm larvae, Pteromalus puparum (L.) was the main pupal parasite of the latter. Altogether, 10 parasites were reared from the cabbage looper and 10 from the imported cabbageworm.