Interrelationship of Cabbage Variety, Season, and Insecticide on Control of the Cabbage Looper and the Imported Cabbageworm1

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Abstract
Feeding damage and populations of the cabbage looper, Trichoplusia ni (Hübner), and the imported cabbageworm, Pieris rapae (L.), were studied on numerous commercial varieties of cabbage. Based on feeding damage, the most resistant varieties evaluated were Mammoth Red Rock and Savoy Perfection Drumhead; the most susceptible Were Copenhagen Market 86 and Stein’s Flat Dutch. These 4 varieties were selected for detailed studies. Interactions between varieties and larval sizes were significant for both insect species. This fact was exemplified in the antibiosis of Mammoth Red Rock to the cabbage looper. More eggs and small larvae were found on Mammoth Red Rock than on the other 3 varieties, but there were fewer large larvae, and feeding damage on it was relatively light. Almost all eggs on all varieties were deposited on the outer leaves. Maturing larvae of both insect species migrated to the heads. This habit, coupled with antibiosis, probably accounted for the relatively light feeding damage to the heads of varieties which were preferred for egg deposition. Resistant varieties responded more favorably to insecticidal treatment than susceptible varieties. However, this difference tended to disappear under the heavier infestations of late season.

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