Trichoplusia ni growth and preference on broccoli and eight common agricultural weeds

Abstract

Larval growth and feeding, and adult ovipositional preference of the cabbage looper, Trichoplusia ni Hübner, were investigated on broccoli (Brassica oleracea var. italica L.) and eight common agricultural weeds: cow cockle (Saponaria vaccaria L.), common groundsel (Senecio vulgaris L.), lamb’s-quarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), sheep sorrel (Rumex acetosella L.), shepherd’s purse (Capsella bursapastoris L.), stinkweed (Thlaspi arvense L.), and wild mustard (Sinapsis arvensis L.). Leaves from greenhouse grown plants were removed and fed to 1st instar larvae in a 7-d growth trial. Broccoli-fed larvae grew larger than those fed on cow cockle, redroot pigweed, sheep sorrel, stinkweed, and wild mustard. Only one insect of 64 survived for 7 d on stinkweed. In a leaf disc choice bioassay, 4th instar larvae showed a significant feeding preference for common groundsel over broccoli. Broccoli was preferred for oviposition over three of the weeds (common groundsel, lamb’s-quarters, and shepherd’s purse). Stinkweed showed promise as a dead-end trap species for this insect in broccoli, since more insects oviposited on stinkweed compared with broccoli yet larval survival on stinkweed was almost nil. Key words: Trichoplusia ni, broccoli, Thlaspi arvense, oviposition, feeding deterrence