SEASONAL ABUNDANCE AND DAMAGE ESTIMATES OF CABBAGE LOOPER LARVAE AND 2 APHID SPECIES

Populations of cabbage looper, Trichoplusia ni (Hubner), larvae; adults and nymphs of cabbage aphid, Brevicoryne brassicae (L.); and green peach aphid, Myzus persicae (Sulzer), were determined for 2 years on 2 cabbage plantings per year. Loopers were the most abundant from Sept. to mid-Nov. and in March. Populations of both aphid species begin in Dec. and threaten cabbage production in the lower Rio Grande Valley until commercial production ends in April. Damage estimates of the cabbage looper, based on cabbage head and looper larval weights, indicated that 23 9-day-old (last instar) larvae would be required to destroy 10% weight of each cabbage head at harvest time. When aphid populations average 1 per plant, approximately 12% of the plants are unmarketable and when they average 1 per 2 square inch, 36% of the plants are unmarketable.