Abstract
Studies conducted on winter lettuce grown in the absence of pesticides in coastal southern California in 1963, 1966–67, and 1967–68 revealed that the cabbage looper, Trichoplusia ni (Hubner); beet armyworm, Spodoptera exigua (Hubner); black cutworm, Agrotis ipsilon (Hufnagel); and granulate cutworm, Feltia subterranea (F.); were the principal lepidopterous pests. Altogether, 8 species of lepidopterous larvae were collected. Three species of braconids, 2 ichneumonids, and 3 tachinids were reared from the larvae with Chelonus texanus Cresson, Hyposoter exiguae (Viereck), and Voria ruralis (Fallen) being the most common parasites. Trichogramma pretiosum Riley was the only parasite reared from the eggs. In 1963, 82% of the seedlings were destroyed by lepidopterous larvae within 2 weeks after the seedlings were thinned in early November. The percentage of infested plants and average number of larvae per plant reached a maximum of 56% and 0.9, respectively, on Dec. 6, 1966, and 66% and 1.0 on Dec. 5 in 1967. At harvest in February, the number of larval-infested heads of lettuce averaged 0.7 in 1967 and 0.4% in 1968. Only cutworms were present.
Published Version
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