Various environmental factors were evaluated for their influence on numbers of males of the cabbage looper, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), captured in traps baited with living females or with T. ni synthetic sex pheromone, cis-7-dodecenyl acetate. More males were captured in traps at an elevation of 2 in above the soil surface in a broccoli planting than in those at higher (3- or 4-m) or lower (0-, 0.3-, or 1-m) elevations. Captures in traps placed on trunks of citrus or eucalyptus trees tended to remain steady or increase through an elevation of 4 m. Captures in traps situated up to 3200 m from the nearest planting of a cole crop were about as high as captures at the plantings. Seasonal highs and lows of numbers of males captured during 2 years occurred around September and January, respectively. However, a large variation in seasonal trends occurred during the 2 years. No correlations could be obtained relating daily variations in captures with daily (or nightly) variations in temperature and relative humidity. Periods of full moonlight did not influence numbers of males captured. The time of the median capture occurred around midnight in July and occurred progressively earlier through August and September to around 8 PM in October.
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Saario et al. (1970) studied this question.