The Biology of Trichoplusia ni (Lepidoptera: Noctuidae). I. Life History and Behavior1

Abstract

Studies of Trichoplusia ni (Hiibner), the cabbage looper, were conducted in, a greenhouse and laboratory at constant temperatures, and in the field in southern California. When larvae were reared on lima bean leaves, the total developmental time from egg deposition to adult emergence from the pupa averaged 95, 32, and 24 days for males, and 92, 30, and 23 days for females, at 14°, 23°, and 32° C, respectively. When cabbage was provided as food at 23°, 34 days were required for development of males and 35 days for females. The pupal stage of individuals reared at 14° tended to be lengthened disproportionately, and these pupae were heavier than those formed from larvae reared at 23° or 32°. Male pupae tended generally to be heavier than female pupae. Adults became active in the field shortly after sunset, but captures at a black light trap gave no evidence of definite peaks of nocturnal flight activity. However, fewer adults were captured after 11 p.m. than before, and the ratio of females to males generally declined as the night progressed. All matings observed among caged adults occurred after midnight, the average time of initiation being 2:10 a.m. No matings were observed until the second night after emergence from the pupa, and mature eggs were not found in the common oviduct of females until 2 days after emergence. Female adults maintained in the greenhouse at 27° successfully mated an average of 2.0 times. For cabbage loopers reared on lima bean leaves the ratio of males to females was 46:54. Males can be distinguished from females in large larvae by the appearance of the developing testes in the male, in pupae by the location of the genital pore, and in adults by the presence of characteristic light brown hairs on the abdomen of the male. A rearing procedure is described whereby the larvae were raised on the young primary leaves of lima beans growing in flats containing vermiculite. Behavior patterns observed during mating, oviposition, hatching, molting, and pupation are described.