The cabbage looper (Trichoplusia ni) is a medium-sized moth in the family Noctuidae, a family commonly referred to as owlet moths. Its common name comes from its preferred host plants and distinctive crawling behavior. Cruciferous vegetables, such as cabbage, bok choy, and broccoli, are its main host plant; hence, the reference to cabbage in its common name. The larva is called a looper because it arches its back into a loop when it crawls.
While crucifers are preferred, over 160 plants can serve as hosts for the cabbage looper larvae. The adult cabbage looper is a migratory moth that can be found across North America and Eurasia, as far south as Florida and as far north as British Columbia. Its migratory behavior and wide range of host plants contribute to its broad distribution.
The cabbage looper larva is a minor vegetable pest, especially for crucifers. While it is not significantly destructive, it is becoming difficult to manage due to its broad distribution and resistance to many insecticides. Numerous methods are being researched in order to control this species.
Taxonomy
The cabbage looper larva is a type of cabbage worm, a general term for a Lepidopteran pest that primarily feeds on crucifers. They closely resemble each other, in that they are all smooth and green, but they are not closely related in terms of phylogeny. In fact, none of the cabbage worms bear close phylogenetic relations, as they are all from different families. The cabbage looper is a member of the family Noctuidae, one of the largest families in Lepidoptera. It is related to other vegetable pests, like the cutworm and armyworms.
Reproduction and life cycle
Mating
When ready to mate, cabbage loopers display by elevating their abdomen and fanning their wings. Males also fan out their abdominal hairs, open their genital claspers, and partially stick out their spermatophores. Males gradually expose more of their spermatophores as they wait for a mate. Upon interest, a potential mate examines the other's abdomen with antennae, and mating occurs if both agree. Mating on average occurs at 2am, but has been observed occurring between 12 and 4am. Mating generally occurs 3–4 days after emergence, but can occur up to 16 days afterwards. Usually, mating does not occur before the third day, as eggs are not fully developed upon emergence and require a few days to reach maturity.
Multiple matings is a mating strategy where individuals have multiple mates in their lifetime. This is in contrast to monogamy, where individuals have one mate for life. Mating multiply can be advantageous to both sexes, which is why this strategy has evolved in many species, including the cabbage looper. For female cabbage loopers, rate of oviposition increases with the number of matings, and ultimately lay more eggs total. While it was once believed that multiple matings were necessary to fertilize all eggs, evidence shows that only one mating is needed to fertilize almost all eggs. Instead, it is more likely that the spermatophore provides nutrients to the female that confers reproductive benefits. This may explain why males produce female-attracting pheromones, as females may be seeking nutrient-rich spermatophores. For male cabbage loopers, multiple matings did not affect the quality of their spermatophores, suggesting that they can maximize reproductive opportunities without decreasing fecundity.
Sexual role reversal
Conventional mate-finding strategy involves males seeking and competing for females and females caring for offspring. In many animals, however, the opposite occurs, where the females competes for males and males care for young. This role reversal can occur for a variety of reasons: environmental conditions, timing of fertilization, and biased sex ratios. For example, male fish often provide more parental care because, after females lay their eggs, males have to ensure that their sperm fertilizes the eggs and does not get washed away. It may be beneficial for the female to lay more eggs instead of caring for the eggs, so she departs as the male fertilizes the eggs, leaving him to care for the eggs. The cabbage looper generally utilizes typical mating strategies, in that males compete for females. However, occasionally the reverse occurs, where females will seek males. This only happens under particular selection conditions, such as a shortage of males or host plants that bias the sex ratio towards females.