Distribution. Cross-striped cabbageworm is recorded principally from North America east of the Rocky Mountains, but is infrequent in the northernmost states and eastern Canada. This insect is known as a common pest only in the southeastern states and in Central America, and even in the southeastern states it usually is a minor component of the defoliator complex. It is likely a native insect, though its close relatives are native to Europe. Cross-striped cabbage-worm was accidentally introduced to Australia and Jamaica.
Host Plants. Broccoli, Brussels sprouts, cabbage, collards, kale, rutabaga, and turnip are among the vegetable crops known as hosts. Brussels sprouts and collards tend to support relatively large numbers of cabbageworms, and cabbage and kale relatively few. Other crucifers such as rape, and many weeds, likely support this insect.
Natural Enemies. Several parasitoids are known, including Cotesia congregata Say, C. xylina (Say), and C. orobenae Forbes (all Hymenoptera: Braconidae). Except for C. orobenae, the importance of the parasi-toids has not been thoroughly assessed, and predators and diseases are undocumented. Mays and Kok (1997) reported on C. orobenae, and showed that the occurrence of this parasitoid closely tracked the abundance of its host.
Life Cycle and Description. Development time, from egg to adult stages, ranges from 61 days at 20°C to 18 days at 35°C. The number of annual generations is three in Illinois, and four in Maryland. Cross-striped cabbageworm tends to be most abundant during the autumn generation in the north. In the south, however, it can be quite abundant during the winter-and spring-cropping period.
Cross-striped cabbageworm larva.
The biology of cross-striped cabbageworm was given by Chittenden (1902) and Mays and Kok (1997). A key including the adult stage of cross-striped cabbageworm was contained in Munroe (1973). Cross-striped cabbageworm is included in the key to "cabbageworms" in Appendix A.
Larvae feed on foliage, creating small holes. They prefer the terminal buds. If disturbed, they have a tendency to drop from the foliage on a silken thread. Larvae also may burrow into the center of developing heads.
Cross-striped cabbageworm, along with several other lepidopterous defoliators, exhibits a positive response to nitrogen fertilization of host plants. However, indications are that unlike the case with piercing-sucking insects, it is not the increased nitrogen levels per se, but the increased foliar biomass that favors the abundance of the cabbageworms (Jansson et al., 1991b). In general, methods used for management of imported cabbageworm, Pieris rapae (Linnaeus), are appropriate for this insect.
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