Autoplusia egena Guenee Lepidoptera Noctuidae

Natural History

Distribution. This insect is a native to tropical areas of the western hemisphere. The northern limits of its range are the Gulf Coast states and California. Its distribution extends southward through Central and South America to Brazil, and the Caribbean Islands.

Host Plants. As suggested by its common name, the principal host is bean. However, other vegetables sometimes consumed include cabbage, carrot, and celery. Soybean, tobacco, mint, spearmint, comfrey, chrysanthemum, marigold, hollyhock, verbena, and larkspur are other economic plants eaten.

Natural Enemies. Several parasitoids were found to affect bean leafskeletonizer in California; Copido-soma truncatellum (Dalman) (Hymenoptera: Encyrti-dae) was the only parasitoid affecting a significant proportion of the leafskeletonizers (Lange, 1945). An undetermined fungal disease was also noted among the larvae. There has not been adequate study to determine the relative importance of the natural enemies.

Life Cycle and Description. The complete life cycle requires about 45 days. The number of generations appears to be undetermined, but Lange (1945) reported "several" in California.

Egg and Larva. The duration of the egg is about five days. Larvae have five instars, the duration of which is 4.4, 3.4, 4.0, 4.1, and 7.8 days, respectively. Mean (range) of head capsule widths are 0.25 (0.25-0.25), 0.45 (0.42-0.46), 0.93 (0.66-1.10), 1.40 (1.21-1.57), and 2.16 (2.03-2.32) mm for instars 1-5, respectively. The body color is green, and pale white stripes usually are evident. The head is green, but marked with black spots at the base of setae. Numerous black tubercles are found dorsally on the body. The body bears micro-spines, but they are quite small and difficult to detect. The larva attains a length of about 22-33 mm at maturity. The lack of nipple-like structures on abdominal segments three and four separates bean leafskeletoni-zer from cabbage looper, Trichoplusia ni (Hubner), and soybean looper, Pseudoplusia includens (Walker). The lack of dark lateral bands on the head helps to distinguish bean leafskeletonizer from most of the other common loopers. A key to common vegetable-feeding loopers can be found in Appendix A.

  1. Larvae roll the foliage, form a silken cocoon within the rolled leaves, and pupate within. The pupa measures about 18 mm long. Duration of the pupal stage averages about 13.7 days.
  2. The front wings of the adult are distinctively rusty brown, blending into gray, cream, or yellowish-brown. The front wings lack the distinctive silver or white spot found centrally in most loopers. The hind wings are light grayish-brown basally and darker brown distally. Under laboratory conditions the adults survived only about 5.3 days.
Bean leafskeletonizer larva.

The only detailed report on biology was provided by Casanova (1977). Useful information and diagnostic characters were given by Crumb (1956), Eichlin and Cunningham (1978), and LaFontaine and Poole (1991).

Damage

Both the leaf tissue and pods of beans are eaten. Although generally regarded as only a minor pest, this insect reportedly was very damaging at times to several varieties of beans in California. In Puerto Rico it is most damaging to tobacco.

Management

Foliar insecticides are effective if needed.

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