|Crop Knowledge Master|
Agrotis ipsilon (Hufnagel)
Jayma L. Martin Kessing, Educational Specialist
Ronald F.L. Mau, Extension Entomologist
Department of Entomology
The black cutworm attacks the seedlings of most crops. Crops attacked include beans, broccoli, cabbage, carrot, Chinese broccoli, Chinese cabbage, Chinese spinach, corn, eggplant, flowering white cabbage, green beans, head cabbage, lettuce, mustard cabbage, potato, spinach, sugarcane, sweet potato, tomato, turnip, as well as many other plants. An extensive listing of hosts of the black cutworm may be found in Rings (1975).
This insect is nearly cosmopolitan and occurs in the U.S., Europe, Canada, Japan, New Zealand, South Africa, South America, and the Pacific. This pest was first found on Oahu in 1879 and is now present on all islands.
This pest has solitary habits. They commonly feed on seedlings at ground level, cutting off the stem and sometimes dragging the plants into their burrows. Most of the plant is not consumed but merely eaten enough to cause it to topple. Since the larvae occur burrowed near the roots of the host, it sometimes feeds on roots and the below ground stem. Because of the nature of their feeding on young plants, this pest can do great damage in newly planted fields.
The life cycle from egg to adult is completed in 32-67 days. The duration is primarily governed by temperature. In temperate regions, the larvae overwinter and pupate in the late spring. In Hawaii, there are many generations per year.
The creamy white eggs are globular with a ribbed surface and are approximately 1/5 inch in diameter. They are laid singly or in small clusters, primarily on leaves, and hatch in 2 - 9 days. They are often found on plants in low spots of the field or in fields that have been subjected to flooding.
Newly hatched caterpillars are 1/25 inch long and mature larvae are nearly 2 inches long. The larvae are thin, cylindrical and dark brown to greasy gray in color with faint lighter stripes running laterally on each side of the body. The head is dark brown with two white spots. Larval development takes from 28-34 days.
Mature larvae burrow several inches into the soil where they form a pupation cell. Pupae are dark brown and are about 3/4 inch in length. Pupal development is completed in 10-30 days.
Adults have a wingspan of 1-5/8 to 2 inches. Forewings are gray with dark brownish or black markings. Hind wings are almost white except for a dark fringe at the tips and are folded under the forewing when the adult is inactive. The body is gray.
Females can lay as many as 1800 eggs (Hill, 1983).
Larvae remain below the surface of the ground, under clods of soil, or other refugia (shelters) during the day and feed at night. The first two larval stages feed on the foliage of the plant. The third and later stages often become cannibalistic and thus adopt solitary habits (Hill, 1983).
Cutworms are often difficult to control, especially when populations are epidemic in proportion. Large populations may cause severe crop damage with indications that the pest is the black cutworm. Unfortunately, by the time the pest is identified, the cutworms would have already developed into a life stage which is not as susceptible to insecticides as the early larval stages. The sporadic nature of cutworm populations can make preventive treatments futile in some areas. An additional problem for control is the soil-dwelling habits of the larvae, often beneath heavy foliage, making it difficult for insecticides to reach their targets (Hill, 1983).
Check for cutworms in surrounding weeds before planting a field or before the crop emerges. Cutworms often recur in the same fields and areas from year to year. Areas that have had a dense stand of weeds, crop residue disced-in soon before planting, or located near an alfalfa field often have high populations. Damage is worst where large numbers are present before planting (Flint, 1985).
After the crop emerges, monitor for adult densities using pheromone traps and check for a row of four or five or more wilted plants with completely or partially severed stems. Monitor for cut worms by digging around the base of the damaged plants and sifting the soil for caterpillars. They are best found at dawn or at night.
Weed hosts on outlying areas are often preferred sites of oviposition and serve as food for the younger larvae. Thus destruction of these weeds may help reduce black cutworm populations.
Deep ploughing of fields between crops turn up larvae and pupae to the soil surface making them susceptible to predators and sun.
Depending on the crop, flooding of the infested field may be a feasible control method in some cases.
In small gardens, manual collection of the larvae is sufficient for control.
Several natural enemies attack cutworms. However, none are effective enough to provide reliable control. The following insects have been listed as possible parasites of the black cutworm in Hawaii by Zimmerman (1958): Archytas cirphis (Curran) (Mexican cutworm tachinid), Chaetogaedia monticola (Bigot), Chelonus texans (Cresson), Eucelatoria armigera (Coquillet), Euplectrus platypenae (Howard), Hyposoter exiquae (Viereck), Meteorus laphygamae
(Viereck), Pseudamblyteles koebelei (Swezey), and Pterocormus rufiventris (Bruelle). He also listed Calosoma blaptoides tehuacanum (Lapouge) as a predator.
Because of the protected environment of the cutworm larvae, it is necessary to apply high-volume sprays (at least 1000 1/ha) of insecticides. The spray should be directed along the plant rows, aiming at a run-off to the soil below (Hill, 1983). Applications should be timed to hit the young larvae while they are feeding on the plant leaves or on the soil surface.
Applications of granular insecticides directly to the soil are probably the most effective method of controlling this pest. Baits are more effective when food sources are limited. If cutworms are found, distribute baits before the crop emerges, especially where cutworms have caused damage before. Treat as soon as possible if seedlings are already present when you notice damage. Baits of moist bran mixed with the appropriate insecticide may be effective against older caterpillars (Hill, 1983).
Flint, M.L. 1985. Other Seedling Pests, Cutworms. pp. 32. In Integrated pest Management for Cole Crops and Lettuce. University of California Publication 3307. 112 pages.
Hill, D.S. 1983. Agrotis ipsilon (Hfn.). pp. 357-358. In Agricultural Insect Pests of the Tropics and Their Control, 2nd Edition. Cambridge University Press, Cambridge, London, New York, New Rochelle, Melbourne, Sydney. 746 pages.
Metcalf, C. L., and W. P. Flint. 1962. Cutworms. pp. 476-480. In Destructive and Useful Insects Their Habits and Control, Fourth Edition. Revised by: R. L. Metcalf. McGraw-Hill Book Company, Inc. New York, San Francisco, Toronto, London. 1087 pages.
Rings, R.W., F.J. Arnold and B.A. Johnson. 1975. Host Range of the Black Cutworm on Vegetables: A Bibliography. Bull. Entomol. Soc. Am. 21(4):229-234.
Zimmerman, E.C. 1958. Agrotis ipsilon. pp. 253. In Insects of Hawaii. A Manual of the Insects of the Hawaiian Islands, including an Enumeration of the Species and the Notes on their Origin, Distribution, Hosts, Parasites, etc. Volume 7. Macrolepidoptera. University of Hawaii Press, Honolulu. 542 pages.