Helicoverpa armigera (Hübner)
Common name: African bollworm, cotton bollworm, corn earworm, Old World bollworm.
Geographical distribution: Between north and south 45° latitudes, recently also found in Brazil. CIE Map #15 (revised), 1993.
Morphology: Adult body is 12-20 mm in length, female forewings yellow to brown, green-gray in males, with a brown spot near the anterior margin. Hindwings pale yellow with a brown band at the posterior edges and a dark round spot in the middle. The larva is 35-40 mm in length, its pale-green to dark-brown color depends on the host plant, and with a dark, dorsal stripe. The head, pronotum, the thoracic legs and the five pairs of abdominal prolegs are dark brown or black.
Host plants: Highly polyphagous, feeding on about 200 plant species, mainly annuals, developing on a wide range of food, fiber, oil and fodder crops as well as on many wild plants and perennial horticultural crops.
Life cycle: Like other Noctuidae, the adults emerge after sunset, being active at night. The females mate several times and lay 300-3000 eggs during their lifetime, which lasts up to 3 weeks in summer. The eggs are laid singly on stems, leaves, and fruit. The hatching larvae feed and reach a length of 40 mm, then leaving the plants to enter the soil, where they pupate. In summer the pest develops in 25-40 days, in the cold season within 6-7 months. In the Middle East the pest completes 4-5 annual generations, some of which overlap. Most bollworm populations in the Middle East undergo a pupal diapause during winter, emerging in early spring. This pest may migrate over long distances, borne by winds.
Economic importance: The damage caused by H. armigera is annually estimated, world-wide, to exceed US$2 billion, and the bollworm is listed as an A2 quarantine pest by EPPO. In the Middle East it is a major pest of cotton, tomatoes and other solanaceous crops, legumes like peas and beans, and maize (corn). Attacking cotton, the larvae initially feed on leaves, later boring into flowers and bolls. As bolls are infested while too small to sustain the larvae, they move from boll to boll; the affected bolls fail to develop and the quality of the lint is severely spoilt. Slightly damaged bolls are also damaged due to being invaded by rot microorganisms. In tomatoes, the larvae bore into immature, ripening and ripe fruit, preferring the latter, and cause rot. In maize, larvae bore into stems and can cause serious plant lodging. Infesting the developing cobs, larvae penetrate mainly through the “silk” and feed on the seeds. In all cases, the economic value of the crops, for commercial or for industrial use, is much reduced.
Sampling: Traps with the female sex pheromone are examined from mid-April and on, the signal for chemical treatments being four days after 3-4 males are trapped during two consecutive examinations.
Plant resistance: Partial resistance to the pest has been noted in some varieties of the major crops but none appear to be completely immune.
Horticultural control: The removal of susceptible crop residues and weeds and deep plowing in autumn or winter, intended to destroy the overwintering insects.
Genetically improved crops: The sowing of Bt cotton (genetically modified cotton that produces the Bacillus thuringiensis (Bt) toxins (“Bollgard” and “Ingard”) can greatly reduce pesticide applications. However, the pest is developing resistance to Bt in Australia.
Chemical control: Organochlorides, pyrethroids, carbamates and organophosphates were formerly in use, but the pest has developed considerable resistance to them. One approach is to rotate these chemicals every few weeks during the season. Preparations of B. thuringiensis are effective during the early part of the season. Spinosad is still effective. A novel method is to apply “Noctovi”, a product that attracts bollworms from up to 50 meters, integrated with a pesticide, to kill the pests.
Biological conttrol: Several hymenopterous parasitoids, including Hyposoter didymator and Bracon hebetor attack the pest in Israel. Other antagonists include Hemipteran predators like Chrysopa carnea Stephens Chrysopidae and Orius spp. (Anthocoridae), but their effectiveness is often negated by pesticide applications. Coccinellidae are important predators in Egypt. The egg parasitoids Trichogramma spp. (Trichogrammatidae) and H. hebetor attack the pest in Syria. In Australia the Heliothis nuclear polyhedrosis virus and B. thuringiensis formulations control H. armigera, when their action complement high levels of egg parasitism by Trichogramma. A densovirus was recently isolated from H. armigera, but its effect is unknown.
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Broza, M. 1986. Seasonal changes in population of Heliothis armigera (Hb.) (Lepidoptera; Noctuidae) in cotton fields in Israel and its control with a Bacillus thuringiensis preparation. Journal of Applied Entomology 102: 363–370.
Fédière, G. (and 9 co-authors) 2004. A new densovirus isolated from the African cotton bollworm Helicoverpa armigera Hbn. (Lepidoptera: Noctuidae) in Egypt. Arab Journal of Biotechnology 7: 289-298.
Gunning, R.V., Dang, H.T., Kemp, F.C., Nicholson, I.C. and Moores, G.D. 2005. New resistance mechanism in Helicoverpa armigera threatens transgenic crops expressing Bacillus thuringiensis Cry1Ac Toxin. Applied and Environmental Microbiology 71: 2558–2563.
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OEPP/EPPO, 1981. Data sheets on quarantine organisms No. 110, Helicoverpa armigera. Bulletin OEPP/EPPO 11.
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Tay, W.T. (and 7 co-authors). 2013. A brave new world for an old world pest: Helicoverpa armigera (Lepidoptera: Noctuidae) in Brazil. PLoS One 8 (11): e80134.
Torres-Vila, L.M., Rodrı́guez-Molina, M.C., Lacasa-Plasencia, A. and Bielza-Lino, P. 2002. Insecticide resistance of Helicoverpa armigera to endosulfan, carbamates and organophosphates: the Spanish case. Crop Protection 21: 1003–1013.
Zhou, X., Applebaum, S.W. and Coll, M. 2000. Overwintering and spring migration in the cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae) in Israel. Environmental Entomology 29: 1289-1294.