Other common names
Heliothis, Tomato grub
Photo by Andrew Weeks, Cesar Australia
Caterpillars of the corn earworm (or cotton bollworm) are the major pest of cotton, but can also be problematic in pulses, canola and occasionally cereals. They are more common in the northern or coastal regions of eastern Australia, particularly in warmer regions. This species has developed high levels of resistance to insecticides and management needs to draw on biological and cultural options and the use of appropriate insecticides.
The corn earworm is a common and widely distributed pest that has been recorded from all states and territories within Australia. They are more common in eastern Australia, particularly in warmer regions such as northern New South Wales and southern Queensland. In cooler regions such as Victoria, South Australia and Tasmania they are generally only problematic in summer, and are most commonly associated with irrigated horticultural crops such as tomatoes and sweet corn. They are occasionally found in dryland broadacre crops such as winter canola and wheat or summer forage brassicas.
Corn earworm is a warm season pest with a wide host range particularly cotton.
Adult moths have a wing-span of 30-45 mm and are light brown to red-brown in colour with numerous dark spots and blotches. The hind wings are pale with a dark band along the lower edge.
Larvae reach 40 mm in length and there can be substantial colour variation that includes shades of brown, green and orange. All colours usually have darkish strips along the body and bumpy skin with sparse stiff stout hairs. They have a ‘saddle’ on the 4th body segment and have a sharp downward angling at the rear of the body. Larvae have white hairs around the head and black hairs along the body.
Corn earworm generally has 4 to 5 generations per season. Larval activity increases in warmer conditions, and larval activity and feeding cease when temperatures fall below 12°C. Corn earworm populations mostly arise from agricultural and horticultural industries, not from native non-crop plants.
Corn earworm larvae are rather aggressive, occasionally carnivorous and may even cannibalise each other. If disturbed, they fall from the plant and curl up on the ground.
Similar to Top
Caterpillars and moths are similar to the native budworm and lesser budworm. They can only be distinguished using a microscope. They may also be confused with armyworms and cutworms, although these have smoother bodies with fewer distinct hairs.
Crops attacked Top
Corn earworm has a wide host range and can attack all field crops, particularly cotton, sorghum, maize, sunflowers, chickpeas, lupins and lucerne. The species is also occasionally found grazing on wheat and barley heads. They can cause damage to foliage, flowers and pods on canola.
Larvae attack all stages of plant growth. Feeding on stems and leaves is rarely extensive. Larvae can damage seedlings by eating terminal buds but in more advanced growth, larvae will attack all above ground plant parts, including pods and seeds. Most damage occurs in late spring and summer. Corn earworms are at their most damaging when they feed on the fruiting parts and seeds of plants. Holes or chewing damage may be seen on pods and/or seed heads. In cotton, the main damage is to squares, flowers and bolls.
Losses attributed to corn earworms come from direct weight loss through seeds being wholly or partly eaten. Grain quality may also be downgraded through unacceptable levels of chewed grain. Caterpillars eat increasing quantities of seed and plant material as they grow. The last two growth stages (5th & 6th instar) account for over 90% of their total grain consumption.
Because corn earworm moths are less inclined than native budworm moths to undertake long-distance migratory flights, problems in spring and summer generally arise from local populations that survive over winter as diapausing pupae in winter crops.
Sweep netting is a quick and easy method to sample most crops. Monitor crops for activity by taking a minimum of 5 sets of 10 sweeps and calculating the average number of larvae per 10 sweeps. The use of pheromone traps (which attract male moths) can provide an early warning of moth arrival to an area or their emergence from local winter diapause. These should be set up in early spring. Visual sampling for eggs and larvae is the main technique used for routine sampling in cotton.
Economic thresholds Top
• Flowering – podding: 5-10 larvae per m2 (Berlandier & Baker 2007), or >5 larvae (10 mm or longer) per m2 (McCaffery 2009)
• Flowering- podfilling:
o Albus lupins for human consumption: 1- 2 larvae per m2 (<5 mm long)
o Stockfeed: 1-2 larvae per 10 sweeps
Field peas (NSW):
• Flowering – podding:
o Stockfeed: >4 larvae (4- 9 mm) per 10 sweeps
o Human consumption: 1-2 larvae (4- 9 mm) per 10 sweeps
• 1- 4 per m2 (using a beat sheet) or 5 per m2 (using a sweep net). Use QDAFF formula to fine tune threshold.
Faba beans (NSW):
• 2- 4 larvae per m2 (less than 10 mm)
• Human consumption: 1 per m2
• up to flowering, > 2 larvae per metre row.
• After flowering, a standard egg threshold is > 5 brown eggs per metre row. Thresholds for Bt cotton are higher (Bailey, 2007).
Management options Top
There are many natural enemies that attack corn earworm. These include shield bugs, damsel bugs, assassin bugs, native earwigs, tachinid flies, orange caterpillar parasite, two-toned caterpillar parasite, the egg parasitoid Trichogramma wasps, lacewings and spiders. Naturally occurring fungal diseases and viruses also play an important role in some seasons.
In southern crops, windrowing canola or desiccating pulse crops such as field peas may be an option to advance the drying of crops when small-medium size larvae are present. Cultivating and slashing can reduce pupal and larvae survival.
In northern areas, chickpeas can be used as a trap crop to capture overwintering populations merging from diapause. Avoid successive plantings of summer legumes. Weed management in and around crops can prevent the build-up of corn earworm and other insect pests.
There are numerous insecticides registered against corn earworm. Control is complicated because field populations are resistant to endosulfan, synthetic pyrethroids and carbamates, as well as lower levels of resistance to organophosphates, spinosad and indoxacarb (there is a substantial literature on this, see References). In cotton, a comprehensive resistance management framework exists for growers to follow.
Timing of chemical applications and coverage are critical. Target small larvae up to 7 mm in length and apply insecticides before larvae move into flowering pods. Soft options include the use of Bt (Bacillus thuringiensis) and nucleopolyhedrosis virus (NPV) based biological insecticides.
Corn earworm populations are resistant to several insecticides and control can be complicated.
This article was compiled by Paul Umina (cesar), Garry McDonald (cesar) and Sandra Hangartner (cesar).
References/Further Reading Top
Anon. 2005. Understanding Helicoverpa ecology and biology in Southern Queensland: know the enemy to manage it better. Agdex No. 612. Queensland Department of Primary Industries and Fisheries.
Bailey PT. 2007. Pests of field crops and pastures: Identification and Control. CSIRO Publishing, Melbourne, Australia.
Baker GH, Tann CR and Fitt GP. 2011. A tale of two trapping methods: Helicoverpa spp. methods: (Lepidoptera, Noctuidae) in pheromone and light traps in Australian cotton production systems. Bulletin of Entomological Research 101: 9-23.
Baker GH and Tann CR. 2012. Mating of Helicoverpa armigera (Lepidoptera: Noctuidae) moths and their host plant origins as larvae within Australian cotton farming systems. Bulletin of Entomological Research 103: 171-181.
Bellati J, Mangano P, Umina P and Henry K. 2012. I SPY. Insects of Southern Australian Broadacre Farming Systems Identification Manual and Education Resource. Department of Primary Industries and Resources South Australia (PIRSA), the Department of Agriculture and Food Western Australia (DAFWA) and cesar Pty Ltd.
Berlandier FA and Baker GJ. 2007. Winter oilseeds. In: Pests of field crops and pastures: identification and control. (ed. PT Bailey) pp 135-154. CSIRO Publishing: Melbourne.
Bird LJ and Akhurst RJ. 2007. Variation in susceptibility of Helicoverpa armigera (Hübner) and Helicoverpa punctigera (Wallengren) (Lepidoptera: Noctuidae) in Australia to two Bacillus thuringiensis toxins. Journal of Invertebrate Pathology 94: 84-94.
Bird LJ and Akhurst. 2007. Effects of host plant species on fitness costs of Bt resistance in Helicoverpa armigera (Lepidoptera: Noctuidae). Biological Control 40: 196-203.
Bird LJ and Downes SH. 2014. Toxicity and Cross-Resistance of Insecticides to Cry2Ab-Resistant and Cry2Ab-Susceptible Helicoverpa armigera and Helicoverpa punctigera (Lepidoptera: Noctuidae). Journal of Economic Entomology 107: 1923-1930.
Bird LI. 2015. Baseline Susceptibility of Helicoverpa armigera (Lepidoptera: Noctuidae) to Indoxacarb, Emamectin Benzoate, and Chlorantraniliprole in Australia. Journal of Economic Entomology, in press.
Cotton CRC Extension Team. 2009. Cotton Pest Management Guide 2009-10. Cotton Catchment Communities CRC, Narrabri and Industry & Investment NSW, Orange, Australia.
Downes S and Mahon R. 2012. Successes and challenges of managing resistance in Helicoverpa armigera to Bt cotton in Australia. GM Crops & Food: Biotechnology in Agriculture and the Food Chain 3: 228-234.
Downes S and Mahon R. 2012. Evolution, ecology and management of resistance in Helicoverpa spp. to Bt cotton in Australia. Journal of Invertebrate Pathology 110: 281-286.
Endersby NM, Hoffmann AA, McKechnie SW and Weeks AR. 2007. Is there genetic structure in populations of Helicoverpa armigera from Australia? Entomologia Experimentalis et Applicata 122: 253-263.
Gunning RV, Dang HT, Kemp FC, Nicholson IC and Moores GD. 2005. New Resistance Mechanism in Helicoverpa armigera Threatens Transgenic Crops Expressing Bacillus thuringiensis Cry1Ac Toxin. Applied and Environmental Microbiology 71: 2558-2563.
Jallow MFA and Zalucki M. 2003. Relationship between oviposition preference and offspring performance in Australian Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae). Australian Journal of Entomology 42: 343-348.
Joussen N, Agnolet S, Lorenz S, Schoene SE, Ellinger BS and Heckel DG. 2012. Resistance of Australian Helicoverpa armigera to fenvalerate is due to the chimeric P450 enzyme CYP337B3. PNAS 109: 15206-15211.
Mangano P, Michael P and Hardie D. 2006. Management of native budworm in pulse and canola crops in the south-west of Western Australia. Farmnote: 184. Department of Agriculture and Food Western Australia.
McCaffery D (ed). 2009. Canola best practice management guide for south-eastern Australia. GRDC. ISBN 978-1-875477-85-2.
Mensah RK and Moore C. 2011. Exploitation of semiochemicals for the management of pest and beneficial Insects with special emphasis on cotton cropping systems in Australia: A Review. Journal of Biological Control 25: 253-269.
Robin G. 2012. Insecticide Resistance in Helicoverpa spp. Inside Cotton.
Scott KD, Lawrence N, Lange CL, Scott LJ, Wilkinson KS, Merritt MA, Miles M, Murray D and Graham GC. 2005. Assessing moth migration and population structuring in Helicoverpa armigera (Lepidoptera: Noctuidae) at the regional scale: Example from the Darling Downs, Australia. Journal of Economic Entomology 98: 2210-2219.
Scott KD, Wilkinson KS, Lawrence N, Lange CL, Scott LJ, Merritt MA, Lowe AJ and Graham GC. 2005. Gene-flow between populations of cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae) is highly variable between years. Bulletin of Entomological Research 95: 381-392.
Walsh TK, Downes SJ, Gascoyne J, James W, Parker T, Armstrong J and Mahon RJ. 2014. Dual Cry2Ab and Vip3A resistant strains of Helicoverpa armigera and Helicoverpa punctigera (Lepidoptera: Noctuidae); testing linkage between loci and monitoring of allele frequencies. Journal of Economic Entomology 107: 1610- 1617.
Young SJ, Gunning RV and Moores GD. 2005. Effect of pretreatment with piperonyl butoxide on pyrethroid efficacy against insecticide-resistant Helicoverpa armigera (Lepidoptera: Noctuidae) and Bemisia tabaci (Sternorrhyncha: Aleyrodidae). Pest Management Science 62: 114-119.
Zalucki MP, Cuningham JP, Downes S, Ward P, Lange C, Meissle M, Schellhorn NA and Zalucki ZM. 2012. No evidence for change in oviposition behaviour of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) after widespread adoption of transgenic insecticidal cotton. Bulletin of Entomological Research 102: 468-476.
Zhang H, Yang Q, Qin QL, Zhu W, Zhang ZF, Li YN, Zhang N and Zhang JH. 2013. Genomic sequence analysis of Helicoverpa armigera nucleopolyhedrovirus isolated from Australia. Archives of Virology 159: 595-601.
|February 2015||1.0||Paul Umina (cesar), Sandra Hangartner (cesar) and Garry McDonald (cesar)||Bill Kimber (SARDI)|
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