Two species of helicoverpa (previously known as heliothis) are serious pests of field crops (particularly pulses, cotton, some cereals and oilseeds) in the northern grains region of Australia.
- Helicoverpa armigera (cotton bollworm or corn earworm) is generally regarded as the more serious pest because of its greater capacity to develop resistance to insecticides, broader host range, and persistence in cropping areas from year to year.
- Helicoverpa punctigera (native budworm) numbers in cropping regions fluctuate based on conditions in inland breeding areas.
Understanding the life cycle and behaviour of helicoverpa improves our chances of managing this pest sustainably.
On this page:
- Life cycle
- Host preference
- Sources of moths
- Estimating populations
- Further information
- See also:
- Eggs are 0.5 mm in diameter and change from white to brown to a black head stage before hatching.
- Newly hatched larvae (neonates) are light in colour with tiny dark spots and dark heads. As larvae develop they become darker and the darker spots become more obvious. Both species look the same at the egg and small larvae stages.
- Medium larvae develop lines and bands running the length of the body and are variable in colour. H. armigera have a saddle of darker pigment on the fourth segment and at the back of the head and dark-coloured legs. H. punctigera have no saddle and light-coloured legs.
- Large larvae of H. armigera have white hairs around the head; H. punctigera have black hairs around the head.
- Pupae are found in soil underneath the crop. Healthy pupae wriggle violently when touched. H armigera pupal tail spines are more widely spaced than those of H. punctigera
- Moths are a dull light brown with dark markings and are 35 mm long with a 30-45 mm wingspan. Forewings are brown to reddish brown in the female and dull greenish to yellow or light brown in the male. Hindwings are pale with a broad, dark outer margin. H. armigera has a small light or pale patch in the dark section of the hindwing while the dark section is uniform in H. punctigera.
Helicoverpa take about 4-6 weeks to develop from egg to adult in summer, and 8-12 weeks in spring or autumn.
Fertile eggs hatch in about three days during warm weather (25°C average) and 6-10 days in cooler conditions, changing from white to brown to a black-head stage. Physical factors can dramatically affect egg survival and larval establishment. Heavy rainfall and wind can force eggs off leaves. High temperatures can dehydrate and kill eggs and very small larvae.
The hatching larva (neonate) eats through the eggshell. Neonates are 1-1.5 mm long, with a brown-black head and white or yellowish-white, dark-spotted body. Larvae develop through six growth stages (instars) and become fully grown in 2-3 weeks in summer or 4-6 weeks in spring or autumn. Development is more rapid at higher temperatures, up to 38°C, after which development slows. Larval activity and feeding stops when temperatures fall below 12°C. Fully grown sixth instar larvae are 40-50 mm long with considerable variation in colours and markings.
Fully grown larvae crawl to the base of the plant, tunnel up to 10 cm into the soil and form a chamber in which they pupate. Pupal duration is determined by temperature, taking around two weeks in summer and up to six weeks in spring and autumn. However, diapausing (overwintering) pupae take much longer to emerge. Both species survive the winter as pupae in the soil when host plants are scarce. Substantial numbers of overwintering H. armigera pupae can be found under late summer crops such as sorghum, maize and cotton, particularly when helicoverpa activity has been high in late March.
The forewings are brownish or reddish-brown (females) or dull greenish to yellow or light brown (males). Hindwings are pale with a broad, dark outer margin. H. armigera moths have a pale patch near the centre of this dark region. Moths feed on nectar and live for around 10 days. Females lay around 1000 eggs in singles or clusters on growing points, leaves, flower buds, flowers and developing fruits, and sometimes on stems. Moths tend to lay eggs on the top third of healthy plants and on vigorously growing terminals.
The two helicoverpa species prefer different hosts:
- H. punctigera attacks broadleaf species (e.g. cotton, chickpea, sunflower, soybean, mungbean, navy bean, lucerne, canola, peanut, faba bean, safflower, linseed and azuki bean). It is not found on grass or cereal crops, such as wheat, barley, sorghum or maize.
- H. armigera will attack all field crops, but is less common in wheat and barley. Larvae feed on leaves but are most damaging when feeding on growing terminals, buds or squares, flowers, pods, seed and/or fruit. This includes both direct losses through shedding and reduced quality of retained grain.
Crop and pasture weeds such as noogoora burr, common sowthistle, fat hen and marshmallow are also hosts.
Larvae feed on leaves, flower buds and flowers, developing pods, fruits and seeds. In most crops, young larvae will graze on leaves alone, moving on to feeding on developing pods, bolls, cobs and grain once they are third instar or older (8 mm or longer). In some crops, such as mungbeans and cotton, larvae infest reproductive structures (flowers, squares) as soon as they hatch. Once established in these concealed feeding locations, larvae are much more difficult to control with insecticides.
90% of all feeding (and therefore damage) is done by larva from the third instar (8-13 mm long) onwards. Large larvae (longer than 24 mm) are the most damaging stage, since larvae consume about 50% of their overall diet in the fifth and sixth instars. Larvae need to be targeted for control when they are still small (less than 7 mm).
Most H. armigera moths visible in spring come from local populations. Although both species are capable of travelling hundreds of kilometres on high altitude winds, this characteristic is more typical of H. punctigera.
- From southern Queensland and areas further south, the majority of H. armigera moths overwinter as pupae in the soil. These overwintering pupae survive in a state of suspended development (diapause).
- In Central Queensland and further north, winter temperatures are warm enough for H. armigera not to enter diapause; these regions experience year-round activity.
In most seasons, diapausing pupae can be found under late summer crops such as sorghum, maize and cotton, with moths emerging during October. After one or two generations in spring and early summer, H. armigera numbers increase to become the dominant species in mid-summer to autumn.
Helicoverpa punctigera breeds during winter on flowering plants in inland Australia, when there is sufficient rainfall for broadleaf vegetation to flourish. When this inland vegetation dies off in late winter/spring, moths reach the eastern cropping areas by flying on the warm winds that precede cold fronts in spring. While H. punctigera can overwinter in southern cropping regions, pupae numbers are usually low.
Spring migratory flights make H. punctigera an early season pest; the likely magnitude of these influxes can be estimated by monitoring the breeding areas in inland Australia.
Pheromone traps and computer modelling are two tools used routinely to monitor the arrival of the first H. punctigera moths, and the emergence from diapause of local H. armigera.
- Pheromone traps attract male moths using the sex pheromone (a chemical attractant) that female moths emit to attract mates. H. armigera and H. punctigera pheromones are different, so each species can be monitored separately. Read more about our helicoverpa pheromone trapping program…
- A diapause and emergence computer model uses current local temperatures to calculate the rate of development of pupae in the soil, and predicts the timing of emergence of moths. Pheromone traps specific to H. armigera can confirm the timing of the emergence. This computer model can also be used to predict the beginning of diapause of H. armigera, to identify fields at-risk for pupae busting in any given year.
Strategies such as integrated pest management (IPM) and area-wide management (AWM) aim to restrict the build-up of helicoverpa populations to below damaging levels. Once thresholds for larvae are exceeded, chemical controls are the most practical option. Read more about helicoverpa management…