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Helicoverpa and insecticide resistance

Photograph showing a row of Helicoverpa coloured larvae in lucerne
Range of Helicoverpa colours
© State of Queensland
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Background to insecticide resistance in Helicoverpa

Helicoverpa are important economic pests of most crops, particularly pulses, cotton, some cereals and oilseeds. Helicoverpa costs Australian agriculture $225 million per annum. The Helicoverpa life cycle consists of moth, egg, larva and pupa. It is the larva form that causes crop damage.

We are very dependent on insecticides for the management of Helicoverpa. The extensive usage of a limited group of compounds against successive pest generations has imposed severe selection pressure resulting in resistance. With continued insecticide application, the frequency of resistant individuals within a population increases, leading to field control failures.

Within our cropping systems we deal with two species of Helicoverpa: Helicoverpa armigera and H. punctigera. Helicoverpa armigera occurs on both monocots (sorghum, maize, triticale, barley, wheat, canary etc.) and dicots (chickpea, soybeans, mungbeans, linseed, faba beans, canola, some broad leaved weeds etc.) while H. punctigera is limited to dicots.

These two species have different insecticide resistance profiles. Helicoverpa armigera larvae have multiple resistances to chemical groups and are more difficult to control. Helicoverpa punctigera are susceptible to all current chemicals and are relatively easy to control. If H. punctigera is the dominant pest, then endosulfan, pyrethroids and carbamates will give satisfactory control on their own. If H. armigera is the dominant species then appropriate mixtures or alternative chemicals are usually necessary. Spray timing is crucial to achieve satisfactory results.

These differences are partly as a result of different ecologies and behaviours. Helicoverpa armigera and H. punctigera are both migratory, but H. punctigera is more so. Moths are capable of flying long distances as well as moving extensively among fields within a region.

Helicoverpa punctigera frequently reproduce during the winter season on flowering plants within inland regions of Australia. With the onset of spring, these ensuing generations of moths often migrate to cropping areas of the eastern coast. The number of moths participating in this migration is largely determined by rainfall and the abundance of 'outback' host vegetation during the winter period, and the passage of favourable winds to carry them east.

In contrast, H. armigera tends to overwinter as pupae in the soil of late-planted summer crops and therefore remains in the local area. Moth emergence from these overwintering pupae often begins between September and October. Small numbers of H. armigera emerge in spring and often take several generations to build up to high numbers. Crop damage by H. armigera is therefore most common during the later part of the summer season.

These ecological differences are partly responsible for H. punctigera being predominantly an early summer pest and H. armigera a late summer pest. The localised activity of H. armigera within cropping regions also contributes to its ability to readily build resistance to insecticides. Without large-scale migrations of H. armigera from unsprayed areas of 'outback' native vegetation to dilute localised resistant populations, the phenomenon of insecticide resistance compounds rapidly.

See more information on Helicoverpa biology and ecology.

Insecticide Resistance Management Strategy (IRMS)

This strategy is developed each year in order to contain the increase in resistance of H. armigera to insecticides including pyrethroids, carbamates, organophosphates and endosulfan. In its present form it mainly applies to summer crops, especially cotton, but as more insecticides are registered in grain crops the IRMS is being expanded to a Farming Systems IRMS (FS-IRMS) that considers insecticide use in all broadacre crops throughout the year.

The FS-IRMS aims to ensure that there is a sufficient break, of at least one Helicoverpa generation, in the use of each insecticide group, across all crops. For example, there is a recommended end-date for the use of Steward® (indoxacarb) in chickpeas, to allow a break in Helicoverpa exposure to indoxacarb before the product is available for use in cotton.

See Current Cotton Insecticide Resistance Management Strategy.

Major FS-IRMS guidelines

  1. Currently there are no restrictions on the number of pyrethroid sprays that can be applied to non-cotton crops, but there are a number of considerations that apply to the use of pyrethroids in the farming systems.
  2. It is strongly recommended that pyrethroids not be used on Helicoverpa armigera, as they are unreliable.
  3. Pyrethroids should be targeted only on small larvae (i.e. less than 7 mm long) as application on larger resistant larvae will be ineffective and will increase levels of pyrethroid resistance. (Note: even for insecticide groups for which resistance is not established, small larvae are still more susceptible than larger larvae).
  4. If you are intending to spray a population of Helicoverpa, consider where the moths that laid the eggs may have originated. If they are likely to be survivors from a crop that was previously sprayed (e.g. with a pyrethroid), spraying again with the same insecticide will exacerbate resistance.
  5. Avoid using broad-spectrum sprays such as organophosphates or pyrethroids early in the season. They reduce the numbers of beneficial insects and increase the chances of aphid, mite and further Helicoverpa outbreaks.
  6. Be aware that in 2005 there were major changes to the registration for endosulfan. Endosulfan has been withdrawn from use in grain crops, with a few exceptions for control of pests in seedling crops. Endosulfan can no longer be used in soybean, sunflower, mungbean or other summer grain crops.
  7. Do not use StewardTM (indoxacarb) against Helicoverpa on chickpea after 15 October (southern regions) or 15 September (Central Queensland). This cut-off date aids resistance management by allowing a full generation of Helicoverpa to develop between the last use in chickpea and the first possible use in cotton.
  8. The use of ovicides may be warranted in the event of high egg pressure - use methomyl before the black-head egg stage.
  9. Use recommended larval thresholds to minimise pesticide use and reduce resistance selection. Sprays should only be applied if the larvae are doing economic damage (i.e. the value of the crop saved should exceed the cost of spraying).
  10. Cultivate chickpea and other host-crop residues as soon as possible after harvest to destroy pupae. Cultivation must be completed no later than one month after large larvae were observed in the field, otherwise the moths will emerge and move elsewhere.
  11. Do not respray an apparent failure with a product of the same chemistry.

Helicoverpa control on an area-wide basis

Farmers are faced with increasing problems of controlling resistant Helicoverpa. In response to this a Helicoverpa Regional Management Strategy (HRMS), or area-wide management strategy, was formulated by producers, consultants, researchers and extension personnel and was implemented in two pilot study areas on the Darling Downs in 1998-2001.

The HRMS was designed to manage Helicoverpa at a regional level rather than each farmer making Helicoverpa control actions in isolation. The HRMS pilot trial resulted in a high level of communication and cooperation between farmers and consultants in an effort to better manage Helicoverpa.

The basic principles of the strategy involve a yearly cycle of management practices, which includes tactics that aim to reduce:

  • the population of overwintering Helicoverpa pupae (March-June)
  • the early season build-up of Helicoverpa on a regional/district scale (July-November)
  • the mid-season population pressure on Helicoverpa-sensitive crops (December-March).

Key components of area-wide management include:

  • crop checking
  • pupae busting
  • improved management for commercial chickpea crops
  • chickpea trap crops
  • using information from pheromone traps
  • monitoring the contribution of beneficial insects
  • insecticide management.

Many areas outside the original pilot study areas are now implementing similar strategies. In the pilot study areas, many of the original HRMS/AWM groups continue to meet and discuss pest management issues. Contact your local extension officer, consultant or Department of Employment, Economic Development and Innovation IPM Development Extension Officer for information on existing groups in your region, or how to form a new group.

Control considerations

Presently there are few control options other than the use of chemical insecticides, or virus, for Helicoverpa larvae once in a crop. Spraying should be carried out promptly once the threshold for each insect has been reached.

Spray small or spray fail

Helicoverpa grow rapidly and a few days delay in spraying can result in major crop damage and increased difficulty in control. If a spray application is delayed for more than 2 days, for any reason, the crop should be rechecked and reassessed.

Make sure that crops are being checked when they are susceptible to Helicoverpa damage. Early detection of infestation is critical to ensure the most effective timing of sprays.

Ensure Helicoverpa larvae in the crop are at an appropriate size to control effectively with the product you are intending to use. Spray only if the larvae are doing economic damage (i.e. the value of the crop saved should exceed the cost of spraying).

Seek professional advice to ensure you are NOT:

  • spraying unnecessarily (i.e. below threshold)
  • planning to use an insecticide to which the pest is likely to be resistant
  • promoting the further development of resistance through your choice of insecticide.

Common insecticides and registered application rates can be found by individual crop. These are not complete lists of all products registered in winter crops and it is recommended that you check Infopest before applying a chemical. As always, read the label.

Due to the resistance that Helicoverpa has developed to major chemical groups, it is important to remember that registered chemicals will not necessarily give adequate control in each situation. Local knowledge of which chemicals are working in a particular area should be sought from consultants and agronomists in your area.

Montitoring for insecticide resistance in Helicoverpa

The cotton industry monitors levels of Helicoverpa resistance to key insecticide groups throughout the summer. This information is available on the Cotton Catchment Communities CRC website. From 2006-7, with an investment by the Grains Research and Development Corporation, this monitoring was expanded to include monitoring of Helicoverpa from grain crops.

Further information

Last updated 04 April 2011