Helicoverpa insecticide resistance surveillance

The surveillance program and its benefits

Each year the NSW Department of Primary Industries and Regional Development (DPIRD) conducts a Helicoverpa armigera insecticide resistance surveillance program in the major summer cropping regions of Queensland and New South Wales.

The program provides growers and advisors with an early warning system for potential resistance outbreaks in the northern region, helps maximise the effectiveness of spray applications, and is essential for informing ongoing review and improvement of industry-endorsed resistance management strategies.

The program utilises F₂ screening for detecting resistance to key selective insecticides used to control helicoverpa (including spinetoram, emamectin benzoate, indoxacarb and chlorantraniliprole) which have broad registration in pulses and horticulture and are also permitted for use to target fall armyworm. This type of screening is highly sensitive for all types of known and novel resistance even when resistance genes are recessive.

This predictive capability means industries can implement management tactics for reducing economic losses well before spray failures occur, as well as minimising further spread of resistance genes throughout the wider H. armigera population.

Chemical Mode-of-Action Groups Tested

GROUP 5 Spinetoram (e.g. Success Neo®, Entrust®)
GROUP 6 Emamectin benzoate (e.g. Affirm®, Proclaim Opti®)
GROUP 22A Indoxacarb (e.g. Steward®, Avatar®)
GROUP 28 Chlorantraniliprole (e.g. Vanticor®, Coragen®)

F₂ screening involves testing the grandchildren of moths from field populations to generate F2 progeny though a step-wise process shown in Figure 1.

Figure 1. F2 screen for detection of resistance alleles. Moths are collected from pheromone traps and, in this example, one parent has one copy of the resistance gene (RS). Their F1 progeny are sib-mated to produce the F2 generation. If resistance is completely recessive then only 1 in 16 of the F2 progeny will be homozygous (RR) for the resistance gene and will survive a diagnostic dose of insecticide. The remaining susceptible (SS) and heterozygous (RS) progeny will be killed.

Summary of results from 2025-26 and comparison to long term trends

Group 5: Spinetoram (e.g. Success Neo®, Entrust®)

No resistance detected to spinetoram. Although low levels of resistantance have been detected in the past to this insecticide, there have been no cases detected since 2023-24, indicating genes for Groups 5 resistance are very rare.

Group 6: Emamectin benzoate (e.g. Affirm®, Proclaim Opti®)

No resistance detected to emamectin benzoate. This is consistent with historical trends that show genes for Group 6 resistance are very rare.

Group 22A: Indoxacarb (e.g. Steward®, Avatar®)

Industry average resistance across central Queensland was 10%. Likewise, resistance in southern Queensland was 11%. Elevated indoxacarb resistance in the Darling Downs this season was consistent with levels seen in previous seasons (Table 1). Levels of indoxacarb resistance in northern NSW were also higher than previously recorded at 14%.

Table 1. Regional indoxacarb resistance in H. armigera 2025-26. Resistance determined from F2 screens conducted on insecticide-incorporated diet using a diagnostic dose of indoxacarb at the LC99.9 level. Data from the previous three seasons is included for comparison.

Together, these frequencies have resulted in an increase in the southern average to 12% and contributed to an overall increase in industry wide resistance to 11%, a significant increase in indoxacarb resistance in 2025-26 compared to the long-term average of 6% (Figure 2).

Figure 2. Annual industry-wide average indoxacarb resistance in H. armigera compared with northern (NQ & CQ) , southern Qld (SQ & NSW) averages and individual regions ± binomial standard error (SE).

In previous seasons, validation testing of positive cases confirmed that all survivors of the diagnostic screening process were heterozygous for resistance (i.e. were carrying only one copy of the resistance gene). However, in the 2025-26 season, one iso-female line established from the Emerald region produced F₂ progeny with 68% survival at the discriminating dose of indoxacarb.

This level of survival was similar to that expected (75%) if the field-caught male parent was homozygous for indoxacarb resistance, and demonstrates the first case of putative homozygous resistance in H. armigera detected since F₂ screening was implemented in 2013.

Group 28: Chlorantraniliprole (e.g. Vanticor®, Coragen®)

No resistance detected to chlorantraniliprole. Low resistance was previously detected in southern and central Queensland during 2018-19, but there have no further cases detected since, indicating genes for Groups 28 resistance are very rare.

Management implications

The continued pattern of very low resistance to spinetoram, emamectin benzoate and chlorantraniliprole is a positive sign that these insecticides will continue to provide effective control in the coming season.

However, significant increases in indoxacarb resistance across all sampling locations in 2025-26 along with the first case of putative homozygous indoxacarb resistance detected in CQ indicates that the future frequency of resistance to this insecticide may approach levels that could result in increased mating events between heterozygous carriers of resistance.

Therefore, it is important to adopt industry best practices for resistance management, particularly during the peak spray periods for helicoverpa in pulses and cereals to minimise the risk of resistance building to dangerous levels that could result in spray failures.

To reduce the risk of lost productivity due to resistance, growers and agronomists are urged to consult the Resistance Management Strategy (RMS) in grains for key recommendations.

The RMS is based on best practice product use windows and restrictions on the number of sprays to minimise selection pressure from the same chemical group across consecutive generations of H. armigera. Using a broad range of IPM options reduces over-reliance on any one chemical group. Following the strategy’s recommendations and complying with label instructions will minimise the risk of spray failures and support sustainable management of H. armigera.

General principles to minimise resistance development:

Comply with all directions on product labels – DO NOT cut rates or exceed the recommended applications per crop per season.
Avoid repeated use of insecticides from the same chemical group; if a spray fails due to resistance or unknown cause, do not re-spray using that group in the same season.
Monitor regularly, using appropriate sampling techniques.
Correctly identify the pest to ensure the most effective insecticide and rate is used.
Monitor beneficial populations to determine if chemical control of helicoverpa is warranted.
If available, use economic thresholds when making spray decisions.
Avoid prophylactic sprays
Where possible, use target-specific ‘soft’ chemicals rather than broad-spectrum pesticides.
Consider the impact on all species present when applying insecticide sprays; be aware of potential implications for fall armyworm and cluster caterpillar resistance when managing for helicoverpa.
Ensure spray rigs are calibrated properly and sprays achieve effective coverage.
Monitor post-treatment for evidence of loss of field efficacy and report field failures.

For more information:

Read the GRDC’s resistance management strategy for Helicoverpa armigera and check relevant spray windows. The science behind the Helicoverpa armigera RMS is available at IPM Guidelines for Grains.