Helicoverpa insecticide resistance surveillance

The surveillance program and its benefits

Each year the NSW Department of Primary Industries conducts a helicoverpa insecticide resistance surveillance program in the major summer cropping regions of NSW and Queensland, focused on detecting helicoverpa resistance to key helicoverpa-selective insecticides.

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

The program utilises F2 screening for detecting resistance to indoxacarb, emamectin benzoate and chlorantraniliprole which now have broad registration in pulses. 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

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.

What the monitoring says

To date in 2021-22, no insects have tested positive for resistance to emamectin benzoate. This is consistent with the historical trend of very low resistance to this insecticide.

To date in 2021-22 no insects have tested positive for resistance to chlorantraniliprole. However, in past seasons resistance to this insecticide was detected at levels higher than the industry average in the Darling Downs and Dawson Callide regions (Figure 2).

Figure 2. Annual frequency of H. armigera chlorantraniliprole resistance in all regions where resistance was detected compared with the industry average ± binomial standard error (SE).

Resistance to indoxacarb can vary significantly between regions and between seasons (see Table 1 and Figure 3).

  • Resistance in central Qld (CQ) and northern Qld (NQ) was higher than the industry average in all years up to and including 2018-19 where it peaked at 13.6% and was 2.4-fold above than in the southern regions. It then declined in 2019-20 and has stabilised over the past two seasons with regional averages ranging from 2.9% to 5.9%.
  • The overall industry average increased from 2019-20 (5.6%) to 2020-21 (6.8%), driven largely by elevated resistance in the Macquarie region of central west NSW, and to lesser extent by increases in southern Qld and northern NSW.
  • So far in 2021-22 the regional average in southern growing areas is consistent with last season due to elevated resistance in the Darling Downs (14.5%) and Macquarie valley (8.3%) while resistance in northern NSW remains low at 3.9%.

Table 1. Regional indoxacarb resistance in the past two seasons (n = number of tests).

Figure 3. Annual frequency of H. armigera indoxacarb resistance in central Qld (CQ) and north Qld (NQ) compared with the industry and southern (southern Qld and NSW) averages ± binomial standard error (SE).

Management implications

The continued pattern of very low resistance to emamectin benzoate and chlorantraniliprole is a positive sign that these insecticides will continue to provide effective control of helicoverpa. Stabilisation of indoxacarb resistance in CQ is also encouraging. However there are signs of selection for resistance to this insecticide in southern Queensland and to a lesser extent in the Macquarie region of NSW and it will be important to adopt best practice for resistance management during the peak spray periods for helicoverpa in winter and summer pulses 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 are urged to consult the Resistance Management Strategy (RMS) in grains for key recommendations.

The strategy 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. The use of a broad range of IPM options will reduce 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.
  • 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 helicoverpa resistance when managing for fall armyworm.
  • 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.

Related Beatsheet articles:

This surveillance is supported by GRDC through project DAN1908-005RTX ‘Resistance surveillance for sustainable management of Helicoverpa in grains’.

Page last updated February 2022.