Helicoverpa insecticide resistance surveillance

The surveillance program and its benefits

Each year 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 hot-spots 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 genesthroughout 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

No insects tested positive for resistance to emamectin benzoate in 2020-21 and follows a continuing trend of very low resistance to this insecticide.

Resistance to chlorantraniliprole was approx. 0.5% on average since 2015-16. During the period from 2017 to 2019 resistance was detected at levels higher than the industry average in the Darling Downs and Dawson Callide regions (Figure 2). However, in 2020-21 no insects tested positive for resistance to chlorantraniliprole.

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).

In contrast, industry-wide resistance to indoxacarb increased significantly. In central Qld (CQ) and northern Qld (NQ) levels remained higher than the industry average in all years up to and including 2018-19 where resistance was 2.4-fold higher than in the southern regions (Table 1, Figure 3). By the end of the 2018-19 an average of 13.6% of the H. armigera population in CQ & NQ carried at least one gene for indoxacarb resistance. Average frequency declined in 2019-20, driven by lower resistance in CQ and NQ (Figure 3).

Results from individual regions in 2019-20 showed significant declines in resistance compared with the previous year, with the industry-wide average declining from 8.7% in 2018-19 to 5.6% in 2019-20. The most marked reductions occurred in CQ and NQ with a 2.2-fold decline from 13.6% in 2018-19 to 6.3% in 2019-20 (Table 1).

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

In 2020-21 average resistance in CQ and NQ was similar to the previous year at 6% with some variation between regions. Resistance in the Emerald and Dawson/Callide regions was lower than the previous year, while resistance increased slightly in the Clermont region (Table 1). Although levels in the Burdekin had increased from 6.6% to 11%, resistance was still significantly lower than in 2018-19 where it peaked at 16.7% (Table 1). However, in 2020-21 the industry-wide average increased from 5.6% to 6.8% (Figure 3) due to elevated resistance in the Macquarie region in the central west of NSW (Table 1). This represents the highest level of indoxacarb resistance recorded in NSW to date and was a significant increase from 2017 when resistance levels were between 2 and 4% in the Macquarie region. There were also minor increases in indoxacarb resistance detected in southern Qld and northern NSW which contributed to an overall increase in average indoxacarb resistance in the southern growing regions from 4.2% in 2019-20 to 7.4% in 2020-21 (Table 1).

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 decline in indoxacarb resistance observed since 2019-20 is a positive sign that this insecticide will remain effective against Helicoverpa in key grains production areas like CQ. The continued pattern of very low resistance to emamectin benzoate and chlorantraniliprole is also encouraging for news for grain growers.

However, an increase in indoxacarb resistance in central western NSW is a reminder to growers not to become complacent because resistance can increase rapidly anywhere and at any time, with the development of a resistant population likely to significantly reduce yield and/or quality of crops.

Therefore, it is critical that H. armigera is managed to minimise the risk of resistance building to dangerous levels that could result in spray failures.

This means adoption of best practice for resistance management during the peak spray periods for Helicoverpa in winter and summer pulses.

To reduce the risk of lost productivity it is recommended that growers continue to be guided by the Helicoverpa Resistance Management Strategy (RMS). The strategy aims to slow the rate of resistance development to those insecticides that are currently very effective, and on which the grains industry is reliant.

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.

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.
  • 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.
  • 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’.