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 utilizes F2 screening to increase capacity 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 in 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

This program of surveillance is now in its seventh season and the recent pattern of very low emamectin benzoate resistance has continued in 2019-20, with no insects testing positive for resistance to this insecticide.

Resistance to chlorantraniliprole remained at about 0.5% on average since 2015-16. From 2017 to 2019 there were instances where higher resistance levels were detected in the Darling Downs and Dawson Callide regions (Figure 2). However, in 2019-20 no insects tested positive for resistance to chlorantraniliprole.

Figure 2. Annual regional frequency of chlorantraniliprole resistance in all regions compared with the eastern Australian average ± binomial standard error (SE).

In contrast, industry-wide resistance to indoxacarb increased significantly in 2016-17 and 2018-19 (Figure 3), particularly in central and northern Queensland where resistance was up to 2.4-fold higher than in the southern regions. 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.

Figure 3. Annual regional frequency of indoxacarb resistance in central/northern Qld compared with the industry and southern averages ± binomial standard error (SE).

Results from individual regions in 2019-20 showed a significant reduction in resistance compared with the previous year, with the industry-wide frequency declining from 9.8% in 2018-19 to 5.7% in 2019-20. The most marked reductions occurred in central and northern grains regions of Queensland with a 2.2-fold decline from 13.6% in 2018-19 to 6.2% in 2019-20 (Table 1).

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

Management implications

The decline in resistance has likely come about as a result a downturn in production due to the severity of drought conditions experienced in 2018-19, resulting in reduced spraying and reduced selection pressure for resistance.

Although this is a positive sign for industry, it will be important for growers not to become complacent because it is highly likely that resistance will increase rapidly if there is over-reliance on chlorantraniliprole and indoxacarb, with the development of a resistant population likely to significantly reduce yield and quality of pulse crops. H. armigera must be managed to minimise the risk of resistance increasing to dangerous levels that could result in spray failures.

Therefore, it will be important for growers to maintain best practice for resistance management in the upcoming peak spray periods for helicoverpa in winter 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 good 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’.