Helicoverpa insecticide resistance surveillance

About the surveillance program

Each year NSW Department of Primary Industries conducts a Helicoverpa insecticide resistance surveillance program in the major summer cropping regions of NSW and QLD.

In 2013, NSW DPI introduced a program of F2 screening to increase capacity for detecting resistance to selective Helicoverpa insecticides indoxacarb, emamectin benzoate and chlorantraniliprole.

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 are the benefits?

F2 screening is capable of identifying all previously detected and potentially new types of resistance to these insecticides which are pivotal to Helicoverpa management in northern farming systems.

F2 screens are important in pre-emptive resistance management because they can measure underlying resistance by detecting heterozygous carriers of resistance, even when the resistance alleles are recessive.

This effectively 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.

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 has also remained consistently low over the past seven seasons with an average annual frequency of 0.5%. Nevertheless, there was significantly above average resistance detected in areas of central Queensland during the last two years (Figure 2).

So far in 2019-20 we have not detected any resistance to chlorantraniliprole from samples collected from chickpea fields in central Queensland.

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 then again in 2018-19 (Figure 3). This was driven by significantly higher levels of resistance in central and northern QLD where resistance was up to 2.4-fold higher than in the southern regions.

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

By the end of 2018-19 an average of 13.6% of the H. armigera population in central and northern QLD carried at least one gene for indoxacarb resistance.

Regionally, indoxacarb resistance in the northern highlands around Clermont was similar to that recorded in the Emerald Irrigation Area (11.7% and 12.5%, respectively). Resistance in the Dawson/Callide regions was 14.5%, while the highest frequency was recorded in the Burdekin region (16.7%) (Figure 3).

So far in 2019-20 we have seen a significant reduction in indoxacarb resistance in samples collected from chickpea fields in the Clermont, Emerald and Dawson/Callide regions of central QLD. This is likely due to reduced insecticide use due to reduced plantings of winter pulses as a result of ongoing drought conditions in eastern Australia.

Implications for management

H. armigera has a very strong track record for developing resistance in response to selection pressure from insecticides. The risk of resistance to chlorantraniliprole and emamectin benzoate remains low based on current resistance frequency data. However, it is highly likely that resistance will increase rapidly due to selection pressure if there is over-reliance on these products

Although indoxacarb resistance has declined in spring cohorts of H. armigera from central QLD, research shows there is still a high risk for indoxacarb resistance to redevelop in this region. Therefore the key message is:

Do not be complacent and continue to ensure that H. armigera is managed to minimise the risk of resistance increasing to dangerous levels that could result in spray failures.

To support resistance management in grains an RMS for H. armigera was developed in consultation with the grains industry. The focus of the strategy is to slow the rate of resistance development to those insecticides that are currently very effective, and on which the grains industry is reliant.

Indoxacarb and chlorantraniliprole are of particular concern because they are pivotal insecticides across a range of farming systems and are now at increased resistance risk from over-use in the pulse industry.

The strategy is based on best practice product windows and usage restrictions 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 in the same season using a product from the same chemical group
  • Where possible, use target-specific ‘soft’ chemicals rather than broad-spectrum pesticides
  • Correctly identify the pest to ensure the most effective insecticide and rate is use.
  • Monitor beneficial populations to determine if chemical control of Helicoverpa is warranted
  • Consider the impact on all species present when applying insecticide sprays
  • 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.
  • Be aware of potential implications for helicoverpa resistance if considering spraying for fall armyworm.

For more information:

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

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