Insecticide resistance results in reduced product efficacy and represents a major cost to agricultural production in terms of economic, environmental and social consequences. The cotton bollworm, Helicoverpa armigera is notoriously difficult to manage because of its capacity to develop resistance to a wide range of insecticides. Resistance risk in H. armigera is a major concern in mixed production systems that provide a range of hosts for this pest, and is a key stewardship issue shared by the cotton and grains industries. The Helicoverpa spp. insecticide resistance surveillance program has implemented highly efficient and sensitive methodologies to deliver scientifically measurable outcomes for supporting industry sustainability by reducing resistance risk associated with insecticide use.

Resistance surveillance and associated research underpins strategic response to emerging resistance issues. Outcomes from this project have been essential for informing a broader process of formulating the Insecticide Resistance Management Strategy (IRMS) used primarily by the cotton industry. This is a key industry pathway for delivering information and recommendations incorporating all pest species and all registered products. However, since the expansion of the pulse industry in eastern Australia in the early 2000’s, the grains industry has become a major user of Helicoverpa insecticides, and the cotton IRMS may not be sufficiently effective for managing resistance risk in insecticides utilized to target H. armigera across multiple commodities. Moreover, risk is elevated due to ecological factors unique to northern populations which will also favour resistance selection. This could have important implications for long-term sustainability of these products in cotton and highlights the need for a cross-industry approach that promotes stewardship of key Helicoverpa insecticides.

To support resistance management in grains, a resistance management strategy (RMS) for H. armigera specifically designed for grains crops was released in April 2018. A key aspect of its development was industry-wide consultation with leading growers and advisors in the cotton and grains industries which highlighted regional concerns about resistance risk due to product overuse in pulse crops. However, there is little value in industry adoption of an RMS without an ongoing monitoring program to support the strategy. Therefore project expansion involving targeted surveillance in northern grains regions provided regionally-specific information for quantifying resistance frequency with benefits to the cotton industry through improved preparedness.

While the cotton and grains RMS’s are critical for pre-emptive management of risk factors at the field level, characterisation of the causal factors underlying resistance is also an important predictive tool for future-proofing Helicoverpa insecticides and has been a key focus of this project. For example, the isolation and quantitative genetic analysis of indoxacarb resistance in H. armigera has been a key outcome from this project and was also central for developing collaborations resulting in elucidation of a putative molecular mechanism of resistance to this insecticidal class.

Importantly, while molecular technologies in resistance diagnostics will continue to improve, field-based surveillance by bioassay is currently the mainstay of resistance programs because it provides a direct measure of resistance frequency regardless of the molecular basis of resistance. This is important because the limit of detection of new or novel mechanisms from field-based bioassay is high, even if these mechanisms have not been previously identified and/or characterised. Therefore, continued surveillance and research to increase our understanding of emerging field resistance mechanisms will be critical to ensuring that industries retain efficacy of as many rotational options as possible.

For more information please contact: lisa.bird@dpi.nsw.gov.au