Bisexual Attract-and-Kill: A Novel Component of Resistance Management for Transgenic Cotton in Australia

Abstract

In Australia, destruction of overwintering pupae of Helicoverpa armigera (Hübner) and Helicoverpa punctigera (Wallengren) (Lepidoptera: Noctuidae) has been a key component of mandatory resistance management schemes to constrain development of resistance to Bt toxins in transgenic cotton. This has been accomplished by tillage (‘pupae busting’), but it is expensive and can interfere with farming operations. Bisexual attract-and-kill technology based on plant volatile formulations offers a potential alternative in some circumstances. We discuss strategies for using such products and describe two trials in which three applications of an attract-and-kill formulation substantially reduced the numbers of Helicoverpa spp. moths and the numbers of potentially overwintering eggs they laid. One trial tested a curative strategy in which the last generation of moths emerging from transgenic cotton was targeted. The other tested a preventive strategy which aimed to reduce the numbers of eggs in the last generation. The preventive strategy reduced egg numbers by about 90% and is now included as an optional alternative to pupae busting in resistance management strategies for Australian cotton. It is limited to fields which have not been defoliated prior to 31 March and was developed to be used primarily in southern New South Wales. In the 2020–2021 cotton season, it was adopted on approximately 60% of the eligible cotton area. We describe the process whereby the strategy was developed in collaboration with the transgenic technology provider, supported by the cotton industry, and approved by the regulatory authority.

Is ‘pupae busting’ or destroying overwintering pupae of Helicoverpa spp. (Lepidoptera: Noctuidae) still relevant today in Australian Bt cotton?

“…It appears that rather than Magnet attracting moths over a large range, active moths moving over a large area are arrested by the product (Gregg, Del Socorro, & Binns 2016). While an early study found that Magnet increased Helicoverpa egg lays in the treated field in the first but not the second year studied (Mensah & Macpherson 2010; the explanation they gave for this was that the odour could have dissipated before the residual moths reached the treatment zone), other studies have showed a reduction in egg lays after application (Del Socorro et al 2003; Gregg et al 2022). A field experiment using Bollgard 3 cotton identified that the best cohort of moths to target for seasonal quarantining using attract and kill was the generation of moths laying the eggs that develop into overwintering pupae (the penultimate generation).…”

“…In wet years, it may be impossible to cultivate these southern regions at all before the next season, and therefore, other measures may be needed to compensate for not pupae busting. These challenges have seen the adoption of bisexual attract‐and‐kill techniques to remove late season moths (Gregg et al 2022) as a replacement for pupae busting.…”

“…A field experiment using Bollgard 3 cotton identified that the best cohort of moths to target for seasonal quarantining using attract and kill was the generation of moths laying the eggs that develop into overwintering pupae (the penultimate generation). Killing this generation radically reduced egg lays and therefore the number of larvae exposed to Bt cotton that could become overwintering pupae (Gregg et al 2022). Therefore, in the southern Bollgard 3 RMP region where pupae busting can be problematic, they use the attract‐and‐kill strategy, targeting the penultimate generation of moths.…”

“…Of these, five species were less abundant in areas sprayed with Magnet, indicating that Magnet repels these species. While there have been reports on the number of moths killed in trials (Del Socorro et al 2010; Gregg et al 2022; Mensah & Macpherson 2010), there have been no records of the beneficials killed, although two studies reported kills of non‐target moths (Gregg, Del Socorro, & Binns 2016; Gregg, Del Socorro, Hawes, & Binns 2016). In both cases, these were mainly other pest moth species.…”

“…It is laced with broad-spectrum insecticides, such as the carbonate thiodicarb, to kill the moths. Because the insecticide/ Magnet ® cocktail is very effective at attracting Helicoverpa moths, only a small amount of insecticide per hectare is required (500 mL/100 m of row in bands of 1-2 m spaced 72 m apart; Gregg et al 2022). Measuring the efficacy of a bisexual attract-and-kill formulation, such as that with Magnet targeting Helicoverpa, is difficult because Helicoverpa is highly mobile.…”