Pyrethroid and carbamate resistance in Australian Helicoverpa armigera (Lepidoptera: Noctuidae) from 2008 to 2015: what has changed since the introduction of Bt cotton?

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Introduction

The cotton bollworm, Helicoverpa armigera (Hübner) is one of the most serious global insect pest species of agriculture having by far the most reported cases of insecticide resistance worldwide, including field-evolved resistance to pyrethroids, carbamates, cyclodienes, and organophosphates (McCaffery, 1998), spinosad (Gunning, 2002), indoxacarb (Bird, 2016) and toxins derived from Bacillus thuringiensis (Mahon et al., 2007). This capacity to develop resistance is associated with its highly polyphagous nature, wide geographical distribution (Zalucki et al., 1986; Fitt, 1989) and an ability to migrate long distances (Feng et al., 2005). Historically, H. armigera had a range of distribution throughout the Old World, with more recent work confirming a major incursion into South America (Czepak et al., 2013; Mastrangelo et al., 2014; Murúa et al., 2014).

In Australia, there is considerable experience in managing H. armigera in agricultural systems. Following the widespread failure of insecticides to control field populations of H. armigera in the 1980s (Gunning et al., 1984), a windows-based Insecticide Resistance Management Strategy (IRMS) was designed and implemented to manage resistance by restricting the use mode-of-action group by rotation, and the number of applications (Forrester et al., 1993). In addition, a monitoring programme was established to detect changes in insecticide resistance frequencies based on a discriminating dose technique highly effective for detecting incipient resistance. This programme was important for assessing the effectiveness of IRMS and also provided a basis for the timely implementation of pre-emptive responses to control resistant populations (Forrester & Bird, 1996; Rossiter et al., 2008). Although the IRMS did not overcome pyrethroid resistance in Australian H. armigera, it proved to be an effective tactic for delaying resistance and extending the useful life of these insecticides prior to the commercialization of genetically modified cotton producing the δ-endotoxin genes of B. thuringiensis subsp. kurstaki (Bt). The phased introduction of commercial scale Bt cotton to control H. armigera and the native Helicoverpa punctigera (Wallengren) began with the single gene variety, Ingard® (producing Cry1Ac toxin) in 1996, followed by two gene cotton, Bollgard II® (producing Cry1Ac and Cry2Ab) in 2003.

Concurrent with the introduction of Bt cotton was a reduction in the...