The adoption of transgenic (Bt) cotton varieties has markedly reduced feeding damage by noctuid pests, Helicoverpa armigera and H. punctigera, in Australian cotton crops. However, the potential for Bt resistance to evolve within these insect pests is a major concern. To reduce the likelihood of Bt resistance occurring, it is mandatory for growers of Bt cotton to also grow refuge crops which produce large numbers of Bt-susceptible moths. We present here findings from a series of field studies which sought to identify the relative Helicoverpa productivity of different refuge crop options. The abundance of Helicoverpa pupae (during the cotton season) was compared under crops of Ingard® (transgenic, single Bt gene) cotton, sprayed conventional cotton, and various unsprayed refuge crops (cotton, sorghum, maize, pigeon pea) from 1996 to 2003 in the major cotton-producing regions of northern New South Wales, plus St George and Dirranbandi in southern Queensland. Unsprayed, conventional cotton was used as the ‘control’ refuge in these studies. Productivity of adult Helicoverpa was estimated by surveying for pupae and discounting those that were parasitised and dead. Some supplementary experiments were also conducted to evaluate specific issues, in particular the value of additional refuge crops sown late in 2000–01 (due to accidental over-planting of Ingard® cotton that year) and the potential productivity of mixed plantings of various refuge crops which individually flowered at different times throughout the cotton season. Unsprayed refuges generally produced many more pupae than sprayed, conventional cotton and Ingard® cotton. Overall, pigeon pea, which has the advantage of prolonged flowering and thus on-going attractiveness to Helicoverpa, was the most reliable and productive refuge option, producing about twice as many pupae as unsprayed cotton. The seed mix refuge is perhaps a viable alternative option, although logistically more difficult for growers to adopt. Laboratory rearing of live pupae until moth emergence indicated that parasitism can be a substantial source of mortality in some refuge crops, especially sorghum. The most common parasitoid of Helicoverpa pupae was the ichneumonid wasp, Heteropelma scaposum. Such parasitism can greatly reduce productivity of adult Helicoverpa from refuges and needs to be taken into account when assessing relative refuge ‘value’, although such refuges will obviously contribute to the abundance of these beneficial species across the landscape.

Pheromone and light traps have often been used in ecological studies of two major noctuid pests of agriculture in Australia, Helicoverpa armigera and H. punctigera. However, results from these two methods have rarely been compared directly. We set pheromone and light traps adjacent to or amongst cotton and various other crops for 10-11 years in the Namoi Valley, in northern New South Wales, Australia. Catches in pheromone traps suggested a major peak in (male) numbers of H. punctigera in early spring, with relatively few moths caught later in the summer cropping season. In contrast, (male) H. armigera were most abundant in late summer. Similar trends were apparent for catches of both male and female H. armigera in light traps, but both sexes of H. punctigera were mostly caught in mid-summer. For both species, males were more commonly caught than females. These catch patterns differed from some previous reports. At least three generations of both species were apparent in the catches. There was some evidence that the abundance of later generations could be predicted from the size of earlier generations; but, unlike previous authors, we found no positive relationships between local winter rainfall and subsequent catches of moths, nor did we find persuasive evidence of correlations between autumn and winter rainfall in central Australia and the abundance of subsequent 1st generation H. punctigera moths. Female H. punctigera were consistently more mature (gravid) and more frequently mated than those of H. armigera. Overall, our results highlight the variability in trap catches of these two species and question the use of trap catches and weather as predictors of future abundance in cropping regions.

For Helicoverpa punctigera (Wallengren), and to a lesser extent Helicoverpa armigera (Hübner), native host plants in non-cropping regions of inland Australia are believed to be contributors to populations which migrate in spring to infest cropping regions of south-east Australia, and southwestern Australia. Non-crop hosts were sampled using sweep nets in 71 survey trips in 19 years between 1987 and 2017 for larvae of H. punctigera and H. armigera, over about 2.4 million km 2 in inland Australia. Of 1976 samples, H. punctigera larvae were present in 50.5%, distributed throughout the study area. Larvae were found on 106 host plant species in 24 families, including 61 new host records. H. armigera larvae were found on 33 plant species from eight families, including 14 new host records. However, only 4.3% of samples were positive for this species, and they were mostly in the east of the study area and had fewer larvae than the positive H. punctigera samples. H. punctigera larvae were found in each of six habitats, being, in order of mean numbers per sample: sandy deserts > floodplains > mulga, grasslands and saltbush > stony downs. Host status was determined for both species by plotting relative incidence against relative abundance, and the good hosts for H. punctigera differed between habitats. We discuss the value and limitations of this approach for identifying key hosts in broad scale population dynamics, and primary hosts which may have close co-evolutionary histories with the insects.

Summary 1.House mouse Mus domesticus outbreaks in the grain-growing areas of south-eastern Australia occur irregularly and may be local or widespread, covering thousands of square kilometres. All natural and agricultural habitats are occupied when house mouse numbers are high, and the question we addressed was whether we can distinguish source and sink habitats within these agricultural landscapes so that management practices can be better targeted. 2. Live-trapping on replicated grids in 15 habitats, including eucalypt woodland, cypress pine woodland, areas of permanent water and crop habitats, was carried out from 1983 to 1988 at 9-week intervals. 3. Agricultural cropland (including crops, fallow and pastures), farm buildings, seepage areas and natural woodland could be source habitats. Farm buildings, seepage areas and saltbush areas all had high mouse densities entering the 1983-84 outbreak and were refuge habitats for mice. 4. Cropland habitats quickly became the source area in spring 1983, and woodlands were initially sinks that lagged 2-4 months behind the population growth shown in crops. 5. Adult female mice in cropland habitats were more often in breeding condition compared with mice in natural woodland. Mice also had higher indices of residency in cropland than in natural woodland. 6. Synthesis and applications . In non-irrigated cereal production areas of south-eastern Australia, house mice move from refuge habitats in seepage areas and farm buildings into crops, build up in numbers in cropland habitats, and then invade woodland habitats, which by themselves cannot generate outbreaks of this pest species. Monitoring for incipient outbreaks should concentrate on refuges in seepage areas and crops and their associated fence lines as source habitat indicators. Population control in these habitats in spring would reduce the likelihood of population outbreaks in autumn, leading to reduced rodenticide use and a concomitant reduction in environmental hazards.

Transgenic (Bt) cotton dominates Australian cotton production systems. It is grown to control feeding damage by lepidopteran pests such as Helicoverpa armigera. The possibility that these moths might become resistant to Bt remains a threat. Consequently, refuge crops (with no Bt) must be grown with Bt cotton to produce large numbers of Bt-susceptible moths to reduce the risk of resistance developing. A key assumption of the refuge strategy, that moths from different host plant origins mate at random, remains untested. During the period of the study reported here, refuge crops included pigeon pea, conventional cotton (C3 plants), sorghum or maize (C4 plants). To identify the relative contributions made by these (and perhaps other) C3 and C4 plants to populations of H. armigera in cotton landscapes, we measured stable carbon isotopes (δ(13)C) within individual moths captured in the field. Overall, 53% of the moths were of C4 origin. In addition, we demonstrated, by comparing the stable isotope signatures of mating pairs of moths, that mating is indeed random amongst moths of different plant origins (i.e. C3 and C4). Stable nitrogen isotope signatures (δ(15)N) were recorded to further discriminate amongst host plant origins (e.g. legumes from non-legumes), but such measurements proved generally unsuitable. Since 2010, maize and sorghum are no longer used as dedicated refuges in Australia. However, these plants remain very common crops in cotton production regions, so their roles as 'unstructured' refuges seem likely to be significant.