Do the plant host origins of Helicoverpa (Lepidoptera: Noctuidae) moth populations reflect the agricultural landscapes within which they are caught?

Abstract

The use of Bt cotton varieties has greatly reduced the amount of conventional insecticides required to control lepidopteran pests, Helicoverpa armigera and Helicoverpa punctigera, in Australia, but the possibility that these moths might become resistant to Bt remains a threat. Consequently, a Resistance Management Plan, which includes the mandatory growing of refuge crops (pigeon pea and non-Bt cotton; both C3 plants), has been established for Bt cotton farmers. However, knowledge of the relative contributions made to overall moth populations from the many host origins (both C3 and C4 plants) available to these insects throughout cotton production regions remains limited, as do the scales of movement and spatial mixing of moths within and between these areas. This study used stable isotope signatures (in particular δ13C) to help identify where moths fed as larvae within separate cotton production regions which differed in their proportions of C3 and C4 host crops (e.g. cotton and sorghum, respectively). C3-derived moths predominated in the early season, but C4-derived moths increased in frequency later. The overall proportion of C4 moths was higher in H. armigera than in H. punctigera. Whilst the relative proportions of C3 and C4 moths differed between regions, no differences in such proportiorns were found at smaller spatial scales, nor were there significant correlations between crop composition and isotope signatures in moths. Overall, these results suggest that C4 host plants are likely to be very important in offsetting the development of Bt resistance in these insects and such influences may operate across multiple regions within a single growing season.

Survival of immature Helicoverpa punctigera (Wallengren) (Lepidoptera: Noctuidae) on some C4 and C3 plants

“…The host status of saltbushes such as these two species (and perhaps others in genera such as Atriplex and Maieriana) has not previously been recognised. These and other C4 plants such as P. oleraceae and T. terrestris could support some level of larval survival to pupal and adult stages, and may account for the finding of H. punctigera with the C4 isotope profile in cropping areas (Baker et al 2019).…”

“…In particular, the poor performance of A. vesicaria in Assay two was not repeated here, indicating that the factors which make it a poor host act mainly on early-stage larvae. The C4 plants P. oleracea and T. terrestris are common around cotton fields as weeds, and it is plausible that these species may explain the presence of C4 moths in the work of Baker et al (2019).…”

“…Gregg et al (2019) found no larvae on several plant species in the Chenopodiaceae and Zygophyllaceae in inland Australia, and no sampling was done on plants in the Portulacaceae. However, Baker et al (2019) reported significant numbers of H. punctigera from cropping areas in eastern Australia, which had stable carbon isotope profiles indicating that they had fed on C4 plants, and we (Bawa et al in press) have shown that gravid H. punctigera females will lay eggs on two widely distributed and abundant saltbush species, even when given the choice of known C3 hosts. Some of these plants are found in close association with each other in the inland regions of Australia (Gregg et al 2019).…”

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

“…Stable carbon isotope ratios were determined using techniques described by Baker and Tann 2013 to ascertain whether they originated from larvae fed on plants with the C3 photosynthetic pathway (including cotton) or from plants with the C4 pathway. In the curative experiment only, H. armigera moths were tested for host plant origin because it was considered that H. punctigera had no C4 host plants, but, for the preventive experiment, recent evidence ( Baker et al 2019 , Bawa et al 2021 ) had required a revision of this assumption, so both species were tested.…”

Dinâmica populacional, hibridação e adaptação a hospedeiros em >i<Helicoverpa>/i< spp. (Lepidoptera: Noctuidade)

“…Normalmente o monitoramento de pragas utiliza como estratégia de captura as armadilhas com luz ou com feromônio, sendo que esta atrai principalmente os machos (Baker et al, 2011). Porém ao atrair indivíduos adultos, em espécies polífagas, não conseguimos associar com à fonte alimentar dos estados larvais e consequente conhecer a amplitude de hospedeiros que está sendo explorada pela espécie (Baker et al, 2019). A análise de isótopos estáveis é uma ferramenta que ajuda a determinar a rota de carbono dentro de diferentes organismos nos ecossistemas, utilizando como princípio a diferença existente nos isótopos de carbono em grupos de plantas com diferente metabolismo fotossintético C3 e C4 (Rounick & Winterbourn, 1986).…”