BackgroundUnderstanding genomic and phenotypic diversity among cryptic pest taxa has important implications for the management of pests and diseases. The diamondback moth, Plutella xylostella L., has been intensively studied due to its ability to evolve insecticide resistance and status as the world’s most destructive pest of brassicaceous crops. The surprise discovery of a cryptic species endemic to Australia, Plutella australiana Landry & Hebert, raised questions regarding the distribution, ecological traits and pest status of the two species, the capacity for gene flow and whether specific management was required. Here, we collected Plutella from wild and cultivated brassicaceous plants from 75 locations throughout Australia and screened 1447 individuals to identify mtDNA lineages and Wolbachia infections. We genotyped genome-wide SNP markers using RADseq in coexisting populations of each species. In addition, we assessed reproductive compatibility in crossing experiments and insecticide susceptibility phenotypes using bioassays.ResultsThe two Plutella species coexisted on wild brassicas and canola crops, but only 10% of Plutella individuals were P. australiana. This species was not found on commercial Brassica vegetable crops, which are routinely sprayed with insecticides. Bioassays found that P. australiana was 19-306 fold more susceptible to four commonly-used insecticides than P. xylostella. Laboratory crosses revealed that reproductive isolation was incomplete but directionally asymmetric between the species. However, genome-wide nuclear SNPs revealed striking differences in genetic diversity and strong population structure between coexisting wild populations of each species. Nuclear diversity was 1.5-fold higher in P. australiana, yet both species showed limited variation in mtDNA. Infection with a single Wolbachia subgroup B strain was fixed in P. australiana, suggesting that a selective sweep contributed to low mtDNA diversity, while a subgroup A strain infected just 1.5% of P. xylostella.ConclusionsDespite sympatric distributions and the capacity to hybridize, strong genomic and phenotypic divergence exists between these Plutella species that is consistent with contrasting colonization histories and reproductive isolation after secondary contact. Although P. australiana is a potential pest of brassicaceous crops, it is of secondary importance to P. xylostella.Electronic supplementary materialThe online version of this article (10.1186/s12862-018-1183-4) contains supplementary material, which is available to authorized users.

Populations of cotton aphid, Aphis gossypii Glover, were surveyed for insecticide resistance. Pirimicarb, organophosphate, endosulfan and pyrethroid resistance was identified. Aphis gossypii from New South Wales cotton‐growing districts were organophosphate and pirimicarb susceptible, whereas populations from similar districts in Western Australia, Queensland and Northern Territory displayed high to extreme resistance that was linked to control failure. New South Wales populations, however, were often endosulfan and pyrethroid resistant. Resistant A. gossypii have the potential to seriously impact on the Australian cotton industry and their resistance management is now incorporated into the resistance management strategy for Australian cotton.

The addition of a DRT oil is an effective way to reduce the spray solution drift potential across all nozzle types and tank mixes evaluated in this study. The greatest reduction in drift potential can be achieved by changing nozzle type, which can reduce the losses of the spray to the surrounding environment. Venturi nozzles greatly reduce the drift potential compared with standard nozzles by as much as 85% across all three insecticide spray solutions. Results suggest that a significant reduction in drift potential can be achieved by changing the nozzle type, and can be achieved without a loss in control of DBM. © 2016 Society of Chemical Industry.

Cotton aphids, Aphis gossypii, may be more troublesome in transgenic (Ingard®) cotton, because an overall reduction in pesticide use in transgenic cotton for the control of pests such as Helicoverpa spp., gives reduced control of concurrent aphids. Additionally, coincidental cotton aphid in conventional cotton is being exposed to an increasing number of organophosphate insecticides targeted against Helicoverpa spp. Resultant insecticide sprays targeted specifically at cotton aphid, are likely to increase and must be managed to maintain insecticide susceptibility. As a first step to studying resistance in cotton aphid, two strains were collected from unsprayed sources and tested against 21 registered or experimental insecticides by laboratory bioassay, to establish baseline data for resistance monitoring. The LC99.9 of the more susceptible strain was used arbitrarily as a discriminating concentration to detect resistance in three populations of cotton aphid collected in cotton growing districts of New South Wales. In contrast to overseas studies, our results suggest that Australian cotton aphid was resistant to endosulfan and pyrethroids but not to carbamates or organophosphates.