Population genomics of Drosophila suzukii reveal longitudinal population structure and signals of migrations in and out of the continental United States.

Drosophila suzukii, or spotted-wing drosophila, is now an established pest in many parts of the world, causing significant damage to numerous fruit crop industries. Native to East Asia, D. suzukii infestations started in the United States a decade ago, occupying a wide range of climates. To better understand invasion ecology of this pest, knowledge of past migration events, population structure, and genetic diversity is needed. In this study, we sequenced whole genomes of 237 individual flies collected across the continental United States, as well as several sites in Europe, Brazil, and Asia, to identify and analyze hundreds of thousands of genetic markers. We observed strong population structure between Western and Eastern US populations, but no evidence of any population structure between different latitudes within the continental United States, suggesting that there are no broad-scale adaptations occurring in response to differences in winter climates. We detect admixture from Hawaii to the Western United States and from the Eastern United States to Europe, in agreement with previously identified introduction routes inferred from microsatellite analysis. We also detect potential signals of admixture from the Western United States back to Asia, which could have important implications for shipping and quarantine policies for exported agriculture. We anticipate this large genomic dataset will spur future research into the genomic adaptations underlying D. suzukii pest activity and development of novel control methods for this agricultural pest.

Dwarf-cashew resistance to whitefly (Aleurodicus cocois) linked to morphological and histochemical characteristics of leaves.

BACKGROUND: The cashew whitefly (CW), Aleurodicus cocois, is an important pest of cashew in Brazil. The use of resistant plants may be an effective strategy for the control of this pest. In a preliminary assay, we found that dwarf-cashew clones show different levels of resistance to CW. Here, we hypothesized that such resistance is associated with morphological characteristics of cashew leaves and their content of phenolic compounds. RESULTS: We determined (i) the attractiveness and suitability for oviposition of five dwarf-cashew clones towards CW, (ii) the leaf morphology and chemistry of those clones, and (iii) the relationship between leaf characteristics and resistance to CW. In greenhouse multiple-choice assays, PRO143/7 and CCP76 showed, respectively, the lowest and highest counts of both CW adults and eggs. Scanning electron microscopy (SEM) analysis revealed that PRO143/7 and EMBRAPA51 have, respectively, the highest and lowest numbers of leaf glandular trichomes. We found a negative correlation between number of trichomes in the abaxial surface of cashew leaves and CW oviposition. In addition, confocal microscopy analysis and histochemical tests with ferrous sulfate indicated a higher accumulation of phenolic compounds in the resistant clone PRO143/7 relative to the other clones. Dwarf-cashew clones did not significantly differ based on the number of leaf epicuticular striations, and the thickness of both leaf lamina and the epidermal layer. CONCLUSION: The resistance of dwarf-cashew plants to CW is associated with an elevated number of trichomes and accumulation of high levels of phenolics in leaves. Additionally, the contribution of epicuticular striation density and thickness of leaf lamina/epidermal layer are insignificant. © 2019 Society of Chemical Industry.

Factors affecting the biology of Pachycrepoideus vindemmiae (Hymenoptera: Pteromalidae), a parasitoid of spotted-wing drosophila (Drosophila suzukii).

Pachycrepoideus vindemmiae is a wasp that parasitizes and host-feeds on pupae of the invasive spotted-wing drosophila (SWD, Drosophila suzukii). Few studies have addressed interactions between these two species and little is known about the potential of this parasitoid as a biocontrol agent of SWD and the different variables that may affect it. Here, we investigated the impact of extrinsic and intrinsic factors on life-history traits of P. vindemmiae. Both constant (entire adulthood) and limited (30 minutes) supplies of water + honey, honey, or host increased parasitoid survival compared to controls (water or fasting). Water + honey caused the highest parasitoid survivals (35-60 days), independent of supply period, sex, and host availability. Females were intrinsically more resistant to water- and honey-deprivation than males, and host-feeding elevated such resistance even higher. Constant honey supply (either with or without water) supported the highest host-killing capacities (= capacity to kill hosts) (ca. 600 SWD pupae/wasp). However, in young females (4-9 days old), the impact of honey availability (with or without water) was insignificant while water deprivation (either with or without honey) caused the highest host-killing potential. This indicates that although sugar becomes a critical nutritional resource as females age, young females depend more on water than sugar to reproduce. Neither water nor honey affected the sex ratio of young females, but when we considered the entire adulthood, the availability of honey caused the lowest proportion of females (0.50), independent of water availability. Neither water nor honey affected parasitoid emergence rate (0.97), independent of female age. Based on survival and host-killing capacity, we conclude that P. vindemmiae has a tremendous biocontrol potential against SWD. Both limited and constant supply of water, sugar, and host increase parasitoid survival, while constant supply of water and/or honey enhance its host-killing potential and decrease sex ratio depending on maternal age.