Location: Horticultural Crops Research Unit
2016 Annual Report
Objectives
Objective 1: Determine risk across landscapes to improve management of pests such as spotted wing drosophila by understanding their behaviors (i.e., host range and preference, dispersal).
Obj. 1.1: Describe flight parameters and energy used in flight of spotted wing drosophila.
Obj. 1.2: Compare effects of temperature and sugar feeding on spotted wing drosophila.
Objective 2: Develop biological control strategies for pests such as spotted wing drosophila, brown marmorated stink bug, and azalea lace bug, using commercially available and endemic natural enemies and habitat conservation.
Obj. 2.1: Study endemic natural enemies of spotted wing drosophila, and pupation habits of spotted wing drosophila.
Obj. 2.2: Study endemic natural enemies and using the volatile methyl salicylate for brown marmorated stink bug.
Obj. 2.3: Study endemic natural enemies, augmentative release and methyl salicylate for azalea lace bug.
Objective 3: Develop RNAi technology to control pests such as spotted wing drosophila by finding and evaluating target genes, and developing large-scale production methods.
Obj. 3.1: Identify potential RNAi target genes from spotted wing drosophila.
Obj. 3.2: Evaluate RNAi impact(s) on development of spotted wing drosophila.
Obj. 3.3: Develop large-scale dsRNA production methods.
Objective 4: Develop receptor-based drug discovery for pests such as spotted wing drosophila by finding and evaluating insect neuropeptides and receptors to disrupt critical physiological signals in the pests.
Obj. 4.1: Cloning and functional expression of the specific G-protein coupled receptors from spotted wing drosophila and other pests.
Obj. 4.2: Develop receptor-based screening method.
Approach
Objective 1 includes studying spotted wing drosophila (SWD) on a flight mill or other suitable arenas and measuring their nutrient reserves, such that basic flight parameters and energetics can be obtained. For SWD, its movement across landscapes may be influenced by its ability to find resources in the surrounding habitat and temperature and nutrient stores.
Objective 2 includes surveying the endemic natural enemies present that attack important pests such as SWD, brown marmorated stink bug (BMSB), and azalea lace bug (AzLB). Trials will determine if the release of predators or use of attractive plant volatiles can improve control of these pests in nursery and fruit crop fields.
Objective 3 will identify genes in SWD for RNAi targets, and measure the impact on treatment on SWD longevity and activity. Also, a large-scale method to produce dsRNA will be tested using E. coli with inserted vectors.
Objective 4 will screen G-protein coupled receptors that are important in the development or adult stages of SWD, and will clone and test expression of them.
Progress Report
This reports progress for project 2072-22000-040-00D, "Biologically-based Management of Arthropod Pests in Small Fruit and Nursery Crops," which started in October 2015, and replaces project 2072-22000-037-00D, "Integrated Pest Management for Insect Pests of Horticultural Crops."
To improve control of the invasive spotted wing drosophila (SWD), we studied their biology, biological control, potential transfer of a pathogen, chemical ecology, food adaptation, RNA interference (RNAi) approach, large scale double-stranded RNA (dsRNA) production, and specific receptors for targeted insecticides. We found that SWD predominantly leaves the fruit as larva and forms into a pupa in the soil beneath the crop (Objective 2.1). This is important because it suggests that further research on biological control and cultural practices might be directed on the ground surface. For biological control, naturally-occurring predators reduced infestations in fruits by 19-49% and removed 61-91% of pupae placed on the soil in fruit fields (Objective. 2.1). For pathogen transfer, we found SWD to transfer spores of Botrytis (grey mold) to uninfected fruit, however, the presence of SWD around inoculated fruit appeared to inhibit the development of infection. This has important implications for mold management in small fruits. For chemical ecology, we found that chemicals washed off the surface of male and female SWD did not appear attractive to other SWD that were flying within one foot of the compound.
To understand food adaptation within SWD, we investigated detoxification enzymes, oxidative stress, and CO2 tolerance on the feeding activity by biochemical, genetic and molecular biological tools. We found that SWD has significantly reduced glutathione-S transferase (GST) activity and gene numbers, and fructose concentrations compared to D. melanogaster. Our study strongly suggests that the altered food preferences of SWD may stem from evolutionary adaptations to fresh foods accompanied by alterations in carbohydrate metabolism and GST activities. We also studied SWD population diversity among different geographical strains, seven independent clones including Oregon, Hawaii, New York, Japan, and Korea. Molecular cladogram analysis of 46 DNA sequences showed that the China population is closely related to the New York clones. The Oregon clones and Hawaii clones showed a greater distance from the China. However, none of the mutations could be used as a geographical marker, owing to the wide genetic variation within populations.
For the RNAi approach, we have selected 13 SWD RNAi target genes, identified these targets, then synthesized dsRNAs for each of the RNAi targets. We have established a microinjection technique for dsRNA to enable a fast screening and evaluation of RNAi targets on SWD adults (Objective 3.1, 3.2). We evaluated the impacts of RNAi of the initial 13 targets on SWD through the microinjection and monitoring mortality in adult flies (Objective 3.2). For large scale dsRNA production we have established a microbial-based dsRNA production system. This produces large scale quantities of dsRNA for any target to be utilized for a non-transgenic RNAi approach through a series of biological processes (Objective 3-3). This will enable us to have a cost-effective RNAi approach for large scale studies of RNAi for SWD and other small fruit pests.
To find specific G-protein coupled receptors (GPCR) from SWD we identified two SWD neuropeptide GPCRs, the pyrokinin receptor and the diapause receptor. We functionally expressed and confirmed through binding assays with corresponding ligands. The differential expressions of these receptors has also been investigated during all life stages (Objective 4).
To better understand and control the new invasive brown marmorated stink bug (BMSB), we studied their nutrient physiology and biological control. Related to physiology, we found that overwintering adult females do not carry eggs, and their nutrient stores (lipid, glycogen, sugar) continuously decrease as they remain in the overwintering location. Once they emerge in spring, they quickly feed and restore their nutrient levels. With regard to biological control, we found that methyl salicylate (oil of wintergreen) could increase predation rates on BMSB eggs (Objective 2.2). This is a potentially quick management tool that is non-toxic.
To improve the control of azalea lace bug, a pest of azaleas and rhododendrons, we surveyed cultivars for potential resistance, followed their generations in Oregon, and examined biological control with release of predators. Related to cultivar resistance, we found that some rhododendrons with dense indumentum (fuzz) on the underside of leaves were less likely to be infested by this pest. In terms of life cycle, we found that mostly eggs and some adults overwintered in Oregon, and there was three generations in the field. With regard to biological control, we found that green lacewing larvae readily consumed the immature stages of the pest, but had difficulty consuming the adult stage (Objective 2.3).
Accomplishments
1. Reduced spray for spotted wing drosophila. Growers frequently spray fields with insecticides to control spotted wing drosophila, a serious pest in small fruits and cherries. ARS scientists in Corvallis, Oregon, cooperated with other researchers in Oregon to test the efficacy of reduced spray coverage. Alternate row sprays in raspberry and border row sprays of blueberry fields often resulted in similar levels of pest control as fields sprayed entirely. As a result, some growers are now reducing the spray area to control spotted wing drosophila.
2. Pupation behavior of spotted wing drosophila. The pupation habits of spotted wing drosophila (SWD), a serious pest of small fruits and cherries, was mostly unknown. ARS scientists in Corvallis, Oregon, monitored fruit infested with pest larvae and their pupation behavior. Most of the resulting pupae ended up on the soil surface, as larvae that were inside hanging fruit dropped to the ground. As a result, growers and researchers have moved beyond just targeting SWD adults with sprays, and now focus on targeting SWD pupae on the soil surface as a component of an integrated pest management program for SWD.
3. Selection of RNAi targets for spotted wing drosophila (SWD). There is a public need for non-toxic insecticides, and RNA interference (RNAi) have potential as insecticides that only target a specific pest such as the spotted wing drosophila (SWD) fly, a pest of small fruits and cherries. ARS scientists in Corvallis, Oregon, selected three potential RNAi target genes to study. Double stranded RNAs to induce silencing of these genes were prepared in-vitro and injected into adult flies to determine their potential as insecticides. These targets caused significant mortality (34-61%) in SWD adult flies, and ARS researchers are now evaluating the effect of these genes on SWD in feeding assays and larger-scale studies.
4. Biological control of spotted wing drosophila. Given that growers are often spraying fields to manage the small fruit and cherry pest, the spotted wing drosophila fly, they have requested alternative control measures that are immediately available to them. ARS scientists in Corvallis, Oregon, tested the rate at which larvae in fruit and pupae on the soil were removed by naturally-occurring predators. In unsprayed fields, natural predation or removal rates can be quite high, 19-91%. This outcome shows the importance of naturally-occurring beneficial insects, and suggests that biological control may suppress pest populations in unmanaged areas that surround grower fields.
5. Development of biologically-based control for spotted wing drosophila. Non-toxic insecticides especially those available for organic growers are being sought for control of the small fruit and cherry pest spotted wing drosophila. ARS scientists in Corvallis, Oregon, found that non-nutritive sweeteners, erythritol and erythrose, have insecticidal effects against SWD adults in laboratory studies. Artificial sweeteners were dissolved in water and fed to SWD adults, which resulted in more than 60% mortality within four days. Data suggests that these two sugars can potentially be used for organic insecticides, and for feeding stimulants to increase the delivery efficiency of RNA interference (the biological process to suppress specific gene expression in cells).
ARS scientists at Corvallis, Oregon, participated in activities supporting small farmers in the nursery industry with a Nursery Biological Control Workshop tour at the North Willamette Research and Extension Center in Aurora, Oregon, and local nurseries. Activities supporting small farmers in the small fruit industry include blueberry, raspberry, and strawberry commission meetings in Oregon and Washington.
Review Publications
Nguyen, P., Kim, A., Jung, J., Donahue, K.M., Jung, C., Choi, M.Y., Koh, Y. 2016. The biochemical adaptations of spotted wing drosophila (Diptera: Drosophilidae) to fresh fruits reduced fructose concentrations and glutathione-S transferase activities. Journal of Economic Entomology. 109(2):973-981. doi: 10.1093/jee/tow019.
Hamby, K.A., Bellamy, D., Chiu, J.C., Lee, J.C., Walton, V.M., Wiman, N.G., York, R.M., Biondi, A. 2016. Biotic and abiotic factors impacting development, behavior, phenology, and reproductive biology of Drosophila suzukii. Journal of Pest Science. 89(3):605-619. doi: 10.1007/s10340-016-0756-5.
Tochen, S., Walton, V., Lee, J.C. 2016. Impact of floral feeding on adult Drosophila suzukii survival and nutrient status. Journal of Pest Science. 89(3):793-802. doi: 10.1007/s10340-016-0762-7.
Wallingford, A.K., Lee, J.C., Loeb, G.M. 2016. The influence of temperature and photoperiod on the reproductive diapause and cold tolerance of spotted-wing drosophila, Drosophila suzukii. Entomologia Experimentalis et Applicata. 159(3):327–337. doi: 10.1111/eea.12443.
Choi, M.Y., Ahn, S., Park, K., Vander Meer, R.K., Carde, R.T., Jurenka, R. 2016. Tarsi of male heliothine moths contain aldehydes and butyrate esters as potential pheromone components. Journal of Chemical Ecology. 42(5):425-432. doi: 10.1007/s10886-016-0701-3.
Lee, J.C., Dalton, D.T., Swoboda-Bhattarai, K., Bruck, D.J., Burrack, H.J., Strik, B.C., Woltz, J.M., Walton, V.M. 2015. Characterization and manipulation of fruit susceptibility to Drosophila suzukii. Journal of Pest Science. 89(3):771-780. doi: 10.1007/s10340-015-0692-9.
Wiman, N.G., Dalton, D.T., Anfora, G., Biondi, A., Chiu, J., Daane, K.M., Gerdeman, B., Gottardello, A., Hamby, K., Isaacs, R., Grassi, A., Ioriatti, C., Lee, J.C., Miller, B., Rossi Stacconi, M., Shearer, P.W., Taniogoshi, L., Wang, X., Walton, V.M. 2016. Drosophila suzukii population response to environment and management strategies. Journal of Pest Science. 89(3):653-665. doi: 10.1007/s10340-016-0757-4.
