Research Project: Integrated Approach to Manage the Pest Complex on Temperate Tree Fruits

Location: Temperate Tree Fruit and Vegetable Research

2021 Annual Report

Objectives
The long-term objective of this project is to provide the basic and applied information needed for the development and transfer of safe and environmentally sustainable tools or methods for management of arthropod pests of temperate tree fruits. Specifically, during the next five years we will focus on the following objectives: Objective 1: Develop and improve tools and approaches for early detection, prediction, and monitoring of arthropod pests and their natural enemies in temperate tree fruits. • Sub-objective 1A: Determine if pre-harvest commercial pear is an acceptable host for apple maggot fly. • Sub-objective 1B: Identify volatile attractants from pear trees for early detection of orchard-colonizing winterform pear psylla. • Sub-objective 1C: Identify the primary non-orchard habitats that are sources of orchard-colonizing winterform pear psylla. • Sub-objective 1D: Identify the thermal tolerances of brown marmorated stinkbug and Trissolcus japonicus to more accurately determine potential establishment and spread. Objective 2: Provide basic and applied information of the physiology, biochemistry, behavior, and landscape ecology of arthropod pests and their natural enemies necessary to develop new or improve existing integrated pest management strategies in temperate tree fruits. • Sub-objective 2A: Determine the thermal kinetics of apple maggot. • Sub-objective 2B: Determine functions of proteins key to codling moth reproduction, development, physiology, and behavior. • Sub-objective 2C: Determine extent of cryptic species diversity in minute pirate bug fauna of the western U.S. in both orchard and non-orchard habitats. • Sub-objective 2D: Examine non-target effects of herbicides on key natural enemies of arthropod pests of apple and pear. Objective 3: Develop new or improved integrated management strategies to control arthropod pests in temperate tree fruits. • Sub-objective 3A: Improve control strategies for apple maggot in organic waste. • Sub-objective 3B: Develop pest management strategies for cherry fruit fly that incorporate newer and less toxic insecticides. • Sub-objective 3C: Model the relationship between estimated populations of Trechnites adults and rates of parasitism of pear psylla. • Sub-objective 3D: Develop management practices that increase the retention time of released natural enemies of arthropod pests of apple.

Approach
Objective 1. Sub-objective 1A: Behavioral and development bioassays will determine if pear is an acceptable host for apple maggot and whether pear fruit is a potential source for apple maggot introduction in export countries. Subobjective 1B: Volatiles will be identified from pear trees using GC-MS, and electroantennogram, behavior assays, and field trials will determine whether isolated volatiles elicit responses from pear psylla. The resulting lure will be used to monitor pear psylla populations. Sub-objective 1C: Gut content analysis will be used to where pear psylla overwinter. Sub-objective 1D: Differential scanning calorimetry will be used to determine the thermal capacity of brown marmorated stink bug and its parasitoid, and to identify climates that are favorable to their establishment and spread. Objective 2. Sub-objective 2A: The thermal death kinetics of apple maggot will be determined using differential scanning calorimetry and micro-respiration. Results will be used to improve management of apple maggot in commercial composting facilities located in apple maggot free zones. Sub-objective 2B: Candidate codling moth genes will be silenced using CRISP-Cas9 and behavior assays will be used to identify the function of the silenced genes. Results will identify viable gene-targets for use in codling moth control. Sub-objective 2C: Morphology of Orius will be examined to identify diagnostic traits and to possible new species, and a diagnostic key will be developed to identify species belonging to the group of important natural enemies. Sub-objective 2D: Standard laboratory bioassays will be used to examine the effects of herbicides and additives on mortality and fecundity of the key orchard predators Galendromus occidentalis, Amblydromella caudiglans, and the European earwig. Results of this study will allow growers to adapt orchard floor management strategies that conserve key natural enemies. Objective 3. Sub-objective 3A: Laboratory experiments will be conducted to determine whether 100% of apple maggot flies are killed by exposure to 55 degrees, the temperature found in commercial composting operations. Sub-objective 3B: Standard bioassays will be used to determine whether the insecticides tolfenpyrad, pyrifluquinazon, azadirachtin, and pyrethrins kill or reduce fecundity of cherry fruit fly and can be used as an alternative to spinosad as an attract and kill approach to fruit fly management. Sub-objective 3C: Adult populations of Trechnites will be monitored using traps and psylla parasitism rates will be monitored by dissection of psylla or by PCR and the relationship between adult populations of Trechnites and actual parasitism rates will be modeled to allow growers to incorporate biological control provided by Trechnites in psylla management practices. Sub-objective 3D: Field studies will be conducted in commercial apple orchards to test whether nutritional supplements including Typha spp. pollen or brine shrimp cysts increase the retention of released natural enemies, Orius insidiosus, Chrysoperla rufilabris, or Cryptolaemus montrouzieri. Results will improve augmentative biological control in commercial orchards.

Progress Report
Substantial progress was made on all four objectives and their sub-objectives, with the overall goal to improve management of insect pests of temperate tree fruits. The goal of Objective 1, which has four sub-objectives, is to develop or improve tools and approaches for early detection, prediction, or monitoring of tree fruit pests with a focus on apple maggot, pear psylla, and brown marmorated stink bug. Under Sub-objective 1A, laboratory experiments were initiated to determine whether pre-harvest unripe pear fruit is susceptible to attack by apple maggot fly. Results of these ongoing experiments will be used to improve monitoring of apple maggot in pear and to predict whether transportation of harvested pear is a risk for introduction of apple maggot fly to new regions. Under Sub-objective 1B, a method was developed to collect volatiles simultaneously from multiple orchard-grown pear trees. This method was used to collect volatiles from Bartlett pear trees on a semiweekly basis from late winter through early spring. Collected volatiles will be analyzed to determine if there are differences in quantities or types of compounds emitted by the trees as they progress from dormancy to the bud burst stage. This information will then be used to identify smells that help pear psylla find pear trees, which could then be used to create a lure to help monitor the arrival of overwintered pear psylla in pear orchards in early spring. Under a subordinate project related to the overall goal of Sub-objective 1B, to develop lures for monitoring key insect pests, known attractants for wasps were adapted and used to trap the invasive 'Asian giant hornet'. The captured hornets were used in laboratory experiments to identify species-specific attractants, which will be used to capture and monitor the Asian giant hornet in Washington state. For Sub-objective 1C, overwintered pear psylla adults were collected in early spring of 2021 from pear orchards located in Washington and Oregon. Gut content analysis will be performed on these insects to study their landscape-level movements prior to their capture and to identify the plants or habitats that are used by overwintering pear psylla. This information will then be used to improve decision aid models that predict which orchards are most at risk of first being colonized by pear psylla in early spring. In support of Sub-objective 1D, a technique called differential scanning calorimetry was used to determine the thermal limits for growth and development of brown marmorated stink bug, an invasive insect pest that has recently become established in the Pacific Northwest tree fruit growing regions of the Pacific Northwest. The thermal limits for growth and development were determined for all developmental stages of stinkbugs in two separate experiments that measured metabolic heat rates at single temperatures or at increasing temperatures. This information is needed in order to predict the limits of geographical expansion and colonization by brown marmorated stink bug and to understand the potential effects of climate change on the geographical expansion of this invasive insect. The overall goal of Objective 2, which includes four sub-objectives, is to provide information on the basic biology and ecology of tree fruit pests and their natural enemies. Differential scanning calorimetry was used for Sub-objective 2A to determine the thermal limits of survival by apple maggot pupae. This information is critical for development of temperature treatments to kill apple maggot in commercial composting facilities that are located in apple maggot free zones and that receive green yard waste from regions under apple maggot quarantine. This information will also be useful for predicting the effects of climate change on the geographical expansion of apple maggot fly. Under Sub-objective 2B, ongoing assessments are being made of odorant receptor and neuropeptide gene expression patterns in codling moth female abdomen tip and ovipositor. Preliminary findings indicate differences in odorant receptor expression in mated versus non-mated females, which will be confirmed in follow-up experiments. Results from these experiments will provide guidance on functional assays of specific receptor proteins. Gene editing experiments have been initiated to disable a single odorant receptor that is present in female codling moth but not present in males. If editing is successful, studies will be conducted to assess the role of this odorant receptor on female codling moth olfactory behavior. Collectively, this knowledge will inform the development of sustainable pest management strategies aimed at controlling codling moth damage in fruit orchards. Under Sub-objective 2C, the extensive collection of unidentified minute pirate bugs (Anthocoridae) housed at the Illinois Natural History museum was examined to identify traits that can be used to separate closely related species within species complexes of these important predators. Many of the specimens had been collected in the 1970s as part of the International Soybean Program and were housed at the Natural History Museum without having been identified to genus or species. Over 6,000 specimens of minute pirate bugs and relatives were examined, identified, sorted, labeled, and returned to the museum for housing. Patterns in color, size, and markings among specimens were discovered that will assist ongoing efforts to develop identification keys to the minute pirate bug faunas of North America and Mexico. In support of Sub-objective 2D, a colony of the predatory mite Amblydromella caudiglans was established and a reliable commercial source of the predatory mite Galendromus occidentalis was identified to provide mites for experiments. A series of three bioassays were conducted to examine the non-target effects of seven herbicides, five adjuvants, and various combinations of herbicides and adjuvants on these predatory mites. A subordinate project related to Sub-objective 2D expanded the examination of the non-target effects herbicides and adjuvants to include three orchard spider species, green lacewings, convergent ladybeetles, and minute pirate bug, and allowed us to include several more combinations of herbicides and adjuvants beyond the initial workplan. This information will be used to improve pesticide spray practices for conservation of beneficial arthropods. The overall goal of Objective 3, which has four sub-objectives, is to develop new or improved integrated pest management strategies to control arthropod pests in temperate tree fruits. Progress toward completion of Sub-objective 3A included initiation of experiments to test various heat regimes to identify the temperature needed to kill 100% of apple maggot fly pupae in composting yard waste. Under Sub-objective 3B, bioassays were conducted to test whether alternative low toxicity insecticides mixed with or without sugar kill or prevent oviposition by western cherry fruit fly. This information will meet a critical need by growers for safe alternative materials to protect cherries against this pest. Under Sub-objective 3C, we compared two methods for detecting parasitism of pear psylla by Trechnites, including dissection of pear psylla nymphs and a molecular approach involving polymerase chain reaction (PCR). We found that rates of detection using PCR were higher than those using dissections, so PCR will primarily be used in future studies. Pear psylla and Trechnites were sampled from April to August in several pear growing regions of Washington and Oregon. DNA has been extracted from all pear psylla nymphs and the PCR work has begun. A postdoctoral associate was hired using extramural funds to complete a subordinate project related to Sub-objective 3C with the goal to use artificial intelligence/machine learning to predict the level of biocontrol by Trechnites that can be expected during any given year and to identify grower management practices that maximize biocontrol by Trechnites. This model will be developed using information obtained from a trapping network that includes Washington, Oregon, California, Utah, and several east coast states and from grower management records. Under Sub-objective 3D, we have identified growers who are willing to collaborate by allowing trials to be conducted in their orchards, which will substantially increase plot sizes and plot separation compared with our original experimental design. Experiments have begun to test releases of the predators called mealybug destroyers in orchards for control of mealybugs. A subordinate project related to Sub-objective 3D was started to examine biocontrol of aphids by releasing two different species and life stages of predators called lacewings. This work will be completed in pear and apple orchards.

Accomplishments
1. Demonstration that males and females of a sap sucking insect (psylla) of pear engage in an acoustic mating duet. Understanding factors that help bring the sexes of pest insects together for mating open up avenues for developing new technologies for managing pests through disruption of mating. Many psyllids are known to use acoustic cues in mate searching behavior, but this behavior had never been demonstrated for pear psylla, the most damaging insect pest of pears in North America. ARS researchers in Wapato, Washington, and scientists at Washington State University in Pullman, Washington, developed methods to record, describe, and synthesize the acoustic signals of male and female pear psyllids that govern mate location behavior. Results showed that the two sexes engage in a formalized acoustic duet that allows searching males to locate singing females for mating, and that males respond to a synthesized mimic of the female signal. These findings create an opportunity to develop a mating disruption program for psylla by hiding the true female signal via saturation of pear orchards with the synthetic acoustic mimic.

2. The artificial sweetener, erythritol, is miticidal to two pest mites, but relatively harmless to a beneficial predatory mite. The artificial sweetener, erythritol, is non-toxic to humans but is insecticidal when ingested by certain insects. Organic options are desperately needed for management of two key pests of pears, two spotted spider mite and pear rust mite, because existing products are not effective. However, it is highly desirable that pesticides for controlling these pests are not harmful to their key predator, the western predatory mite. ARS researchers in Wapato, Washington, in collaboration with scientists at Washington State University in Pullman, Washington, examined the effects of erythritol on pest and predatory mites. Results of laboratory experiments showed erythritol causes high mortality in rust mites, moderate mortality in spider mites, and does not kill western predatory mite. This demonstrates the potential of incorporating erythritol into mite management in pear orchards, without disrupting the natural control provided by predator mites.

3. Gut content analysis of brown marmorated stink bug. The brown marmorated stink bug is an invasive pest of temperate tree fruits that recently arrived in the Pacific Northwest where most United States tree fruits are grown. This pest is challenging to manage in part because the non-crop sources of stink bugs moving into orchards remain unknown and difficult to determine. ARS researchers in Wapato, Washington, in collaboration with scientists at Washington State University in Wenatchee, Washington, developed a method to detect plant DNA in the guts of brown marmorated stink bug, thereby allowing the researchers to determine which plants the stink bugs fed upon prior their capture. The researchers will use this method to identify the non-crop plant sources of brown marmorated stink bugs captured in tree fruit orchards, which will allow them to develop areawide management approaches for this pest.

4. Apple maggot larvae and pupae are highly tolerant to water submersion. Apple maggot fly is a quarantine pest of apple in certain regions of the Pacific Northwest of the United States. Identifying mechanisms in which apple maggot flies are capable of dispersal and colonization of new regions is important for maintaining apple maggot free zones. ARS researchers in Wapato, Washington, found that apple maggot larvae and pupae can survive in water for 2-12 days. These results show that immature stages of apple maggot can likely disperse in rivers, streams, and irrigation canals to establish in new habitats, such as currently apple maggot-free regions where apple is grown commercially. This information will be used by government agencies to monitor and prevent the spread of apple maggot into legally-designated apple maggot-free zones.

5. Two spotted spider mite management: miticide efficacy and resistance. Two spotted spider mite is a worldwide pest of over 100 crops. This pest is difficult to manage because it rapidly reproduces and is notorious for developing resistance to pesticides. ARS researchers in Wapato, Washington, in collaboration with scientists at Clemson University, and Washington State University, examined nine populations of spider mites in South Carolina specialty crops for resistance to all registered miticides and performed efficacy testing in two different crops. Results showed that resistance to bifenthrin and fenbutatin-oxide was widespread, but that the tested populations were still susceptible to other pesticides. Paired with the results from efficacy studies, specialty crop growers can use this information to choose only the most effective acaricides, reducing pesticide applications, resulting in increased savings and reduced resistance development.

6. Western cherry fruit fly pupae are highly tolerant of temperature extremes. Understanding the thermal tolerance of pest species is important for predicting the ability for the pest to establish and spread in new environments as an invasive species, and to understand the impact of climate change on pest biology and risk. ARS scientists in Wapato, Washington, used differential scanning calorimetry to determine the upper and lower limits of metabolism of diapausing pupae of western cherry fruit fly, a major pest of cherry that spends most of its lifecycle as pupae. Cherry fruit fly pupae developed a high level of tolerance to low and high temperature extremes within 14 days of pupariation and retained this tolerance throughout diapause up to adult emergence. They also found that pupae largely rely upon glycogen as a metabolic reserve. This information will be used to better understand the underlying mechanisms governing diapause thermotolerance and the ability of this pest to establish and spread to other environments.

7. Divergence of cherry fruit fly species occurring on different host plants. Ascertaining the causes of adaptive radiation is central to understanding how new species arise and come to vary with their resources, but mechanisms for speciation remain elusive. ARS researchers in Wapato, Washington, in collaboration with University researchers in the United States, Mexico, Argentina, Italy, Austria, and France, studied genetic variation and reproductive isolation for several closely related species of cherry fruit flies to identify the factors that contribute to speciation of cherry fruit flies. They found that the major contributors to cherry fruit fly speciation include presence of the bacterial endosymbiont, Wolbachia, which causes reproductive incompatibilities among insect populations, and host shifts that divide and isolate populations.

Review Publications
Schmidt-Jeffris, R.A., Moretti, E.A., Wickings, K., Wolfin, M.S., Northfield, T.D., Linn, C.E., Nault, B.A. 2020. Conventional soil management may promote nutrients that lure an insect pest to a toxic crop. Environmental Entomology. 50:433-443. https://doi.org/10.1093/ee/nvaa167.
Schmidt-Jeffris, R.A., Snipes, Z., Bergeron, P. 2021. Acaricide efficacy and resistance in South Carolina tomato populations of twospotted spider mite. Florida Entomologist. 104(1):1-8. https://doi.org/10.1653/024.104.0101.
Schmidt-Jeffris, R.A., Beers, E.H., Smytheman, P., Rehfield-Ray, L.M. 2021. Erythritol, an artificial sweetener, is acaricidal against pest mites and minimally harmful to a predatory mite. Journal of Economic Entomology. 104(4):1701-1708. https://doi.org/10.1093/jee/toab101.
Bergeron, P., Schmidt-Jeffris, R.A. 2021. Spider mite resistance to miticides in South Carolina strawberry and implications for improved integrated pest management. Experimental and Applied Acarology. 84:407-418. https://doi.org/10.1007/s10493-021-00621-7.
Farfan, M.A., Coffey, J., Schmidt-Jeffris, R.A. 2021. Suitability of food resources for Proprioseiopsis mexicanus (Garman), a potentially important natural enemy in eastern U.S. agroecosystems. Experimental and Applied Acarology. 84(2):121-134. https://doi.org/10.1007/s10493-021-00622-6.
Lewis, D., Cutulle, M., Schmidt-Jeffris, R.A., Blubaugh, C. 2020. Better together? Combining cover crop mulches, organic herbicides, and weed seed biological control in reduced-tillage crop systems. Environmental Entomology. 49(6):1327-1334. https://doi.org/10.1093/ee/nvaa105.
Schmidt-Jeffris, R.A., Coffey, J.L., Miller, G., Monica, F. 2021. Residual activity of Acaricides for controlling spider mites in watermelon and their impacts on resident predatory mites. Journal of Economic Entomology. 114(2):818-827. https://doi.org/10.1093/jee/toaa320.
Schlum, K., Lamour, K., De Bortoli, C.P., Banerjee, R., Emrich, S.J., Meagher Jr, R.L., Pereira, E., Murua, M.G., Sword, G.A., Tessnow, A.E., Dillon, D.V., Linares Perez, A.M., Akutse, K.S., Schmidt, R.A., Fangneng, H., Jurat-Fuentes, J.L. 2021. Whole genome comparisons reveal panmixia among fall armyworm (Spodoptera frugiperda) from diverse locations. BMC Genomics. 22. Article 179. https://doi.org/10.1186/s12864-021-07492-7.
Yee, W.L. 2021. Temperature effects on oviposition by Rhagoletis indifferens (Diptera: Tephritidae) vary in different developmental stages of sweet cherry. Environmental Entomology. 50(3):514-522. https://doi.org/10.1093/ee/nvab003.
Helper, J., Cooper, W.R., Beers, E. 2020. Host plant signal persistence in the gut of the brown marmorated stink bug, Halyomorpha halys. Environmental Entomology. 50(1):202-207. https://doi.org/10.1093/ee/nvaa152.
Doellman, M.M., Schuler, H., Saint Jean, G., Hood, G.R., Egan, S.P., Powell, T., Glover, M.M., Bruzzese, D.J., Smith, J.J., Yee, W.L., Goughnour, R.B., Rull, J., Aluja, M., Feder, J. 2019. Geographic and ecological dimensions of host plant associated genetic differentiation and speciation in the Rhagoletis cingulata (Diptera: Tephritidae) sibling species group. Insects. 10(9). Article 275. https://www.mdpi.com/2075-4450/10/9/275.
Yee, W.L., Goughnour, R.B., Feder, J.L. 2020. Distinct Adult Eclosion Traits of Sibling Species Rhagoletis pomonella and Rhagoletis zephyria (Diptera: Tephritidae) Under Laboratory Conditions. Environmental Entomology. 50(1):173-182. https://doi.org/10.1093/ee/nvaa148.
Wentz, K.M., Cooper, W.R., Horton, D.R., Kao, R., Nottingham, L.B. 2020. The artificial sweetener, erythritol, has insecticidal properties against pear psylla (Hemiptera: Psyllidae). Journal of Economic Entomology. 113(5):2293-2299. https://doi.org/10.1093/jee/toaa124.
Horton, D.R., Miliczky, G., Waters, T., Burckhardt, D., Halbert, S. 2021. Exotic psyllids and exotic hosts: accumulation of non-native Psylloidea in North America (Hemiptera). Annals of the Entomological Society of America. 114(4):425-447. https://doi.org/10.1093/aesa/saab014.
Miliczky, E., Horton, D.R., Waters, T., Wohleb, C. 2020. Observations on the life history and ecology of Clubiona pacifica Banks in Washington State (Araneae Clubionidae). Journal of Arachnology. 48(1):49-50. https://doi.org/10.1636/0161-8202-48.1.49.
Neven, L.G., Wakie, T. 2020. Effects of irradiation on codling moth (Lepidoptera: Tortricidae) 1st-3rd instars in sweet cherries. Journal of Entomological Science. 55(4):570-577. https://doi.org/10.18474/0749-55.4.570.