There is a lack of knowledge of the arthropod communities in both wild hazelnut and cultivated hybrid hazelnut ecosystems in the Midwestern United States. Our goal was to characterize the composition of these arthropod communities in hazelnut plantings. We surveyed six experimental plantings of hazelnuts in Wisconsin and two in Minnesota during growing seasons, from May 2017 to August 2021. We used four methods to survey the arthropod community of these plantings: ad libitum survey of specimen observations and collection, dissection of hazelnut buds and nuts, cone traps placed on the ground, and beat sheet sampling of plants. We registered 116 different morphospecies of five classes and 83 families. Arthropods with known feeding habits were grouped into four guilds: 59 herbivores, 36 carnivores (predators, parasites, and parasitoids), 4 decomposers (detritivores and scavengers), and 4 omnivores. While we registered 12 herbivorous species that could potentially cause damage to hazelnuts, we directly observed nine of them feeding upon or damaging plant parts: Phytoptus avellanae s.l. Nalepa (Eriophyoidea: Phytoptidae), Curculio obtusus Blanchard and Strophosoma melanogrammum Förster (Coleoptera: Curculionidae), Popillia japonica Newman (Coleoptera: Scarabeidae), Parthenolecanium sp. (Hemiptera: Coccidae), Euschistus servus euschistoides Say (Hemiptera: Pentatomidae), aphids (Hemiptera: Aphididae), Acleris sp., and Choristoneura rosaceana Harris (Lepidoptera: Tortricidae). We also registered eight species of parasites or parasitoids that could offer biocontrol services in the cropping system. These findings provide a foundation for future targeted studies on potential pests and beneficial arthropods, as well as ecological interactions within the hybrid hazelnut ecosystem in the Midwest.

Phytoptus avellanae is an eriophyid mite that feeds on and damages the vegetative and floral buds of hazel (Corylus) species by forming galls that impact hazelnut yield. Phytoptus avellanaehas been identified on hybrid hazels (European hazel, Corylus avellana × American hazel, Corylus americana) that have been developed for hazelnut production in the eastern United States and Canada, but year-to-year variation in distribution and severity of P. avellanae damage within a field has not been studied. Additionally, whether P. avellanae differentially infests and damages the hybrid hazel plants vs. native Corylus americana plants is unknown. We assessed the spatial trends and species preferences of P. avellanae within a mixed-species field of hazels over a four-year period. All hazels were surveyed for galls caused by P. avellanae each spring and assigned a qualitative damage rating. We found that damage from P. avellanaewas higher on hybrid hazel plants than on C. americana in each year of the study. In general, P. avellanae ratings increased towards the center of the field in most years. Our results showed that plants surrounded by infested neighbors often had higher damage ratings, suggesting that P. avellanae moves between adjacent plants. Understanding the within field distribution and host-plant preferences of P. avellanae will contribute to the development of scouting and management recommendations, provide insight on risk of mite movement between wild hazels and hybrid plantings in North America, and inform breeding efforts for this harmful pest.