A New Look at Cultivar Preference in Hoplocampa testudinea (Hymenoptera: Tenthredinidae) on Apple in the Annapolis Valley of Nova Scotia, Canada

(1) Background: The European apple sawfly, Hoplocampa testudinea Klug (Hymenoptera: Tenthredinidae), can be an economically important pest in eastern Canada and shows preference for apple cultivars in Nova Scotia, Canada. We hypothesized that this preference could be due to oviposition by female H. testudinea (preference-performance hypothesis) during the bloom period or differential larval survival during development due to fruitlet physicochemical properties. (2) Methods: Fifteen commercial and experimental apple (Malusdomestica Borkh.; Rosaceae) cultivars located at the Kentville Research and Development Centre (Kentville, Nova Scotia) were chosen and examined for H. testudinea oviposition, larval performance during fruitlet development, fruitlet physicochemical properties and damage assessment at harvest from 2016–2019, inclusive. (3) Results: H. testudinea showed significant cultivar preference during oviposition, during development and at harvest, but the ranking of these cultivars was not the same throughout the season. Total impact by H. testudinea was consistent for most cultivars over multiple years of the study. (4) Conclusion: Correlation of oviposition with damage provided weak evidence for the preference-performance hypothesis. We propose that this relationship is weak due to differential survival of larvae during development

Oviposition, Feeding Preferences and Distribution of Delia Species (Diptera: Anthomyiidae) in Eastern Canadian Onions

Delia antiqua, Delia platura and Delia florilega are three root maggot species commonly considered pests in Eastern Canadian onions. The onion maggot, D. antiqua, is considered the primary root maggot pest in onion but it remains unclear whether the other two species are also causing damage. In order to develop updated management strategies for root maggot, we tested adult oviposition and feeding preference by Delia larvae on four growth stages of onion using bioassays and we determined the Delia species composition across the four major onion growing regions in eastern Canada. Delia species oviposit readily on onion at the 5–7 true leaf growth stage but damage on onions is not statistically different between Delia species in our zero-inflated models. The four eastern Canadian onion growing regions have different proportions of Delia species. Southern Ontario and Quebec were the only two regions where Delia antiqua was collected. The highest average numbers of Delia spp. were caught in Quebec and Nova Scotia. Our study shows that timing is important in implementation of management strategies for root maggot in Eastern Canadian onions