Effect of Apple Rootstock on Hoplocampa testudinea (Klug) Host Choice and Larval Performance

Hoplocampa testudinea, the European Apple Sawfly, is an important pest in apple throughout Canada. Losses can be up to 80% in some areas. Adults of H. testudinea are active during the bloom period and larvae are contained with the developing fruitlet, creating a challenging management situation. Chemical treatments applied either pre- or post-bloom may not reduce the population sufficiently to prevent damage in the current year. H. testudinea has been shown to exhibit a preference for some apple cultivars over others in Europe and North America, offering a potential host-based option to reduce impact from this pest. In this study, we explored whether rootstock would impact H. testudinea development as demonstrated in cultivar. A selection of rootstocks from within ‘Honeycrisp’ and Modi® plantings located at the Kentville Research and Development Centre were selected and the following variables were studied: percentage of clusters with eggs and number of eggs oviposited during bloom, development of the larvae within the fruitlets, titratable acid firmness and soluble solids evaluated at two times during fruitlet development, and damage observed at harvest. Results showed that female H. testudinea did not oviposit significantly more on certain rootstocks over others, even though the percentage of apples showing damage at harvest was significant across rootstock for ‘Honeycrisp’. Percentage of fruitlets showing secondary damage and dropping from the tree was significant across rootstock with a ‘Honeycrisp’ scion in 2021. Secondary damage in this planting correlated with change in acidity. These results suggest that rootstock does not strongly affect H. testudinea performance.