The first instar larvae tunnels just under the epidermis of the fruit, resulting in the typical ribbonlike scar (primary injury). Photo by G. Krawczyk.
Description and life cycle
European apple sawfly adults are about 5∕16 inch long and wasplike insects, but with a broad attachment of the thorax and abdomen. Sawfly larvae resemble caterpillars, but have prolegs on each abdominal segment. Sawfly overwinter as larvae in the soil and have only one generation per year. Adults emerge during late pink and early bloom. Eggs are laid on the calyx end of developing fruit.
The first instar larvae tunnels just under the epidermis of the fruit, resulting in the typical ribbonlike scar (primary injury). These apples usually remain on the tree, and the presence of the scars at harvest can reduce fruit value. The second and older instar larvae bore deeply into the seed chamber of the fruit and can penetrate additional fruit, usually causing fruit abortion. Later instar injuries on fruit with a brownish frass at the entry are called "secondary damage."
Monitoring and management
Sticky, rectanglular, nonultraviolet-reflecting, white traps should be placed at a density of one per 3 to 5 acres along the orchard periphery at the pink stage of apples on the south sides of trees at 5 to 6 feet above the ground. Insecticide treatment thresholds are 5 flies per trap by petal fall if no prebloom insecticide has been applied. An application of an effective insecticide as soon as pollination is complete is the best control tactic for orchards with a history of this sawfly.
Numerous predators and parasitoids of European apple sawfly are reported from Europe, but no native biocontrol agents are reported to be effective in North America. A partially successful classical biological control program was initiated in Canada to introduce a solitary larval endoparasitoid Lathrolestes ensator Brauns (Hymenoptera: Ichneumonidae) for the control of this pest. Other options for biological control of European apple sawfly are the Heterohabditid and Steinernematid entomopathogenic nematodes, which are still being investigated in laboratory and semifield conditions.