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Ministry of Agriculture, Food and Rural Affairs

Dock Sawfly

Dock sawfly damage Dock sawfly damage
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Beginner

Scientific Name
Ametastegia glabrata

Identification
Eggs:

  • Kidney shaped,
  • White,
  • Approximately 0.8 mm long.

Larvae:

  • Bright green with a brown-black head,
  • Slender and hairless with several conspicuous white tubercles,
  • Seven pairs of prolegs,
  • Final instar larvae are 14-17 mm in size.

Adults:

  • A wasp about 7 mm in length,
  • Metallic blue-green back, and orange body,
  • Wings are a transparent bronze with a metallic blue streak at the front of each wing.

Damage:

  • Small round holes in fruit which usually develop a brown discolouration around the entrance with no frass present,
  • Damage usually occurs at the calyx and stem ends and generally appears in orchards near harvest,
  • Inside the apple, larvae burrow and create an irregular outline, curved or straight; there is one to several burrows within an apple.

Often Confused With

  • European apple sawfly- The adult European apple sawfly has an orange body, and the larva is white.

Period of Activity
Activity begins in early spring, however apples are only attacked by the last generation usually just as the fruit begins to approach maturity (late summer early fall).

Scouting Notes
Monitor for the presence of fruit with 2 mm round holes in skin. Cut open fruit to reveal the larva curled up inside the hole. Dock sawfly is a rarely a problem in commercial apple orchards. An affective weed management program for weeds in the buckwheat family (dock, sorrel, knotweeds, bindweeds, etc) can help to prevent problems with this pest.  

Thresholds
None established.

Advanced

Scientific Name
Ametastegia glabrata

Identification
The egg is kidney shaped, white and about 0.8 mm long. Larvae are bright green with a brown-black head, slender and hairless with several conspicuous white tubercles. Dock sawfly larvae have seven pairs of prolegs. Final instar larvae are 14-17 mm in size. The adult dock sawfly is a wasp about 7 mm in length, with a metallic blue-green back, and orange body. The wings are a transparent bronze with a metallic blue streak at the front of each wing.

A dock sawfly will burrow into the apple, leaving small round holes which usually develop a brown discolouration around the entrance. There is no frass at the entrance of the hole in the fruit. Damage usually occurs at the calyx and stem ends, or where the apple touches a leaf or another apple. Inside the apple, larvae burrow as deep as 5 cm. The burrows have an irregular outline and are curved or straight. There is one to several burrows within an apple, regardless of how many larvae are present. After the larva burrows into the fruit, it begins to pupate. The holes left in the apples from the burrowing insect make the fruit more susceptible to fungi and decay. A single larva bores several holes in one or more fruits before constructing its pupal chamber.

Often Confused With

  • European apple sawfly- The adult European apple sawfly has an orange body, and the larva is white.

Biology
Dock sawfly overwinters as a mature larva, usually in the dry stem of a weed host, but occasionally under the skin of fruit. The larvae pupate in early spring, and adults emerge over approximately seven weeks, with peak emergence in late April. Adults mate and females lay eggs individually in the leaf tissue of weeds. Females lay up to 100 eggs. The eggs hatch and the first instar larvae begin to skeletonize leaves of weeds while later instars chew large holes in the leaves. Larvae pass through several instars, and the final instar does not feed but seeks out a pupation site. There are four generations of dock sawfly each year with only the last generation attacking apples.

Period of Activity
Activity begins in early spring, however apples are only attacked by the last generation usually just as the fruit begins to approach maturity (late summer early fall).

Scouting Notes
Monitor for the presence of fruit with 2 mm round holes in skin. Cut open fruit to reveal the larva curled up inside the hole. Dock sawfly is a rarely a problem in commercial apple orchards. An affective weed management program for weeds in the buckwheat family (dock, sorrel, knotweeds, bindweeds, etc) can help to prevent problems with this pest.  

Thresholds
None established.

Management Notes

  • Damage is more likely in orchards with reduced insecticide programs or where weeds (primarily in the buckwheat family) within the row are not well controlled.
  • The best way to manage this pest is using selective herbicides to control weeds (docks, sorrels, knotweeds) the dock sawfly requires to survive.
  •  Adults are not strong fliers and these insects are unlikely to move into an orchard from nearby ditches and meadowlands.
  • Keep heavily fruited branches from touching the ground and mow to reduce damage from this pest.
  • Insecticides applied to control other pests in the orchard are effective in managing dock sawfly, and special sprays for this pest are not needed.