Blueberry Stem Gall Wasp

Blueberries November 14, 2011 Print Friendly and PDF

Blueberry Stem Gall Wasps are small kidney shaped to irregular spherical growths on the stems of blueberry plants. They range in size from .19 inches to .98 inches. The adult wasps are tiny, being only .078 inches to .098 inches in length. The head, thorax and abdomen are black. The legs and scape of the antenna are light amber. The antennal club is black. The wings are infuscated with black. The larvae are creamy white legless grubs.


Facts:

The adult wasps emerge from galls during or after bloom and lay several eggs in young stems.

  • The adults are almost entirely females, and emerge from the gall in late May to early June, before the buds break.
  • Adult wasps seek out a developing blueberry shoot and lay several eggs in the stem. The majority of galls (up to 70%) are formed on stems within the leaf litter.
  • After laying her eggs, the female climbs to the tip of the shoot and stabs the tissue at the tip of the stem several times causing it severe damage.

Egg laying damages the plant cells near the eggs, which causes abnormal tissue growth.

  • A chamber is formed around each egg.
  • The eggs typically hatch in 12 - 14 days, and the larvae feed on tissue of the wall of the chamber. During larval feeding the plant cells divide and multiply into large masses of tissue which eventually form the gall. On average each gall will contain about 12 larvae. The gall continues to grow throughout the summer and reaches its maximum size by late August. The outer covering is at first soft, but becomes hard and woody by maturity. The larvae spend the winter in the gall, and pupate within the gall, in the spring.

Damage:

  • Stem gall wasps cause kidney-shaped or spherical growths (.78 inches to 1.57 inches in diameter) on blueberry stems.
  • Galls develop around the stems during the year, turning from green to brown.

Control:

  • Pruning the galls out of the fields is the most effective control for this insect.
  • There are no chemical controls registered for this insect.
  • Burning as a pruning method may have some effect.

Sources:

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This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.