Galls are some of the most interesting effects of insect feeding on plant tissues. The hickory gall phylloxera (Phylloxera sp.) causes round galls up to 5/8” in diameter on leaves and petioles of hickory and pecan.
The phylloxera are tiny light tan colored insects. They have dark heads and transparent gray wings. Young phylloxera are wingless.
The number of galls present varies from year to year and from tree to tree. The damage caused by the galls is primarily aesthetic and does not harm the host tree. Infested leaves may dry out and drop prematurely as the galls dry out.
Hickory gall phylloxera overwinter in the egg stage within the dead female’s body in cracks or crevices of bark, old galls, or fallen leaves. Nymphs hatch out in the spring and crawl to expanding buds where they feed on the young tissues. This feeding causes galls to form around the insects. Eggs are laid once the phylloxera mature and these hatch, filling the galls with nymphs. Eventually, the gall splits open and these phylloxera lay eggs on the leaves. The hatchlings from these eggs are male and female that mate followed by egg laying by the females.
No control measures are recommended for this insect.
Look for some of these other galls this summer:
Blueberry stem gall wasp (R. Isaacs, Michigan State University)