Poplar petiole gall aphid (Pemphigus populitransversus)
Pest description, damage, biology, and life history There are numerous aphid species on cottonwood. Some cause galls on the midrib or petiole, others feed on leaves. Some of the aphids have alternate hosts on crops such as lettuce or on weeds. Pemphigus aphids can be distinguished from other aphids by their short antennae (less than one-third body length) and undeveloped cornicles. Gall aphids feeding at the base of leaf petioles cause the petioles to enlarge and enclose the insects. Hard, pale green, rounded galls form along the petiole or at the base of the leaf. Aphids found inside the galls look grayish and waxy. The leaves are not damaged, but may twist at right angles to the petiole. They develop into adults and reproduce once on poplar before migrating to summer hosts in Brassica or Aster species. In late summer, winged forms reappear, and these migrate back to poplar to mate and lay eggs.
For biology, life history, monitoring and management
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