Poplar petiole gall aphid
Appearance and Life Cycle
The life history of the aphids is very complex, with migration to a secondary host usually occurring. In the spring, the overwintering eggs hatch producing wingless females known as stem mothers. Stem mothers are parthenogenetic (can reproduce without mating), and give birth to a generation of wingless, parthenogenetic females inside the galls they create. Several generations are produced, until late summer when the galls become overcrowded. At that time, the females produce a generation of winged, parthenogenetic females which migrate to a secondary host. Several generations of winged and wingless parthenogenetic females are produced. The winged females return to the poplars where they give birth to sexually reproductive male and female aphids. After mating, the females lay overwintering eggs in cracks and crevices, completing the life cycle. Petiole gall aphids vary in size and colour depending on the life stage and species. Stem mothers are generally yellow to greenish in colour and are approximately 2 millimetres long. Nymphs are dark and smaller than stem mothers.
Galls or hollow swellings are formed at the base of the leaf blade or on the petiole. The galls are unsightly and may cause premature leaf drop, but no permanent damage is done.
Hand picking infested leaves when galls are first noticed will greatly reduce populations. Chemical control is required only in severe infestations and will only be effective if sprayed when the aphids are not inside the galls. Insecticides that may be used are: carbaryl; dicofol; malathion; permethrin or an insecticidal soap.
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