Balsam Twig Aphids
Balsam twig aphids, spring adults on branch.
Balsam twig aphid eggs inserted in bud scar.
spp., commonly stated as M. abietinus Koch which is an European
species. Several species of Mindarus are found on firs in North
Distribution: Northern North America.
These pests have been reported from nine species of fir, especially balsam fir and Fraser fir. They occasionally can be found on white spruce and juniper.
The Mindarus twig aphids produce considerable honeydew which soon is supporting a good growth of black sooty mold. Ants and bees may also be present. The most important damage is caused by the first spring adults (fundatrix) which feed on the expanding buds and resultant wingless females (fundatrigenia) which cause the new needles to curl over and twist.
Description and Life Cycle:
These aphids have complex life cycles in which four distinct forms are found. In mid- to late April, overwintering eggs hatch into small blue-green nymphs. While feeding at the bases of buds, these nymphs molt three times to form the mature, wingless, asexual "stem mothers" (fundatrices). The stem mothers give live birth to the second form, the fundatrigenia. These wingless forms move to the now expanding buds and feed at needle bases. The developing nymphs produce white, waxy threads and molt three times. The fundatrices and fundatrigenia may give live birth to the winged sexuparae during this time. The adult sexuparae have fully developed wings and can fly to new trees. Once settled, the sexuparae produce the third form, the sexuales. The sexuales are either male or female and these feed on the needles. By mid-June, the sexuales mature, mate and the females attach eggs to the tree bark. These eggs remain dormant until the next spring.
New plantings of fir seedlings should take some time to become infested unless the nursery was infested or older fir trees surround the new planting. However, once established, this pest builds up damaging populations quickly.
Option 1: Biological Control - Encourage Natural Predators and Parasites - Hover flies (syrphids) seem to be the most common predators attacking this pest. However, insecticide sprays usually kill these beneficials rendering them ineffective in a plantation.
Option 2: Chemical Control - Oil and Soap Sprays - Dormant oil sprays (3-5%) applied in late fall and early spring have not been very successful in killing the overwintering eggs. This is probably due to the eggs being placed under flaps of bark on the trunk and stems. Horticultural oil (1.5-2%) and insecticidal soaps have been very effective for control of the early spring mothers. These are usually present before the buds break or bud sheaths loosen.
Option 3: Chemical Control - Spring Insecticide Sprays - Insecticides are effective in prohibiting needle damage only if applied before bud elongation. Sprays should be applied to control the spring mothers before the bud sheaths become loose.