The cottonwood twig borer is widely distributed throughout the entire
range of eastern cottonwood, from Canada to the Gulf States and west to
Missouri. The larvae of the cottonwood twig borer feed in the terminals
of the host. This feeding results in reduction of terminal growth and
forked and crooked trunks. Damage is especially severe on young trees.
[Illustration: Cottonwood twig borer damage to cottonwood sapling.]
[Illustration: Three-year-old cottonwood stunted by twig borers.]
The female moth lays eggs on the upper surface of leaves along the
mid-rib, singly or in groups of two to eight. Hatching occurs in about
five days and the young larvae cover themselves with silk mixed with
trash, and then tunnel into the mid-rib. After the first molt, larvae
leave the tunnels and bore into tender shoots. Larvae reach maturity in
about 21-23 days and begin moving down the trunk of the tree where they
spin cocoons in sheltered bark crevices, in litter, or between leaf
folds. The adult moths emerge in eight or nine days. It takes from 40-45
days to complete the life cycle in mid-summer.
The most effective natural control is a potter wasp, _Eumenes_ sp. which
tears open tender cottonwood shoots and removes twig borer larvae from
their galleries. Other wasps parasitizing the twig borer include _Bracon
mellitor_ (Say), _Apanteles clavatus_ (Provancher) and _Agathis_ sp.