COTTONWOOD TWIG BORER, Gypsonoma haimbachiana (Kearfott)
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.
Cottonwood twig borer damage to cottonwood sapling.
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.
COTTONWOOD BORER, Plectrodera scalator (F.)
The cottonwood borer is limited in range to the southern half of the United States. Hosts include cottonwood, poplars and willows. The adults feed on the tender shoots of young trees causing them to shrivel and break off. The larval stage of this insect tunnels in the inner bark and wood at the base of the tree and may kill or severely weaken it.