Phenology and infestation patterns of the cottonwood twig borer (Lepidoptera : Tortricidae) in Iowa

Cottonwood twig borer, Gypsonoma haimbachiana (Lepidoptera: Totricidae), ph enology and infestation patterns on Populus spp. were examined over a 2-yea r period in Iowa. Weekly sampling of infested shoots during the host growin g season verified the existence of five instars. Head capsule size increase d nonlinearly from the first to the fifth instar and corresponded to a conc omitant geometric increase in the volume of larval feeding galleries. The s ampling indicated that the cottonwood twig borer had two generations per ye ar in Iowa. Corresponding with the two generations, two peaks of larval abu ndance were observed; one in the second week of June and the other in the f irst week of August. Greater volume of feeding galleries occurred in the ea rly season generation compared with the late season generation. Sampling of infested shoots revealed that more than 80% of infested terminals containe d only one active attack (freshly bored hole in tree terminal with frass pr esent); more than 88% of feeding galleries contained only one larva; and mo re than 80% of the larvae were found in the first active attack nearest the terminal apex. These data were compared with results published on the phen ology and attack patterns of the cottonwood twig borer in the southern Unit ed States.