Caterpillar (Orthosia hibisci) Infestation Causes Defoliation

Observation by Alberta Walker:

These are eating all the leaves, leaving the willows to dry up.

Comments from LEO Editors:

About a year ago in the community of Holy Cross, about 40 miles south downriver of Anvik, hundreds of caterpillars near the villages tribal building and school lawn observed a large number of the similar insects species. Jessie Moan, Statewide IPM Technician mentions in the earlier post, "To the best of my knowledge, these are native insects. I can't give you an exact identification but I believe these to be the same (or very similar) caterpillars to ones we have observed feeding on willow, alder, and cottonwood. Specimens of those have been collected and are being reared to adulthood to hopefully get a better identification." This observation has been shared with UAF Cooperative Extension Service for a follow up of the previous posted observation and its potential connection to the observation. Moses Tcheripanoff

Derek Sikes, Entomologist with University of Fairbanks Museum, writes:

These are probably Orthosia hibisci, which have been identified from an outbreak in SW Alaska last year and earlier this year.

Joshua Pierce, Wildlife Biologist for Alaska Department of Fish and Game, writes:

Willow leaves are a part of the diet of moose, but they are not as critical as willow stems. When willow leaves are available for foraging by moose, there are also many other forage choices available to moose (summer). Most moose populations in Alaska are regulated by predation rather than forage, meaning that there is room for forage resources to vary without significantly impacting the moose population. To sum up, we do not know what effect these willow pathogens have on moose populations, but we are not seeing anything out of the ordinary that might indicate that there is a negative effect.