Duff temperatures and survival of bark beetles. At bottom left of photo is an electronic paper chart recorder (under plastic rain protection) connected to 4 integrated circuit thermometers at several depths in the forest litter or duff. In the center (near forest edge) is a pipetrap to monitor flight activity as bark beetles are attracted to pheromone baits, while the two screened cages on the right of the photo are for monitoring the flight takeoff attempts of Ips typographus during the day. Many bark beetles, such as Ips typographus overwinter in the forest duff. The spruce needles and other organic debris that comprise the duff form an excellent insulation layer which keeps the beetles from freezing to death . Also, snow will help insulate the beetles from the most bitterly cold temperatures in the middle of winter. Beetles begin to become active in May and will attempt to fly away when the air temperature is above 18-19° C . One strong beetle has been observed to fly for 6 hours on a flight mill in the laboratory (which means almost 45 km is possible in one flight without aid by the wind).

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Images © 1996 by John A. Byers, Chemical Ecology.