The Walking Stick as a Forest Defoliator

Abstract

The following is substantially the author's summary: Outbreaks of the Phasmid, Diapheromera femorata, Say, are becoming common in the north-central part of the Lower Peninsula of Michigan and will probably result in the infestation of practically all suitable stands. These forests are characteristic of the sandy moraine region and are the direct result of logging, followed by repeated fires. The black oaks provide the insect with an especially desirable food-supply and constitute the only forest type in which outbreaks have been observed in Michigan. The eggs hatch in late spring and early summer, and the young insects crawl from the ground to the tree-tops, where they feed on the foliage. They reach full size in August and continue to feed, mate and oviposit until autumn. The small bean-like eggs are dropped to the ground and probably two winters pass before they hatch. The long incubation period is not necessarily invariable, however, as indicated by laboratory observations in which eggs exposed to fluctuating winter temperatures hatched in the spring following oviposition. In the Ogemaw State Forest, the insects appear in alternate years, elsewhere each year. The latter condition is probably explained by alternating broods. Infestations spread slowly at a maximum rate of about a furlong a year. The sex ratio is normally 0.5, but males predominate both in newly infested spots, because of their relatively active habits, and in places where the infestation is dying out, probably because of the differential mortality of the sexes under adverse food conditions. Although defoliation occurs late in the season, the insects can kill the trees after 10-15 years of defoliation. More than half of the black oaks in an infested area are likely to be killed, but the white oaks and other trees are not injured. The selectivity on the part of the insect will result ultimately in improving the composition of the forest. The improvement might be hastened by planting white oaks and conifers under black oaks, either before or after an outbreak has occurred, with subsequent cultural operations. Conversion of the forest to non-susceptible types is the least expensive and most permanent method of control, but requires at least 10 to 15 years to become effective. Such improvements, as a protection for the future, should be made promptly wherever possible, especially round resort areas. Where it is advisable to use direct measures of control, calcium arseriate should be applied at the rate of 20 lb. per acre either as a liquid spray or in the form of a dust. Insect parasites and disease-causing organisms have not been observed in the outbreaks in Michigan, but birds flock into the infested areas and feed upon the insects.