PROC. ENTOMOL. SOC. WASH. 91(1), 1989, pp. 66-70 NATURALLY OCCURRING HOST SITES FOR XYLOPHILIC CECIDOMYIIDAE (DIPTERA) Emily A. Rock and Dale Jackson (EAR) Wayne General and Technical College, 10470 Smucker Road, Orrville, Ohio 44667; (DJ) Department of Biology, The University of Akron, Ohio 44325. ^torac?.— Existing data on host sites for xylophilic Cecidomyiidae larval development are derived from observations of sawn trees and logs. Field studies of hardwood trees at three sites in northeast Ohio show that strong winds and animal activity break live branches of suitable size and thus expose vessels of >75 ^ which are used for larval development. Such damaged branches can support large populations of midges. Larvae develop in both the proximal and distal sides of the break. Branches remain suitable for oviposition and larval development for one to several months, depending on branch diameter and weather conditions. Key Words: wood loving, tree damage, squirrel activity Xylophilic Cecidomyiidae use freshly ex-posed vessels of hardwoods as a larval hab-itat. Relationship between host selection and vessel diameter has been previously re-ported (Rock and Jackson 1985, 1986). As with that of other investigators (Kieffer 1 900, Brues 1922), our initial encounter with these cecidomyiids began when we observed fe-males swarming on the cut surfaces of logs and stumps of trees exposed in logging op-erations. Although we also used cut logs during earlier studies, we speculated on the availability of such niches under natural conditions. Our current investigation ex-amines 1) the role of strong winds and an-imal activity in exposing larval niches, 2) utilization of vessels in live branches that remain on the tree, 3) the number of larvae that one branch can support and 4) the length of time after exposure that a branch remains suitable for use. Methods Storm and squirrel damage.— Two sites in northeast Ohio were monitored for two years (1985 and 1986) for live, broken branches. One site was a small island of approximately 7500 square meters located near a lake shore with five mature oak (Quercus alba L.) and one mature ash (Frax-inus americana) trees (known xylophilic cecidomyiid hosts (Rock and Jackson 1986)). The other was part of a large sub-urban garden with a study area of 5625 square meters with five mature oak and three mature ash trees. The areas below the trees were mowed regularly to facilitate collection of fallen twigs and branches. We recorded the diameter of only the live branches be-cause previous studies have shown that dead wood is not a suitable larval habitat. Some larger branches were kept at the field site to monitor their use by cecidomyiids. The suitability of the branches for larval devel-opment was verified by subsequent collec-tion of larvae from the branch ends. Squirrels were active at the field sites and numerous live host tree branches were col-lected that squirrels had severed by chew-ing. Branches broken by squirrels were
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