Seasonal abundance and distribution of treehole Culicoides spp. in eastern Tennessee

Collections were made in two physiographic regions of eastern Tennessee and western North Carolina: the Unaka Mountain Region (UMR) and the Ridge and Valley Region (RVR). Organic material was collected biweekly from 30 to 40 separate treeholes biweekly from March to November 1990, and weekly from 30 treeholes every week from March to September of 1991. Organic material was removed from each treehole, placed into a plastic bag, taken to the laboratory, and placed in a 0.5 liter container. A 2.5 cm² hole was cut in the container lid. The hole was covered with a thin acetate strip coated on the inner surface with a sticky adhesive. Containers were placed outside under a roof and thus were exposed to ambient temperatures and relative humidity, but not to direct sunlight or rain. Acetate strips with trapped emergent insects were removed from the containers weekly, and adhering Culicoides specimens were collected and identified to species. At the time of field collections, descriptive data were collected from both the tree and the treehole. Culicoides guttipennis was the most abundant species in 1990 and emerged from the greatest number of treeholes. The least abundant species for 1990 was C. hinmani, but when the emergence data were adjusted for a common dry weight (Culicoides spp. / 10 grams of dried sample) it became the most abundant species. This suggests that C. hinmani prefers treeholes with small quantities of organic material. C. hinmani emerged from mid-June until late September. It was found only in a very restricted area and collected in only 5 localities. Culicoides lahillei was the most abundant species in 1991, comprising 33% of the total individuals collected. C. guttipennis was third in abundance in 1991. The least abundant was C. footei, with 5.5% of total individuals in 1991. C. lahillei, C. paraensis, C. hinmani, and C. nanus were found more frequently in the RVR, while C. flukei and C. guttipennis and C. footei were found equally in both regions. The duration of emergence of each species was similar for both years. The seasonal emergence of the seven most commonly collected species occurred from March through mid-September, with the majority emerging from mid-May to mid-August. C. paraensis and C. flukei occurred in mid-March, earlier than the other species. C. hinmani was the only species to begin emerging in mid May. In general, overall emergence was highest in spring and declined through summer and fall. Most of the common tree species (red maple, northern red oak, Ohio buckeye, American elm, American beech, sourwood and yellow poplar) associated with the two regions were suitable larval habitats for treehole Culicoides species. Less common tree species from which substantial numbers of Culicoides emerged were hackberry, sassafras, shagbark hickory, boxelder and black walnut. Several species (flowering dogwood, rhododendron, eastern red bud, shingle oak and black cherry), although sampled frequently and commonly found, were poor producers of Culicoides. In general, many variables of the tree and the treehole appeared to have little or no relation to the number or kinds of Culicoides species collected