Evaluation of the physical and environmental characteristics of the tree hole habitats of Culicoides species (Diptera: Ceratopogonidae)

Tree holes are important habitats for certain Culicoides species (biting midges: Diptera: Ceratopogonidae) that transmit epizootic hemorrhagic disease virus (EHDV) and bluetongue virus (BTV) to ruminants. However, very little is known regarding the habitat associations of tree hole Culicoides species, limiting the establishment of effective midge control strategies. In this study, we characterized the physical and environmental characteristics of the tree holes associated with Culicoides species and identified the key variables important for adult emergence. Tree holes ( n = 33) were surveyed at Bob R. Jones Idlewild Research Station, Louisiana, USA, and various physical/environmental characteristics of the habitats were recorded. In addition, substrate samples from the tree holes were collected/incubated for adult insect emergence. A total of 133 Culicoides adults emerged from the samples: C. hinmani Khalaf (44.4%, 59/133), C. guttipennis Coquillett (22.6%, 30/133), C. arboricola Root and Hoffman (18.0%, 24/133), C. nanus Root and Hoffman (7.5%, 10/133), C. paraensis Goeldi (3.8%, 5/133), C. debilipalpis Lutz (3.0%, 4/133), and C. beckae Wirth and Blanton (0.8%, 1/133). Culicoides species emerged from only 42.4% of the tree holes (14/33) that belonged to four tree species: American elm ( Ulmus americana , 100.0% [1/1]), Chinese privet ( Ligustrum sinense , 100.0% [2/2]), sweetgum ( Liquidambar styraciflua , 63.6% [7/11]), and water oak ( Quercus nigra , 36.4%, [4/11]). Midge emergence (mean ± SE) was the highest from American elm (12.0 ± ND [Not Determined, because of small sample size, n = 1]) and sweetgum (6.4 ± 4.5), followed by Chinese privet (4.5 ± 3.5) and water oak (3.8 ± 2.0). The presence of standing water, tree species identity, tree hole direction, and tree hole orientation had a significant effect on the presence and abundance of total Culicoides species. However, the key variables influencing midge abundance varied between Culicoides species. Our findings suggest that some tree holes are more productive midge habitats than others, likely reflecting a variation in their environmental characteristics. Overall, this study provides new insight into the habitat characteristics of tree hole Culicoides species and provides valuable information toward the identification of productive midge habitats that can be targeted for biting midge control in/around livestock facilities in Louisiana.