Vertical stratification of Culicoides biting midges at a Florida big game preserve.

BACKGROUND: Many important vector arthropods are known to stratify vertically in forest environments, a phenomenon which has important implications for vector-borne disease transmission and vector control. Culicoides Latreille biting midges (Diptera: Ceratopogonidae) have been documented using the forest canopy; however, studies of this phenomenon are lacking for many Culicoides species found in great abundance in the state of Florida, USA, some of which have been implicated as suspected vectors of hemorrhagic diseases of white-tailed deer. The present study aimed to determine whether common Culicoides species in Florida stratify vertically and to determine whether strata used by midges corresponded to host use.

METHODS: Trapping was conducted at a big game preserve in Gadsden County, FL, USA. Over two summer field seasons in 2016 and 2017, CDC miniature light traps were set at two levels, one set at 1.37 m, designated as the ground trap, and a nearby trap in the forest canopy set at 6 m during 2016 and 9 m during 2017. Species abundance, physiological status, and blood-meal sources were analyzed and compared between trap heights.

RESULTS: Species abundances for C. haematopotus, C. stellifer and C. venustus were not significantly different between trap heights during the 2016 season; however, canopy traps were found to have significantly higher abundance of C. arboricola, C. biguttatus, C. debilipalpis, C. haematopotus, C. insignis and C. stellifer than ground traps in 2017. Greater numbers of blood-engorged midges were collected in the canopy compared with ground traps during both study years, and 98.6% and 98.7% of blood meals from canopy collected midges were taken from ground-dwelling mammals in 2016 and 2017, respectively.

CONCLUSIONS: Culicoides species in Florida, including species implicated as vectors of hemorrhagic disease viruses, are found in great abundance in the forest canopy. Many midges are feeding on host species that are known reservoirs of hemorrhagic disease and then moving into the forest canopy, which has implications for the calculation of vectorial capacity. These data contribute valuable ecological information on Culicoides species found in Florida and provide a framework for developing effective vector control strategies to target these species.