1st Place: Conductive and convective heat, but not infrared radiation, mediate stable fly, Stomoxys calcitrans, and horn fly, Haematobia irritans, alighting and probing responses on thermally different targets

Stable flies, Stomoxys calcitrans, and horn flies, Haematobia irritans, are blood-feeding ectoparasites which inflict severe damage to livestock industries. In order to survive and reproduce, these flies must locate and recognize a animal host in a potentially complex environment. As with mosquitoes and other hematophagous insects, the body heat radiating out from a warm-blooded animal may serve as one of several host cues. Using temperature-controlled heat plates, we tested whether stable fly females differentially alight on, and probe, test stimuli according to their thermal characteristics. We compared the attractiveness of room-temperature controls against plates set to temperatures characteristic, or not, of host animals. By presenting flies with plates housed in columns occluding convection and conduction heat, we further determined whether infrared radiation (IR) alone elicits host-seeking behavior. We used thermography to confirm the temperatures of all test stimuli and to measure the thermal emittance of cattle body surfaces. In bioassays, stable flies preferred heat plates with a temperature range of 40-45 °C over all other temperatures tested. In the absence of convected and conducted heat, but with IR present, both stable flies and horn flies failed to respond to heat plates set to either 40 °C or room-temperature. Our findings demonstrate that host-seeking flies prefer to alight on substrates bearing surface temperatures within the range of 40-45 °C, and that IR does not appear to affect the flies’ responses. An effective thermal cue may be used to enhance current trapping systems which rely on visual and olfactory host foraging cues.