Sand flies are tiny, biting insects that can be a nuisance and, in some regions, transmit diseases. Understanding their attractants is important for developing effective prevention and control strategies. This article explores the various factors, from sensory cues to environmental conditions, that attract sand flies.
How Sand Flies Detect Attractants
Sand flies possess specialized sensory capabilities to locate potential hosts. Their sense of smell (olfaction) is a primary detection mechanism. They use antennae and maxillary palps, covered with sensory hairs called sensilla, to detect volatile organic compounds (VOCs) in the air.
They also sense heat (thermoreception), crucial for identifying warm-blooded hosts. Vision also plays a role in their host-seeking behavior, though less significant than their chemical and thermal senses. They can detect movement and general shapes, helping them orient towards a host once within visual range.
Human-Derived Attractants
Humans emit several cues that are highly attractive to sand flies. Carbon dioxide (CO2) from human breath is a primary long-range attractant. Sand flies can detect changes in CO2 concentration, allowing them to follow a plume of exhaled air to its source, even from a distance. Studies show sand flies respond to CO2 levels equivalent to multiple humans, indicating its potency as a lure.
Body odor, a complex mix of volatile organic compounds (VOCs) from human sweat and skin bacteria, also attracts sand flies. Compounds such as lactic acid, ammonia, and various fatty acids in human body odor can draw these insects closer. Research indicates that individuals with higher concentrations of certain proteins in their sweat or body odor may be more appealing to sand flies, highlighting how individual body chemistry influences attraction. Once a sand fly is in close proximity, body heat acts as a short-range attractant.
Environmental Factors and Other Cues
Environmental factors and other cues also contribute to sand fly presence and attraction. Some sand fly species are drawn to artificial light sources, leading them towards human dwellings or outdoor activities. While green and blue light-emitting diodes (LEDs) show some effectiveness, ultraviolet (UV) light is very attractive to certain species, with a secondary peak in the blue-green-yellow range.
Visual cues, such as color and movement, also attract sand flies. Sand flies may be more attracted to dark clothing, and the movement of a potential host can trigger their predatory instincts, making it easier for them to locate a target. Furthermore, sand flies prefer humid environments and seek out sheltered, damp places such as leaf litter, animal burrows, or cracks in walls for resting and breeding. The presence of such preferred habitats in an area can indirectly increase the likelihood of sand fly encounters for humans.