Sand fly behaviour

In the next section, the behaviour of the sand flies will be considered; focusing on their feeding, mating, dispersal and resting behaviours.

Sugars are used as food for males and female sand flies. Sugars may be taken from a variety of sources including flower nectary’s, fruit juices). Sugar meals are stored in a chitinous sack called the crop that gradually deliver them into the midgut for digestion. Sugars are also necessary for opening the gut of the female sandlfy before a blood feed and the completion of Leishmania development in sand flies and generation of the infectious metacyclic promastigote form (Sacks and Kamhawi, 2001).

The need of sandflies for sugar feeding can be exploited as a novel control strategy in the form of spraying plant sugar sources with insecticides or utilizing sugars in what is known as attractive toxic sugar baits, ATSBs (Schlein and Müller, 2010).

Male sand flies do not blood feed and are therefore not vectors of Leishmaniasis. The mouthparts are short and penetrate less than 1 mm into the skin. The female mouthparts are barbed, allowing them to lacerate the upper dermal capillaries forming a pool of blood – they are known as pool feeding vectors and share this feature with blackflies, midges and tsetse flies.

The blood meal choice of sandflies varies from species to species. However, sandflies are to known to be opportunistic feeders, their host preference is also dictated by host abundance and availability. They generally blood feed during the night at peak times around dusk and dawn. The majority of sand flies feed outside (exophagic), however most vector species that transmit human leishmaniasis feed inside dwellings (endophagic) such as Lutzomyia longipalpis, Lutzomyia intermedia, Phlebotomus papatasi and Phlebotomus argentipes except in the main endemic area in East Africa where the sandfly vector Phlebotomus orientalis is predominantly exophagic

Unlike most Dipteran vectors sand flies do not swarm in the air to mate. Instead, males aggregate on or near a host on the ground or tree buttresses, while performing a courtship dance and releasing a sex pheromones. This behaviour is called leking and attracts females to mate and take blood. This behaviour is called leking and attracts females to mate and take blood. When a female lands near a lek, males perform courtship behaviour which can include parading, wing flapping, leg and antenna touching and a song by vibrating their wings. The image featured on the fourth slide in the video shows Phlebotomus argentipes males leking on the flank of a cow.

Male and female sand flies are readily identified by their general shape and external genitalia. Blood fed or gravid with eggs females are bigger than males. Even when unfed the females are slightly stouter than the males and have thicker, rounded abdomens. Males are thinner and have a distinctive set of genital claspers protruding from the end of their abdomen, giving it an upturned appearance.

Male and female genitalia are used to speciate sand flies. When in the correct position, the male claspers grasp the female for copulation, in which the male and female abdomens are connected end to end. Genital filaments, lying in the aedeagus (penis) within the claspers penetrate the female and inject sperm. The sperm travel to a storage structure in the female genitalia known as the spermathecae where they receive nutrition and are periodically released to the oviducts for fertilization of eggs that are passed from the ovaries. The internal structures of the female genitalia, including the spermathecae, are used for species identification.

Sand flies are considered weak fliers that can not fly in strong winds. They fly in short bursts and have a characteristic hopping flight. As a result, they do not disperse more than a few hundred meters, especially in dense vegetation. This is thought to be one of the main reasons why leishmaniasis tends to be a focal disease.

After taking a blood meal sand flies choose sites to rest and safely and efficiently digest their meal. Often these sites are dark, humid and sheltered The majority of sand flies rest outdoors (exophillic) such as Lutzomyia wellcomei in Brazil and P.orientalis in East Africa. Some species are known to rest indoors (endophillic), such as Lutzomyia peruensis in the Andes and P. papatasi in the Old World. The resting habitats of many sand flies are unknown but they are likely to be near their preferred breeding sites.