3.4

Skip to 0 minutes and 9 secondsDr Matthew Rogers: In the next section, the behaviour of sandflies will be considered, focusing on their feeding, mating, dispersal, and resting behaviours. Sugars are used as food for males and female sandflies. Sugars may be taken from a variety of sources, including flower nectaries, fruit juices, or from the honeydew of plant-sucking insects, such as aphids. Sugar meals are stored in a chitinous sack called the crop, from where it is delivered into the midgut for digestion. Sugars are also necessary for Leishmania to efficiently complete their development in sandflies to generate the infectious metacyclic promastigote form.

Skip to 0 minutes and 50 secondsThe need for sugar feeding is currently being exploited as a novel control strategy in the form of spraying plant sugar sources with insecticides or incorporated into sugar-baited traps, known as Attractive Toxic Sugar Baits, or ATSBs.

Skip to 1 minute and 8 secondsMale sandflies do not blood feed, and are therefore not vectors of leishmaniasis. Only the adult female has the piercing mouth parts, or proboscis, that permit blood feeding. The mouth parts are short and penetrate less than 1 millimetre into the skin. The female mouth parts 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. Their choice of blood meal varies from species to species, but this is mostly dictated by the host abundance and availability. They generally blood feed during the night at peak times around dusk and dawn. The majority of sandflies feed outside-- exophagic.

Skip to 1 minute and 51 secondsHowever, most vector species that transmit human leishmaniasis feed inside dwellings-- endophagic-- such as Lutzomyia longipalpis, Lutzomyia intermedia, Phlebotomus papatasi, and Phlebotomus argentipes.

Skip to 2 minutes and 8 secondsUnlike most Dipteran vectors, sandflies do not swarm in the air to mate. Instead, males aggregate on a host or tree buttresses and release sex pheromones. To aid dispersal of the pheromone, they flap their wings. This behaviour is called lekking, and attracts females to mate and take blood. When a female lands near a lek, males perform courtship behaviour, which can include parading, leg and antenna touching, and a song by vibrating their wings. The image shows Phlebotomus argentipes males lekking on the flank of a cow. Male and female sandflies are readily identified by their general shape and external genitalia. When blood fed or gravid with eggs, females are bigger than males.

Skip to 2 minutes and 53 secondsIn an unfed state, females are slightly bigger than males and have a thicker, rounded abdomen. 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 often used to speciate sandflies. 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 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 ovaries for fertilisation.

Skip to 3 minutes and 37 secondsThe internal structures of the female genitalia, including the spermathecae are used for species identification. Sandflies are considered weak fliers that can't 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 metres, especially in dense vegetation. This is thought to be one of the main reasons why leishmaniasis tends to be a focal disease.

Skip to 4 minutes and 8 secondsAfter taking blood, sandflies choose sites to rest. Often, these sites are dark, humid, and sheltered to safely and efficiently digest their meal. The majority of sandflies rest outdoors-- exophilic-- such as Lutzomyia wellcomei in Brazil. Some species are known to rest indoors-- endophilic-- such as Lutzomyia peruensis in the Andes. The resting habitats of many sandflies are unknown, but they are likely to be near their preferred breeding sites.

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.

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This video is from the free online course:

Control and Elimination of Visceral Leishmaniasis

London School of Hygiene & Tropical Medicine