Phlebotomine sand flies - Factsheet for experts
SPECIES NAME/CLASSIFICATION: Phlebotomus spp. (Diptera: Psychodidae)
COMMON NAME: Sand fly
Phlebotomine sand flies occur throughout the tropics and sub-tropics, as well as in temperate zones. Phlebotomus spp. occurs in Africa, where it is an important vector in certain regions, Europe (particularly the Mediterranean region), the Middle East and Asia (particularly the Indian subcontinent). A number of sand fly species are present in Europe, and in recent years, their range has increased. Phlebotomus mascittii has been recorded in Switzerland, France, Belgium, Germany, Austria and Corsica [8-13] . Phlebotomus ariasi occurs in France, Spain, Portugal and Italy and has also been reported in Andorra . Recently, it has been reported in more northerly provinces of Spain and at higher altitudes in France and Andorra [14-16] . Phlebotomus perniciosus is known to be present in Bulgaria, Croatia, France, Malta, Portugal, Spain, southern Switzerland and western Germany and has recently been found for the first time in Andorra [9,15] . There is evidence of increased distribution of Phlebotomus perniciosus in Italy [17,18] , and its range is predicted to expand in Spain and Germany with climate warming [19,20] . The current known distribution of Phlebotomus perfiliewi encompasses Albania, Bosnia and Herzegovina, Croatia, Cyprus, Georgia, Greece, Hungary, Italy, Montenegro, Romania, Serbia, south-eastern France, the former Yugoslav Republic of Macedonia, Turkey and Ukraine . Phlebotomus neglectus is found in Albania, Croatia, Greece, Hungary, Italy, Montenegro, Serbia, the former Yugoslav Republic of Macedonia and Turkey . Phlebotomus papatasi is distributed throughout southern Europe in Albania, Bulgaria, Croatia, Cyprus, Greece, Hungary, Italy, Montenegro, Portugal, Serbia, southern France, Spain and Turkey . Phlebotomus sergenti occurs in Bosnia and Herzegovina, Bulgaria, Cyprus, Greece, Italy, Portugal, Spain, southern France and Turkey . Two other species, Phlebotomus similis and Phlebotomus tobbi, are currently confined to south-eastern Europe (Greece, Turkey and surrounding countries) .
Sand fly distribution is limited to areas that have temperatures above 15.6oC for at least three months of the year . Below 10oC, sand flies must enter a dormant state in order to survive winter, therefore reducing the breeding population . In addition, sufficient moisture in the environment is required because humidity is an important factor for egg survival [2,22,23] . However, peaks in rainfall are followed by reductions in sand fly numbers as excess precipitation reduces the amount of suitable diurnal resting sites for adult insects and limits adult flight activity, as well as killing immature stages .
Predicted spread in Europe
The temperature in northern Europe is likely to become milder and precipitation will increase. In addition, winter temperatures will increase at higher altitudes. These climatic changes are predicted to lead to an expansion in the range of phlebotomine sand flies in Europe, as they will be able to survive in areas that are uninhabitable today, including large areas of north-western and central Europe and at higher altitudes in regions where they are already established . It is predicted that should climate change result in suitable temperatures, sand fly species could rapidly establish in countries currently on the edge of their range, including inland Germany, Austria and Switzerland, as well as along the Atlantic coast [11,12,25,26] .
- SPECIES NAME/CLASSIFICATION: Phlebotomus spp. (Diptera: Psychodidae)
- COMMON NAME: Sand fly
Morphological characters and similar species
Of the five psychodid subfamilies, only the sand flies (Phlebotominae) have piercing mouthparts capable of taking blood. The phlebotomines tend to have an elongated and more fragile structure, in contrast to the squatter and more robust appearance of the other psychodid flies. Sand flies are tiny insects 1.5‒3.5 mm in length, with a hairy appearance, large black eyes and long, stilt-like legs. They can be distinguished from other small flies by their wings, which are hairy and extended at a 40o angle over the body when the fly is at rest or blood-feeding. Identification of phlebotomine sand flies to species level is difficult, usually requiring examination of internal structures [1,2].
Development and life cycle
Sand flies have a four-stage life-cycle: egg, larva, pupa and adult. Eggs hatch after 4‒20 days, although this is likely to be delayed in cooler weather . Larval development involves four instars, and is completed after 20‒30 days depending on species, temperature and nutrient availability. Environmental extremes (e.g. heat, cold, or drought) can cause larvae to diapause, prolonging development time for months. Larvae are mainly scavengers, feeding on organic matter (e.g. fungi, decaying leaves, animal faeces and decomposing arthropods). The pupal stage lasts 6‒13 days before the adult sand flies emerge.
Adult feeding behaviour
Both male and female sand flies feed on plant juices and sugary secretions. Females also blood-feed to produce eggs. Sand flies use their mouthparts to probe exposed skin, leading to the formation of a pool of blood from which they feed. Sand fly saliva contains pharmacologically active components that aid in the feeding process . Feeding activity is influenced by temperature, humidity and air movement (sand flies are weak fliers so even light wind can inhibit flight and reduce biting). Most species feed at dusk and during the night, when temperature falls and humidity rises . The majority of species feed outdoors, although daytime biting can occur indoors in darkened rooms or among shaded vegetation/trees, especially if disturbed by human activity.
Reproduction and oviposition
Adult sand flies mate soon after emergence; males locate females at resting sites or on vertebrate hosts, with the aid of pheromones. Female sand flies usually lay 30‒70 eggs during a single gonotrophic cycle, which are deposited in cracks and holes in the ground or in buildings, animal burrows and among tree roots . The eggs require a microhabitat with high humidity in order to survive, but are not laid in water. Generally, one blood meal results in the production of a single batch of eggs .
Activity (incl. dispersal, seasonality, overwintering)
The extent to which sand fly population densities vary throughout the year depends on the local climate, with significant seasonal changes in temperature and precipitation resulting in fluctuations in sand fly numbers, which will be lowest during the coldest and/or driest seasons of the year . In tropical areas, some species are common all year, whereas others show marked changes related to wet and dry seasons. In temperate regions adult sand flies are only present during the summer. In addition, the various species of sand fly have different seasonal activity periods and daily peaks of biting activity. Adult sand flies are weak fliers, travelling with a characteristic short hopping flight, and usually disperse no more than a few hundred metres from their breeding sites. Most species fly horizontally near ground level. In temperate and arid regions, sand flies may overwinter as diapausing mature larvae .
Phlebotomus spp. occur predominantly in warm, humid and tropical climates, usually in savannah and semi-desert vegetation habitats, although a few species occur in temperate zones. They are able to colonise rural, peri-urban and urban areas. Sand flies require a humid microclimate in order for their eggs to develop and larvae need a cool, moist habitat with decaying debris. Adult sand flies often inhabit rock crevices, caves, and rodent burrows, and in peridomestic settings rest in cool, dark and humid corners of animal shelters or human dwellings [4,5]. Both rodent burrows and peridomestic areas provide ready access to bloodmeals in addition to shelter from the elements.
Female sand flies feed on a wide variety of vertebrate hosts, including humans, livestock, dogs, urban and wild rodents, reptiles, amphibians, and birds [2,5]. Each species of sand fly may have its own specific host preferences, although host availability is an important factor in determining blood feeding behaviour. It is likely that many species of sand fly are opportunistic and feed on animals to which they have easiest access, as the same species collected from different biotopes often display different feeding patterns . A study of sand fly species from farms and kennels in Italy found that Phlebotomus papatasi, Phlebotomus perniciosus and Phlebotomus perfiliewi fed primarily on the host species (livestock and humans) that were present at the collection site . If many different animals were present, both Phlebotomus perfiliewi and Phlebotomus perniciosus were found to feed on all of them , suggesting that choice of host is influenced by the presence and proportion of each host. As a result, it is likely that in urban and peri-urban settings humans and domestic dogs are the main targets for sand flies.
Public health (surveillance/control)
Surveillance of sand flies is important, as they are vectors of human and canine leishmaniasis, and sand fly fevers caused by phleboviruses. Further surveillance is required in order to determine the extremes of sand fly distribution in Europe and to provide data on the presence or absence of this vector in European countries where sand fly surveillance has not yet been carried out. Increased sharing of surveillance data through the VBORNET project will facilitate risk assessment and planning activities.
Appropriate sampling strategies
For initial surveillance studies, a combination of sampling methods is desirable in order to determine the presence and abundance of various sand fly species. Once the ecology and habits of the sand fly population are known, one or two sampling approaches can be chosen to suit the situation . A variety of sampling methods are available; the most commonly used are light traps to catch host-seeking females, and sticky traps and aspirator collection to catch resting flies. Emergence traps can be used to catch flies as they leave resting sites such as animal burrows. Animal-baited traps are another option useful for sampling host-seeking flies, and human landing catches represent a productive method for sampling anthropophilic species. Variation in climatic conditions such as temperature, humidity and wind speed can affect sampling success.
As with many disease vectors, control requires an integrated approach that utilises a number of different methods and is tailored to the local situation.
P phlebotomine sand flies are susceptible to insecticides, such as pyrethroids, and residual spraying of houses and animal shelters is an effective control strategy in peridomestic environments. Application of insecticides to outdoor resting sites (if known) can also be effective. Control of immature stages is difficult as the breeding sites of most species are unknown. Resistance to several insecticides has been reported in some sand fly species [26,2]
The use of protective clothing, insect repellents and insecticide-impregnated bed nets are effective in reducing human-sand fly contact.
M measures such as resurfacing walls to cover cracks and holes, demolition and removal of uninhabited buildings and removal of organic waste and unwanted vegetation can help to discourage sand fly breeding. Destruction of the habitat of reservoir hosts, such as rodents that enable sand fly populations to become established, is also an effective control method .
Where animals such as dogs and rodents act as reservoir hosts for disease, infected hosts can be culled in order to reduce disease transmission risk. Deltamethrin-impregnated dog collars are effective for preventing sand fly bites, and are a low-cost, more humane intervention. Spot-on and spray insecticide formulations can be applied to reduce biting .
Bacillus sphaericus have been shown to reduce survival and fecundity of phlebotomine sand flies [28,29] . This bacterium is applied to sugar solutions which can be used at sand fly habitats .
Key areas of uncertainty
The effects that climate change will have on the distribution of disease vectors are currently unknown . It is important to investigate the relationships between climate factors, geographical distribution of vectors and seasonal host activity .
The key issue is the lack of a complete picture of the current distribution of phlebotomine sand flies in Europe. It is essential that data on the presence/absence and abundance of these vectors across the continent are recorded, as well as delineating the extremes of each sand fly species’ range .
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