Circadian activity rhythm of blood-sucking midges (Diptera simuliidae) in different natural and climatic subzones of the South of Tyumen Region


O.A. Fiodorova*

Blood-sucking midges of the family Simuliidae - small two-winged insects belonging to the suborder nematocerans (Diptera: Nematocera). Midges are one of the most important components of blood-sucking Diptera of the gnats' complex. Simuliidae are widespread in all landscape and geographical zones of the Russian Federation, and in foreign countries the ecology has been poorly studied so far, but great attention is being paid to the study of human disease vectors. The aim of the study was to study the circadian activity rhythm of blood-sucking midges (Diptera Simuliidae) in different natural and climatic subzones of the South of Tyumen Region. The censuses of blood-sucking midges was performed by standard methods. The circadian activity rhythm of blood-sucking midges (Diptera Simuliidae) depends on the species composition, attack, weather features, climatic conditions. In all landscape and climatic zones of the region under study, blood-sucking midges have two population numbers increase. Midges are diurnal fliers, they are not active at night. According to V.P. Chernyshev's (1996) circadian activity types, midges are only active at certain time of day, remain active for a long period of time and their activity is associated with transitional conditions. That is, the circadian activity of midges is of morning-evening-type. Registrations conducted in the open area and in the forest, showed a different pattern in their ratio. The fact of alternating population numbers increase of blood-sucking midges activity in the subzones in the evening from 18 to 23 o'clock and in the morning has been established. The midges flight begins from 5 to 9 o'clock. Midges fly and attack, under favourable conditions, around the clock, with two distinct increase in activity - in the mornings and evenings. The midges are less active during the day and at night. The decrease in activity during the day is caused by a strong wind (above 3 m/sec., with gusts of up to 8 m/sec.), high illuminance (45000 lux), rarely high temperatures. At night, the limiting factor is the low temperature (6-7 °C). In addition, the circadian activity of midges depends on the biological characteristics of species. For example, the most photophilous species in our studies was B. maculatus, and Sch. pusilla and р. Simulium midges are timed to the morning and evening time. The species diversity in the open area and under the forest canopy is the same. During the period of maximum activity, which is in the mornings and evenings, the highest activity of midges is seen in the open area. Mass species in both stations is Byssodon maculatus. Currently, the studies of the midges fauna is relevant. Owing to global warming, scientists are assuming that the most flexible species of blood-sucking arthropods can move to the Northern regions, which will have a direct impact on the epidemiology and epizootiology of vector-borne diseases.

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