E. B. Vinogradova

The discovery of a hybrid population of mosquitoes of the Culex pipiens L. complex (Diptera, Culicidae) on the Kos Island (Greece) by means of molecular markers

The mosquitoes attacking humans in hotel rooms on the Kos Island (Greece) were identified by means of several molecular markers and proved to be hybrids of Culex pipiens and C. quinquefasciatus. The former species is a typical local inhabitant, whereas the latter was probably introduced with some transport from a more southern region. The mosquitoes were anthropophilic, and their bites induced strong lasting allergic dermal reaction.

Effect of food and temperature on the reproduction of the blowfly, Calliphora vicina R.-D. (Diptera, Calliphoridae), a popular model object in biological research

Egg maturation in Calliphora vicina is known to occur within a wide range of temperatures, from 12°C to nearly 30°C (Vinogradova, 1991). Photoperiodism has no effect on this process. Some females enter diapause already at 20°C; their fraction increases at lower temperatures and reaches 100% at 6°C. Reproducing females with eggs can survive for a long time and even lay eggs at low temperatures (4–5°C). Experiments with C. vicina from Leningrad Province revealed some effects of the diet (liver or fish) and temperature on the fly reproduction. At 20 and 25°C, 7–10-day old females begin to oviposit, but at 20°C egg maturation is observed in 98% of females feeding on liver and in only 5% of females feeding on fish. On the liver diet, the mean daily fecundity is significantly correlated with the day of oviposition but not with the temperature. At 20°C a significant correlation is observed between the mean daily fecundity and both the day of oviposition and food. The total number of eggs laid by flies after feeding on fish is half that produced after feeding on liver. The optimal conditions for Calliphora vicina cultivation are a 16-h light day, temperatures within the range from 20 to 25°C, and liver as food.

The sex structure of the larval populations of the urban mosquito Culex pipiens pipiens f. molestus Forskal (Diptera, Culicidae) in St. Petersburg

The study of sex ratio in larval populations in the urban mosquito Culex pipiens pipiens f. molestus inhabiting underground sites in St. Petersburg was carried out for the first time in 1997–2001, as part of monitoring of local populations of this mosquito in order to estimate its reproductive potential. Samples of the immature stages were regularly collected in the underground breeding places flooded with water with a varying degree of pollution in five city districts (altogether 27 samples, 14 251 larvae). Pupation was observed under laboratory conditions at 20°C for 6–46 days. The sex was determined at the pupal stage. In 19 samples collected in basements of dwelling houses the incidence of males widely varied from 40.2 to 65.6%, and the sex ratio (males: females), from 0.7: 1 to 1.9: 1. Medians defining the percentage of males in the populations in different basements during a certain period (from 3 to 11 months) were 57.5%, 47.0%, and 50.2%. The greatest incidence of males (the median being 62.2%) and sex ratio from 1.1: 1 to 3: 1 was observed in autumn in 1999–2001 in populations inhabiting the sewer pipe. Analysis of all the 27 samples showed that the males constituted on the average 54.5%, i.e., that is the sex ratio was close to the normal value of 1: 1. Such important population characteristics as normal sex ratio at the pupal stage and the high autogeny rate are indicative of high reproductive potential of the urban mosquito in St. Petersburg. The hydrotechnical (mostly drainage of basements) and special mosquito control measures are needed to decrease mosquito abundance and restrict their further dispersal within the city.

Variability of quantitative morphological traits of mosquito larvae in some species of the Culex pipiens complex (Diptera, Culicidae)

The variability of 13 larval morphological characteristics in the urban mosquito, Culex pipiens f. molestus and Culex torrentium, was investigated. These species, belonging to the Culex pipiens complex, are characterized by rapid ecological and evolutionary processes following the human-induced environmental changes. A comparison of 4 geographical larval populations of C. pipiens f. molestus and Culex torrentium revealed different rates of divergence of different morphological traits. In the older form in terms of evolutionary development, C. torrentium, the two local populations differed in the structures of the trophic morphological complex characterized by a higher functional trophic load, while the structures with a lower functional load did not differ between the populations. On the contrary, the populations of the younger form, C. pipiens f. molestus, which had recently colonized new urban sites, differed in the structures with a low functional trophic load (some structures of siphon and abdominal segment IX), whereas structures of the trophic morphological complex were similar in different populations. The possible mechanisms of these morphological transformations and their role in the evolution of mosquito larvae are discussed.

The rate of preimaginal development of the blowfly, Calliphora vicina R.-D. (Diptera, Calliphoridae) under field and laboratory conditions

Open field experiments with the blowfly, Calliphora vicina originating from the environs of St. Petersburg showed that the correlation between the rate of its preimaginal development under the natural conditions and the mean daily temperature could be very closely approximated by linear regression. The sum of effective temperatures required for development from the egg to the puparium constituted ca 140 degree-days and from the egg to the adult, ca 320 degree-days with the lower thresholds of 5.8 and 4.8°C, respectively. The minimum duration of development (6–8 days from the egg to the puparium and 16–20 days from the egg to the adult) was recorded during the period of the highest mean temperatures (22–23°C) from July 8 to August 15 of 2010 and 2011. The rate of development under natural thermorhythms was not siggnificantly different from that under the laboratory conditions at constant temperatures from 12 to 23°C.

Ecological prerequisites for spread of bloodsucking mosquitoes

The spread of mosquitoes beyond the initial ranges and the ecological prerequisites for colonization of new territories are considered for several mosquito species which are active bloodsuckers and vectors of many disease agents. The invasion of homodynamic Aedes aegypti from Africa into the tropical zone of several continents has probably occurred during the last 400 years by means of transportation of the eggs and larvae mainly by sea ships. In the new areas mosquitoes occupied breeding places similar to those in their native ranges. On the contrary, the urban mosquito Culex pipiens f. molestus, introduced from the subtropical areas of Africa into Europe and other continents in the XX century, found a new type of habitat: underground constructions with polluted water where the mosquito develops the year round. This was preconditioned by such specific biological features as autogeny, stenogamy, and homodynamy (seasonal development without diapause). Aedes albopictus originated from Southeast Asia and invaded four continents (Europe, North and South America, and Africa) in 1980–2000 owing to its high capacity of adaptation to various climatic conditions (high viability of eggs, variation in the ability for diapause and mechanisms of diapause control between the strains, etc.). The eggs and larvae of this mosquito were transported by sea in used car tires. The models predicting the distribution of invasive species and the ways of their spread (by sea, air, motor transport) are discussed.

Monitoring of local populations of the urban mosquito Culex pipiens pipiens f. molestus Forsk. (Diptera, Culicidae) in St. Petersburg

Monitoring of local populations of the urban mosquito Culex pipiens pipiens f. molestus was carried out in St. Petersburg (Russia) in 1999–2006 for the first time. It included the estimation of the autogeny rate, mean fecundity and wing length of females, sex ratio, and siphonal index of the larvae. The mosquitoes were found in 27 out of the 39 examined basements of dwelling houses in five city districts. The perennial populations can exist only in heated basements flooded with sewage or mixed waters with high level of organic pollution and temperature between 10 and 34°C. Most of the local populations are characterized by high autogeny rate: 80–100% of females lay the first egg batch without blood-feeding, ensuring a long-term existence of autonomous local populations. The mean wing length and mean fecundity varied both between and within local populations, ranging from 3.1 to 5.4 mm and from 32.9 to 105.7 eggs per female, respectively. A significant positive correlation was revealed between autogeny rate and fecundity, on the one hand, and the wing length of females, on the other hand. The latter, in its turn, is affected by the temperature and pollution of basement waters during the larval development. Monitoring of the local populations of the urban mosquito in St. Petersburg has shown them to possess high reproductive potentials, a normal sex ratio, and no infections. The sanitary, hydrotechnical (first of all drainage of basements) and mosquito control measures are necessary in order to reduce mosquito abundance and prevent their further dispersal in the city.

Seasonal development of the blowfly Caliphora vicina R.-D. (Diptera, Calliphoridae) in the environs of St. Petersburg

Four-year monitoring of phenology of the blowfly Caliphora vicina under quasi-natural conditions in the environs of St. Petersburg demonstrated development of two complete generations and overwintering of the third generation. The duration of preimaginal development (from egg laying to adult emergence) of the 1st and 2nd generations varied from 19 to 32 days; the required sum of effective temperatures (SET) was 326 ± 31 degree-days with a threshold of 5°С. Reproductive maturation of females (the period of time from adult emergence to laying of the first eggs) lasted from 15 to 31 days (SET was 262 ± 39 degree-days with a threshold of 5°С). The duration of development of one complete generation (from egg stage to the beginning of oviposition) during the period of observation varied from 34 to 57 days (SET was about 600 degree-days with a threshold of 5°С). The first diapausing larvae hatched from the eggs laid in the middle of August. In September, at shorter day lengths and at a temperature of 10–11°С, 80–100% of the larvae entered diapause. A small fraction of the larvae of the 1st and 2nd generation and most of the larvae of the 3rd generation overwintered. Successful overwintering of adults in the environs of St. Petersburg is hardly possible.

A study of the mosquito Culex pipiens (Diptera, Culicidae) population structure in the transcaucasia using molecular identification methods

The mosquito species Culex pipiens consists of two forms, or ecotypes: the typical pipiens form and the molestus form. These forms are similar morphologically but have significant ecophysiological differences. The Cx. pipiens population structure was studied in open and underground habitats (house basements) in several localities in Abkhazia, Georgia, and Azerbaijan. The pipiens and molestus forms were identified by a molecular method, namely by restriction analysis of the amplification products with HaeIII endonuclease. Altogether, 90 individuals from 10 local populations were studied. The pipiens form was found only in surface water bodies (8 cases); in two cases both forms were found in one habitat. Homogeneous molestus populations were recorded in two underground habitats. Analysis of the Cx. pipiens population structure by the molecular method agrees with the results of biological and ecological studies of this mosquito in Georgia by Sh. Sichinava (1974, 1978, 1989). Thus, molecular diagnostics of intraspecific forms in Cx. pipiens populations is doubtlessly reliable.

Some principles of selecting natural material for rearing and the endogenous processes in laboratory strains of the blowfly Calliphora vicina R.-D. (Diptera, Calliphoridae)

The ability to enter reproductive and larval diapauses should be taken into account when natural populations of the blowfly Calliphora vicina are selected for laboratory rearing. The reproductive diapause occurring at 20–25° in some females retards their maturation and decreases the reproductive activity of the laboratory strain. On the other hand, diapausing females conditioned by low temperature may be used for temporary conservation of the strain. However, keeping the diapausing larvae is the most reliable way of storage. The endogenous variation of the incidence of larval (from 0 to 100%) and reproductive (from 0 to 55%) diapauses was observed in successive generations of several laboratory strains developing under constant photoperiodic and temperature conditions. The significance of such endogenous processes for interpretation of experimental data is discussed. For over 20 years of laboratory breeding of C. vicina, cases of strain depression were observed, when the number of the egg rafts decreased and then oviposition ceased, abnormal puparia appeared, the flies hardly emerged, etc. Such depressed strains may be revived by changing the photoperiodic regime.