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M W Service

Publications and source records attributed to M W Service.

At least 19 recordsLinked to original sources
PubMed1995

Differential lipid reserves influence host-seeking behaviour in the mosquitoes Aedes cantans and Aedes punctor.

Lipid reserves of bait-caught female Ae.cantans and Ae.punctor mosquitoes (Diptera: Culicidae) were significantly higher than in teneral females. Female Ae.cantans given access to 10% w/v sucrose solution post-emergence showed an ability to synthesize lipid and, after 192 h, they were willing to take a bloodmeal from a human volunteer. At this point, mean lipid reserves were not significantly different from mean lipid reserves of bait-caught females. Prior to 192h, females would not take a bloodmeal and lipid reserves were significantly lower than in bait-caught females. Female Ae.punctor given access to 10% w/v sucrose solution post-emergence also showed an ability to synthesize lipid. Females of this species were willing to feed from a human host after only 48 h, at which point lipid content was not significantly different from that in bait-caught females. The level of lipid reserves in females coming to bait differs significantly between species: Ae.cantans has lipid reserves approximately double those of Ae.punctor. In addition, Ae.punctor is able to synthesize lipid to a level comparable with that found in bait-caught females after only 24 h, whilst it takes 192 h for Ae.cantans females to synthesize the amount of lipid found in host-seeking females, when allowed free access to sugar. Physiological differences in lipid synthesis and the level of lipid reserves required may therefore explain the differences observed between the species in the time taken to initiate host seeking.

Aedes↗
PubMed1995

Can we control mosquitoes without pesticides? A summary.

Up to now insecticides have remained the main tool for both killing mosquitoes and controlling mosquito-borne diseases, but perhaps we should broaden our horizons by looking at the effectiveness of traps in controlling tsetse flies. The problem is that we have not developed any really efficient mosquito traps, and of course population densities and reproduction rates of mosquitoes are far greater than those of tsetses. To interrupt disease transmission we do not need to eradicate vectors, but must reduce their populations to a critical threshold (breakpoint). Despite much enthusiasm, true biological control agents have not generally proved very effective, especially against floodwater species. Insect growth regulators and insect repellents have their uses but they do not provide any panacea for control. Understanding the ecology of mosquitoes is usually of paramount importance in developing control programs, especially those employing biological agents. We need, for example, to understand the intricacies of density-dependent population regulation, and computer modeling can help us to do this, as well as assist in identifying the most efficient control strategies. We need to promote noninsecticidal control of mosquitoes, but until we have developed more efficient methods, there will continue to be reliance on chemical control.

Animals↗
PubMed1995

Vectorial capacity and entomological inoculation rates of Anopheles gambiae in a high rainfall forested area of southern Sierra Leone.

We report the first study of gonotrophic cycle duration, survival rates, pre-gravid rates, vectorial capacity and chromosomal polymorphism of Anopheles gambiae s.s. in Sierra Leone. In the village of Bayama in the Southern Province, An. gambiae was the only species found to be naturally infected with Plasmodium falciparum and it constituted 99.7% of 22,541 anopheline mosquitoes caught. Chromosomal studies revealed only An. gambiae s.s. out of 66 females examined for chromosomal polymorphism, 61 (92.4%) had the 2LA inversion in the standard arrangement. Other inversions observed in low frequencies included 2Rcu and 2Ru. We estimated a gonotrophic cycle length of three days and survival rate per gonotrophic cycle of 0.59 for this species. The mean daily survival rate of An. gambiae was 0.85 and the entomological inoculation rate was 1,235 infective bites/person/year. Blood-meal ELISA tests showed that the species was very anthropophagic and that there were an estimated 35.4 daily inoculations per infective case. The epidemiological significance of these entomological parameters is discussed in the light of parasitological results for nearby villages.

Animals↗
PubMed1994

Origin of blood meals in indoor and outdoor resting malaria vectors in western Kenya.

Blood meals were obtained from indoor and outdoor resting malaria vectors in three villages of western Kenya and tested by sandwich ELISA to determine host preferences and their human blood index (HBI). Anopheles gambiae s.s. collected indoors at Kisian village had a HBI of 0.97 while that of Anopheles arabiensis collected at Ahero was 0.23. However, the HBI of A. arabiensis varied depending on the availability of outdoor resting shelters. Most female A. arabiensis (98.9%) collected outdoors in granaries at Ahero had fed on cattle. Indoor-collected female Anopheles funestus had mainly fed on people (93.0%), but taken at least some of their blood (20.2%) from cattle. Although small numbers of A. arabiensis fed on sheep or goats and birds, none of the female A. gambiae s.s. and A. funestus tested had fed on these hosts. The absence of human-fed A. arabiensis in outdoor shelters indicated that exiting after feeding, a behaviour pattern that mitigates indoor insecticidal spraying, is not prevalent in this species in western Kenya.

Animals↗
PubMed1994

Malaria in a rural area of Sierra Leone. III. Vector ecology and disease transmission.

Studies were undertaken on the role of Anopheles gambiae and An. funestus in the transmission of malaria in four villages in a high-rainfall, forested area in the Bo district of southern Sierra Leone. Anopheles gambiae s.s., identified chromosomally as the Forest form, was the most important vector, with a mean annual sporozoite rate, based on ELISA, of 7.4%. Anopheles funestus, which was found in considerably lower numbers, was mainly a dry season vector, with an annual sporozoite rate of 11.4%. Despite these relatively high sporozoite rates, vector populations were at a low level, with approximate mean densities of only 1.0 An. gambiae and 0.1 An. funestus resting females per house room, and average biting rates of just 1.1 and 0.1 bites/person/night by these two species, respectively. In the rainy season, biting rates peaked at 9.5 An. gambiae bites/person/night and 1.0 An. funestus bites/person/night. Annual sporozoite inoculation rates by An. gambiae and An. funestus were 0.088 and 0.007 infective bites/person/night, respectively. ELISA showed that both species were highly anthropophagic. Exit-trap collections and outdoors searches showed that An. gambiae exhibited a considerable degree of exophily. Light traps inside houses caught nine anopheline species, whereas pyrethrum spray collections in houses caught only An. gambiae, An. funestus and An. hancocki.

Animals↗
PubMed1994

Size variation and reproductive success in the mosquito Aedes cantans.

A link between density-dependent larval competition and adult size of the mosquito Aedes cantans was demonstrated in northern England. Ponds containing high larval densities produced smaller larvae which, in turn, resulted in smaller adults at emergence. In both 1989 and 1990, parous mosquitoes caught at human bait were larger than nulliparous ones, suggesting that larger mosquitoes are more successful at host location and egg-laying and also that they may be longer lived. Larger mosquitoes produced larger egg clutches than smaller females: however, there was no difference in the size of eggs laid by large and small females.

Aedes↗
PubMed1994

Host finding, feeding patterns and evidence for a memorized home range of the mosquito Aedes cantans.

ELISA tests of Aedes cantans bloodmeals in woodland near Liverpool during 1989 and 1990, revealed preferences for sheep and cows, these hosts representing more than 60% of the total. Dispersal studies carried out on newly-emerged adults and those caught at human bait, indicated that individuals move freely between the two woods studied, mixing as a single population. Mean recapture rates for mosquitoes marked with paint were 2.28% in 1989 and 6.3% in 1990. Recapture rates for mosquitoes marked with powder were 3.66% in 1989 and 6.25% in 1990. The patterns of dispersal of adult females suggest that Aedes cantans has a learned and memorized familiar area map and possesses a sense of location.

Aedes↗
PubMed1993

Community participation in vector-borne disease control.

Because vertical approaches, such as insecticidal house-spraying, to vector control problems have not been very successful in many instances in reducing the incidence of diseases such as malaria and Chagas, combined with the fact that there have been resurgences of some diseases, greater attention has been focused on 'bottom-up'-type control strategies. However, many attempts to actively involve the community in reducing its risks of becoming ill have met with failure. It has usually proved difficult to motivate communities into action, but there have been some successes, although it is generally too early to know whether such successes can be sustained. Apart from greater efforts to educate communities to disease risks and disease prevention methods, sociologists and anthropologists argue that we need to listen more to the people and pay greater attention to their beliefs and customs. The present paper discusses the problems of introducing self-help methods to minimize vector-borne disease transmission, and reviews the successes and failures of this approach.

Animals↗
PubMed1993

Plasmodium falciparum sporozoite and entomological inoculation rates at the Ahero rice irrigation scheme and the Miwani sugar-belt in western Kenya.

Anopheles arabiensis and An. funestus were collected by pyrethrum spray sheet collections in houses and by human-bait catches at a village in western Kenya adjacent to the Ahero rice irrigation scheme; and using the same methods, An. gambiae s.l. and An. funestus were collected at Miwani, a village in the sugar-cane belt. Plasmodium falciparum sporozoite rates were determined by ELISA. At Ahero the mean sporozoite rates were 1.1% and 4.3% in An. arabiensis and An. funestus, respectively, while at Miwani the rates were 6.0% in An. gambiae s.l. and 4.3% in An. funestus. Entomolgoical inoculation rates (EIR) were derived from both human-bait collections (IR-HBC) and by the proportion of human blood-fed females caught resting indoors (IR-HBF). The IR-HBF appeared to be a more realistic index of EIR. At Ahero and Miwani people were exposed to an average of 416 and 91 infective bites/person/year, respectively. The main vectors were An. funestus at Ahero and An. gambiae s.l. at Miwani. In view of the intense and perennial malaria transmission at Ahero, vector control by insecticides should be considered, while at Miwani, where transmission is seasonal, permethrin-impregnated bed nets could be an alternative to indoor spraying. These measures must be augmented with availability of effective antimalarials.

Animals↗
PubMed1993

Field testing an enzyme-linked synthetic oligonucleotide probe for identification of Anopheles gambiae s.s. and An. arabiensis.

Tests were carried out in Kenya to determine whether the enzyme-linked synthetic oligonucleotide probe (pAna 1) developed for identifying species of the Anopheles gambiae complex could be used under field conditions. The An. arabiensis male-specific pAna 1 probe was able to identify all male larval instars and adult males. However, the non-radioactive assay was not sufficiently sensitive to identify male sperm DNA in all the mated female An. arabiensis. Although the ratio of An. arabiensis to An. gambiae s.s. identified with pAna 1 in males during the dry season was in agreement with the ratio in half-gravid females identified cytogenetically, the ratios were different during the wet season. This study demonstrates that the enzyme-linked DNA probe assay is applicable under field conditions.

Alkaline Phosphatase↗
PubMed1993

The ecology and behaviour of the forest form of Anopheles gambiae s.s.

Studies on the ecology of Anopheles gambiae s.s. and the transmission of malaria were undertaken in a high rainfall forested area in southern Sierra Leone. Anopheles gambiae s.s., identified by chromosomal techniques as the Forest form, was the only malaria vector in the study village. Surprisingly, rice fields or swamps were not favoured breeding places for this species; breeding mainly occurred in temporary pools. The mean annual sporozoite rate of An. gambiae s.s. determined by ELISA was 3.9%. Pyrethrum spray, human bait, and exit trap collections, as well as identification of mosquito blood-meals using the ELISA method, showed that the forest chromosomal form of An. gambiae s.s. was highly anthropophagic and exophilic.

Animals↗
PubMed1992

Importance of ecology in Aedes aegypti control.

Aedes aegypti is one of the world's most widely distributed mosquitos and is of considerable medical importance as a vector of dengue and yellow fever. Not surprisingly therefore there has been more written on its biology than any other mosquito. The present paper summarizes ecological studies undertaken on this vector, including those on pre-adult mortalities, life-tables, adult dispersal and survival rates. In discussing surveillance techniques it is pointed out there are still no reliable methods for monitoring adult populations. The importance of the resting habits of adults and house construction in insecticidal control of Ae. aegypti is discussed. The question is, have ecological studies and population modeling resulted in any more understanding of the epidemiology of dengue, or helped formulate better control strategies? The answer seems to be not usually, possible because there have actually been relatively few good ecological studies on Ae. aegypti. Although mathematical modeling indicates that better control might be achieved if it were directed at the larvae, not adults, this has not usually been taken into consideration by those engaged in control. There is clearly need for greater collaboration between those practicing control, and ecologists and modelers.

Aedes↗
PubMed1991

Agricultural development and arthropod-borne diseases: a review.

A review is presented of the interrelationships between arthropod vectors, the diseases they transmit and agricultural development. Particular attention is given to the effects of deforestation, livestock development and irrigation on the abundance of vectors and changing patterns of diseases such as malaria, trypanosomiasis, leishmaniasis, Chagas' and some arboviral infections. The question as whether keeping livestock diverts biting away from people and reduces diseases such as malaria--that is zooprophylaxis, or whether the presence of cattle actually increases biting populations is discussed.

Agriculture↗
PubMed1984

The effect of domestic detergents on the population dynamics of the immature stages of two competitor mosquitoes, Culex cinereus Theobald and Culex quinquefasciatus Say (Diptera, Culicidae) in Kenya.

In some rural areas of Kenya pit latrines are the most important breeding places of Culex quinquefasciatus, but this vector is often rapidly displaced by a competitor, Culex cinereus, which then breeds prolifically in the latrines. In urban settlements, however, cesspools are the main breeding sites of C. quinquefasciatus and no such species replacement occurs. These latter habitats contain water contaminated with domestic detergents. When detergents were introduced into a pit latrine colonized only by C. cinereus this mosquito was eliminated after about 3 weeks. When both species were reared in water containing detergents C. cinereus had lower pupal yields than C. quinquefasciatus. In two pit latrines where C. cinereus normally displaced C. quinquefasciatus, the addition of detergent prevented this, and after their coexistence for a few weeks, C. cinereus eventually disappeared. These observations suggest that during the last few decades domestic detergents, together with other pollutants such as insecticides, may have contributed to the elimination of competitors, such as C. cinereus, from C. quinquefasciatus breeding sites.

Animals↗
PubMed1983

Value of cuticular and internal hydrocarbons for the identification of larvae of Anopheles gambiae Giles, Anopheles arabiensis Patton and Anopheles melas Theobald.

Gas chromatographic profiles of the cuticular and internal lipids extracted from 4th-instar larvae of the Anopheles gambiae complex have shown quantitative differences in their chain length distributions. For example, hydrocarbons extracted with 95% ethanol showed relative differences in peak heights eluting at Kovat indices (KI's) 2840 (An. gambiae 1.21, An. arabiensis 1.39 and An. melas 1.14) and 3150 (An. gambiae 6.73, An. arabiensis 13.40 and An. melas 13.50). However, while using the non-hydrocarbon fractions, differences were obtained at a KI of 2160 (An. gambiae 0.45, An. arabiensis 0.45 and An. melas 1.16) and at a KI of 2430 (An. gambiae 2.90, An. arabiensis 1.81 and An. melas 3.50). Utilizing the total ethanol extract and omitting the TLC (thin layer chromatography) step, thus saving four hours of analysis time, good separation was achieved at a KI of 2060 (An. gambiae 0.60, An. arabiensis and An. melas 0.0) and at a KI of 2430 (An. gambiae 1.13, An. arabiensis 0.69 and An. melas 1.59). Other differences were also noted in the profiles which could identify one or more of the three species. Good separation could be made on single larvae as well as on small batches of specimens. It was concluded that analysis of cuticular and internal lipids provides a useful biochemical method of distinguishing larvae of these species, but further studies are needed on these and other species of the An. gambiae complex collected from many localities in Africa.

Animals↗