Isotopic composition and concentration of Pb in suspended particulate matter of the Irish Sea reveals distribution and sources.

The isotopic composition and concentration of Pb was measured in suspended particulate matter of the Irish Sea. Aerosol, surficial and pre-industrial sediment was also analysed to provide information on sources terms. Concentrations of Pb in suspended sediments were lower than previously reported which presumably reflects the international effort to reduce Pb inputs to the environment. Lead concentrations were highest in Liverpool Bay and lowest in the western Irish Sea. A significant negative relationship between Pb and salinity suggests that present inputs and the resuspension of relict lead associated with particles in areas significantly affected by freshwater discharges are the predominant sources of Pb to the Irish Sea. The isotopic composition of Pb in the stratified region of the western Irish Sea demonstrates that atmospheric sources are also significant to this region, which is consistent with current knowledge on the hydrography. Pb isotopic ratios show that water entering the Irish Sea through St George's Channel is significantly influenced by anthropogenic inputs prior to additional contamination by direct inputs to the Irish Sea.

The distribution and transport of Sellafield derived 137 Cs and 241 Am to western Irish Sea sediments.

Sellafield derived (137)Cs and (241)Am were analysed in surficial sediments at 23 sites in the western Irish Sea. Concentrations varied between 3-175 Bq (137)Cs/kg and 1-147 Bq (241)Am/kg. There are two distinct basins in the western Irish Sea separated by an area of restricted depth and this bathymetry is reflected in the radionuclide concentrations. Highest concentrations were found in the northerly samples and substantially lower concentrations further south. This pattern of distribution can be explained by the predominantly northerly residual flow and the existence of seasonal stratification in this area of weak tides. (137)Cs/(241)Am ratios were also highest in the northern basin, and it is suggested that this is caused by differences in the mechanisms of transport of the two elements. The direct physical migration of contaminated particles from the eastern Irish Sea is the dominant transport mechanism in the north of the study area, whereas transport in the dissolved phase is most important to the southern region. Concentrations of both elements were best correlated with the percentage <15 microm particulate fraction suggesting that particles within this range are most important for direct transport and scavenging from the soluble phase.

PAH contamination of western Irish Sea sediments.

Concentrations of the sum of 15 PAHs in 22 surficial sediment samples from the western Irish Sea ranged from below 100 ng g(-1) in sandy sediments to a maximum of 1422 ng g(-1) in the centre of the mud basin. The concentrations are typical of coastal shelf sediments, but greater than those observed for aquatic sediments remote from known anthropogenic sources. Organic C and the % sediment <15 microm were positively correlated with sigmaPAH. sigmaPAH was normalised to organic C and particle size (i.e. expressed as sigmaPAH/C(org) and sigmaPAH/% < 15 microm) and significant relationships were still observed with organic C and % < 15 microm. The results are discussed in the context of using organic C to normalise concentrations of PAHs to assess contamination levels in sediments.

Sources and geochemical constraints of polycyclic aromatic hydrocarbons (PAHs) in sediments and mussels of two Northern Irish Sea-loughs.

Polycyclic aromatic hydrocarbons (PAHs) were sampled from 30 sediment and 8 mussel (Mytilus edulis) stations in two Northern Irish Sea-toughs. Analysis was performed by gas chromatography coupled to mass spectrometry (GC-MS). Sedimentary organic carbon, % silt/clay and mean grain size were analysed in order to assess the role of geochemistry on PAH distribution. With the exception of two sites in Larne Lough representing localized regions of high contamination, sum(PAHs) in sediments ranged between 83 and 2300 ng g(-1). Regression analysis indicated that particle size and organic C were dominant factors in controlling the distribution of PAHs throughout the sediments. Sources of PAHs in both sea-loughs were dominated by pyrogenic inputs suggesting that diffuse sources such as atmospheric deposition may be a major source to both water bodies. The sum of PAHs in mussels ranged between 95 and 184 ng g(-1). Variations in concentrations may be explained by differences in the condition between mussel populations. Mussels in both sea-loughs exhibit similar metabolic activities towards the PAH compounds which were predominantly bioaccumulated from sediments.

A description and morphometric comparison of eggs of species of the Anopheles gambiae complex.

Eggs of the 6 named species of the Anopheles gambiae complex are described from scanning electron micrographs of specimens obtained from laboratory colonies or wild-caught females. Morphometric measurements of eggs from 5 sources of Anopheles arabiensis, 2 of Anopheles gambiae, one of Anopheles quadriannulatus, 2 of Anopheles bwambae, 2 of Anopheles merus, and one of Anopheles melas are compared, and relationships are analyzed by multivariate statistics. No morphologic characters were species-diagnostic, although tendencies of the saltwater species An. merus and An. melas to have wider decks and shorter floats were confirmed. Species and populations overlapped considerably in principal components and discriminant function analyses based on 10 attributes of eggs. Nevertheless, discriminant functions revealed similarities in eggs of species believed to be most closely related, namely, An. gambiae and An. arabiensis, An. merus and An. melas, and An. quadriannulatus and An. bwambae.

SEM examination of the eggs of five British Aedes species.

Ultrastructure descriptions are given of the eggs of five British Aedes species, namely Aedes (Aedes) cinereus Meigen, Aedes (Ochlerotatus) cantans (Meigen), Aedes (Ochlerotatus) punctor (Kirby), Aedes (Ochlerotatus) detritus (Haliday), and Aedes (Ochlerotatus) rusticus (Rossi). Eggs of the first 4 species are broadly cigar/boat-shaped, with those of Ae. cinereus being characteristically long and narrow, in contrast to the overall shape of Ae. rusticus, which is quite distinct, being in profile almost subtriangular with rounded corners, and is completely species-diagnostic. In Ae. cantans, Ae. punctor, and Ae. rusticus there is usually a single large tubercle in each chorionic cell and there is little, if any, difference in the sculpturing of the ventral and dorsal surfaces, whereas in Ae. detritus each cell contains more than 20 tubercles, and in Ae. cinereus there are usually 6 tubercles per cell ventrally, but dorsally there are no tubercles or distinct cells but numerous cone-shaped papillae. All 5 species can be separated from each other by SEM examination of their chorionic patterns.

Mosquito (Diptera: Culicidae) dispersal--the long and short of it.

A review is presented of all aspects of adult mosquito dispersal, encompassing transportation of mosquitoes by ships, airplanes and trains, long distance wind-assisted dispersal, and much shorter almost daily flights that mosquitoes make to locate mates, blood sources, nectar, oviposition sites, and resting sites. The many definitions and concepts of animal migration are debated, and instances of so-called mosquito migration, that is long distance wind-assisted flights, and the ecological advantages and disadvantages of such journeys are examined. It is concluded that there is little evidence that mosquitoes make purposeful long distance flights that can be classified zoologically as migration. It is argued that it is better to regard all mosquito flights as dispersal. Host orientation cues are not discussed, but the contentious idea of a memorized home range between feeding and oviposition sites is presented.

Resting behaviour, ecology and genetics of malaria vectors in large scale agricultural areas of Western Kenya.

In Kenya indoor and outdoor resting densities of Anopheles arabiensis and Anopheles funestus at the Ahero rice irrigation scheme, and Anopheles gambiae s.s., An. arabiensis and An. funestus at the Miwani sugar belt were assessed for 13 months by pyrethrum spray collections in houses and granaries. The vector's house leaving behaviour was evaluated with exit traps and it was noted that early exophily (i.e., deliberate) was not detected in any of the vectors. Assortative indoor/outdoor resting behaviour was studied by a capture-mark-release-recapture method and showed that in An. arabiensis both indoor and outdoor resting traits were present in the same individuals. Samples of half-gravid female An. gambiae s.l. were chromosomally identified either as Anopheles gambiae s.s. or An. arabiensis and in a subsample chromosomal inversions were read. Anopheles gambiae s.s. and An. arabiensis had the 2Rb inversion but in addition the 2La inversion was found in An. gambiae s.s. and this is an indication of low chromosomal variation. At Ahero An. arabiensis was most abundant when the rice crop was immature and An. funestus when the crop was mature. This succession of vectors facilitated the transmission of malaria throughout the year. At Miwani, An. gambiae s.l. population peaked during the long rains but the proportion of An. arabiensis was highest during the dry season. The indoor resting density of males of the three vector species was less than half of the females.

Resting habits of Anopheles arabiensis in the Awash river valley of Ethiopia.

The indoor- and outdoor-resting habits of Anopheles arabiensis were studied over 2 years in central Ethiopia. Pyrethrum-spray catches and outlet-window-trap collections were carried out in both DDT-sprayed village huts and unsprayed huts. Mosquitoes were also collected from pit shelters and natural outdoor-resting sites. Females were marked and released in order to investigate their daytime-resting sites in sprayed and unsprayed huts. The An. arabiensis population in the study area is partially (37.5%) exophilic, while those females resting indoors tend to avoid DDT-sprayed surfaces and thus their contact with the insecticide is minimized.

The relationship between female body size and survival rate of the malaria vector Anopheles arabiensis in Ethiopia.

The relationship between female mosquito body size and survival rate was studied in field populations of Anopheles arabiensis in the Awash valley, central Ethiopia. Body size was quantified by measuring the wing-length. Highly significant correlations were found between size, parousness and insemination. It was concluded that larger An.arabiensis females have a higher probability of survival, being inseminated and producing more egg batches than smaller adults. Implications for vectorial capacity and vector competence of mosquitoes are discussed.

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.

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.

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.

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.

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.

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.

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.