Various morphological characters of larvae of Aedes (Stg.) simpsoni complex collected from different localities in Uganda were studied in an attempt to characterise the species in the Ae. simpsoni complex. Morphometrics of larval characters revealed wide ranges of variation most of which separated or grouped populations. Multivariate discriminant analysis and principal component analysis discriminated between different populations. In some populations the males were fairly distinct from the females, while for some characters the populations overlapped considerably. The percent variability of each character alone is low and does not separate the species of the complex. However several characters correlated. Length of antennae (LANT), length of antennae up to Seta 1–4 (LANT4), length of head (LHEAD), and length of siphon up to position of Seta 1-S (LSIPHSET1S) showed fairly significant variability which could be used in conjunction with characters of pupae and adults to separate populations. In the wild we find anthropophilic and non-anthropophilic populations of the mosquitoes, especially in Colocasia plants, bananas (Musa sp.), Dracaenia and Ananas sp. The multivariate analysis carried out could not separate the populations into biting behaviour groups nor breeding habitat groups.

A simple method for storing mosquito bloodmeal samples, which permits extraction and detection of human DNA after polymerase chain reaction (PCR) amplification of target DNA sequences, was tested. Abdomens of bloodfed field-collected Anopheles gambiae s.l. and An. funestus mosquitoes (Diptera: Culicidae) were directly expressed onto filter paper, air-dried and stored at room temperature. DNA was extracted and amplified at human hypervariable loci TC11, VWA and D1S80. The amplified products were separated using polyacrylamide gel electrophoresis, visualised by silver staining, and results compared with those from mosquitoes that had been preserved in liquid nitrogen. DNA from blooded abdomens stored on dried filter papers could be amplified with greater than 95 % success for any locus, storage temperature, mosquito species or storage duration. Collection and drying of mosquito bloodmeals directly onto filter paper appears to be a more convenient method for sample transportation and storage than the conventional method involving cryopreservation.

Les effets de trois métaux lourds (Cu, Hg, Cd) sur le développement d'Anopheles hispaniola, vecteur potentiel du paludisme, de Culex pipiens et Culex hortensis ont été étudiés dans l'oued N'fis près de la station Agadir Tachraft, dans les bassins expérimentaux de traitement des eaux usées de Marrakech (Maroc) et dans un bassin d'élevage des grenouilles. Les effets varient selon l'espèce, en fonction du développement et selon la nature et la dose du métal. A. hispaniola au stade L4 se montre le plus sensible aux trois métaux Cu, Hg, Cd. La CL50 (24h) est respectivement de 3,78, 1,52 et 4,81 mg.L-1, plus faible que celle de C. hortensis (5,02 , 3,1 et 9,91 mg.L-1) et de C. pipiens (5,91, 4,43 et 17,48 mg.L-1). Par contre, la sensibilité au Cd ne diffère pas significativement chez A. hispaniola et C. hortensis au stade L2 selon le test de Newman - Keuls. Cette étude montre qu'A. hispaniola qui a un cycle de vie relativement court et qui est facile à élever au laboratoire, présente une sensibilité 2 fois plus élevée pour le Hg, 3,4 fois plus élevée pour le Cd et 8,6 fois plus importante pour le Cu que Aedes aegypti. Cette dernière est proposée comme espèce-test pour les mêmes propriétés pour étudier les effets biologiques des métaux lourds sur les insectes aquatiques.

A list of 88 nominal taxa of mosquito species (Diptera: Culicidae) originally described from Uganda is given. The list includes 68 valid species, 7 subspecies, 6 varieties, and 7 synonyms, within 10 tribes, 14 genera, and 13 subgenera. All 3 subfamilies of Culicidae (Anophelinae, Toxorhynchitinae, and Culicinae) are represented. The type localities of the different species are updated for quick identification based on the present political boundaries within Uganda. The species stages that are as yet not fully described in the literature, and those species whose breeding habitats are unknown are indicated.

Laboratory studies were conducted to assess the toxicity and growth-inhibitory activity against Aedes aegypti larvae, of the crude acetone extracts of Polygonum senegalense (Meissn.) leaves, its flavonoid component 2',6'-dihydroxy-4'-methoxydihydrochalcone and the internal tissue flavanol quercetin. The first two showed significantly high insecticidal and growth-inhibitory activity even at low concentrations, whereas quercetin was toxic only at concentrations above 7μg/ml.

One hundred forty-nine Anopheles gambicie s.l. and 260 A. funestus were collected from the field in Namawala, Tanzania in June 1994. The mosquitoes were dissected and examined for plasmodium oocysts using two microscopic techniques and the polymerase chain reaction (PCR) method. The oldest and simplest technique, the saline test, detected oocysts in 94 out of the 97 mosquitoes found to have oocysts by the more sensitive merbromin stain and PCR techniques. The saline test was found to be a sensitive and reliable field technique for detection of large Plasmodium oocysts in mosquitoes. The merbromin staining technique was as sensitive as PCR, detecting even small oocysts.

The stage-specific and age-specific survivorship of the immature stages of Anopheles gambiae Giles s. l. were studied in Baringo District Kenya, using vertical life-table methods.

Survivorship from first instar to adult emergence was 0.085, giving a mortality of 91.5% during the rainy season. However, survivorship dropped to zero (100% mortality) in the dry season.

Mortality was most severe in the first and second instars in all cases. Mean life expectancy increased significantly for larvae that survived beyond the first 3 days of life. Suspected predators of mosquito pre-imagines in the breeding sites were collected and counted. From their large numbers and diversity it was inferred that predation was probablyan important mortality factor.

Culex quinquefasciatus (Wiedemann) mosquitoes, which are refractory to Brugia pahangi (Buckley and Edeson) microfilariae, were fed simultaneously on Wuchereria bancrofti (Cobbold) and B. pahangi microfilariae. A selected stock of Aedes aegypti (L) which is susceptible to both of these filariae was used as a control. The exsheathment and migration rates of B. pahangi in C. quinquefasciatus increased significantly as compared to those of B. pahangi when given as a feed by itself. These two processes did not show any trend with time. On dissection, 12 and 14 days postinfection, 27% of C. quinquefasciatus were found to be infected with an average of two larvae per mosquito. Of the total number of larvae found 78% were W. bancrofti while 22% were B. pahangi.

Feeding C. quinquefasciatus on in vitro exsheathed B. pahangi microfilariae suspended in serum did not increase the rate of migration, whereas 71–100% of Ae. aegypti became infected with a mean of 3.5 larvae per mosquito.

Inoculation of C. quinquefasciatus mosquitoes into the thorax and abdomen with exsheathed B. pahangi did not increase their infection rate, whereas in Ae. aegypti 67–82% became infected.

The behavioural process by which a mosquito finds a potential host organism is mediated by olfactory receptors on the insect's antennae. Lactic acid (LA) is a host-related odour common to all potential hosts. On the antennae of the female are two LA-sensitive neurons; one of these is excited by LA but the other is inhibited by LA. Furthermore, the sensitivity of the LA-excited neuron is correlated 1:1 with the presence of host-seeking behaviour such that when host-seeking behaviour is inhibited following a blood meal, the sensitivity of the LA-excited neuron is markedly decreased. The inhibition of host-seeking behaviour and the decrease in LA-sensitivity are induced by a hemolymph-borne factor released during oocyte maturation. The source of this factor is the fat body of blood-fed females, which requires a vitellogenic ovary for its production and/or release. The combined activity of the two types of LA-sensitive neurons together with the shift in sensitivity of the LA-excited neuron from a range where host levels of LA are present to a range exceeding LA levels expected from a host are sufficient to account for the inhibition of host-seeking behaviour following a blood meal.

Reasons for dissatisfaction with insecticidal control of disease vectors include their presumed harmfulness to non-target organisms, their cost and difficulties of organizing effective spraying programmes and physiological and behavioural resistance in vector populations. The validity of these objections and possible ways of resolving them are discussed. The importance of assessing the actual field impact of cases where resistance has been detected with laboratory tests is stressed. With regard to behavioural resistance, some data are presented on tests for genetic variation in the tendency of mosquitoes to rest outdoors and hence to avoid contact with sprayed walls. Most of the failures of insecticidal control of vectors can be attributed, not to problems of resistance, but to organizational difficulties. The impregnation of mosquito bed nets with pyrethroids, which householders can do for themselves, is therefore being field tested in several parts of the world. Such impregnation makes nets effective even when they are torn. This method will probably be particularly advantageous against mosquitoes which enter houses to feed, but do not rest on walls.

Abdomen homogenates of refractory C. quinquefasciatus and Anopheles stephensi prepared from equal and varying wet weights of abdomen, were shown to inhibit endopeptidase induced in vitro exsheathment of Brugia pahangi microfilariae. This inhibitory effect was removed by heat treatment and centrifugation of the homogenates. Abdomen homogenate from susceptible Aedes aegypti did not inhibit exsheathment. This suggested the presence of some inhibitory factor in the abdomens of the two insusceptible species of C. quinquefasciatus and An. stephensi. There was no evidence of this inhibitory effect in the midgut homogenates of the three mosquito species. Foetal calf serum and bovine serum albumin also inhibited endopeptidase induced exsheathment of B. pahangi microfllariae, suggesting that the protein concentration of the proteinaceous substances also determined the extent of inhibition. In the absence of endopeptidase, incubation in midgut homogenate of the 3 species of mosquito did not initiate exsheathment, suggesting that the conditions present in vitro did not simulate those persisting in the mosquito midgut in vivo.

Brugia pahangi microfilariae obtained from peritoneal washings of jirds (Meriones unguiculatus) were incubated with midgut tissue of Culex quinquefasciatus and Aedes aegypti (susceptible stock), in the presence or absence of blood and also in thoracic tissue and salivary glands in various media. Exsheathment took place in the presence of midgut tissue with or without blood and in thoracic tissue, but not in the presence of salivary glands.

Percentage exsheathment was variable and not reproducible for each type of tissue. Exsheathment also occurred in the presence of mosquito cells in suspension and in monolayers. In the latter, percentage exsheathment in some cases was higher than that observed in vivo in the midgut of C. quinquefasciatus, which is refractory to B. pahangi microfilariae.

Entomological investigations in Dubai showed that, irrespective of whether they had been fed on water or 10% sugar solution, about 47% of Aedes caspius females matured eggs autogenously during their first ovarian cycle. Several blood-fed females were trapped in cages, and precipitin tests showed that some had fed on birds and camels as well as man.

Absence of autogeny combined with an examination of male terminalia showed that adults of the Culex pipiens complex were in fact Culex quinquefasciatus. The population was unusual because females were not inseminated when kept in cages, and appeared only weakly anthropophagie. CDC light traps and out of door resting cages proved useful in sampling adults. Precipitin tests showed 31.7% to have fed on birds, 7.9% on camels and only 3.2% on humans.

The number of eggs matured by Ae. caspius and Cx. quinquefasciatus were determined, and studies were made on the hatching pattern of Ae. caspius eggs. Larval habitats of Ae. caspius were unusual in having high concentrations of calcium chloride. Breeding places of Cx. quinquefasciatus comprised very polluted waters. Collections of the immature stages allowed the construction of stage-specific age-frequency histograms for both species, and survivorship curves to be plotted.