Mansonia Uniformis Research Articles

The succession of mosquito species (Diptera, Culicidae) in rice fields in the Kisumu area of Kenya, and their possible control

AbstractThirty-five species of mosquitoes (10 782 adults) were caught in modified CDC light-traps during the 27-week rice cultivation cycle at Ahero, Kenya, in the period September 1972 to March 1973. Only 0·8% were blood-fed and 5·1% gravid, indicating that the traps were sampling newly emerged adults. During weeks 1–7, before rice seedlings were transplanted, catches were small, but increased markedly from then until harvest (week 20). Two groups of mosquito species were recognised: the first, including Mansonia uniformis (Theo.), M. africana (Theo.) and Mimomyia splendens Theo., bred throughout the rice cycle; the second, including Anopheles gambiae s.l., A. pharoensis Theo., A. ziemanni Grünb., Culex poicilipes (Theo.) and C. antennatus (Becker), were affected by water depth and height of the rice crop. The slurry of shallow muddy pools which follows transplanting stimulated intense breeding of A. gambiae and A. pharoensis. Once the young plants were established, reflooding of the fields and subsequent growth of water plants and algae favoured the breeding of A. ziemanni and C. poicilipes. Towards the end of the rice cycle large numbers of C. antennatus were caught. It is concluded that mosquito control by means of insecticides or by irrigation management would be possible.

A study of the host selection patterns of the mosquitoes of the Kisumu area of Kenya

The results of 12,168 precipitin tests on blood meals of mosquitoes of the Kano Plain caught by a variety of catching techniques indicate that to gain an accurate overall picture of feeding patterns both the indoor and the outdoor biotope must be sampled. CDC light traps operated inside houses and Monkswood type light traps operated under the outside eaves of houses were found to collect larger numbers of blood fed specimens from a wider range of species than battery driven aspirators collecting from natural resting sites. The results indicated that 7 mosquito species entered houses to bite man in appreciable numbers in the Kisumu area. These were Anopheles gambiae s.l., A. funestus, A. pharoensis, Mansonia uniformis, M. africana, Culex antennatus, and C. univittatus. Eight mosquito species were found to bite man and domestic animals in the outdoor biotope in large numbers. These were: A. pharoensis, A. ziemanni, M. uniformis, M. africana, C. antennatus, C. univittatus, Aedes circumluteolus, and Ae. ochraceus. From an epidemiological point of view, species with a narrow range of hosts are most likely to be of importance as vectors of parasitic diseases such as malaria and into this category fall the major man biting anophelines A. gambiae and A. funestus. Those mosquito species which switch from one group of hosts to another according to local circumstances are more likely to be involved in arbovirus transmission and in this group the following species must be considered: A. pharoensis, A. ziemanni, M. Uniformis, M. Africana, C, antennatus, C. univittatus and Ae. circumluteolus.

The pattern of flight muscle damage in relation to the distribution of developing filarial larvae inAedes aegyptiandMansonia uniformis

The pattern of flight muscle damage in relation to the distribution of developing filarial larvae in<i>Aedes aegypti</i>and<i>Mansonia uniformis</i>

Cell replication in the follicular epithelium of the adult mosquito

Females of the mosquitoes Culex pipiens molestus, Aedes togoi, Mansonia uniformis, and Aedes aegypti show active mitosis and an increase in cell number in the follicular epithelium of the ovary immediately after emergence from the pupa. Development up to stage III in the autogenous species, when mitosis in the follicular epithelium ceases, depends upon the continuity of cell proliferation over the first 48 hr after emergence ( C. p. molestus, A. togoi) and on the number of cells originally in the follicle at emergence ( A. togoi). The follicular epithelium in the anautogenous species ceases to divide in Mansonia, or the rate of division is considerably reduced in A. aegypti, 24–48 hr after emergence. Mitosis in the follicular epithelium of A. aegypti is renewed after the blood meal. A number of cells are released from phase G2 of the mitotic cycle into mitosis and other cells are initiated into DNA synthesis within 4 hr of the mosquito feeding on blood.

The range of attraction of animal baits and carbon dioxide for mosquitoes. Studies in a freshwater area of West Africa

In an inland area of the Gambia the density of flying mosquitoes at successive distances from a pair of bait-calves or an equivalent source of carbon dioxide was measured with ramp-traps to determine the maximum range at which orientation towards the bait was initiated. Thirty-six traps were operated at intervals of 7·5 m up to a distance of 60 m from the bait, on 66 nights. Anopheles ziemanni Grünb., Mansonia uniformis (Theo.) and Aedes spp. were responding to the presence of the baitcalves from a distance of 22·5–30 m; with carbon dioxide as bait the same species showed a clear response at 15 m but, with the doubtful exception of M. uniformis, not at 22·5–30 m. M. africana (Theo.) responded to both calf and carbon dioxide baits at 15 m but not at more distant ranges. Culex thalassius Theo. and C. univittatus Theo. showed a response at 7·5 m but not at any greater distance. C. decens group showed no response to either bait even in the nearest traps (7·5 m). The parous rate in Mansonia spp. varied with distance from the bait. Similar variation in the proportion of females infested with mites was not detected.

Preliminary louvre-trap hut studies on the egress of Anopheles gambiae Giles, Mansonia uniformis (Theo.) and Culex pipiens fatigans Wied. from untreated huts

The louvre-trap hut was designed to be cheaper and simpler to use than the verandah-trap hut. The eaves are closed, and mosquitoes enter by way of a row of five louvre frames and leave by a window fitted with a window trap. In three trials at Magugu, Tanzania, window traps fitted over one or all louvre frames showed that the efficiency of the louvres in preventing egress was 66–79% for Anopheles gambiae Giles, 51–73% for Mansonia uniformis (Theo.) and 74–78% for Culex pipiens fatigans Wied. Egress through the louvres of A. gambiae is only slightly more, and of M. uniformis much less, than through the eaves of a verandah-trap hut.

Histological changes in mosquito flight muscle fibres associated with parasitization by filarial larvae.

1. Serial sections were examined of thoraces of a selected strain of Aedes aegypti infected with either Brugia pahangi or subperiodic B. malayi and of wild-caught Mansonia uniformis infected with the latter parasite.2. A few badly damaged flight muscle fibres are seen in the early stages of infection but many more fibres are destroyed at the time when the mature filarial larvae leave the muscle and enter the haemocoel. In the intervening period, when the larvae are growing within the muscle fibres, only minor damage develops, affecting nuclei and/or mitochondria. The nature of such minor damage and the mechanism of complete muscle breakdown differs in the two species of mosquitoes.3. It was concluded that the muscle damage was sufficiently severe to explain the significant mortality often observed among experimentally infected mosquitoes at the time when the mature filarial larvae enter the haemocoel.I am very grateful to Dr W. W. Macdonald, of the Liverpool School of Tropical Medicine, who supplied the Aedes aegypti mosquitoes and who has given invaluable help and advice throughout this study. Mr Cheong Weng Hooi and his colleagues in Kuala Lumpur kindly supplied, and partly processed, the Mansonia uniformis mosquitoes. Miss M. A. Johnson assisted with the care of the A. aegypti colony and Mrs J. Oliver helped with some of the histological work.

The effects of smoke from mosquito coils on Anopheles gambiae Giles and Mansonia uniformis (Theo.) in verandah-trap huts at Magugu, Tanzania

The effects of smoke from mosquito coils containing pyrethrins or DDT on Anopheles gambiae Giles and Mansonia uniformis (Theo.) were investigated by burning coils for five nights per week in three man-baited verandah-trap huts. Three other verandah-trap huts served as controls. Smoke from 004–0–3% pyrethrins coils deterred 24–84% of A. gambiae and 71–93% of M. uniformis from entering treated huts, and that from 7–3–130% DDT coils deterred 91 % of A. gambiae and 92% of M. uniformis.In pyrethrum-treated huts 62–76% A. gambiae were unfed (33–67% in the controls) and 80–99% were in the exit traps (43–79% in the controls). In DDT-treated huts 85% A.gambiae were unfed (48% in the controls) and 100% were in the exit traps (55% in the controls). With M. uniformis, 61–84% in the pyrethrum-treated huts were unfed (38–54% in the controls) and in the DDT-treated huts 71 % (69% in the controls). The effects of the smokes on the egress of M. uniformis could not be assessed since 82–100% were in the exit traps in the treated and in the control huts. Overall mortalities never exceeded 22% of A. gambiae and 12% of M. uniformis, but some dead mosquitoes may have been removed by ants. With pyrethrum coils, feeder-survivor indices were 15–84% for A. gambiae and 90–98% for M. uniformis, and with the DDT coils, 94% and 96%, respectively. When caged A. gambiae females were exposed all night in the huts, 24-h delayed mortalities caused by 019–0–30% pyrethrins coils were 38–56%, by 009% pyrethrins coils 12–27%, and by 004% pyrethrins coils 3–5%. DDT coils produced 99–100% mortality in 24 h, but this may have been due to contact with contaminated mosquito netting.

Assessment of methoxy-DDT as a residual spray against mosquitoes in verandahtrap huts at Magugu, Tanzania

The effects of residual sprays of methoxy-DDT wettable powder at 2 g/m2 on the mortality and behaviour of Anopheles gambiae Giles, Mansonia uniformis (Theo.) and Culex pipiens fatigans Wied. females were investigated in four verandah-trap huts, one of which was used as control. The overall mortality of no species ever exceeded 29%, and no consistent deterrent effect on entry was demonstrated. The proportions of mosquitoes in the exit traps were, for A. gambiae 80–90% in treated huts and 29–70% in the control, for M. uniformis 90–100% in treated and control huts, and for C. p. fatigans 26–84% in treated huts and 38–66% in the control. There were more unfed mosquitoes of all three species in the treated huts than in the control, for A. gambiae 35–64% and 10–53%, respectively, for M. uniformis 38–84% and 35–64%, respectively, and for C. p. fatigans 22–58% and 21–43%, respectively. Bioassays with wild-caught A. gambiae exposed to the treated surfaces for one hour, showed that the deposits remained highly toxic for 16 weeks on grass, six weeks on iron and two weeks, or less, on mud.

Notes on the ecology of Seychelles mosquitoes

Entomological investigations preliminary to a filariasis study were carried out over a period of eleven months in fourteen islands of the Seychelles group. Thirteen species of mosquitoes were found in collections of larvae from over 700 breeding places and occasional hand-catches of adults. These were: Aedes aegypti (L.), Ae. albopictus (Skuse), Ae. albocephalus (Theo.), Ae. (Skusea) sp. n., Ae. vigilax vansomerenae Mattingly ' Brown, Culex pipiens fatigans Wied., C. scottii Theo., C. simpsoni Theo., C. stellatus van Som., C. wigglesworthi Edw., Uranotaenia browni Mattingly, U. nepenthes (Theo.) and U. pandani (Theo.). Mansonia (Mansonioides)uniformis (Theo.), previously reported from the islands, was not found during the present survey.

Large-Scale Irrigation and Arbovirus Epidemiology, Kano Plain, Kenya1: I. Description of the area and preliminary studies on the mosquitoes2

During May and June 1969, the distribution and abundance of adult and larval mosquito populations were studied on an irrigation scheme designed for rice production in Nyanza Province, Kenya and compared with an unmodified ecosystem 12 km to the southwest. Twelve species, 4 anopheline and 8 culicine, were recorded as adults. Biting studies using human bait showed that activity was almost exclusively at night. Although the numbers taken in night catches at the 2 sites (23,641 and 22,966 respectively) were very similar, the species composition was different. In the village adjacent to the ricefields Anopheles gambiae Giles made up 65% of the catch, Mansonia uniformis Theo., 28% and Culex pipiens fatigans Weid., 5%, while in a village in the unmodified area, M. uniformis constituted 86% of the catch, A. gambiae less than 1% and only 3 C. p. fatigans were taken. Larvae of A. gambiae were most abundant in nursery padi while among older, denser plants C. antennatus Beck was the dominant species. In ecologically similar microhabitats in the unmodified area, A. gambiae was the dominant species although 4 times less abundant than in young padi; adult and larval abundance are related. Due to the cropping regime, 2 population peaks a year are to be expected. Elsewhere in East Africa arboviruses have been isolated from 4 of the species recorded here. Birds were abundant in the rice, particularly heron, stork and ibis, and 2 species, the Cattle Egret ( Bubulcus ibis ) and Sacred Ibis ( Threskiornis aethiopicus ), play a role in the maintenance Sindbis and West Nile viruses elsewhere in southern Africa. Rodents, particularly Arvicanthis niloticus and Mastomys natalensis , were found and could play a role in the epidemiology of arboviruses, rickettsial infections, plague and leptospirosis. Other diseases which may become associated with the irrigation scheme are considered.

Aggregation by ovipositing Mansonioides mosquitoes.

Egg masses of Mansonia ( Mansonioides ) uniformis were laid on the underside of floating leaves of water lilies, water fern and grasses in a swamp at Maha Induruwa in Ceylon. The leaves of the water lilies were mapped in an area of about 1.5 m2 and the distribution of egg masses on leaves and the contribution of new egg masses overnight were recorded daily. The results showed that the more a leaf was used for oviposition the more likely it was to be used by other ovipositing females. Ovipositing females also aggregated on certain leaves overnight. Laboratory experiments with M. uniformis failed, however, to show clearly that leaves, or paper discs, once they had an egg mass deposited on them, were imprinted and then made more attractive to other gravid females; females showed little or no tendency to oviposit on the same leaf, or paper disc, on the same night. The density of oviposition in the field appeared to be related to the presence of 2 coconut palm trees and higher ground, but the selection of certain individual leaves in the swamp under these trees as oviposition sites cannot be completely explained in relation to these large topographical features. A total of 384 egg masses was deposited in the study site over 24 days, although the swamp was slowly drying. Only 1 female was captured in emergence traps placed over the site for 14 days and no larvae or pupae of Mansonioides were found on the roots of grasses and water lilies at the end of the experiment.

The distribution of larvae of Brugia malayi and Brugia pahangi in the flight muscle fibres of Aedes aegypti and Mansonia uniformis.

1. The distribution of filarial larvae in the dorsoventral and dorsal-longitudinal muscle fibre groups was studied in serial sections of mosquitoes of a susceptible strain of Aedes aegypti infected with Brugia pahangi or subperiodic B. malayi and of wild-caught Mansonia uniformis mosquitoes containing the latter parasite.2. The experiments showed that more larvae were situated in the dorsal-longitudinal muscle than in the dorsoventral and that the difference in numbers was highly significant.

A study of potential mosquito vectors of Dirofilaria immitis Leidy, on Okinawa, Ryukyu Islands.

Laboratory and field studies were conducted to determine the potential mosquito vectors of Dirofilaria immitis Leidy, on Okinawa. Eleven mosquito species were either infected within the laboratory or examined from field collections to establish microfilarial intake, and their ability to harbor developing and infective larvae. Seasonal abundance, over a 2-year period, was also recorded to define the availability of all potential vectors. Aedes togoi, Mansonia uniformis , and Culex bitaeniorhynchus proved highly susceptible to D. immitis infection. However, Culex quinquefasciatus and C. tritaeniorhynchus represent over 80% of all larval collections on Okinawa. Laboratory studies demonstrated that 4.8–11.2% of all the C. quinquefasciatus and C. tritaeniorhynchus examined harbored infective larvae of immitis .

Ricefield development and arbovirus epidemiology, Kano Plain, Kenya

During May and June 1969, adult and larval mosquito populations were compared in an unmodified area and in a newly irrigated area in Nyanza Province, Kenya. The numbers taken on human bait in 14 night catches in the two localities were 22,966 and 23,641 respectively. In a village in the unmodified area, Mansonia uniformis constituted 86% of the catch while in a village adjacent to the new ricefields Anopheles gambiae made up 65% of the catch and Culex fatigans 5%. Larvae of A. gambiae were most abundant in nursery rice while among older, denser plants C. antennatus was the dominant species. In ecologically similar microhabitats in the unmodified area, A. gambiae was the dominant species although 4 times less abundant than in young rice. Birds were abundant in the rice, particularly heron, stork and ibis. Rodents, particularly Arvicanthus niloticus and Mastomys natalensis were common. Viruses were isolated from M. uniformis, M. africana and A. gambiae and antibodies to o'nyong-nyong, chikungunya and Nyando viruses found in sera from school children.

A verandah-trap hut for studying the house-frequenting habits of mosquitoes and for assessing insecticides. 3. The effect of DDT on behavior and mortality.

The effects of DDT on the behaviour and mortality of Anopheles gambiae Giles, A. funestus Giles, Mansonia uniformis (Theo.) and Culex pipiens fatigans Wied., entering experimental huts, have been studied with the assistance of gas-chromatographic techniques.Sixty to 70% of A. gambiae and 70–80% of M. uniformis were deterred from entering verandah-trap huts treated indoors with a nominal dosage of 200 μg/cm2 of DDT active ingredient. Gas chromatographic techniques indicate that the chemical basis of the deterrency was a steadily diminishing outflow of DDT from the hut, either as a dust or vapour, and the build-up of deposit on the untreated overhanging eaves to 0·02 to 0·27 μg/cm2 seven months after treatment. A. funestus was less deterred than A. gambiae and M. uniformis, but the behaviour of C. p. fatigans was almost unaffected by the DDT deposit.Overall mortalities were highest in A. funestus and M. uniformis, lower in A. gambiae and extremely low in C. p. fatigans.There was a marked irritant effect of the DDT deposit on recently blood-fed A. gambiae, some 50–70% being driven out of the treated huts. This behaviour occurred to a lesser degree in A. funestus but was absent in M. uniformis and C. p. fatigans. The chemical basis of the irritant effect was indicated to the extent that surviving mosquitoes, that left the treated hut, showed 1·5 ng/insect of DDT. Mosquitoes that died, whether indoors or after leaving the hut, picked up amounts ranging from 7 to 20 ng/insect.

The Egress of Anopheles Gambiae and Mansonia Uniformis from Experimental Huts with Corrugated-Iron Roofs

The Egress of Anopheles Gambiae and Mansonia Uniformis from Experimental Huts with Corrugated-Iron Roofs

Biology of the Simian Malarias of Southeast Asia. III. Sporogony of the Cambodian Strain of Plasmodium cynomolgi

The sporogony of the Cambodian strain of Plasmodium cynomolgi in six species of mosquitoes (Anopheles maculatus, A. kochi, A. philippinensis, A. vagus, A. letifer, and Mansonia uniformis) has been studied in detail. Sporozoites appeared in anopheline hosts as early as 7.5 days after infection. Evidence is presented to suggest that sporozoites undergo morphological changes with time after they reach the salivary glands. It is concluded that the minimum time required for maturation of oocysts, their size, and the time required for sporozoites to reach the salivary glands are factors controlled by the species and/or strain of the malaria parasite. The success of the oocysts in maturing and of the sporozoites reaching the salivary glands is apparently controlled by the species of mosquito. The number of recognized species of malaria parasites in Asian monkeys has greatly increased since 1958 (Eyles, 1963), making identification based on the morphology of the asexual stages of the parasites more and more difficult. Recently Bray (1963) employed such factors as the morphology of the exoerythrocytic stages and/or the effect of the parasite on Macaca mulatta Zimmerman to elevate Plasmodium cynomolgi bastianelli Garnham and P. cynomolgi cyclopis Inoki to specific rank. The taxonomy of simian malarias has largely depended on the morphology of the asexual stages in the blood of the vertebrate host but relatively little attention has been given to the study of sporogony in the invertebrate host. The staff of the Far East Research Project in Kuala Lumpur, Malaysia maintained several strains of Plasmodium cynomolgi Mayer and some of their experimental vectors. This situation provided the opportunity to make a comparative study of the sporogony of different strains of P. cynomolgi and to evaluate the differences found as to their possible taxonomic value. In this paper we will describe the Received for publication 28 January 1966. * Contribution from Far East Research Project, LPC, NIAID, National Institutes of Health, Kuala Lumpur, Malaysia. t Present address: Ontario Research Foundation, 43 Queen's Park Crescent East, Toronto 5, Canada. I Institute for Medical Research, Kuala Lumpur, Malaysia. 632 sporogony of the Cambodian strain of P. cynomolgi in five anopheline and one culicine host, giving particular attention to the pattern and rate of development of the parasite in the different species of mosquitoes. MATERIALS AND METHODS Rhesus monkeys (Macaca mulatta) imported from New Delhi, India, were used throughout the study. None of the large number of this species used in our laboratory has been found naturally infected with malaria parasites on their arrival from northwestern India. Confirmation of their uninfected status was obtained by the examination of one or more blood films prior to their use. Monkeys previously infected with parasites of malaria were also used. Such animals were treated with chloroquine and/or primaquine before their reuse. Sporogony was studied in six species of mosquitoes, Anopheles maculatus Theobald, A. kochi Donitz, A. philippinensis Ludlow, A. vagus Donitz, A. letifer Sandosham, and Mansonia uniformis Theobald. All of the mosquitoes used in the experimental feedings were reared in the laboratory with the exception of Mansonia uniformis. They were obtained as wild-caught adults from areas where no natural infections with malaria had been found. The infected monkeys were tranquilized and then exposed to the bites of uninfected mosquitoes. The fed mosquitoes were maintained in an insectary at 27 C and 80 to 90% relative humidity. Mosquito feedings were done at night; dissections were done in the morning. Thus the sporogonic development of the parasite was recorded on the half day, i.e., 8.5, 9.5, 10.5, etc. The Cambodian strain of P. cynomolgi was obtained from a naturally infected Macaca irus in Cambodia (Bennett and Warren, 1965) and maintained in Macaca mulatta by both sporozoite and This content downloaded from 207.46.13.111 on Sat, 21 May 2016 06:17:38 UTC All use subject to http://about.jstor.org/terms BENNETT ET AL.-SPOROGONY OF CAMBODIAN STRAIN OF PLASM. CYNOMOLGI 633

Biology of the Simian Malarias of Southeast Asia. IV. Sporogony of Four Strains of Plasmodium cynomolgi

Detailed study of the sporogonic development of four strains of P. cynomolgi in Anopheles maculatus, A. kochi, A. vagus, and Mansonia uniformis reveals strain differences in the average size of the mature oocysts as well as the time required for sporozoites to reach the salivary glands. These differences occurred with the same strain of the parasite in different species of mosquitoes and were therefore considered to be characteristic of the Plasmodium and not dependent upon the environment provided by the mosquito. Sporozoites were found in the salivary glands in the shortest period with the parasite producing the smallest oocyst and conversely sporogony required a longer time for completion with the strain of parasite producing the largest oocysts. The strain differences in sporogony should be useful in identification. Because the five strains of P. cynomolgi from Southeast Asia which have been studied are believed to represent only a small part of an extensive complex, classification at other than the strain level seems unjustified at the present time. The development of the Cambodian strain of P. cynomolgi in five anophelines and one culicine mosquito was discussed in the preceding paper (Bennett et al., 1966b). The present paper presents the results of studies on four additional strains of P. cynomolgi in Anopheles maculatus, A. kochi, and, to a limited extent, in A. vagus and Mansonia uniformis. MATERIALS AND METHODS The four strains used in this study were isolated in Malaya. The M strain is considered to be the type for the species which was first described by Mayer in 1907. The B strain was described by Garnham in 1959 in Macaca irus from the east coast of Malaya. The Gombak and Berok strains were from the west coast of Malaya and their sources are discussed in more detail by Bennett et al. (1966a). The strains were maintained in the laboratory by a combination of blood and sporozoite transfers. All mosquitoes except M. uniformis were laboratory reared. Infected monkeys were exposed to selected lots of mosquitoes and blood-fed specimens were maintained in an insectary at 27 C and 80 to 90% relative humidity until dissected (Warren et al., 1963 and Bennett et al., 1966b). Mosquito feedings were carried out at night; dissections were made in the morning and therefore time was recorded on the half day, i.e., day 5.5, 6.5, etc. Received for publication 28 January 1966. *Present address: Ontario Research Foundation, 43 Queen's Park, Toronto 5, Ontario, Canada. t Institute for Medical Research, Kuala Lumpur, Malaysia. RESULTS Plasmodium cynomolgi (M strain) Sporogony in Anopheles maculatus Combined data from three experiments are given in Table I and Figure 1. Oocysts were spherical in shape and the largest specimen measured 95 tx. Differentiation was first seen on day 7.5; degenerating forms were observed on day 8.5. Sporozoites were first present in the salivary glands on day 9.5 and oocysts in the same mosquitoes averaged 67 tu in diameter. The rapid, uniform growth and the small Ql and Q3 (the median 50 percentile) range indicated that the gut of this mosquito provided a suitable environment for oocyst development. However, the large number of degenerating oocysts and the low number of infected salivary glands suggested that the host-parasite relationship was less than optimum. Sporogony in Anopheles kochi Data from one experiment are given in Table II and Figure 2. The oocysts were not as large as those seen in A. maculatus and the rate of growth was slower and more erratic. The time of oocyst differentiation was 2 days later and the appearance of sporozoites in the salivary glands was 1 day later than in A. maculatus. Despite the heavy oocyst infection and the numerous differentiated oocysts, the number of infected

A verandah-trap hut for studying the house-frequenting habits of mosquitos and for assessing insecticides. 2. The effect of dichlorvos (DDVP) on egress and mortality of Anopheles gambiae Giles and Mansonia uniformis (Theo.) entering naturally.

Assessment of the effects of dichlorvos (DDVP), released from a Ciba XI dispenser, on females of Anopheles gambiae Giles and Mansonia uniformis (Theo.) entering a verandah-trap hut in the Umbugwe area of Tanzania was made over a period of two months in 1964. Of the numbers of A. gambiae that entered one treated and one untreated hut, 27 per cent, of those entering the hut treated with dichlorvos and 48 per cent, of those entering the untreated hut left again. Of the numbers leaving each hut, 38 per cent, left through the eaves of the treated hut as compared with 9 per cent, in the untreated one. In the case of M. uniformis, 88 per cent, of those entering the treated hut and 94 per cent, of those entering the untreated hut left again. Of the numbers leaving each hut, 59 per cent, left through the eaves of the treated hut as compared with 61 per cent, in the untreated one.Over-all mortalities were 56 per cent, for A. gambiae and 34 per cent, for M. uniformis when the eave-egress fraction from the treated hut was taken into account, compared with 62 per cent, for A. gambiae and 43 per cent, for M. uniformis when the eave-egress fraction was ignored.The results of bioassays and of chemical analyses showed that the problem of mortality from fumigation in situ was considerably less in verandah traps than indoors or in window traps fitted with funnels of cotton netting.