In this paper a list, with brief notes on prevalence, behaviour and habitat is given of 121 species, sub-species and varieties of mosquitos taken in the last 12 years during field work on the Kenya coast. Two species and one sub-species of the mosquitos found are not yet described. Notes on variation have been included for species that show interesting features in this respect and the distribution of the species in East Africa is also included where it is of interest.

The seasonal biting-incidences on man of several species of mosquito inside and outside huts of villages on Ukara Island, Tanganyika, between 7 p.m. and 3 a.m. East African Standard Time are recorded. Anopheles gambiae Giles and A. funestus Giles were by far the most common indoor biters in both of the villages which received study: they were also taken biting outdoors in fair numbers. Tacniorhynchus africanus (Theo.) and T. uniformis (Theo.) were common outdoor biters in a village near a swamp, but were taken in only small numbers off human “bait” in a cone hut.

A study of sleeping arrangements in huts showed that people between six and sixteen years of age were most exposed to the risk of mosquito bites at night, since they were least protected by covers and clothing.

The inhabitants were bitten by Aëdes africanus (Theo.) and Aë. apicoargenteus (Theo.) outdoors by day, and by small numbers of A. gambiae and A. funestus in huts during daylight hours in April.

The results are given in detail of dissections for developing filarial worms in over seven thousand mosquitos. Proboscis infections occurred in A. gambiae and A. funestus. Immature (thoracic) forms were found in A. pharoensis Theo., T. africanus, T. uniformis and Culex antennatus (Beck.).

It is concluded that the biting-habits of A. gambiae and A. funestus point to them as more likely vectors of bancroftial filariasis than other species with developing filarial worms.

Precipitin tests show that, on Ukara Island, Tanganyika, man and ox are the chief sources of blood to hut-resting mosquitos. Anopheles gambiae Giles and A. funestus Giles feed almost entirely on man. A. pharoensis Theo. feeds more on man than on ox. Culicines feed more on ox than on man.

Hand-catches off man, cow and goat in a hut confirm the results of precipitin tests on hut-resting mosquitos.

An account is given of the mosquito fauna of natural and artificial outdoor resting places and of the results obtained in precipitin tests on blood-fed mosquitos from outdoor resting places.

Blood-fed mosquitos resting indoors and outdoors were examined for nucleated red corpuscles in blood-meals. A. gambiae and Gulex annulioris Theo. feed on domestic fowl.

Experiments in the laboratory, to find the facility with which different species of mosquito will feed on small wild animals of the island, show that A. gambiae and certain Culicines feed on a wide variety of hosts.

A. gambiae and A. funestus are incriminated as almost entirely responsible for the transmission of bancroftial filariasis on Ukara Island. A little transmission may take place by A. pharoensis.

Tsetse flies (Glossina morsitans Westw.) were marked and released at Daga-Iloi, in Tanganyika on four or, usually, six days weekly for over 15 months, at 75 catching points situated 100 yards apart on an “octagonal spiral” whose successive rings were separated by 250 yards. Outer “spirals” were also traversed occasionally.

The country was hilly and dominated by woodland of Brachystegia tamarindoides, broken by more open grassland with Combretum on the one hand and by thicketed ravines on the other. The ungulate animals included zebra, buffalo, bushbuck, roan antelope, hartebeest, reedbuck, duiker, wart-hog and bushpig, with very occasional elephant, rhinoceros, waterbuck and klipspringer. Baboons and Cercopithecus monkeys were also present. Spoors of the ungulates were recorded on the daily rounds: bushbuck were most common about the ravines, but in general the ungulates tended to be most common in the open grassland with Combretum.

G. morsitans was most numerous in tall Brachystegia woodland where the slope was moderate, and where open grasslands were not too far away. Thicketed ravines were avoided. The highest apparent densities were observed on the outer “spirals”, perhaps because of disturbance on the inner one traversed almost every day.

During the rains, well-marked concentrations of flies occurred in certain parts of the Brachystegia woodland, and these re-formed in the second year. The hungriest flies were always found outside the Brachystegia, and hunger was higher in the dry season. Hunger was measured objectively by the proportion of non-teneral males alighting head-upwards on members of the catching party, which hungry flies mostly do.

There was a negative correlation between numbers of flies and numbers of ungulates, and a positive correlation between the numbers of ungulates and hunger of the flies. This is in accordance with the feeding-ground theory, and is very generally observed with G. morsitans in East Africa. Certain movements of individual flies also accorded with the theory, against which, however, the suggestion has now been made that flies caught in the putative feeding grounds have not ventured out into them until attracted there by the sight of the catching party. This suggestion is to some extent countered by quotations from previous work, but it deserves further thought, and carefully planned experiments.

Passage of large herds of buffalo through portions of the “spiral” were not apparently accompanied by mass movements of flies, even when the animals passed by day and many flies fed on them.

Blood smears from 378 examples of Glossina morsitans Westw. from the Daga-Iloi fly-round were tested by serological methods, including a new test involving the inhibition of agglutination of tanned red blood cells.

About half the feeds were derived from wart-hog or bushpig, though these apparently formed only some ten per cent, of the ungulate mammals present.

Six soil samples from elephant-grass leys at Kawanda, Uganda, gave collections representing a population of 87,147 arthropods per sq. metre in the top 12 in. of soil.

Six samples from adjacent cultivated ground gave collections representing a population of 26,150 arthropods per sq. metre.

These numbers are compared with the population of arthropods found in the soil of grazed pastures in East Africa.

The greater population under elephant grass is attributed to the presence of a crumb structure and to the protection afforded by elephant grass against insolation.

It is suggested that the nitrogen contained in these soil arthropods, especially that locked up in the chitin and sclerotin of their skeletons, is part of the nitrate that becomes available some weeks or months after elephant-grass leys are cultivated.

It is suggested that if the vapour of an insecticide is rapidly adsorbed by a substrate the rate of volatilisation of the molecules of insecticide particles lying on the substrate is greatly increased. This explains the rapid loss of effectiveness of wettable powders on some soils. After the insecticide has been sorbed it is concentrated at and near the treated surface but afterwards slowly diffuses inwards. This diffusion reduces recoveries of insecticides from surface scrapings.

DDT can be recovered quantitatively from Uganda mud blocks 12 months after sorption is complete. Therefore, on this mud at least, catalytic decomposition does not occur.

A test has been devised for measuring the sorptive capacities of soil samples for non-polar vapours. It indicates if a soil is highly active but those with lower or negligible activities do not give a good correlation.

A survey of 18 soils from different parts of the world suggests that rapid inactivation of an insecticide by sorption should be expected on any red lateritic soil. Generally, others are inert or show only low activity.

Attempts to reduce or abolish the sorptive powers of Uganda soil have not been successful and the only effective method known at present is to limewash the walls before spraying. Pretreatment with a size solution also stops sorption but, unlike limewashing, at the same time reduces the efficiency of a subsequently applied wettable powder.

Finally, work by various authors on the inactivation of insecticides on mud surfaces is reviewed.

Changes in numbers of adult Coccinellids on nettles infested with Microlophium evansi (Theo.) and on three experimental bean plots infested with Aphis fabae Scop. are described for the spring and summer of 1952 at Rothamsted. Of the three common species, Adalia bipunctata (L.), Coccinella septempunctata L. and Propylea quatuordecimpunctata (L.), the first was always the most abundant.

The overwintered Coccinellids produced two broods: one on nettles in the spring and one on beans in early summer.

On bean plots, changes in numbers of the adult insects occurred in three phases: (1) overwintered ladybirds, dispersing from nettles and other places, accumulated on the beans in the early stages of the infestations by Aphis fabae; (2) ladybirds, which had developed from eggs laid by the overwintered insects on nettles, emigrated from nettles and accumulated on the beans when A. fabae populations were at their height; (3) ladybirds, developed from eggs laid on the beans also by the overwintered insects, reached the adult stage when the bean aphid infestations had finished. The rise and fall of the A. fabae populations are discussed.

One of the bean plots had always a high population of Coceinellids, which was attributed to its situation between two of the nettle sites. The other two bean plots were remote from nettles and one was sheltered by trees and buildings; their coccinellid populations were much lower.

A recent extension of the fly-belt in Songea, southern Tanganyika, has been delimited.

The preferred habitat of the tsetse in this region is constituted by open, short-grassed glades, representing old village sites, in well-grown Brachystegia woodland, with a double-canopied interzone between glade and woodland.

Destruction of this interzone by clearing of the upper canopy will undoubtedly prove effective in causing eradication of the fly.

The effect of photoperiod and temperature on the production of the various forms of Acyrthosiphon pisum (Harris) has been studied. In this study apterous virginoparous females were exposed throughout their lifetime to two photoperiods (8 hr./24 hr. and 16 hr./24 hr.) and six different temperatures. At each of the temperatures the apterae (parent Aphids) received one of four treatments of photoperiod, i.e., (1) 8 hr./24 hr. photoperiod throughout their whole life; (2) 8 hr. /24 hr. photoperiod during the period from birth until the last (imaginal) moult (nymphal period), followed by 16 hr./24 hr. photoperiod from the last (imaginal) moult until death (the adult period); (3) 16 hr./24 hr. throughout life; (4) 16 hr./24 hr. during the nymphal period followed by 8 hr./24 hr. during the adult period. The offspring produced by the various parents were collected at successive intervals, and their form determined.

Four main forms of offspring were produced: apterous and alate virginoparae, males and oviparae. In addition, a subsidiary form of the apterous virginoparae was obtained, which had sensoria on the hind tibiae.

Laboratory tests are described for determining the protective value of a number of physically and chemically active insecticidal dusts against Bruchid infestation of peas and beans. Acanthoscelides obtectus (Say) and Callosobruchus chinensis (L.) were used as the test insects and were found to be very susceptible to most of the treatments tried. Adults of A. obtectus were in general more resistant to the treatments than those of C. chinensis, but the multiplication of the former species was more easily stopped, apparently because of the vulnerability of its first-stage larvae. It is concluded that protection of peas and beans can be achieved by thoroughly mixing into 200 lb. of the commodity 6–8 oz. of one of the following dusts: colloidal silica, colloidal aluminium pentasilicate, finely ground diatomite, 0.05 per cent. y BHC (as lindane) on diatomite or kaolin, 0.5 per cent. technical DDT on diatomite or kaolin. Rock phosphate, kaolin, or talc are not recommended. Where lindane or DDT are used in the dosages given, it is unlikely that the commodity will be tainted or rendered toxic to man or animals, even if no cleaning is undertaken.

An analysis is made of the records of inspections for infestation by insects of cargoes imported into Britain from West Africa. The exporting territories extend from Angola to Senegal but the bulk of cargoes were produce of the four British colonies.

The ready spread of insects from one cargo to another causes infestation to be similar for all cargoes but a few species are especially associated with a particular crop. Groundnuts in shell are normally shipped alone and therefore relatively protected from cross-infestation.

The three major cargoes are cocoa, palm kernels and groundnuts which form four-fifths of the inspected shipments. Fifteen other kinds of produce are also considered.

Twelve species were found on more than ten per cent. of cargoes of cocoa beans. Of these five were probably acquired from groundnuts and one from palm kernels by cross-infestation. Ephestia cautella (Wlk.), Tribolium castaneum (Hbst.) (from groundnuts), Lasioderma serricorne (F.), Necrobia rufipes (Deg.) (from palm kernels) and Araecerus fasciculatus (Deg.) all infested over 40 per cent. of cargoes.

The fluctuations of infestation year by year are examined, and it is shown that these are similar for all the species acquired from groundnuts except T. castaneum. Variations in frequency of other species appear to be unrelated.

The swollen-shoot virus of cacao is transmitted in the Gold Coast by mealybugs, of which Pseudococcus njalensis Laing is the most important, and these are tended by ants of the genus Crematogaster, which build carton tents over the colonies, thus affording them protection against contact insecticides. An account is given of an investigation which was carried out at Tafo, Gold Coast, between 1950 and 1953, of the possibility of controlling mealybugs and thus the spread of the virus, by the use of systemic insecticides. Dimefox, schradan, paraoxon and parathion were tested, although the two last are not strictly systemic in action.

Studies have been made of the bionomics and ecology of Aëdes aegypti (L.) entirely under natural conditions and in its natural habitats on the Kenya coast.

Development from egg to adult under conditions approximating as nearly as possible to those in nature took a minimum of eight days and a maximum of twenty-five.

Males were in excess of females, in the proportion seventeen to ten, from eggs hatched in natural breeding places.

Although the mosquito may be able to propagate in houses, adults from outside habitually enter premises. If this entry is for egg-laying, then eradication by domestic larval control alone, although reputedly achieved elsewhere, is not possible under conditions obtaining in the coastal belt of Kenya. Windowtrap captures, however, indicate that the entry may not be for the purpose of egg-laying.

The seasonal reduction of both larvae and adults in houses during the hot, dry months of February and March is attributed to a combination of the absence of breeding places outside and the shorter life span of the mosquito at this time.

It is shown that both sexes enter and leave native huts throughout the 24-hour period, but the movement is confined almost wholly to the hours of daylight. The flight from houses is much reduced in the cool months (July and August). This corresponds with the season when most enter.