Eggs of Aëdes do not necessarily hatch on becoming mature, even though conditions are known to be compatible with hatching. Even the eggs laid by a single female in a single batch and kept submerged in a single container may hatch in instalments over a very long period and, although on one occasion a high proportion of the eggs may hatch within a given period, on another, for no apparent reason, very few may hatch.

The problem of erratic hatching has been studied here mainly in Aëdes africanus (Theo.) and A. aegypti (L.). It is considered that mature eggs enter a state of diapause, the depth of which varies with the passage of time, and that the manner of this variation with time itself varies from egg to egg. Different batches of eggs laid by females of the same species vary in the proportion of the different kinds of egg present.

Variation in response of the eggs has been studied by the application of a suitable hatching-stimulus in equal daily doses. The stimulus used was sufficiently weak to allow variation in response to be manifested, but sufficiently strong to outweigh uncontrolled variables in the environment.

A large collection of mosquitos made in five atolls of the Maldive Islands has revealed the presence of 15 species. These are listed and notes of taxonomic interest on seven of them are given.

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.

A description is given of the method used for the large-scale breeding of cotton stainers (Dysdercus spp.) at the Cotton Research Station in Uganda. The method entails the use of a standard cage unit, consisting of a shallow tin cylinder with detachable cloth top and bottom. The advantages of this type of unit are outlined, with particular reference to control of disease and to the other hazards of large-scale breeding.

Since the publication of the previous paper (Leeson, 1953), additional information has been accumulated on the geographical distribution of some of the Old World ticks of the genus Ornithodoros and two new species (zumpti and arenicolous) have been described. Much of this additional matter has been communicated to me by correspondents who have been kind enough to give permission for its publication here. Their names are enclosed in brackets after the new data to indicate the source and to these workers I tender my sincere thanks.

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.

Field and laboratory studies have shown that the several root-infesting Anthomyiid flies differ greatly in the number of generations composing their annual cycle and in the minimum temperature conditions necessary for full activity.

Onion flies (Delia antiqua (Mg.) ) were mainly univoltine in laboratory cultures. Of 369 first-generation pupae studied in 1953, only 141 (about 40 per cent.) gave rise to flies in July-August and 228 (about 60 per cent.) entered a diapause, in which 196 (about 85 per cent, of those entering diapause) remained until the following spring. In 1954, 99 per cent, of the first-generation pupae from univoltine flies and 97 per cent, of those from bivoltine flies entered the overwintering diapause in July. It then appeared that exposure to low temperatures during the development of the first-generation larvae had induced diapause in the pupae. This was confirmed by the unexpectedly high proportion (49 per cent.) of wild first-generation pupae which entered the overwintering diapause in July in the cool summer of 1954. It was also established that the spring oviposition period for D. antiqua began about the end of May, and it appeared that, in the field, air temperatures of approximately 70°F. were necessary to stimulate egg-laying. First-generation flies emerged in the second and third weeks of July, their numbers depending on the temperature in June. A few second-generation flies, together with late first-generation flies, may emerge in September, but the temperature is then too low for oviposition and there seem to be no third-generation larvae.

A stimulus is necessary for the hatching of eggs of Aëdes mosquitos, but, while many different kinds of change in the external environment may be adequate as hatching-stimuli, there is variation in the response of the eggs to any given one of them.

Not only is there variation between species as regards behaviour of the eggs, but batches of eggs laid by different females in a single species may vary one from another and there is even variation of behaviour between the eggs laid in a single batch.

The response of the eggs of A. aegypti (L.) has been studied here and evidence produced that both parents contribute to their hatching-behaviour. Egg behaviour has also been studied in two populations of this species, one originating from West Africa and the other from East Africa. In the former, only a very low proportion of the mature eggs (0–9%) responded to the daily application of a suitable stimulus over a short period, whereas in the latter the proportion of responders in the same period with the same stimulus was very much higher (46–100%). The next generation reared from each of these gave very similar results (0–11 and 65–100%, respectively), while reciprocal crosses between them gave a wide range of scatter (16–100 and 4–99%, respectively).

A new species of larch-feeding sawfly, Pristiphora glauca Benson, was first observed in 1950. The activities of this insect appear to be confined to the spring and early summer, and it would appear that it is one of the least widespread of the larch sawflies.

Notes on the biology of this species, including larval descriptions, are given, and field characteristics and distribution discussed. Differences in feeding habits from those of Pristiphora wesmaeli (Tischb.), with which it may be confused, are mentioned.

Australian workers have been interested for some time in the common Ceroplastes on coffee in Kenya as a source from which parasites of Ceroplastes destructor Newst. might be obtained.

The doubt that more than one white waxy scale occurs on coffee in East Africa led to an examination of material of C. destructor and certain other allied species. It was found that C. destructor was present in Uganda and Kenya but did not occur on coffee in Kenya, so far as is known at present. C. brevicauda Hall, here raised to specific rank, was found to occur on coffee in Uganda and a new species, C. luteolus, on the same crop in Kenya.

Descriptions of C. luteolus, Lecaniodiaspis erratica and Pseudococcus latipes, spp. n., all from coffee, are given.

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.

Onions are attacked by larvae of Anthomyiid flies from May to August. Two species are concerned, namely the onion fly, Delia antiqua (Mg.), and the bean seed fly, D. cilicrura (Rond.). The onion fly, which in some seasons is mainly univoltine, attacks the crop in June and July. The bean seed fly, which has. 3–4 generations a year, is most injurious to spring-sown onions in May and to summer-sown onions in August. Attack by D. antiqua is the result of the chemotropic response of the species to its host-plants. Attack by D. cilicrura follows the disturbance of the soil during cultural operations in April-May, and occurs again when seed-beds are prepared for August sowings.

The recognition of this complex pattern of attack makes it necessary to reconsider the value of established control measures. The calomel (mercurous chloride) seed-dressing is unlikely to give control of onion fly because its ovicidal efficiency is impaired by exposure to the air during the three months between the sowing of onion seed (end of February) and oviposition (end of May), and by the growth of the plants, which results in the eggs being laid at some distance from the old seed-coat which carries the ovicide. It is also unlikely to have a direct effect on infestation by bean seed fly, because the eggs of this species are not necessarily laid on the seedlings and, in the case of August sowings, the eggs may have hatched before the seed is sown.

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.

Between 1925 and 1947, 9,929 samples of bees from Great Britain were examined for acarine and Nosema diseases. There was a significantly lower incidence of acarine disease in English samples than in Scottish ones, but a somewhat higher incidence of Nosema disease in England than in Scotland was not significant. A decrease in the incidence of acarine disease over the 22 years was highly significant in both England and Scotland, although the rate of decrease was not significantly different between the two countries.

The average incidence of acarine disease during each month of the year was at its lowest in April, May and June, while Nosema disease reached its maximum in these three months and fell to a minimum in the autumn. Data on the seasonal incidence of Nosema disease in an apiary in Scotland between 1948 and 1953 show a similar distribution to that for Great Britain. Eesults on the incidence of both diseases throughout the year are compared with those of other authors, and possible reasons for the seasonal fluctuations are discussed.

A comparison is made of all the members of the genus Thomasiniana Strand at present known from Rosaceous host-plants, namely T. oculiperda (Rübs.), the Red Bud Borer; T. theobaldi Barnes, the Raspberry Cane Midge; T. crataegi Barnes, the Hawthorn Stem Midge and a hitherto undescribed species from wild blackberry. Although morphologically very similar, each can be readily distinguished in trials on host-plant preference. By this means it has also been shown that there are two strains, favouring apple and rose respectively, within the present species T. oculiperda. Other biological and some morphological evidence is given, supporting the above conclusions, and on this basis the midge from blackberry is put forward as a new species for which the names Thomasiniana fruticosi, sp. n. and “Blackberry Cane Midge” are proposed and a formal description given. The biological and economic status of each species or strain is discussed and a list of the known parasites given.

Anopheles (Myzomyia) farauti Lav. is recorded from the upper reaches of the Nevaka river, south-western Espiritu Santo, New Hebrides, to an altitude of 1,100 ft. and a distance of 12 miles from the coast. The presence of Plasmodium vivax and P. malariae in the blood of children from hill villages with no nearby Anopheline larval habitats is noted. These children, most of whom have never visited the coast, become exposed to infection during prawning trips to the valleys below their homes. The transmission of P. vivax and P. malariae is shown to take place in the interior of Guadalcanal, British Solomon Islands Protectorate, where a proven vector, A. (Myzomyia) punctulatus Dön., breeds at altitudes of up to at least 1,900 ft. above sea level. A. (Myzomyia) solomonis Belkin, Knight & Rozeboom, the status of which as a vector of Plasmodium is unknown, was found breeding at an altitude of 3,000 ft. Neither P. falciparum nor Wuchereria bancrofti were recorded from the hill districts visited. During the investigations several species of Culicines were collected. Features of the larval morphology of some of these are illustrated and briefly discussed in a systematic appendix.

The persistence and toxicity of DDT crystals on thin layers of plant wax were studied. Deposits of crystalline DDT at rates of 2 to 8 microgm. per sq. cm. were applied to glass plates, plain or coated with a 0·5 μ layer of wax obtained from leaves of sisal or cabbage. The plates were stored for various periods at 18°C. and at 43°C. (representing temperature and tropical leaf-temperatures). DDT remaining after storage was estimated biologically by means of its contact action on adult Tribolium castaneum (Hbst.), and chemically by a modification of the Schechter-Haller method. At 18°C, there was no significant change in any of the deposits when estimated chemically. But biological estimation showed that, although the toxicity of the deposits on waxed plates was unchanged, that on glass plates was doubled after storage for eight days. The reason for this change was not discovered. At 43°C., the amount of DDT, estimated both chemically and biologically, diminished rapidly and was negligible after 26 days. The loss of toxicity at 43°C. was shown to be accompanied by loss of weight of the deposits. Loss at 43°C. from plain glass plates could be much reduced by storing them in an atmosphere saturated with DDT vapour. It appeared, therefore, that loss of toxicity at the higher temperature was due to volatilisation of DDT and not to decomposition.

It is confirmed that the scutellaris-growp mosquito of the Tokelau and Ellice Islands is Aëdes (Stegomyia) polynesiensis Marks. No other mosquitos are known from the former Group, but Culex (Culex). annulirostris Skuse, A. (Aëdimorphus) vexans nocturnus (Theo.) and A. (Stegomyia) aegypti (L.) are also recorded from Funafuti, Ellice Islands. C. annulirostris and A. vexans nocturnus are listed—apparently for the first time—from Tarawa, Gilbert Islands. Reference is made to the microfilaria rate at Nukunono in the Tokelau Group, and to some potential mosquito larval habitats, as yet unutilised, in all three Groups.

The biting-habits of mosquitos in the genus Eretmapodites Theobald, as shown by 24-hour catches, display a certain uniformity in that all the species studied are essentially diurnal and bite very close to the ground, in shade. They do not enter dwellings.

When, however, two localities are compared (the Entebbe area and Bwamba County) it is found that there is a fundamental difference in behaviour. At Entebbe there is an exceedingly well-marked wave of activity before sunset. This does not occur in Bwamba, where the cycle shows no pronounced characteristics apart from its generally diurnal nature. It is shown that this difference arises from the fact that in Bwamba the first hour of biting-activity tends to be the most intense (no matter when it occurs) whereas in Entebbe the hour before sunset is almost always preferred.

One group (the E. chrysogaster group) is present in both localities. In Entebbe it shows an activity curve of the one type, and in Bwamba a curve of the other type.

It is concluded that some environmental influence must be involved. At the moment, however, no suggestion can be made concerning the nature of this influence, beyond the fact that the activity-patterns concerned are not easily explained in terms of microclimate.

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.