(1) The Kabaw and Kale Valleys, separated by a low watershed and both draining through lateral gorges, have a combined length of some 250 miles and a width of between 4–10 miles. They lie at an altitude of approximately 500 feet above sea level.

(2) There is heavy rainfall during the months of June to September inclusive and little or no rain in the months November to April inclusive. The Kabaw Valley, the more northerly of the two, is forested and there are only small isolated clearings, but a big area in the centre of the Kale Valley has been cleared. Rice is the main crop grown.

(3) There appears to be no pre-war information about mosquitos and malaria. Information during the war was gathered by several different types of Unit engaged on different types of work but there is sufficient to give a fairly complete picture.

(4) The valleys are highly malarious throughout their length and breadth; only one village out of twenty-three examined had a spleen rate under 60 per cent.

(5) Transmission of malaria takes place throughout the year and is intense during the months May to December inclusive.

(6) 17 species of Anopheles are recorded. Common species during the rains are A. minimus, A. leucosphyrus, A. philippinensis, A. jeyporiensis, A. annularis, A. hyrcanus and A. vagus. A. minimus is only locally abundant at this time; A. leucosphyrus is widespread but confined to the forest.

(7) When the rain ceases, species such as leucosphyrus and vagus, which breed in pools and similar habitats, become reduced in numbers. Species such as philippinensis, jeyporiensis, annularis, hyrcanus and barbirostris, which breed in larger bodies of stagnant water such as rice fields, also become reduced in numbers during the dry season, though more slowly, because their breeding places disappear less rapidly. As the streams and rivers settle down, after the rains have stopped, conditions for A. minimus and A. maculatus become good and these are the only two common and widely distributed species in the dry season.

(8) During the dry season, sporozoite rates of A. minimus were 1/159=0·63 per cent, in October, 19/519=3·66 per cent, in December and 10/514=1·94 per cent. in May and it is an important vector and the only vector. A. maculatus does not apparently attack man and plays no part in malaria transmission. In September the sporozoite rate of A. minimus was only 1/332=0·31 per cent, and the important vector of the period of the rains appeared to be A. leucosphyrus with a sporozoite rate of 2/134=1·49 per cent.

(9) The status of A. leucosphyrus as a vector in the Indo-Burmese border region is discussed. There is good evidence that, under wartime conditions with troops operating in the forest, it is an important vector during the rains. Its significance in peacetime is less easy to assess; as only a few people live in the forest or at the forest's edge, its importance is probably not great. On the other hand it does not rest indoors, and, as in the past reliance has been placed on day catches, it may have been overlooked. There is, however, evidence that military operations in the forest produce conditions which lead to an increase in the numbers of this species.

(10) Adult collections were nearly all made at night in camps or villages. The species found in large numbers near man were A. minimus, A. leucosphyrus, A. philippinensis, A. jeyporiensis, A. annularis, and A. hyrcanus. A. minimus and A. leucosphyrus, the two definitely incriminated vectors, were the most successful at obtaining blood when the host, man, was protected by a mosquito net. The other four species, however, were sometimes filled with blood, undoubtedly of human origin and all may play some part in malaria transmission under war conditions. The chances of a specimen becoming infected were reduced under the conditions existing when the dissections were made and so moderately long series of negative dissections (Table XI) cannot be taken as conclusive evidence that any one species played no part in malaria transmission. In peacetime these four species may feed mainly on cattle, though a description is given of a night catch in a village where A. philippinensis was caught attacking man although cattle were available.

(11) In September very few of any of the eight common species were resting by day in the place where they fed at night and it is presumed that they spent the day in the forest. Unfortunately very few inhabited houses were visited and almost the only available catching places were Army tents and shelters. The results suggest, however, that all the species tend to rest in the forest rather than indoors. In December in the Kale Valley A. minimus rested in houses by day; in May in the Kabaw Valley it did not. It is believed that where, as in the Kabaw Valley, forest comes up to the edge of the village, A. minimus seeks shelter for the day in the forest, but that where, as in the Kale Valley, the village stands in a clearing, it rests by day in the houses near where it has fed. The facts observed, however, do not preclude the possibility of a seasonal change in resting habit. It is clear that A. minimus is not invariably a house rester and the importance of catching by night to gain a true picture of the mosquito population is stressed.

(12) A. hyrcanus was usually the first species to appear after dark, followed by A. philippinensis, A. leucosphyrus and A. minimus in that order, the last named being usually most abundant in the second half of the night. Time of greatest activity was, however, variable in all species. There were only a few isolated instances of Anophelines biting in the forest by day.

(13) A. hyrcanus was attracted to light.

(14) Larvae identified as A. pallidus with the aid of the standard Indian keys invariably proved to be A. philippinensis on emergence.

(15) The variation found in A. minimus was considerable and is briefly discussed. The only constant difference between A. minimus and A. aconitus was found to be the flavescence on the proboscis.

Length, 2·9 mm. General coloration pale yellow. Width of head, across the eyes, 0·7 mm. Tegmen with a brown marking as shown in fig. 1b. Male genitalia as in fig. la.

Type ♂ from Suva, Fiji, collected by R. A. Lever 14. viii. 1943, on bean.

According to Mr. Lever, E. leveri is a vector of a leaf-crinkle on leaves of Madagascar beans (Phaseolus Iwnatus) and cowpea (Vigna unguiculata) in Fiji.

Two leaf miners of coffee, Leucoptera coffeella and L. caffeina are present in the Kilimanjaro and Usambara districts of Tanganyika. The life-histories of L. coffeella and its parasites and a study made during 1937–40 of the populations of the host and its parasites in the Kilimanjaro area in both unshaded and shaded coffee are described. Some observations are made on the “dominant stage” of the host.

A wide range of material has been studied in an investigation of the relationship between “resistance” to attack by Empoasca facialis and “hairiness” of the cotton plant.

A continuous range has been found between full susceptibility and very high resistance.

In general relative susceptibility, as gauged by visual assessment of symptoms, has been found to correspond closely with relative infestation, determined by counts of nymphs.

With attention confined to grown plants, the relative susceptibility of varieties has been found substantially constant under varying levels of exposure to infestation.

Hairiness of the cotton plant has been found to show an extremely wide range in degree, style and distribution. A method has been devised for expressing hairiness numerically, taking into account both length and density of hairs.

A very close and consistent relationship has been found between degree of hairiness of the under surface of the leaf, and degree of resistance to Jassid. Without exception, all thoroughly hairy types have been found highly resistant, and all non-hairy types fully susceptible. Intermediate degrees of hairiness ate associated with intermediate degrees of resistance.

The relationship has been found to hold good between varieties and between plants within varieties, of the species G. hirsutum; also between plants of G. barbadense, and in segregating progenies of hybrids between these two species.

The hairiness of resistant strains of cotton has been found to develop gradually with the growth of the plant; the first few leaves on the seedlings being virtually non-hairy. This lack of hairiness in the early stages of growth is associated with a lack of resistance. Hairiness and resistance to Jassid develop concurrently.

The conclusion is reached that hairiness of the leaf confers resistance to Jassid and that degree of leaf hairiness, measured in an appropriate manner, is a thoroughly reliable guide to degree of resistance.

Length of hairs is shown to be of prime importance, and high densities without adequate length are ineffective.

The relative importance of hairs on lamina and midrib has not been conclusively determined. Both have an influence on resistance but a high degree of midrib hairiness is not essential if the lamina is hairy.

Hairs on stem and petiole are shown to be of very little direct importance.

DDT and “Gammexane” have many advantages over arsenic as acaricidal agents.

The sites of attachment of the common tick species on bovines are recorded and the killing properties of various dilutions of DDT and “Gammexane” are assessed by observations on R. appendiculatus attached on the ears and A. variegatum attached on the udder and flanks of cattle.

The preparations were usually applied as sprays by means of a flit-gun, an Aerograph spray gun, and Kent sprayer or “Solo” hand pump. A “swirling-jet” nozzle was found most suitable. A possible combined spraying-dipping method using a shallow bath is also described.

In preliminary experiments, a spray containing 2·5 per cent. DDT and a preparation containing 1:10 of the “Gammexane” dispersible powder P.530 killed all ticks attached at time of spraying but the residual effects were lost about the 4th day after spraying. Field experiments gave similar results, but 1:20 of the P.530 powder (0·325 per cent. active gamma) proved equal in killing value to the 1:10 preparation.

The addition of coumarone resin did not increase the residual effects of a 2·5 per cent. DDT emulsified solution.

The mosquitos of the reservoir area have been studied mainly with the object of planning suitable methods of controlling malaria. This paper is an account of the work done so far.

The diversity of conditions in the area, which is of such length that it has been divided into three sections, is described with special reference to the river and reservoir levels, predacious fishes, breeding places of mosquitos and water plants among which mosquitos breed.

The mosquito fauna of the area is described and observations on the breeding places and adult habits of the principal species are recorded. The large proportion of “ripe” females among Anophelines dissected is noted.

The probable effects of the reservoir conditions on the mosquitos are discussed.

Notes are given on certain species, and the relation of A. rufipes and A. pharoensis to malaria are discussed from circumstantial evidence. The former is provisionally regarded as a vector.

Control measures are described with particular reference to A. funestus (in the south), A. gambiae and A. rufipes, the latter being a vector of malaria expensive to control in the larval stage. The value of insecticidal dusts in the area is discussed.

The determination of mealybugs closely related to Pseudococcus comstocki (Kuw.) has presented considerable difficulty in the past. Green (1921, p. 189) and Hough (1925, p. 52 and 1925a, p. 13) have given details of the distinguishing features for P. comstocki (Kuw.) and P. maritimus (Ehrh.) but the grounds given for the separation of the former from other closely related species are not fully satisfactory. The representatives of this group of mealybugs are becoming more and more widely spread throughout the world and of greater economic importance yearly. A correct designation of these insects is, therefore, of particular importance not only from the point of view of quarantine legislation but also of control measures. Research work on the morphological characteristics of species closely related to Pseudococcus comstocki (Kuw.) has been carried out on very large quantities of material from different parts of the world.

When DDT and “Gammexane” were first used in Uganda for work on tick control, the absence of a rapid and simple chemical test made it necessary to evolve a biological method which would assess the killing power of the preparations in use. Such a method, if it is to be employed to assess the results of field work, should satisfy the following conditions;

(a) ticks should receive an initial wetting with the preparation comparable to that received when cattle are dipped or sprayed, and

(b) remain on a moist surface for a few hours, and then for a longer period in contact with the dried deposit, as in the case of the animal after it has been dipped or sprayed.

Benzene hexachloride and DDT are relatively new insecticides and their veterinary value when administered orally to bovines has not yet been fully investigated.

The first series of experiments showed that 0·5 gm./kg. on two successive days of D. 929, was toxic; 0·25 gm./kg. on two successive days followed by 0·125gm./kg. on the 3rd and 4th days was well tolerated, and the benzene hexachloride remained in the blood in sufficient concentration to kill feeding tsetse and ticks up to the 41st day. After a single dose of 0·25 gm./kg. the benzene hexachloride remained in the blood for only 10 to 12 days, and failed to protect the animal from East Coast Fever when it was grazed on heavily infested pasture.

Five calves susceptible to East Coast Fever were dosed with D.929 and exposed to attack by the common tick species under African farming conditions. A dose of 0·125 gm./kg. given weekly protected a calf from East Coast Fever, but there was no protection when the same dose was given once a fortnight. A dose of 0·125 gm./kg. given weekly also protected, whereas 0·1 gm./kg. failed. At all these dosages the concentration of benzene hexachloride in the blood was sufficient to kill feeding G. palpalis during the period the calves were under treatment and for periods of 10 to 25 days after the final dose.

D.929 given to animals suffering from East Coast Fever and Trypanosomiasis had no effect on the course of these diseases.

Doses of 0·3 gm./kg. (39 mg./kg. gamma isomer) are toxic to young animals but older animals showed a greater tolerance. Hypersensitivity, muscular tremors, and general paralysis were the main toxic symptoms, and gross pathologicaal changes were most obvious in the liver and urinary system. The median lethal dose of benzene hexachloride given orally for calves is therefore lower than for small laboratory animals as recorded by Cameron (1945). Only crude benzene hexachloride powder (13 per cent, gamma) was used in the preserit experiments, but Slade (1945) has shown that this is markedly less toxic than the purified gamma powder.

Little experimental work was done with DDT as the results with benzene hexachloride were more promising both in the control of ticks and tsetse.

Observations are recorded on the habits and behaviour of wild adult A. amictus hilli and A. punctulatus farauti at Cairns, North Queensland, and of the two subspecies and intermediate forms of A. punctulatus in New Guinea.

The most important points determined, which bear on the control of adults of A. punctulatus, are:—

(1) Females disperse from the breeding area shortly after emergence. During the day, they are rarely found indoors in any numbers, but hide away in moist, sheltered places in the bush in the vicinity of the source of the blood-meal. Fertilisation of the female takes place here, and these diurnal resting places are vacated only for the purposes of feeding and oviposition.

(2) Both before and after feeding, females rest on the walls, etc., of huts and houses, which they readily enter. There is some evidence that the normal flight is dose to the ground, and only comparatively small numbers enter houses built several feet off the ground.

(3) Activity does not usually commence until just after dark, and the peak of abundance occurs in the early hours of the morning.

(4) Females may disperse at least one mile from their breeding grounds in search of a blood-meal.

(5) In New Guinea there is a distinct preference for the native.

(6) Whilst A. pundulatus farauti does not show any marked preference for man, animal or bird, A. pundulatus pundulatus has very definite androphilous tendencies.

The habits of A. amictus hilli are broadly similar to those of A. pundulatus farauti, but differ in important details. It does not rest indoors during the day, but its favoured outdoor habitat awaits determination. Only a few females were found at Cairns in the bush diurnal resting places used by A. pundulatus farauti, whilst the large numbers observed on the breeding area were there for the purposes of oviposition. Fertilisation takes place in the breeding area, where the males remain. There also appears to be a different nocturnal periodicity from that observed for A. pundulatus farauti.

An attempt was made to determine the ages of the females captured at night and during the day by means of the criteria of ovary development, wing condition, presence of blood and of spermatozoa. The interpretation of these criteria was assisted by observations on bred A. pundulatus pundulatus.

Limewashes containing DDT or “Gammexane” were tested for insecticidal action on mosquitos (Aëdes aegypti) by confining the latter in cages with treated walls and ceilings. Only about 60 per cent, of the total internal surface of the cages were treated but the mosquitos were averse to settling on the floor, window, etc., which constituted a large part (28 per cent.) of the untreated area.

Limewashes containing 160 mg. DDT per square foot gave a high kill of mosquitos after two hours' exposure in the cage; and 8 mg. per square foot of the active principle of “Gammexane” gave a high kill with a one hour exposure.

Both treatments remained effective for 6–8 weeks under temperate conditions.

The parasitic larvae of a number of Trombiculid mites are of economic importance as they include the vectors of scrub typhus, and scrub-itch mites of considerable nuisance value. Methods of trapping these mites and various field and laboratory observations on them are described. The methods were evolved and observations made during the course of work, sponsored by the Medical Research Council, in Imphal, Assam and Compton, Berkshire.

Live unfed larvae in the field may be concentrated and trapped by use of a low cover with a central light-admitting aperture and collecting apparatus. This method proved very efficient in trapping harvest mites (Trombicula autumnalis) in England. The rise in temperature within the trap can be made advantageous.

Guineapigs were chosen as bait animals for the collection of T. autumnalis at Compton, most of the larvae attaching near the anus and genitalia. The larvae fed for between 30 and 60 hours.

Engorged larvae may easily be collected as they leave their host (or dead animals and débris) by the funicular laboratory light-trap described.

Observations are made on the collection of adult mites, and to a lesser extent nymphs, from soil flotation in water. The vertical migration of adults in relation to soil moisture and temperature is discussed.

Observations on the appearance of larvae of T. autumnalis on a chalk-down at Compton showed a sharp seasonal peak in September, 1946, and some evidence is adduced that this was related to a peak in oviposition.

Observations are made on attempts to rear T. deliensis, the scrub typhus vector in Assam, and notes are added on the behaviour of larval and nymphal mites.

Investigations on the possible biological control of a particular insect pest usually have as their object the discovery of parasitic or predacious species which, when liberated in a different area without their own natural enemies, will in time bring about an economic reduction in the numbers of the pest concerned. Hence it is desirable to have some standard of comparison between various parasites attacking a pest of their efficiency as controlling agents. The standard normally used is that of the percentage of hosts in a certain stage found to be attacked by a given parasite species. Samples of host material are taken in the field and either dissected or reared in the laboratory. In either case the parasite species present are noted, the percentage of the hosts parasitised by each species worked out (together with the figures for hyperparasitism, if any) and a comparison made between them as to their relative value as controlling agents. Often such estimations of the value of a parasite species are based on a few small localised collections of field material; but apart from any criticism arising from a statistical consideration of the methods of sampling there are certain difficulties of a biological nature inherent in the estimation of the degree of control exerted by individual parasite species, Some of these Will be outlined below.

Glossina morsitans and G. swynnertoni were allowed to emerge for three days from pupae placed in each other's habitats and in that of G. pallidipes.

The morsitans in the habitat of swynnertoni were in poorer condition, and survived less well, than in the previous year. This may have been because the release was done a little later in the season, or because the freshly emerged flies were not up to the nutritional standards of a year or two before.

They were, however, nearly as heavy, in later life, as wild morsitans in their own home, and this is contrary to previous experience.

In relation to initial weight, swynnertoni, whether in their own home or as aliens in the habitats of other species, were heavier than morsitans, and in fat and water the alien swynnertoni were heavier than the native ones. However, the difference between the two species may possibly be caused by the fact that swynnertoni, after taking its first meal, cannot apparently fall much below its initial weight at emergence, as morsitans and particularly pallidipes are able to do, so that very hungry morsitans may be represented by swynnertoni which have been cut off by death, and are not available to the catchers.

The males of morsitans and swynnertoni are relatively inactive in early life, which has an important bearing on estimates of population and mean life made from marked flies. The females on the contrary are relatively inactive in later life.

Generally the relation between wing-fray and age found in the previous year is confirmed, except one aberrant result when swynnertoni was released in the habitat of morsitans. Scanty data suggest that the rate of wing-fray during the rainy season is not very different. As before, the females, especially in later life, fray their wings more slowly than the males.

Teneral (unfed) flies below the average size are comparatively non-viable, and about 10 per cent, are too small to survive to obtain their first meal. There is no suggestion that the same applies to non-tenerals.

The external morphology of early larvae is described; the first instar is provided with an egg-tooth in the mouth, which makes it incapable of feeding. Both the first and the second instars are spiny.

Although copulation between morsitans and swynnertoni is random, insemination from interspecific matings often fails, and the sterile egg is aborted. In such cases the left ovary ovulates before the normal time.

The flies and pupae live at about the temperature of the standard climate as recorded in a Stevenson screen ; possibly the flies are a little cooler and the pupae a little hotter.

The genus Stethorus Weise is of special interest on account of its cosmopolitan distribution and the habit of its species of feeding mainly on mites, some of which are pests of crops, including fruit trees. Its relationship with other members of the tribe Scymnini is also of importance, as it was separated by Dobrzhansky in 1924 into a distinct tribe called Stethorini, which, however, was regarded by Korschefsky (1931) as synonymous with Scymnini. The material on which the present study is based came mainly from the Old World. Much of it had been submitted to the Commonwealth Institute of Entomology for identification, and I am grateful to Dr. W. J. Hall and Dr. T. H. C. Taylor, of this Institute, for giving me facilities and help. The remainder of the material studied was in the collection of the British Museum. I am indebted to Mr. N. D. Riley for procuring, on my behalf, certain type specimens from abroad for examination.

Females of both A. gambiae and A. funestus were found to enter buildings throughout the night, but more A. gambiae entered between 1 and 4 a.m. and more A. funestus just before dawn. Males of both species entered only just before dawn.

The rate of development of the ovaries was studied in individual mosquitos isolated in cages in the laboratory. The mean period between egg layings at a mean temperature of 25·5°C. was about 4¾ days in both species.

It was found that females of A. gambiae and A. funestus did not normally spend more than 24 hours in any one hut; but that they rested outside buildings during the day time only when newly emerged and just before and just after egg-laying.

Observations were made on the feeding and oviposition habits. It was found that females of both species would sometimes feed daily, whereas digestion of a full blood-meal occupied 24–72 hours in A. gambiae and 24–96 hours in A. funestus. The average dry season clutch of A. gambiae was 175 eggs and of A. funestus 123; wet season clutches appeared to be smaller.