The yellow tea-mite should in future be known as Hemitarsonemus latus (Banks) Ewing.

The males have a curious habit of carrying female pupae to younger leaves. The pupa is held above the male's body by means of a sucker-like organ near the tip of his tail-like, posterior terminus. Thus the male plays an active part in distributing the pest.

Mating has not been observed, but normally it occurs as soon as the female becomes adult. It may also occur later in her life.

Unfertilised females give rise to male offspring only, but mated females have mixed families.

(1) Spraying of huts with 0·1 per cent. pyrethrum in kerosene, at the rate of 25 c.c. per 1,000 cubic feet, deterred 90 per cent. of A. minimus from entry on the following night. The repellent effect persisted in diminished degree for at least four days.

(2) A rather larger quantity of pyrethrum, sprayed in a Freon aerosol, produced a similar but somewhat less marked effect.

(3) The repellent effects of Lethane 384 in kerosene were much less marked, and not discernible on the second night.

(4) Different species varied greatly in their sensitivity to the repellents.

(5) Two types of repellent effects were indicated. Repellent effects proper were the most important, and males were more sensitive to these than females of the same species. There was also a masking effect, to which anthropophilic females were sensitive, which resulted from obscuring of attractive human scents by the chemical odours.

A previous investigation by the writer established that the minimum deposit of DDT on both cement and old painted wood necessary to ensure complete mortality of bed-bugs 48 hours after spraying was 0·2 mg. per sq. cm., and that the toxicity of both surfaces diminished slowly over a period of six months. The present work has shown that when DDT is applied with an adhesive agent, the minimum deposit of insecticide necessary on these surfaces to yield a similar kill at the same interval after treatment was only 0·06 mg. per sq. cm. The addition of an adhesive agent to a DDT spray thus effects considerable economy in the use of DDT. Campbell and West (1944), investigating the toxicity to houseflies of coumarine resin and DDT dissolved in white spirit, have reported an increase in the efficiency of DDT when sprayed with an adhesive agent. These authors confined their investigation to a resin only and they suggested that the coumarone resin conferred, in a manner not specified, increased insecticidal activity on the DDT. The present work has shown that relatively small doses of DDT are highly effective in the presence of at least three dissimilar adhesive agents. It is possible, therefore, that instead of increasing the activity of DDT, the agent merely blocks the minute pores of the treated surface, and by minimising absorption of the solution, increases the amount of DDT available to the insect. Alternatively, the adhesive agent may have some affinity for substances on the surface of the bug's tarsi and so assist transfer of DDT from the sprayed surface to the insect.

The residual toxicity of cement treated with DDT and an adhesive agent, like that of a similar surface treated with DDT alone, diminished slowly. The toxicity of painted wood, on the other hand, treated with doses of DDT and adhesive agent ranging from 0·005 to 0·02 mg. per sq. cm., decreased within one month, irrespective of the adhesive agent used. This fall in toxicity is puzzling, particularly in view of the fact that no such decrease occurred when the surface was treated with a heavier deposit of DDT and adhesive agent, namely 0·06 mg. of each per sq. cm. This latter observation seems to preclude a possible interference with the efficiency of DDT by a slow interaction of the paint constituents and the adhesive agent.

The application of these adhesive agents, even in relatively high doses, failed to prevent the removal of DDT from a smooth surface by repeated washing and rubbing; furthermore, an increase in the deposit of adhesive agent does not markedly increase the insecticidal efficiency of a given deposit of DDT.

Experiments are described which illustrate some of the ways in which the results of exposing insects to a spray mist are dependent on either their behaviour or physiological state. Only fine mist dispersals with particles below 10 microns in diameter are considered and in such mists the flight movements of the insects are very largely responsible for the collisions between the insect and the droplets. An increase in flight activity leads to the accumulation of a greater number of spray droplets and consequently a higher kill. Under these conditions insecticides such as pyrethrins which exert a strong irritating action on Aëdes in minimal amounts are superior to DDT which does not have this effect. For practical applications under circumstances where the sprays depend on mist action to produce their effect it is advantageous to mix pyrethrum with the DDT sprays so that the maximum dose of the latter may be accumulated.

Further experiments are concerned with the relative resistance of male and female Aëdes aegypti to insecticides and the change of resistance which takes place on ageing or as a result of a blood meal. It is shown that the male is innately more susceptible to both pyrethrins and DDT and that the resistance of the females is higher after a blood meal. There is also a progressive decrease in resistance with age.

An increased indoor population of Anopheles sacharovi at the start of hibernation is recorded.

Figures are given for dissections of A. sacharovi during the winter months, showing an infectivity rate (sporozoites) of 0·41 per cent.

Eggs of A. sacharovi laid at the end of hibernation are described.

An account is given of an area in Northern Persia where A. sacharovi is present in association with a lower endemicity of malaria than is usual.

We are indebted to Lt.-Col. D. N. Keys, R.A.M.C., Major J. Yofe, R.A.M.C., and Major R. Hillman, R.A.M.C., for their interest and help in these observations.

Myzodes, Mordv., 1914, type Myzodes tabaci, Mordv. (═ Aphis persicae, Sulzer) is a synonym of Nectarosiphon Schouteden, 1901 (nom. nov. for Macrosiphum, Del Guercio, 1900, nec Passerini, 1860). Following Baker's 1920 Generic Classification, Aphis convolvuli, Kalt. (which clearly is Aphis persicae, Sulzer) is the type of Macrosiphum, Del Guercio, and therefore of Nectarosiphon Schouteden, a subgenus of Myzus, Pass.

The investigations were carried out in the Inland Savanna Forest Zone of the Northern Territories of the Gold Coast, the climate of which is characterised by extreme variations in rainfall and relative humidity between the wet and dry seasons.

Glossina palpalis and G. tachinoides are widely distributed along the waterways throughout the zone. They come into intimate contact with the human population and are, in consequence, the most important vectors of human and animal trypanosomiasis.

G. morsitans submorsitans occupies unpopulated and thinly populated regions and so, coming more rarely into contact with man and cattle, is a less important vector of trypanosomiasis.

A pandemic of sleeping sickness, with 30,000 square miles of heavily infected country, lies across the upper reaches of the Volta rivers and involves parts of the north of the Gold Coast. In the areas studied high rates of infection (4–7 per cent.) were found associated with serious population declines which have given rise to secondary evils, the invasion of G. morsitans into depopulated parts and the concentration of populations on the watersheds between infected river valleys, with resultant over-farming, erosion and lowering of the standard of living.

The results of two methods of controlling G. palpalis and G. tachinoides were studied : (1) “ Protective Clearings ”, aimed at breaking the contact between the tsetse and man or cattle at certain points only ; (2) “ Eradicative Clearing ”, aimed at the complete removal of tsetse throughout an area.

The effects of protective clearings on the fly were as follows : Clearings less than 300 yards in length are considered useless, and may cause an increase in fly-incidence by forming artificial feeding grounds. Clearings of 440 yards can effect up to 70 per cent, reduction in fly-incidence measured over a long period, but for several months of the year show no reduction or may even show an increased incidence. Clearings up to 880 yards long can bring about 60–90 per cent, fly reduction, but at two periods during the year, at the end of the dry season and in the middle of the rains, their effectiveness is considerably lowered by the invasion of hungry flies into the clearings. Clearings over a mile in length exclude all but a few vagrant flies, but even five miles of clearing are traversed by occasional flies.

A study of the effects of various applications of protective clearings on the incidence of sleeping sickness led to the following conclusions. To have any value protective clearings must be made in as many places as possible over a wide area. They effect no general reduction in the disease if applied at a few places only. Small clearings, averaging 400 yards in length, if made consistently over a large area, can effect up to 40 per cent, reduction in sleeping sickness in 4–5 years, after which the disease tends to become stabilised at the lower level. Long clearings, averaging 1,000 yards, almost double the rate and amount of reduction, effecting 70 per cent, reduction in three years, but the tendency for the disease eventually to become stabilised remains. Clearings over a mile in length at each village caused a reduction of 85 per cent, in one area.

Protective clearings alone are considered unlikely to be able to effect complete control in areas of serious endemic sleeping sickness. They do not entirely exclude the fly, and they do not touch all the points where the transmission of infection takes place. Further disadvantages arise from the fact that, to attain maximum fly reduction, all vegetation, including tall trees, should be cut. This is expensive and difficult and may lead to erosion and the silting up of water-holes, thus driving the people back to uncleared parts of the river. Finally, animal trypanosomiasis can never be controlled by localised clearings, therefore improvement in animal husbandry, and consequently in agricultural practice and nutrition cannot be fully realised.

Eradication of G. palpalis and G. tachinoides is based on the consideration of the tsetse community of a complete river system as a natural biological unit. During the prevalence of the adverse climatic conditions of the dry season, the breeding and survival of tsetses are possible only in certain restricted habitats from which the flies spread extensively along the water courses during the rains. The dry-season habitats are confined to definite plant associations that are characterised by a limited number of species of trees and shrubs. The removal of only these species throughout a river system renders the habitats untenable during 4–6 months of the dry season and results in the disappearance of the whole fly community.

By the method of selective clearing, 1,050 square miles of country in the northwest corner of the Gold Coast were freed from tsetse between December, 1940 and March, 1945. On the main river of this region, the Kamba, which was cleared by 1942, routine catching after clearing showed 1–8 flies per year in places where the pre-clearing averages had been 2,700–7,500 flies per year. After the clearing of some neighbouring fly-belts, these occasional captures ceased. Wet-season migration from the uncleared Volta, however, brings small numbers of flies 5–9 miles up the lower reaches of the cleared river.

The incidence of sleeping sickness for the Kamba area fell by 92 per cent, between 1938, the year before the start of control measures, and 1944.

Along the Kamba, 160 square miles of land which had become depopulated through trypanosomiasis is being developed voluntarily by the natives, by farming, grazing, etc. Approximately 1,000 people have settled in parts of this area since clearing was finished.

In 1939 G. morsitans invaded the depopulated area, and increased greatly in numbers in the following years. The spread was checked, and finally a high degree of control was established by the disturbance of big game and its reduction in numbers. Settlement of the thinly populated country is needed to consolidate this control.

Selective clearing can be followed by the eradication of essential dry-season habitat vegetation which will enable maintenance to be put on a long-term rotation of about ten years. Permanent reclamation is a possibility that is now being studied.

The relative merits of medical and entomological methods of controlling sleeping sickness are discussed. Mass treatment can have great success, but fails to control under difficult conditions, and has not yet been found able to eliminate the disease. The addition of adequate tsetse control increases the effect of mass treatment. Eradication of the fly is capable of eliminating the disease and does not require the addition of mass treatment to bring this about.

The removal of tsetse throughout the river system, as in selective clearing, has the following additional advantages : It makes possible a sound agricultural development based on the possession of good quality livestock; this reflects also on nutrition. It enables the population to live with impunity in the vicinity of permanent water and, by spreading out at a density optimum for their type of agriculture, to avoid concentrations at local clearings or on dry, hilly country away from rivers; thus the possibilities of over-farming and erosion are avoided and the watersheds and headwaters can be reserved for afforestation. By these means, instead of ground being abandoned to the tsetse, the fly is replaced by a healthy agricultural population.

Laboratory and field observations have been made on the biology of Wheat Bulb Fly in the years 1943–45. The eggs hatch in late January and early February. Severe frosts delay hatching but do not kill the eggs. In a laboratory experiment a high proportion of eggs buried 18 inches below the soil surface, hatched, and the larvae infested plants. Field observations showed that proportions of the eggs also survive prolonged flooding.

The development and habits of the larvae are recorded. It was confirmed that oats are not a suitable host and though a very small number of these plants were infested the larvae did not survive. Occasionally two larvae infest the same shoot and when this happens one larva dies. The larvae leave the plants in April or early May and pupate in the soil. The pupal stage lasts six to seven weeks.

The adults emerge, males first, in June. Copulation occurs about three weeks after emergence and at this time dense aggregations of flies occur. Usually males predominate in these and in certain circumstances all the flies are males. The flies disperse gradually from the field in which they emerged and the females start laying eggs in suitable areas about a month after emergence. In Yorkshire egg laying occurred in July and early August and lasted about a month. Even within the limited area and time of these observations variations up to three weeks were noted in different places and seasons. Lateness was associated with heavy soils.

The present study is based primarily on beetles collected in the field. Although several individuals of Capnodis carbonaria, Klug, and C. tenebrionis, were reared successfully from egg to maturity, these beetles were as a rule weak and short-lived, and consequently unsatisfactory for the purposes of this investigation.

The construction of an inexpensive, simple, hand-drawn fumigator for field plots is described. The general principle employed is the injection of liquid nicotine under pressure into the exhaust system of a two-stroke engine, close to the port. The liquid is vaporised by the heat of the exhaust stream and distributed by it below a drag sheet at the rear of the machine.

The machine is of simple and robust construction, utilising standard plumbing fittings, angle iron, strip iron and second-hand motor-cycle parts and can, therefore, be made where only limited facilities are available.

The machine is self-contained and easily transportable as it can be towed behind a car from one locality to another. It is suitable for use on a wide variety of crops since the track is variable between 43 in. and 67 in. and the clearance between 16 in. and 34 in. With the 18 ft. long sheet used it can fumigate, in good conditions, one acre in about five hours. It is pointed out that the use of a lightweight sheet about 54 ft. long would decrease the time required per acre to about if hours and would enable the machine to be drawn by a tractor if desired; these suggestions have not, however, been tried.

The machine has been in use since 1941 for controlling aphis infestation in connection with work on virus yellows of sugar beet and has given most satisfactory results. Tests showed that a kill of 88–99 per cent, of Aphids was obtained.

A generation of Glossina morsitans was artificially isolated by allowing emergence for three days in the habitat of G. swynnertoni and G. pallidipes.

Most teneral flies (with chitin unhardened before their first meal) were active on day 2 to 4 from emergence. The non-teneral flies first appeared in numbers when a week old. It is possible that they were somewhat inactive while still fairly young, that is, up to two or three weeks, but this was not proved. They are definitely inactive between the first and second meals. The females, on the other hand, are much more active in the first three weeks of life than later on.

The teneral males contained about 12 mg. water, which was increased after several meals to a maximum of about 18 mg. by day 17. Fat started at a mean of 1 1/2 mg., declining to 1 mg. at the first meal, then rising to about 3 mg. at day 17, after which there was no further increase. Residual weight behaved like the water, except that it was relatively very low in teneral flies. The hungry flies which reappear after the first meal have also a relatively low residual weight.

In this experiment there was no evidence that smaller flies were at a disadvantage, as has been suspected from other work.

With reservations concerned with differences in place and time, the mean age of samples of male flies can be accurately deduced from the wear on the trailing margin of the wing. The females do not wear out their wings so quickly.

Males dispersed, in any one direction, to a mean perpendicular distance of 365 yards in a week, 484 yards in two weeks, 772 yards in three weeks, and 941 yards in four weeks.

In spite of undoubted interference by G. swynnertoni, a considerable second generation appeared.

The females and pupae in nature experienced temperatures approximating to those obtained in a screen at a standard meteorological station: they did not live in specially cool eeoclimates.