The results presented in this paper apply to conditions in Wales. Although admittedly based on limited data, they show that of the nine species of ticks found in the Principality, only Ixodes ricinus, L. is found on sheep, cattle and horses.

It has been observed that the distribution of ticks throughout Wales is influenced by superficial soil deposits: studies in north, central and south Wales have shown, however, that the vegetation index from which ticks are recovered is variable. Analysis of soils from which ticks are recovered, gave a pH range of from 4·4 to 5·2, and the relationship between “mat” and soil acidity is discussed.

An investigation of four adjoining tracts of vegetationally different land—rush, bracken, heather-winberry and ley—showed that greater populations and a greater rate of activity were apparent in rush land. The significance of topographical location in relation to tick infestation even on land with the same vegetation index is indicated. A salt marsh adjoining an infested non-salt marsh was found to be free of ticks.

The occurrence of a unimodal activity curve is described for central and north Wales. Within a recognized bimodal activity belt irregularities of tick periodicity on cattle have been observed at some farms. This appears to be related to the nature of the sward, and, where good pasture occurs alongside “islands” of damp ground, such discrepancies are noted.

Such “islands” may harbour ticks, while the rest of the pasture is free. When, as the result of certain influences, cattle move to these “islands” they become infested. A meteorological condition is described which leads indirectly to such movement through the agency of the warble fly.

The study of the common house-fly, Musca domestica, L., has not received the attention it merits by medical entomologists. Although the correlation between fly-borne diseases and climatic factors has interested several workers, this correlation has not been satisfactorily explained. An investigation of the influence of climatic factors on house-flies was therefore undertaken.

House-flies can be reared in the laboratory by a proper choice of the breeding medium and suitable technique. Manures, kitchen refuse and synthetic media may be used but the last mentioned is recommended for the production of a supply of standard insects.

M. domestica chooses the lower humidity on each of the humidity gradients, 20–40, 40–60, 60–80 and 80–100 per cent., at a constant temperature of 25°C. The choice is significant for both sexes, and for dry and wet flies, except for dry flies at the range 60–80 per cent.

The house-fly chooses 30°C. in temperature gradients of 20–30°C. and 30–40°C. at constant humidity, expressed either in the R.H. or the S.D. scale. It chooses 30°C. with dry air if possible, but with moist air if it must. In a gradient of 33–27°C. where dry air is associated with 33°C. in the S.D. scale in the one case, and 27°C. in the R.H. in the other, it chooses 33°C. or 27°C. according as it coincides with dry air. Dry air as represented by low R.H. or high S.D. did not make any difference to its choice, consequently it is not possible to decide whether house-flies choose by the R.H. scale or the S.D. scale. The activity of M. domestica to different combinations of temperature and humidity shows maximum activity with high temperature and low humidity, minimum with high temperature and high humidity; while in the case of low temperature combinations with either high or low humidity, activity lies intermediate in degree. High and low temperatures and high and low humidity within themselves also show significant results by the χ2 test.

The experimental results are explained on physiological grounds and the results obtained in these experiments are compared with those of other workers on similar problems on a variety of insects.

The general experience with regard to house-flies in the field is explained in the light of these laboratory findings.

For a correct analysis of the behaviour of the house-fly in nature, biological stimuli such as feeding, breeding and resting habits must be considered quantitatively in relation to environmental factors such as temperature, humidity, rainfall and light. The present work forms part of such a study.

The unspecialised portion of the shell and the cap of Rhodnius eggs are impermeable to almost all hydrophilic and lipophilic liquids. If water and very small ions pass through the chorion they must traverse a wax layer on the inside of the shell. Certain corrosive materials, e.g., glacial formic acid, may pass through the shell slowly.

These conclusions, based on experiments with pieces of shell, have been confirmed in ovicidal experiments. A range of materials with widely differing properties enter the embryo only through the micropyles, of which there are approximately fifteen in the rim of each shell. At least one micropyle must be traversed to kill an egg but many eggs were killed when only one had been penetrated.

A cement, applied by the female at oviposition, may occlude the outer orifice of a micropyle. The properties of the cement are described; it appears to be a tanned protein. Cement deposits are much more copious on the eggs laid by younger females. Such eggs are more resistant to ovicides because penetration is delayed. This increased resistance is more pronounced when oleophilic liquids are used owing to the rapidity with which they kill eggs from older females. The random distribution of cement is one cause of the variability of replicates in ovicidal tests.

A detailed investigation has been made of factors governing liquids traversing the micropyles. Hydrophilic liquids invade the outer lipophilic part of the micropyle slowly; the displacement of air is the most important factor and small changes in the wetting power of the liquid make little difference to the rate of entry.

Aqueous liquids aie absorbed into the protein lining of the inner portion of the micropyle. They reach the wax layer on the inside of the shell by migrating into and through the inner protein layer. The area which is invaded increases linearly with time. Mortality, therefore, increases as the square of the time of immersion, but it is proportional to the increase in concentration of a solute if the period of immersion is constant.

Oleophilic liquids wet the micropyle actively. They may by-pass air and flow rapidly to the wax at the inner end of the tube. Wax solvents kill very quickly and are much more toxic than other lipophiles.

Water in the micropyle and shell may affect the entrance of either type of liquid. In general it increases the toxicity of aqueous solutions and retards the entry of oils.

Wax-emulsifying materials added to aqueous solutions do not produce great increases in toxicity. They are “filtered out” at the protein lining of the micropyle and do not reach the wax layer for a considerable period of time.

Various substances have been used by different workers as substrata for breeding the house-fly under laboratory conditions. Horse manure was recommended by Hutchison (1916), Glaser (1924), Grady (1928), Derbeneva (1935) and Kusina (1936). A mixture of horse manure and hog manure was used by Hockenyos (1931). Feldman-Muhsam (1944) obtained the best breeding results by using cow dung. Pig dung was preferred by Lörincz & Makara (1935). Lodge (1918) reared house-flies on a mixture of casein, bread, water and banana. Richardson (1932) used another mixture of wheat bran, alfalfa meal, diamalt, yeast and water. Kobayashi (1935) used a by-product of soya beans. Basden (1947) in his large scale experiments, necessitating about 2,500 flies daily, used a mixture of middlings, grass meal, tap water, dry malt extract and dried yeast.

The reactions of Aëdes aegypti females to certain stimuli normally associated with the human surface body have been investigated. The apparatus used was such that the insects were unable to touch the source of stimulation. Attraction to the latter was indicated by the congregation of females in its vicinity.

The following stimuli proved attractive: the intact palm of the hand; collected sweat at room temperature; moisture at room temperature; moisture at body-surface temperature. A warm surface at body-surface temperature produced no apparent effect, either of attraction or of repulsion.

The four types of stimulus found to be attractive also had marked activating effects. The magnitude of these effects was much greater for the hand and warm moisture, than for cold sweat and cold moisture.

Due allowance for the complication introduced by these differences in activation having been made, cold sweat appeared to be slightly, but significantly, more attractive than cold moisture. A reaction to olfactory stimuli is presumed to have been responsible for this. Such stimuli, however, are not considered to have been of much importance in comparison with warmth and moisture; moisture at body-surface temperature had very nearly, and possibly the same, attractive effect as the intact hand.

The results are compared with those of other recent investigations, and the need for caution in applying them where conditions differ from those under which they were obtained is emphasised.

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.

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.

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.

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.

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.