1. A study of mosquito breeding in plant axils was carried out in Bwamba County, an area with much heavy forest in the extreme west of Uganda. Attention was directed mainly to Aëdes (Stegomyia) simpsoni, a known vector of human yellow fever in Bwamba.

2. The various plants studied are described.

3. The results of preliminary surveys are discussed. These confirmed that, as far as mosquito breeding is concerned, the most important plants in Bwamba are the lowland colocasia (Xanthosoma sagittifolium), the “gonja” variety of cultivated banana and the pineapple (Ananas comosus). It was shown that A. simpsoni is the commonest axil-dwelling larva in the inhabited lowland areas, and that it occurs in widely different types of lowland country. Records are given of the occurrence of larvae of Aëdes (Stegomyia) aegypti in plant axils.

4. A survey of 12 different kinds of plants is described, and it is shown that the larval populations depend to a considerable extent on the amounts of water retained by the axils of the various plants concerned. In Bwamba, medium-sized axils with a capacity of 4 to 8 cc. appear to be the most favourable. Certain plants which yielded large numbers of larvae—such as the wild banana (Musa sp.)—were not found to harbour A. simpsoni. Apparently this is due to the fact that they are confined to forest and mountain areas, where A. simpsoni is scarce or absent.

5. A monthly survey of Xanthosoma axils, carried out over a period of 12 months, showed that A. simpsoni larvae were continually present and that the fluctuations in larval population were dependent on growth and harvesting of the plants rather than on rainfall.

6. Scrapings from dry Xanthosoma axils, taken during a short period of drought, were placed in bowls of water in mosquito-proof cages. Larvae of A. simpsoni and Harpagomyia taeniarostris hatched from this material in 2 to 3 days.

7. Temperature measurements in a Xanthosoma axil showed that the water therein was cooler than the surrounding air and also that the axil temperature was remarkably equable.

8. Systematic collections of pupae from Xanthosoma axils showed that the mosquito output (which cannot be gauged directly from the population of larvae) is high and constant. It is estimated that a plot of 500 plants of this species may, under favourable conditions, produce something like 5,000 A. simpsoni (2,000 females) per month.

The influence of predatory larvae (Eretmapodites spp.) on the populations of other species is thought to be considerable.

9. The fauna of plant axils, apart from mosquito larvae, is described briefly.

During development, membranes are added to the inner surface of the chorion in eggs of Rhodnius prolixus. The chemistry and permeability of the membranes have been investigated.

A true fertilisation membrane is produced immediately before oviposition when the egg is fertilised. It is attached to the inner surface of the primary wax layer, recessed into the micropylar region and covers the whole inner surface of the shell.

The membrane is very thin when first formed. It is colourless, comparatively resistant to solvents and apparently composed of “vulcanised” protein. It is semi-permeable to salt solutions but made very permeable to small molecules when immersed in absolute alcohols.

In the following five days of incubation, further material is added to the fertilisation membrane. Over the main part of the shell and cap, this does not cause a great increase in the thickness of the, membrane. The added material is probably proteinaceous, with tanning- and vulcanising substances and it is mostly a product of the serosa.

Opposite the inner openings of the micropyles, material is accumulated at a much greater rate and by six days incubation the membrane may be fifteen microns thick. The inner surface of the egg-shell thus becomes a uniformly ellipsoidal body. The thickened material has been called the epembryonic ring.

At about the, sixth day of incubation, shortly before blastokinesis, the membrane is partially impregnated with a high-melting-point wax. This raises the “transition point” in the egg's water-loss/temperature curve from 42·5°C. to 68°C. Evidence is against this material being arranged as a second wax layer on the inner surface of the membrane.

No further changes were detected until the thirteenth day when the innermost part of the membranes are broken down by the embryo. On the day before eclosion the embryo is surrounded by a liquid containing emulsified wax and proteinaceous material. The properties of the membranes return towards those of the one-day-old egg but do not attain them ; the egg hatches on the 16th day.

The changes in the membranes produce considerable changes in the apparent toxicity of ovicidal liquids; ovicidal experiments are recorded and explained. In general, the egg becomes more resistant to lipophiles over the first six days and less resistant afterwards, due to the wax impregnation. The resistance to hydrophiles increases during development due to the epembryonic layer and secondary wax, but decreases when the membranes are broken down just before eclosion.

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.

Experiments were carried out to study the possibilities of using ground or crop interference with the spray laden slip-stream of a helicopter flying slowly in the ground cushion to obtain a high dynamic catch of spray droplets. Experiments were carried out in 1945 and 1946 with a Sikorski type Y.R.4.B. helicopter and experimental spraying gear designed for the purpose.

The forward portion of the slip-stream annulus was explored by means of spraybars placed in three different positions. The position in the sector between angles of 15° and 45° with the direction of forward flying was found to give the best all-round cover and was the position in which the spray deposit was less influenced by alterations in the control-surfaces of the helicopter.

To obtain a fairly wide swathe of approximately 70 ft., the equivalent of two rotor diameters, the forward speed of 6–8 m.p.h. was found to be optimal, and it was observed that not only was good cover of the upper surfaces of the leaves obtained but the spray-laden slip-stream also gave a good cover of the vertical surfaces of the plants outside the rotary periphery and, in certain boom positions, descended and in rebounding produced a cover of the lower surfaces.

In order to obtain maximum dynamic catch and a good cover of the lower surfaces of leaves, spray-bars must not be more than 6 ft. above ground.

Helicopter spraying is wind dependent and in wind velocities above 12 m.p.h. uniform cover of spray deposit does not appear to be feasible.

The performance of the flattened out slip-stream and rebound depends on the type of crop, and as this affects the dynamic catch to a considerable degree, this phenomenon will be the subject of a special investigation.

The forward portion of the slip-stream was found to give a more even spray deposit than the aft portion because in the latter case vortices are caused by the rotor blades which affect the spray deposit.

In view of its limitations as regards speed and dependence on wind velocity, economic application of spray chemicals by helicopter at a degree of efficiency and workmanship equal to that of ground machines is only possible with a heavy load-carrying helicopter. A specification for such a machine has been issued to the manufacturers of rotory wing aircraft.

It is hoped that this report will be followed by a report on the performance data of the new spraying apparatus designed for the Sikorski S.51 which is based on the results of these investigations.

Several species of Tribolium are important primary and secondary pests of various kinds of cereal products and for this reason have long attracted the attention of entomologists. Some of the species are easily cultured in the laboratory and have therefore become favoured animals for experiments not particularly concerned with their rôle as pests. As a result of the two avenues of approach, a very impressive amount of information has now been accumulated concerning the habits and physiology of a few of the species.

The importance of finding the effect of defoliation on the reproductive capacity of Cordia macrostachya is explained in view of the proposed introduction of two species of leaf-eating beetles from Trinidad into Mauritius for the control of this weed.

An account is given of experiments in which the production of inflorescences and fruits was compared in defoliated and control plants.

The results show that defoliation has a significant effect in reducing the reproductive capacity of the plant.

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.

Langata Forest is a small, detached forest, 11 square miles in area, of the African plateau type, lying 5 miles west of Nairobi at an altitude of 6,000 ft. The forest is mostly secondary and although of evergreen character, much foliage is lost during the long dry seasons. The indigenous trees include olives (Olea chrysophylla), crotons (Croton megalocarpon), muhugu (Brachylaena hutchinsonii) and cape chestnut (Calodendron capense).

The Pea Moth, Laspeyresia nigricana, Steph., is one of the principal pests of garden and field peas in Great Britain. Its larvae feed within the pods causing considerable damage to the developing seeds and giving to their contents a veryunsightly appearance. The insect is widely distributed in England and, according to Meyrick (1927), occurs in Scotland as far north as the Clyde. It is most prevalent, however, in the southern part of England, where in the pea growing counties of Lincoln, Essex and Kent it frequently causes severe losses. It is widely distributed in central and southern Europe while in North America it has spread, since its introduction, to all the main pea producing areas and has become a major pest.

From 1940 up to the time of writing, experiments have been carried out in the savanna country in the north of the Gold Coast on the trapping of Glossina palpalis and G. tachinoides, which are the most important vectors of sleeping sickness in West Africa.

The habitat of these tsetse is described, with special reference to their feeding grounds, since those are the places where, trapping can be most effective and control of the flies is most desirable.

A new type of trap, the Animal trap, was designed to meet the feeding habits of the two species of tsetse whose main hosts in the country where sleeping sickness is prevalent are man and domestic animals.

The construction and maintenance of the Animal trap are described, the essential feature of which is a barrel-shaped body standing out well under good lighting and easily visible from all angles.

Traps with a standardised 2-feet-long body raised 1 foot from the ground combined optimum catching with convenience in construction and portability.

Light brown or khaki covering was slightly better than black, and rough material was decidedly better than smooth. Under poor lighting conditions these differences were less marked.

Comparisons over long periods showed that the Animal trap caught over 20 times as many flies as the Harris trap which was not at all suitable for G. palpalis; about 10 times as many flies as Swynnerton's A.S.B. trap; and about seven times as many flies as Chorley's Crinoline trap.

The correct siting of traps is of the greatest importance.

Traps catch well anywhere in fly-belt but are most effective in open feeding grounds such as ferries, fords, waterholes and animals' drinking places.

The regular presence of an abundance of hosts is the, most important single factor for good siting, and the nearer the traps can be placed to natural hosts the more effective they will prove.

Traps should be placed if possible with their axes at right angles to the regular lines of movement of the flies.

Good visibility of the trap from as wide an angle as possible is of great importance. Traps about five yards from the edge of the fly-belt catch twice as well as traps right at the margin of the bushes and considerably better than traps 40-50 yards out.

Good lighting, especially from overhead, is an advantage but by no means essential.

Good sites remain consistently good as long as the environment is unchanged, and bad sites remain bad.

There is a tendency for the numbers of flies caught to fall by as much as 70 per cent, during the first few weeks when traps are placed in undisturbed fly-belt. This is the effect of skimming off a part of the fly population in the immediate vicinity of the traps and does not represent a real reduction in population.

Comparison of tsetse catches by groups of five traps operating continuously, and by flyboys at the rate of 20 flyboy-days a month from parallel series of observations, gave the following facts for which explanations are offered.

Traps relative to flyboys are more efficient in taking G. tachinoides and less efficient in the cases of G. palpalis and G. morsitans. Flyboys, however, catch a higher proportion of female G. tachinoides but a lower proportion of females of the other two species.

It is considered that Animal traps represent the regular hosts of G. tachinoides and so attract non-feeding males as well as hungry flies of both sexes, whereas in the cases of G. palpalis and G. morsitans the traps represent something outside the range of their preferred hosts arid so attract only hungry flies bent on obtaining a meal.

Traps appear to have a greater efficiency relative to flyboys in groves and clearings where the numbers of flies are small, than in sites in or near heavy and extensive fly-belt with high fly populations. This is possibly the result of competition which would be most evident in small tsetse populations and which would act in favour of the continuously present traps.

There is a striking difference in the annual rhythms of catches by flyboys and by traps; the former showing a double-peaked curve with maxima at the beginning and in the middle of the wet season, the latter with a single peak towards the end of the dry season and a minimum during the rains.

The efficiency of traps relative to flyboys is greatest in January and least in September. In an estimate based on all the available data and comparing 150 trap-days with 20 flyboy-days monthly, the traps at their best were 10 times as good as the flyboys, and at their other extreme were as low as one-fourth of the flyboys' catches.

It is considered that this maximum efficiency in the dry season is not due to the flies' attraction to shade but that it is a complex result of the circumstances which bring about optimum conditions for trapping in the dry season, when the weather frequently puts flyboys at a disadvantage, and the most adverse conditions for trapping in the wet season when they enjoy certain advantages of mobility.

The seasonal rhythm of trap catches has demonstrated the presence of a considerably greater fly population in the height of the dry season than is suggested by the magnitude of boys' catches.

Three possibilities of trapping in the control of sleeping sickness are examined : (1) for extermination of the tsetse; (2) for reduction of the fly population; (3) for destruction of feeding flies in contact with people.

Regarding the first possibility it had been found that continuous catching by teams of four flyboys could eliminate G. palpalis and G. tachinoides from small groves after 8–12 weeks' continuous catching but that, since none of these groves was completely isolated, repopulation took place by immigration, especially in the wet season. Small numbers of traps, 5–7 to the acre, made no apparent difference to limited tsetse populations but concentrations of traps up to 20 to the acre brought about considerable reductions and checked the effects of immigration, but with no approach to extermination of the flies.

Eradication of the tsetse by traps is impossible but reduction of fly populations, if it can be effected over the main area of an epidemic, should, in theory, result in a partial control of trypanosomiasis.

Small groups of traps well sited in feeding grounds bring about considerable reductions in the numbers of active, hungry flies in contact with their hosts although hardly affecting the main fly community. This, in theory, will have a definite protective value to the community, enhanced by the fact that traps show increased catching powers when in close proximity to man and animals and that there is a tendency for people and tsetse to concentrate around waterholes (thus coming into the most intimate contact), during the dry season, the very time when traps are working at maximum efficiency.

It is in this protective role that traps seem to show their greatest possibilities for use in the control of sleeping sickness. The measure is applicable anywhere. It needs only small numbers of traps at each place where infection is being transmitted so that a reasonably big area could be covered economically. It might be a useful adjunct to clearings which fail to exclude the tsetse sufficiently. Traps so used might prove a valuable supplementary control-medium in places, such as the forest, where clearing is unlikely to be easy or cheap. Finally, experiment has shown that the retention of toxicity to Glossina of DDT-impregnated hessian exposed to the weather is sufficient to justify the application of DDT to the material covering the traps in order to increase their killing power.

Cordia macrostachya (Jacq.) R. & S. (Boraginaceae) is a serious pest in Mauritius, to which island it was accidentally introduced from the West Indies. During investigations of the possibility of the biological control of this weed, Kirby (1944 unpublished report, “Insects of Cordia in Trinidad”) and Donald (1945 unpublished dissertation) worked out the biology of the Galerucid, Schematiza cordiae, Barber (J. Wash. Acad. Sci. 37, p. 243, 1947), a defoliating species that gave promise of meriting consideration for introduction into Mauritius.

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.

Glossina, tachinoides, Westwood, 1850, is a common tsetse fly and an important vector of trypanosomiasis in parts of West Africa.

The genus Phlebotomus has been much studied in recent years since the transmission of various diseases by some species has been established.It has now become a matter of importance to be able to identify species accurately in connection with the study of the epidemiology of the disease they are known or thought to transmit. It has been found that those which are closely related morphologically, often show marked biological differences and vary considerably in their rôle as transmitters of certain diseases.

In December 1942 and January 1943, the late Captain T. P. Ward, R.A.M.C., carried out a malaria survey of the island of Socotra accompanied by Private G. F. W. Hart, R.A.M.C., who collected the mosquito material. The following notes have been abstracted from Captain Ward's official report.

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.

1. A selected stock bred on middlings and not diapausing at 25°C. was used in these experiments. None of the larvae reared on Manitoba wheat diapaused at 25°C., 70 per cent. R.H.; some diapaused at 21°C. and 17°C., 70 per cent. R.H. At these lower temperatures development was slower, more food by weight was eaten, and the moths were heavier.

2. More larval substance by weight was needed to produce a male than a female adult.

3. It was possible to subdivide natural foods into 3 groups: (i) Those on which no larvae diapaused at 25°C., 70 per cent. R.H. (ii) Foods on which a fairly low percentage of larvae diapaused at 25°C. 70 per cent. R.H. (iii) Foods on which most, or all of the larvae diapaused at 25°C., 70 per cent. R.H.; these foods were all characterised by a high content of starch. The possible cause is discussed.

4. Larvae moult 4 or 5 times on Manitoba wheat at 25°C. 70 per cent. R.H. Most of the larvae developing on this food under warehouse conditions could be allocated to 6 instars. At 25°C., 35·5 per cent. R.H. the number of larval instars is increased— one larva died in 12th instar.

5. The growth curves, obtained by measuring head capsules of successive instars roughly follow Dyar's law, although the ratio of increase falls off in the last 2 instars.

6. The prepupal stage in E. elutella can be subdivided into five stages, on the basis of withdrawal of ocellar pigment, described in E. kühniella by Kühn and Piepho. Only those prepupae which have reached stages four and five attempt to pupate after the head is ligatured, the other stages remain as “permanent larvae”.

It is now more than ten years since the publication of Harris' list of insects injurious to native food crops in Tanganyika (Harris 1937). It may be well to recall the view expressed in his introduction “… these crops … have achieved, within the limits of their present distribution, an equilibrium with their insect pests. Where there is no reasonable return for his labours, the native has ceased to grow a particular crop. This equilibrium is unstable, since pests increase in numbers at intervals owing to a variety of causes …”.

Species of Rodolia Mulsant (1850) are important as predators of mealybugs, some of which are notorious for their injury to plants. Rodolia cardinalis Mulsant is a classical example of a species that has been successfully introduced into several countries against the cottony-cushion scale, Icerya purchasi Maskell. A campaign against the latter, in South India, has be.en in progress for some time, and a number of local Coccinellid predators, collected by the staff responsible for the work, were sent for identification to the Commonwealth Institute of Entomology. The present study is based mainly on this material, and also on that in the British Museum (Natural History). All the known Indian species are redescribed and three new ones added to the list.