An attempt has been made to assemble the important factors concerned with the atomisation of a kerosene spray and to consider the behaviour of the spray alone, and in its relation with an insect flying through it.

The degree of atomisation attained by the spray gun is dependent upon nozzle design, the spraying pressure, the relative rate of liquid and air flow through the nozzle and such physical properties of the spray fluid as viscosity and surface tension.

All atomisers produce droplets of a variety of sizes which leave the gun with a considerable velocity and are carried along by the air current. At this stage they are at their maximum size and possess their maximum velocity so that the chance of impacting with an insect is great. Later on when the droplets have lost much of their velocity and volume (if they contained a non-volatile insecticide they will have become much more concentrated), they are much less likely to impact. It can thus be seen that a non-toxic carrier can increase apparent toxicity of a spray mist by assisting in the production of the momentum necessary for impaction (David and Bracey, 1944). On the other hand a reduction in the size of the droplet decreases the rate of loss from the air space by precipitation. In connection with evaporation the enormous change in concentration which occurs should be borne in mind. Within a few minutes the smallest droplets will have entirely evaporated, leaving only the non-volatile solute and before this stage is reached the droplet will have become super-saturated. Finally this non-volatile solute will exist as minute nuclei which, when they result from a fairly typical insecticidal formula containing up to say 5 per cent. nonvolatile material, may be so small as to settle only very slowly.

Regarding the response of the insect to the spray mist, it may be said that this depends upon the resistance of the insect and the dose of insecticide picked up. Since the spray mist takes some time to distribute evenly and since it is more easily picked up during or immediately after spraying and by insects in flight, it can be seen that the dose received by individual insects will vary a good deal unless the insects behave identically so that under these conditions there is little correlation between the comparative effect recorded on individuals and their relative innate resistance.

To the above remarks arising out of the theoretical discussion which formed the first part of this paper must be added the following conclusions from the experimental work.

Kashmir valley is the largest deciduous fruit-growing tract in India, and, owing to the increased demand for fruit, many orchards, both large and small, have recently been laid out with technical assistance from the Department of Agriculture. Apple is the first choice of the fruit-growers, but as the trees begin bearing later than many stone-fruits, it is a common practice to plant peaches and nectarines between the rows of the young apple trees; this produces early returns without disturbing and exhausting the soil by ploughing and growing annual crops. With the rapid development of road transport, it is hoped that peaches will find a market outside the valley. The peaches of Kashmir are not so well known as are its apples and pears but with better attention to the trees an increase in production and an improvement in quality should be possible.

1. Two huts were selected which were surrounded by dense bush, which varied in height from 4 to 15 feet. After elimination of this bush within a radius of 140 yards from these huts, the proportion of the population of ♀ A. funestus and ♀ A. gambiae attracted to them was at least 90 per cent. of the proportion which reached them before the bush clearance. This result indicates that bush clearance is not a justifiable measure for reducing Anopheline infestation. Even the male Anophelines entered the cleared area in the same proportion as they did before clearance.

2. While bush clearance was in progress there was a temporary sharp reduction in the infestation, and the proportion of the female Anopheline population attracted declined to between one-third and one-quarter of the proportion attracted before clearance. The proportion of males dropped by one-half. At the same time the ♀ Anophelines were apparently much less able to discriminate between quantitative olfactory stimuli. Both effects are attributed to masking by an obscuring odour from the cut and withering bush.

3. There was no difference between the numbers of A. melas attracted to a hut screened by a 10 yard thick belt of dense high bush and the numbers attracted to an identical hut in the adjacent clearing 25 yards away.

Simple tests have been done to appraise the value of garments impregnated with DDT as an anti-louse measure. It is very toxic to the body louse but its action is relatively slow. Woollen and cotton fabrics can be impregnated with it.

No estimate can be given of the precise length of the insecticidal life of a garment because of variations in wear, etc. But garments have been found to have o·1 per cent. DDT remaining after five launders and three weeks' wear. The minimum safe degree of impregnation as an anti-louse measure appears to be o·1 per cent. By the use of simple biological tests reasonably accurate assessments of the chemical content of garments can be made.

DDT is to some extent resistant to high temperatures. It is suggested that the chief cause of loss of insecticidal power is due to loss of nap. Impregnated garments transfer their insecticidal power to uriimpregnated garments kept in contact with them.

Results show that subsequent mortality is complete or very high among lice which have crawled for three hours on fabrics impregnated with DDT at rates between o·1 and 1·75 per cent. Signs of poisoning may take six hours to be manifested in the louse.

The results obtained with a sleeve test compared very closely with those obtained by the box method used chiefly in this work.

The theory is put forward that DDT enters the body louse through its tactile sense organs.

1. The taxonomy and bionomics of the eight species and subspecies of Eretmapodites found in the Bwamba County, Uganda, are discussed.

2. Experiments are described to show that the larvae of these species are predatory, sometimes very actively so.

3. The females of all the Bwamba species bite man by day, sometimes in large numbers.

4. The larva and pupa of E. inornatus, Newst.; larva, pupa, and adult female of E. penicillatus, Edw.; larva, pupa, and adults of E. ferox, sp.n.; and larva and pupa of E. leucopus subsp. productus, Edw., are described for the first time, special reference being paid to the range of individual variation. The taxonomy of the various previously described species is also treated briefly.

5. Keys are provided for the identification of the known larvae, pupae, males, and females. These keys have been prepared in order to include the new material, and to delete certain unreliable characters previously regarded as of specific value.

Investigations undertaken by the writer involved the determining and sexing of a large number of fleas daily, and it became clear that this would be a laborious process unless an apparatus could be designed which would facilitate separation and examination of the insects by making the process as automatic as possible. The technique finally used, though designed primarily for handling fleas, could be adapted for use with other insects of comparable size where examination under magnification is necessary.

Throughout the world, wheat bran seems to have been the most popular carrier for locust and grasshopper baits. Wheat bran has, however, always been difficult to obtain in East Africa in sufficient quantity for large scale campaigns, and wartime conditions coinciding with a large outbreak of Schistocerca gregaria have made the position even more acute.

Whilst investigating the biology of parasites of the frit-fly (Oscinella frit, L., Diptera, Chloropidae) in North America with a view to introducing possible species for the biological control of this pest in Great Britain, extensive experimental work was done with one species of Chalcid, Spalangia drosophilae, Ashm. (Spalangidae), a parasite of frit puparia. During this work conditions inducing a state of diapause in the mature larvae were investigated. As with many other species, it was found that low temperatures during development favoured entry into diapause, whilst high temperatures favoured emergence of the progeny without arrest in development. However, other factors were found to have some important bearing in this respect. Some individual females produced progeny, all of which entered a state of diapause in the full-grown larval stage, others bred and ovipositing under identical conditions produced progeny all of which emerged without arrested development, others produced progeny that were mixed in this respect. This effect did not seem to be inheritable. The history of each individual female with respect to environmental conditions was found to have an important influence on the propensities of her progeny for entering diapause. These effects will be dealt with more fully at a later date. There was, however, one striking effect which has apparently not been noted before, and which it was felt was of sufficient interest to be recorded separately.

This work was found necessary when the Pong-Tamale Veterinary Laboratory and Livestock Farms were built in 1930–31 in the Naboggo Valley. The site was chosen because of ample water and abundant available ground.

These experiments are part of the series made by No. 2 Entomological Field Unit, R.A.M.C., on the potentialities of DDT (dichlor-diphenyl-trichlorethane) for military purposes. A report on the use of DDT as a mosquito larvicide on still water has already been published (Ribbands, 1945).

In the following pages an attempt is made to deal systematically with a number of Braconids belonging to the subfamily Euphorinae and reared by Dr. T. H. C. Taylor in the course of his investigation into the biology of the Capsid pests of cotton in Uganda. Taylor himself has discussed elsewhere (1945) the importance of the rôle that some of these Braconid parasites are likely to play in the control of their hosts.

Mercury and tin amalgam were tried in mud bins, metallic bins and bamboo bins at different places in the Punjab. Mercury distributed throughout the bin at the rate of 3–4 tolas per maund of wheat proved effective in completely checking the increase of various stored grain pests. Mercury used at the bottom and top 10–12 in. layer of grains in the bin also proved fairly effective. Tin amalgam even with as high a dose as 13½ tolas per maund of wheat did not prove effective. Loss of mercury during use is very slight. Mercury has no deleterious effect on the germination or eating quality of wheat.

Mercury kills the fresh eggs of stored grain pests, but the eggs in an advanced stageof development are not adversely affected. It retards the growth but does not kill the larvae of T. granarium and Bruchus sp. It has no effect on the pupae, but affects the egg laying capacity of adults very slightly.

(1) An adhesive made from 3 or 4 parts (according to the temperature) of the coagulated latex of Carpodinus hirsuta and I part of either shea butter (from Butyrospermum parkii) or palm oil (from Elaeis guineënsis) was found to be very effective against both house-flies in kitchens and Stomoxys spp. in pig pens.

(2) In kitchens, wires (diameter 4 mm.) were treated with the adhesive and suspended over the table on which food was prepared. The wires should be renewed every three or four days when flies are abundant and once a week when the infestation is light.

(3) At Ibadan in 1943, house-flies were abundant from early March to late July; the maximum house-fly infestation of both kitchens and pig pens occurred during the second week of May. The upward trend in adult incidence first became evident in mid-February of both 1943 and 1944 and appeared to be correlated with a rise in temperature at that time.

(4) Ten wires treated with adhesive were suspended under the eaves of each pig pen. Each pen consisted of a covered pen and an open yard divided by a half-wall; a screen made of oil palm fronds was erected above the half-wall with the object of making the innerpen sufficiently dark to deter flies from entering it. About half a million flies (about 27·5 per cent. Stomoxys spp.) were trapped in12 pens in a period of 112 weeks.

(5) Stomoxys spp. (principally S. nigra, Macq.) were abundant between early June and mid-August in 1943 and between early June and late November in 1944. In 1943 there was a short dry season between 25th July and 12th September, whilst in 1944 there was no break in the rains. There is a marked correlation between rainfall and the incidence of S. nigra. Heavy rainfall soaks straw round the stock-yards, heaps of weeds, etc., which decompose and provide suitable media for larval development.