Field experiments have been conducted in Uganda to investigate the use of the insecticides DDT and Benzene Hexachioride for the control of tsetse. Since the Tsetse Research Department of Shinyanga has developed a line of investigation into the possibility of using cattle sprayed with DDT as poison bait for tsetses, it was considered that the alternative method of attack, i.e., treatment of vegetation, should be tried. The preliminarywork has been against Glossina palpalis, R.-D. Results of experiments against this species should provide a basis for work against other species. Experiments have been carried out as far as possible on small islands and headlandson Lake Victoria where the flies exist in isolated communities and where results are nottherefore influenced by infiltration of flies from surrounding bush.

Short summaries have previously been given (1938, 1940) of the results obtained during investigations on the wood-destroying insects in public buildings in Götaland and Svealand, the southern and middle parts of Sweden. The survey has since been continued in Norrland, the northern part of the country, and a short summary of the results obtained may now be given, together with a general survey of the conditions prevailing in the whole country.

The relationship of oviposition to weather, with a standard stimulus (4 per cent. ammonium carbonate), has been tested by a series of 134 exposures of a group of three sheep for one hour. 190 egg clusters were obtained, of which 169 were identified. With the exception of one cluster of L. caesar all were L. sericata.

There was a fairly close correlation (0·586) of oviposition with air-temperature. When the possible effect of other factors was eliminated, the correlation was little affected, showing that temperature was in itself responsible for the variations in oviposition. The lower critical limit of temperature was in the neighbourhood of 56°–58°F.

Solar radiation and oviposition had an apparent correlation, but this was found to be spurious, the effect being due to related air-moisture changes. At temperatures near the lower critical limit, insolation did not increase the oviposition rate, or lower its temperature threshold.

Humidity had an apparent inverse correlation with oviposition, but this also was an indirect effect, due to related temperature changes. Humidity showed a closer correlation when expressed as saturation deficiency than as relative humidity. Evaporation rate from a white atmometer sphere had only a low correlation with oviposition.

It is shown that the partial correlations of both saturation deficit and insolation with temperature effects eliminated, are insignificant, i.e. their apparent effects are due to related temperature changes. The multiple correlation coefficient for temperature humidity and insolation is practically identical with that for temperature.

Independent variations of insolation, i.e. variations not simultaneous with related temperature changes, had a significant effect on oviposition; for a given temperature, a high intensity of insolation was less favourable than a low, and this appeared to be a true insolation effect, and not due to associated humidity changes.

Independent variations of humidity had a suggestive but statistically insignificant effect, humidity tending to be inversely related to oviposition.

The regression of log oviposition on temperature, within the limits of this experiment, i.e. at temperatures up to 72°F., was linear. The slope was not significantly affected by the insolation and humidity factors, the total coefficient being 0·, and the partial coefficient 0·0428. These coefficients are the increase of the log number of egg clusters (plus one) for 1 degree F. increase, i.e. the oviposition rate increased in geometric progression for unit increase of temperature, the value (N+l) for egg clusters doubling itself for 7° increase.

1. The behaviour of A. gambiae and A. melas in houses is described in relation to possible use of pyrethrum and DDT.

Pyrethrum.

2. Mass spraying of isolated villages with pyrethrum in kerosene four times a week reduces the day-time catch of Anopheles to one-third. The sporozoite rate of mosquitos in sprayed villages remains much the same as before treatment.

3. Observations in experimental huts with window traps attached show that pyrethrum exerts a repellent effect on many hungry Anopheles for a day or two after spraying, provided blood meals can be obtained easily in adjacent untreated houses.

4. Where all available huts occupied by man are sprayed, there is no great repellence to hungry mosquitos, which continue to feed in large numbers even in huts sprayed every day.

5. In untreated huts about 20 per cent. of the blood-fed females leave the house at dawn after feeding. In huts sprayed daily the proportion increases to about 80 per cent.

6. The fall in the house catch in villages sprayed 4–6 times a week is not due to any great reduction in the mosquito population, but to a shift from indoor to outside resting places.

7. As intense house spraying with pyrethrum fails to bring about any substantial reduction either in the mosquito population or in their infectivity, it is not likely to be of great anti-malaria value in West Africa.

DDT.

8. Mass spraying of village houses with 5 per cent. DDT in kerosene produces a dramatic fall in the day catch of resting Anopheles in houses. The catch remains very low for 4 weeks after treatment and it is still fairly low after 2 months.

9. Observations in experimental huts (fitted with window traps) treated with DDT in kerosene show that mosquitos may enter and feed within a few days of treatment. By the second week after treatment large numbers of Anopheles may feed every night in treated huts.

10. There is no evidence of mosquitos succumbing to the effects of DDT in kerosene inside the hut. Nearly all the Anopheles feeding in such huts leave after feeding and show no appreciable mortality in the following 48 hours.

11. The DDT in kerosene has a marked residual irritant effect on Anopheles, driving them out of the house after they have fed, and preventing mosquitos resting long enough on treated surfaces to absorb a lethal dose of DDT.

12. The few days complete protection from biting mosquitos which follows spraying inside the house with DDT in kerosene, is shown to be due mainly, if not entirely, to the repellent effect of the heavy dose of kerosene which accompanies the DDT.

13. Treatment of all rooms in an isolated village reduced the day catch to nil during 5 weeks after treatment. In outside resting places beside the village, bloodfed and gravid Anopheles, of which 2 per cent. had sporozoites in the salivary glands, Were taken regularly during this period.

14. The apparent elimination of mosquitos from houses following treatment of rooms with DDT in kerosene is due to a complete shift from inside to outside resting places, on account of the residual irritant, but not lethal, effect of DDT-in-kerosene treated surfaces.

15. The sharp fall in the house catch of Anopheles following treatment Of West African village houses with DDT in kerosene can not, therefore, be accepted as evidence of mosquito reduction or effective control.

1. Certain experiments intended to throw light on problems arising from the practical application of DDT against A. gambiae and A. funestus are recorded. These refer particularly to the action of larvicidal DDT on adult mosquitos; to the effect of varying periods of exposure; and to the possibility of repellence of adults by DDT treatments.

(a) Solutions of DDT on water surfaces produce an appreciable mortality, particularly on laying mosquitos, but also on ♀♀ in earlier stages of ovary development, when confined in cages with a bowl of water so treated.

(b) The greatest effect is produced by a DDT solution in a heavy oil film of long persistency.

(c) The presence of a DDT solution on the water, particularly when applied in a heavy oil, appears to have produced an appreciable inhibition against laying.

3. With a 5-months-old residual film of 200 mgms. DDT per sq. foot on smooth wood, a 60-minute exposure killed 22 per cent. immediately and 100 per cent, within 3 hours. After a 5-minute exposure none was killed immediately, but 17 per cent. were dead within 3 hours, and 73 per cent. at 12 hours. Intermediate periods of exposure gave corresponding results.

4. Anopheles exposed in inter-connecting treated and untreated cages showed characteristic restlessness as a result of contact with a treated surface. When inserted first into a treated cage, and subsequently allowed access to untreated cages, a higher mortality was recorded than when the procedure was reversed. The degrees of mortality and of restlessness appeared to be closely connected.

Two blocks were isolated by 3– or 4–mile clearings on a small river with a narrow strip of riverine bush and a low density of Glossina palpalis fuscipes.

Catchers at the rate of 6 per 1,000 yards of stream caught almost all the G. palpalis in one block in 3 months and all in 6 months.

Eight months later there was ho reinfestation.

All this time G. palpalis persisted in the Control Block.

An area from which G. palpalis was removed by hand catching 10 years ago was examined. It is concluded that it is possible not only to hand catch all the G. palpalis but also to avoid reinfestation.

Hand catching is the quickest and cheapest known method of reclaiming streams of this type from G. palpalis.

Vegetational descriptions are given.

(1) Up to 35 per cent, of adult Dysdercus nigrofasciatus from a heavily infested late cotton crop at Barberton were found to be parasitised by Tachinid larvae at the end of the season.

(2) The predominant Tachinid species was Alophora nasalis; Bogosilla fasciata was present in smaller numbers, and appears to be more common in regions of higher rainfall.

(3) The development of the Tachinid larva within the stainer was a protracted process under local winter conditions, the larval period of A. nasalis being of the order of 2–3 months, and parasitised stainers were correspondingly long-lived.

(4) The possible economic significance of the parasites is discussed.

A full consideration of the systematic position of Dacus armatus F. (the genotype of Dacus) and of Dacus bivittatus (Big.) is not attempted here, but it is necessary, owing to the economic importance of the latter, to clear up the confusion that has arisen between them. I am indebted to and thank Dr. A. J. Hesse, South African Museum, Capetown; Dr. John Smart, British Museum; Sir Guy A. K. Marshall, K.C.M.G., and Dr. F. van Emden, Imperial Institute of Entomology, and Dr. S. L.Tuxen, Zoological Museum, Copenhagen, for help in unravelling the problem.

The ultimate assessment of the efficiency of malaria control is by the number of cases of malaria contracted in the controlled area, but a method that gives a more immediate and definite information is required because of the:—

(i) Delay before the necessary information is obtained. For example, abandonment of larval control will not affect the number of malaria cases for more than a month;

(ii) Shifting populations. People will come into the area and develop malaria acquired outside and conversely people having acquired malaria inside the area will go outside before developing it;

(iii) Difficulty of distinguishing between relapses and newly acquired infections. The number of relapses has no connection with the efficiency of the control;

(iv) Lack of cases of malaria despite infection in a predominantly immune community in which the non-immune persons are protected by suppressive drugs, mepacrine and quinine. This is a common condition in very malarious areas.

Exposure of house-flies to residual films of DDT, deposited on wall-board from kerosene solutions, has shown that the initial toxicity increases (1) as the deposit of DDT per unit area increases, and (2) as the concentration of DDT in the solution increases, although the amount of DDT applied is kept constant. In practice, DDT in kerosene should be applied to absorbent materials at as high a concentration as possible, consistent with reasonable coverage, in order to avoid much of the DDT being carried by the solvent into the substrate, where it is no longer available for contact with the insects.

With wall-board, a critical value for the product of concentration and deposit of DDT has been shown to exist, above which any mechanical stimulus, including movement of flies on the treated surface, will cause the DDT present in supersaturated solution to crystallise, with consequent marked increase in toxicity of the film. Under some circumstances, removal of the crystal carpet is followed by its partial regeneration. If the product of the concentration and deposit falls below the critical value, the residual film is at no time very effective and soon loses its initial toxicity.

The persistence of toxic films of DDT on wall-board has been shown, over an exposure period of 18 months, to be closely bound up with the crystallisation of the deposits and their powers of regeneration during intermittent exposure to flies.

This work has been carried out as part of the programme of research of the Pest Infestation Laboratory, and this account is published by permission of the Department of Scientific and Industrial Research.

Field experiments carried out in 1945 at Rosh Pina in Palestine have proved the great efficiency of DDT residual spray in houses against sandflies.

A high degree of protection against P. papatasii, P. major and P. chinensis was obtained by inside spraying of rooms with DDT in kerosene.

The residual action lasted for 52–58 days during the hot summer months. At the end of this period the effect was still undiminished but the end of the sandfly season made further observations impossible. Judging from observations made elsewhere it may be assumed that the residual effect would have lasted not more than another two weeks.

Dosage of 1 g. per m2 (100 mg. DDT per sq. ft.) was fully effective, and 2 g. per m2 gave no better results. The best method of application is the treatment of all internal surfaces (walls and ceiling). As sandflies tend to congregate in the angle between wall and ceiling, treatment of walls and this angle only gives equally good results.

An attempt to protect a house by spraying “barriers” (vertical surfaces of stone walls etc., within a radius of 50 metres) failed. Sandflies on the outside surfaces disappeared after the DDT treatment but the observations recorded here and those reported by other authors suggest that much larger areas would have to be sprayed in order to make this method effective.

A marked reduction of sandflies in untreated rooms followed the spraying of other Tooms in the same house with DDT. The mechanism of this phenomenon is explained. A general reduction of the sandfly population can be expected when large-scale DDT treatment is carried out in a village or camp area.

1. The method used is founded on those of Dunn (1927) and Harris (1942).

2. Results are given for 1943, 1944 and 1945 from areas in Kenya, Tanganyika and Madagascar.

3. An attempt is made to interpret these results in the light of the theoretical meanings of the Pot Index and the House Larval Index. This demonstrates that these two indices together can be used to assess the fluctuations in an Aëdes population and hence the efficiency of control measures.

4. Finally, the practical value of the Pot Index is discussed.

Reports on the effectiveness of DDT applied to the limewashed interiors of buildings have been conflicting. This question is of importance in the tropics where so many European houses are limewashed. Laboratory tests recorded here were made to determine, firstly, how effective DDT was when applied to limewash, and, secondly, the cause of any loss of toxicity.

In a previous paper (Simmonds 1946*) the biology of Phytodietus pulcherrimus (Cress.), a parasite of Loxostege sticticalis, L., the sugar-beet web-worm, has been described. This paper will be devoted to the habits and life-history of another important parasite of Loxostege in North America, Bracon vulgaris (Cress.). This species appears to be confined to the American continent, all of the records being from Canada and the U.S.A. It has been reared only from Loxostege sticticalis, L., and L. commixtalis, Wlk. From the former species it has been recorded by Paddock (1912), Swenk (1918), Jones, Hoerner and Corkins (1921), Pepper and Hastings (1941), and Simmonds (1946); from the latter species by Hoerner (1933). During the present work it has been reared from L. sticticalis, material from both Montana and Alberta.

During the course of investigations into the use of the insecticides DDT and Gammexane, it has become increasingly clear that there is considerable loss through absorption into the treated surface. This loss of contact-available insecticide is most marked when simple oil solutions are used. Dosages of 100 to 200 mgms. per sq. ft., which on a non-absorbent surface (e.g. glass) are 100 per cent, toxic to flies exposed for very short periods, show little toxicity when applied to absorbent surfaces (e.g. mud).

Cacao was introduced into West Africa in the latter years of the last century and for a time remained relatively free from pests and diseases. It is, in fact, only recently that two major scourges have developed to a point where they are threatening the future of the cacao industry in the Gold Coast and Nigeria. The first, the cacao Mirids (Sahlbergella singularis, Hagl., and Distantiella theobroma, Dist.) is outside the range of the present paper. The second, and most important, is a virus disease, known as “Swollen Shoot”, which is transmitted from tree to tree by at least three species of mealybugs of the family Pseudococcidae.