The new species described in this paper was received from Richard Le Pelley, Government Entomologist, Kenya Colony, British East Africa, for identification. A new genus Eurymyiocnema is erected for its reception. This genus is most closely related to Myiocnema Ashmead, which was placed by its author in the “Aphelininae”, although subsequent authors have regarded Myiocnema as belonging to the Elasmidae. Eurymyiocnema is placed in the Aphelinidae, and the opinion is expressed that Myiocnema, as well as Euryischia Riley, are out of place in the Elasmidae, since both of these genera resemble Aphelinus Dalman much more closely than they do Elasmus Westwood.

1. The paper describes work carried out to find the causes of certain discrepancies in the results of longevity experiments on rat-fleas.

2. The following factors were found to reduce significantly the survival period of unfed adult fleas:—

Rearing larvae together rather than in separate tubes; Parent fleas over 11 days old; Using very fine rather than coarse sand as a matrix for larval food; Drying the blood for larval food by baking rather than in a vacuum over sulphuric acid at room temperature.

3. The following factors were found to have no significant effect upon adult longevity:—

Contamination of larval food by mice and their droppings;

Presence or absence of adult flea faeces in larval food.

4. The effect upon the weight of larvae and the duration of the larval period of some of the above-mentioned factors is described. The female larval period is shown to be shorter than that of the male under all conditions used.

5. It is confirmed that there is no significant difference between the longevity of male and female adults which have fed once or not at all, and that females which have fed frequently before starvation live longer than males.

6. Well developed, unfed, laboratory-bred adult fleas live longer than those which have fed once before starvation, and the latter live longer than those which have fed several times.

7. There is some evidence that unfed wild-caught fleas live longer than wildcaught fleas which have fed, but this needs confirmation.

8. All the available information regarding factors affecting adult longevity is summarised in a table.

In order to assess the potential effectiveness of DDT spray against mosquito larvae living under natural conditions and to determine the characteristics of the most effective form of spray, the variables considered were, area dosage of DDT, oil solutions compared with oil-in-water emulsions, concentration of DDT in the spray liquid, and drop size.

Spraying was carried out over small (20 ft.×40 ft.) areas of canal harbouring larvae of Anopheles maculipennis var. messeae, and A. claviger. The canal was densely packed with vegetation. The central channel was overgrown with Potomogeton natans, so dense that in some regions there was more area of leaf than of open water surface, and in places there were large masses of floating algae (a coarse species of Spirogyra). At the edge of the canal near the bank there was a margin of reeds averaging about 4 ft. wide, and from 1 to 4 ft. in height.

Spraying was carried out with a specially designed spinning disc atomiser giving drops of nearly uniform size and enabling drop-size and dosage delivered to be independently varied over a wide range. The range of DDT dosages investigated was from 4 g./acre to 80 g./acre, delivered in solutions or emulsions of approximately 0·5 per cent. and 5 per cent. concentration and drop sizes of 0·4 and 1 mm. diameter. Assessment of surface dosage in relation to delivered dosage, by spraying dyed solutions, showed that about 30 per cent. of the smaller drops were lost in the wind, but that there was no appreciable loss of the coarser spray.

For 5 per cent. oil solutions of DDT drop size in the range 0·4 to 1 mm. diameter had no effect on the kill, except at low dosages (< 10 g. DDT/acre) when the greater wind loss of small drops produced variable results. Tests on the effect of drop size were not carried out with emulsions.

From the point of view of larvicidal action, the experiments have not shown that is advantageous to distribute DDT in high dilution. 4·3 per cent. DDT oil solution sprayed at 10 g. DDT/acre actually gave a slightly higher mortality than 0·43 per cent, solution at the same dosage area of DDT, but the difference may not be significant owing to uncontrollable variables. Under the conditions of these trials, both oil solutions were superior to 0·43 per cent. AMSO emulsions. Experiments on the effect of concentration at constant area dosage were made only in the reed margin of the canal and data were not obtained for open water.

In the centre of the canal, mortalities greater than 90 per cent, were obtained for both oil solutions and AMSO emulsions at delivered dosages greater than 10 g. DDT/acre, the oil solution being slightly superior. In the reed margin the kill dropped sharply with AMSO emulsions at dosages below 40 g. DDT/acre, the fall-off was much less marked with oil solution. From considerations of the average mortality in all areas, a delivered dosage of 40 g. DDT/acre (small drops) or estimated surface dosage of approximately 30 g. DDT/acre, appears the optimum for economical usage of DDT.

When areas were sprayed the first two larval stages suffered a higher mortality compared with the later larval stages and pupae, and the proportion of pupae and later instars thus rose sharply.

There was no evidence that residual lethal effects of oil films extended beyond three days. The initial kill in these trials was followed by a very low population level, due, it is thought, to a natural decline in the reproductive potential of the population.

The mean hunger-cycles of G. swynnertoni and G. pallidipes have been studied in the field by marking tsetses with cut proboscidae, which have been released and subsequently recaptured.

The length of time that hungry flies are able to survive before dying from starvation varies with the season, probably according to the amounts of reserve fats and atmospheric humidity.

The mean hunger-cycle also varies with the season and correlates significantly with the evaporation rate or other measurements of humidity. The variation of temperature experienced in these experiments was not sufficient to have any appreciable effect on the hunger-cycle.

G. pallidipes, a thicket haunting fly and larger than G. swynnertoni, a thorn bush species, frequently than the latter under moist conditions, but frequently under adverse conditions.

Smaller individuals probably feed more frequently than larger individuals.

The types of the new forms described in this paper are deposited in the collections of the Zoological Survey of India, Kaiser Castle, Benares.

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.

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.

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.

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.

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.

In April 1947, the laboratory stock of Glossina palpalis, R.-D., puparia collected from the Kaduna area suddenly became heavily infested with the pupal parasite, Syntomosphyrum glossinae, Wtstn. Presumably an infected pupa had been brought in from the bush and a few parasites had emerged undetected; it was not until the emergence of their offspring that the mass-infestation was revealed.