It may be stated that the summation of microscopical evidence of harmful effect upon the exposed rats and rabbits as a result of their 28 days' exposure to continuous DDT aerosol as described was nil.

The present paper, which is the last of the series, contains additional data obtained between November 1939 and December 1945.

In 1939, Helopeltis bergrothi, Reut., was found feeding on cacao pods and shoots at Owena by the writer; it was evident that this species was distinct from the cotton Helopeltis, which had been identified as bergrothi by the Imperial Institute of Entomology in 1924. The species attacking cotton is H. sanguineus, Popp., and this name should be substituted for bergrothi in the three papers on food-plants published in 1935, 1937 and 1940.

A variety of insects were exposed to films of insecticides by confining them for various periods on filter papers impregnated by a volatile solvent method. The following results were observed:—

1. Nine species of insect and two species of tick were exposed to films of different insecticides for a standard exposure of two hours at 30°C. It was found that freshly prepared films of Gammexane were most toxic, followed by pyrethrins, DDT and rotenone.

2. The relative toxicity of the films of undiluted insecticides is considerably different from that of the same insecticides applied in oily solution.

3. The very sparse toxic films of Gammexane soon lost their toxicity, apparently by evaporation. The pyrethrin films were also less persistent than those of DDT.

4. The test organisms can be arranged in groups showing different types of susceptibility.

5. Percentage mortality among bugs kept in motion for a specified period over a given deposit of DDT is greater than that among stationary bugs exposed to the same deposit for the same period. The addition of an irritant to a DDT spray would therefore enhance the efficiency of the insecticide.

6. A marked time lag in achieving complete mortality among bugs exposed to dry DDT films is recorded. No such lag was observed among bugs exposed to Gammexane nor among lice and flour beetles exposed to DDT. In these latter cases, percentage mortality gradually increased as the time of the exposure increased.

7. Percentage mortality among bugs exposed intermittently to DDT for a given total period of exposure did not differ appreciably from that obtained among bugs exposed continuously for the same period. After intermittent exposure for a particular total time, the length of the intervals during which the insects were in contact with the insecticide did not influence the percentage mortality.

The distribution of Phlebotomus sergenti in Palestine, Syria and Mesopotamia has received special attention, because of the rôle of this species in the transmission of oriental sore.

Empoasca libyca is a major pest of cotton in the northern and western blocks of the Gezira Irrigated Scheme.

Distribution of the species of the genus of Empoasca and Erythroneura lubiae is given, together with their food plants in the Sudan.

Damage caused by E. libyca is noted; an experiment carried out in 1935/36 showed that Jassids were able to cause such symptoms.

The life-cycle shows that the egg and nymphal stages are of short duration (8 days each) and followed by a long adult life (as long as 2 months) in which the female lays her eggs over a long period.

A new type of cage was used and is figured.

The effect of applications of Bordeaux mixture in reducing the Jassid population and amount of scorch is given as well as physiological data relating to the influence of spraying on different parts of the Jassid-infested cotton plants. It is shown that sprayed plants produced an appreciable increase in the number of green bolls formed and an increase of 11 per cent, in the weight of seed cotton per boll harvested. It is pointed out, however, that Bordeaux mixture has several disadvantages and other more suitable insecticides are being sought.

No Sakel varieties as yet have shown resistance to Jassid attack.

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.

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.

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.

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.

1. An attempt has been made to elucidate the confusion existing about the biology, morphology and nomenclature of the Oat-Apple Aphis, Rhopalosiphum prunifoliae, Fitch. A close study of the problem confirms the observations made by Börner that at least two distinct species have in the past been included under the name of R. prunifoliae. The names Rhopalosiphum padi, L., and Rhopalosiphum crataegllum, Theo., are adopted for these species.

2. Detailed descriptions and figures of the different generations are given and a comparison shows that the two species can readily be distinguished from one another.

3. R. padi appears to be of greater importance as a cereal pest than R. crataegllum. The latter species is a widespread pest of pip-fruit.

4. An account is given of the overwintering of R. padi on Prunus padus, and the results of experiments on estimating the size of the ova-populations is shown.

The author is indebted to Mr. R. A. Harper Gray for allowing him facilities to carry out the investigation; also to Mr. J. A. Dunn for assistance in collecting some of the material and much general help.

1. A sketch is given of the Malaria Control Organisation in Service areas in Mauritius with a summarised history of malaria work in the Island since the first epidemic in 1865.

2. Keys to Mauritian Anophelines and their larvae with notes on their field recognition characters are followed by data on the distribution of adult Anophelines in the Colony and their relation to malaria intensity in different areas. A. melas appears to be absent from coastal swamps.

3. The influence of a number of environmental factors is discussed. It is concluded that temperature is an important limiting factor generally in winter and perennially in the highlands (above 1,000 ft.), but that the flushing action of heavy rains and probably the precipitation of food supply by colloidal iron moving under high rainfall conditions (over 100 ins.) from ferrugineous lavas both play their part in the natural control of A. funestus and A. gambiae.

The behaviour of A. gambiae with respect to temperature is expressed by an area enclosed by two symmetrical catenary curves, that illustrate well the adverse influence on development of low temperatures normally occurring in winter on the coast and all the year round in the residential uplands above 1,000 ft. The thermal death point of A. gambiae larvae is about 42°C. and that of A. funestus 40°C. and the lower limit of larval activity is 16·5°C. A. gambiae develops most rapidly at an estimated temperature of about 37°C.