The differences between the eggs of A. gambiae and A. melas form an absolutely reliable diagnostic character for distinguishing the two species in the Lagos area.

Identification of eggs laid by wild-caught females has formed the basis of work on the seasonal incidence of gambiae and melas adults in houses in different localities in and around Lagos.

In the area as a whole both melas and gambiae are abundant in most localities, but the greater part of Lagos town on Lagos Island is an almost pure gambiae area.

The sporozoite rate of gambiae—10·0 per cent.—is consistently much higher than that of melas—3·5 per cent.—in all catching stations. Fluctuations in sporozoite rate in relation to population density have been studied in both species.

The composition of the mosquito population in houses, and in outside resting places has been studied in relation to the movements of mosquitos into and out of houses. Melas makes use of outside resting places to about ten times the extent of gambiae.

In African village houses about 90 per cent. of the blood feeding by these two species takes place after midnight, the peak of activity being the hour or two before dawn.

An improved design of experimental hut and window trap is described. It has been used in studying the exodus of mosquitos from houses after feeding, and on experiments on host selection by Anopheles.

Swarms of male “gambiae” in nature have been described. In captivity both melas and gambiae have been persuaded to mate by using artificial light.

By cross fertilisation between melas and gambiae a generation of healthy hybrid adults can be obtained. Of these the females are evidently normal sexually, while most if not all of the males are sterile.

The breeding places of melas and gambiae in and around Lagos have been studied in relation to control. In this lagoon area, where conditions are very different from those of Freetown Estuary, melas breeds under a variety of conditions, and Avicennia mangrove is only of limited value in indicating major breeding grounds.

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 construction of a spraying tower for obtaining even deposits of insecticide of known weight is given, and the method of adjustment of this apparatus and procedure adopted during spraying are described.

To determine the weight of deposit obtained with different liquids under various conditions of spraying, a colorimetric method of estimation was adopted. Deposits of dye solution were collected on test-papers disposed at different positions on the area sprayed, the dye dissolved in 50 cc. of solvent and the concentration of dye in this solution measured by means of the Spekker Photo-electric Absorptiometer. By this method estimations of the weight of dye deposited on each test-paper were made to 0·01 mg. with great rapidity. The solutions of dye used in these experiments were 1 per cent. wt./vol. solution of “Oil Golden Yellow 13777” in petroleum distillate and a 1 per cent. wt./vol. aqueous solution of “Orange 60506”.

Series of tests were carried out with both the petroleum distillate and the aqueous dye solutions to determine the replication and distribution of deposits obtained with the spraying tower. It was found that the Standard Deviation of the mean weight of deposit per test-paper for the two spray liquids, both from one test to another and between different positions on the area sprayed in any one test, fell between ±0·8 per cent. and ±3·0 per cent. of the mean under the most favourable conditions for spraying.

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.

In my recent paper on “Lygus simonyi, Reut., as a Cotton Pest in Uganda”*, I referred in the introductory notes to the fact that I had studied the male genitalia and other characters of about 20 species of Lygus in order to determine reliably all specimens collected in the course of the field work on which I was then engaged. In the present paper all of these species are described. Only a few of them occur commonly on cotton, and only one, which must now be called L. vosseleri, Popp., is a major pest of cotton, but the others were encountered, in most cases very frequently, in connection with an investigation of the alternative host plants of the cotton-frequenting species, and two are common on coffee (with L. coffeae, China, which belongs to a different group of species and is therefore not included here). Some of them bear a very close resemblance to L. vosseleri and often occur with it on the same plants and in the same localities; consequently considerable confusion had existed previously as to the identity of the various species collected.

In connection with field work it is often necessary to identify large numbers of specimens rapidly and without adequate facilities for the examination of genitalia. Consequently, the object of my study of the external genitalia of the males was not only to separate the species on the basis of these structures but also to test by means of them the reliability for diagnostic purposes of the few differences, such as those of colour and markings, that occur in both sexes and are readily visible with a hand lens. I concluded that the male genitalia afford the best characters for determination whenever they can be examined, but that colour and markings can suffice in both sexes for this purpose, despite the great variation which occurs in most species. The only other characters that are of value for the separation of species, within the group with which I have dealt, are size and (occasionally) length of rostrum. There is, in fact, a remarkable uniformity throughout this species group, so that in the absence of males or of facilities for examining genitalia, determination must depend upon a combination of a few simple characters, two of which, colour and markings, are variable, often difficult to describe, and can be utilised satisfactorily only after experience has been gained of many species and specimens from numerous localities and plants.

The species described in this paper constitute what may be called the simonyi group of Lygus and have the following features in common:—

1. A smooth, semi-shiny appearance (never very shiny because of slight pubescence and minute punctation).

2. The whole of the dorsal surface, including the hemelytra, and also the ventral surface, rather sparsely covered with very fine, short decumbent hairs directed backwards.

3. The whole of the dorsal surface, including the hemelytra, indistinctly and minutely punctate; the scutellum and (to a lesser extent) the pronotum very slightly rugose transversely.

Field observations on C. cilicrura and C. trichodactyla have shown that in Britain the larvae feed on beans, peas, cabbages, kale, cauliflowers, leeks, onions, cucumbers and lettuce. The importance of C. cilicrura as a pest of beans in spring was well known; its attack on cucumbers was suspected but had not been verified; but the infestation of leeks and brassicas in summer and spring cabbages in autumn had not hitherto been recorded in Britain. An association of larvae of C. cilicrura with rotting vegetation has not so far been established.

Descriptions of adult and larval stages are given. Diagrams are given to illustrate specific differences between larvae of C. cilicrura and those of the onion fly, Hylemyia antiqua.

Field observations have shown that C. cilicrura is on the wing from March to October and there is some evidence of slight activity during the winter months. There are 3–4 generations a year, and peak periods of fly activity occur during mid-April to mid-May, late June to early July, and in fine weather throughout the period August to October.

Larvae have been taken throughout the period May to December. Peak periods of larval activity occur from mid-May to early June on beans, peas, cucumbers and cruciferous crops, during July on leeks and cruciferous crops, and during September to November on spring cabbages.

The close relationship between cultural practice in south Worcestershire and the occurrence of high populations of C. cilicrura is discussed.

A summary of control measures devised by other investigators is given. Modifications of cultural practice that would be likely to reduce attack by C. cilicrura are suggested. Results of preliminary trials with naphthalene and DDT emulsion are given.

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.

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.

Concerning the well-known powerful action of modern contact insecticides the question arises whether these substances exert a specific action on the tissues of insects. It seems quite possible that they possess a general internal toxicity to various groups of animals, but that the insect differs from other animals in that the cuticle is sufficiently permeable to allow the absorption of toxic quantities when these substances are applied to the skin.

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.

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.

Rothschild in 1917 (Novit. Zool., 24, p. 355) stated that the above name, which had previously been accepted as the “Brown-tail” or “Cul brun”, really represents the “Gold-tail” or “Cul doré”. Although this opinion was discussed and agreed to by such writers as Barnes and Benjamin in 1924 (Proc. ent. Soc. Wash., 26, p. 213) and Joannis in 1928 (Encyc. ent., Sér. B III, Lep. 3, p. 99), the great majority of systematic works since published in Europe still adhere to the interpretation of P. chrysorrhoea as the Brown-tail.

In the coastal area of Palestine, Empoasca lybica has eight annual generations. The average number of offspring per female is 16, 81 being the maximum. The adults live in summer up to seven weeks whilst those of the autumn-generation overwinter and live up to five months. The pre-oviposition period, the development of the egg and larva and the total development last from 2 to 23, 5 to 49, 8 to 50 and 15 to 72 days, respectively, according to the season of the year. The threshold of development is between 10 and 12°C. in the various stages of development. The duration of development depends mainly on the temperature. Air humidity has no influence on the duration of development so long as the leaves are sufficiently succulent. Activity of the adults ceases below 14°C. and a temperature above 46°C. results in immediate death. During khamsin-days no oviposition takes place, and many larvae die, especially those of the first stage. The most important local hosts are Solanaceous plants. The characteristic damage is the appearance of yellowish stains on the leaves and leaf-curling; the plants are delayed in development, and shed their flowers and small fruits. Young plants wither when heavily attacked. Damage is most severe in young plants in mid-summer. So far no satisfactory control measures have been found in Palestine.

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.

1. The original purpose of the present work was to confirm a previous finding that, in unfed adult Xenopsylla, longevity varies according to the humidity during the cocoon period, and to find whether this is due to differential loss of water during the prepupal period. The previous finding has been confirmed, but the cause is shown to lie in loss of water during the pupal and not the prepupal period.

2. Prepupae are shown to gain in weight by the absorption of water vapour from the air if kept at 24°C. and any relative humidity from 50–90 per cent. If kept below 45 per cent. R.H. they rapidly dry and fail to pupate.

3. During this period (about three and a half days from cocoon spinning to pupation at 24°C.) the dry weight decreases by about 2 per cent, of the original total weight, and the total weight increases by from 4–29 per cent., with a mean of 14 per cent.

4. The amount of water absorbed is independent of relative humidity within the range 50–90 per cent., and is approximately equal to the increase in total weight.

5. The critical relative humidity, below which the insects die and above which they absorb water, is shown to be substantially the same (from 45 to 50 per cent. R.H.) at 12°, 24° and 35°C.

6. After pupation the insects begin to lose water and continue to do so throughout the period. The rate of loss increases with decreasing humidity, though the effect of humidity is not very great.

7. Adults emerging from pupae kept at higher humidities weigh more, have higher percentage water contents, and live longer without food, than those emerging from pupae kept at lower humidities.

8. The results are discussed in the light of previous work, and suggestions as to the mechanism of the process of absorption of water are made.

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.

A method for testing the physical stability of emulsions is described.

Since the persistent toxicity of residual films is so important in the control of mosquitos and flies, this biological activity of stable DDT emulsions was measured by the response and susceptibility of Armigeres obturbans and Culex gelidus over a protracted period of time.

These discriminating tests were carried out before emulsion concentrates were tried out in the field.

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.

The species described as new is placed in the genus Adelencyrtus, Ashmead, provisionally. The description is published at this time to provide a name, so that biological information concerning the species can be made a matter of record. The new species is most closely allied to Adelencyrtus. It differs from typical species of this genus with regard to the mandibles. In typical Adelencyrtus the mandibles are quadridentate, and the ventral margin is provided with a stout, cone-shaped seta. In the new species only the ventral tooth is distinct; the dorsal margin of the cutting edge appears as a wide truncation, which can scarcely be described as subdivided, and the ventral margin of the mandible lacks the stout conical seta. The most useful character for the identification of this species, and the one which reveals its relationship to Adelencyrtus most surely, is the distinctive male antennae. In this sex the antennal club is enormously cylindrically elongated, and the funicle is composed of two vestigial segments that are contained in a recess at the base of the club. Antennae of a similar kind have been described in the males of Habrolepis, Förster and Anabrolepis, Timberlake, two genera which are closely allied to Adelencyrtus. The males of Adelencyrtus have not been described.