In view of the great diversity of opinion on the subject of sex ratio and order of emergence of the two sexes of adults in laboratory-bred mosquitos and those occurring in nature, 70 experiments spread over a period of 1 year, were conducted in the laboratory at room temperature to study (a) the order of emergence of the sexes, (b) proportions of sexes in the total output in a brood, (c) the effect of larval and pupal mortality, (d) the effect of food, and (e) of temperature on sex ratio. The common species, C. fatigans, was chosen for the purpose.

By a statistical evaluation and graphical representation of the data it has been shown that males hatch out significantly earlier than females, and that the larval life of the males is significantly shorter than that of the females.

It is concluded that the sexes emerge in a 1: 1 ratio, although a small number of aberrant cases with a significant preponderance of one sex or the other may occur.

Larval as well as pupal mortality below 20 per cent. does not seem to affect the sex ratio; nor has it been possible to establish any relationship between sex ratio and mortality in any of the aquatic stages.

The role of visual factors in the attractiveness of bodies to adult A. aegypti was investigated by exposing deer-mice in transparent or opaque, airtight or perforated, plastic containers. The visual factors proved to be roughly equivalent to the airborne emanations in attractiveness, being slightly the more attractive when the mice were normally moving, and the less attractive of the two when the mice were motionless.

The attractiveness of a moving black object was found to be nearly twice that of a stationary one. A deer-mouse immobilised by anaesthesia was roughly one-half as attractive as a normally moving one.

Mirroring surfaces are significantly more attractive than dull ones; a black enamel surface was more attractive than a flat black surface, and a silvered mirror more attractive than a polished metal surface. It was found that enhancement of the attractiveness of a black surface could be obtained by the movement of lines of shadow, not of points of light, across it.

An analysis of detailed observations on flying swarms of the Desert Locust, S. gregaria, on 33 occasions in eastern Africa has demonstrated an association of intermittent flight with higher and of continuous flight with lower saturation deficits. This association, which is consistent with recent laboratory studies on the effects of atmospheric humidity on the flight-performance of suspended locusts, is discussed in relation to the rate of movements of migrating swarms.

As a basis for future investigations on the development and the nature of resistance against insecticides, the regression lines for the toxicity of γ-hexachlorocyclohexane to D. melanogaster were estimated by means of

1. A contact method, in which the insects (adults) were exposed to a treated surface.

2. A skin-application method, in which measured doses of an acetone solution of the poison were used.

3. An injection method in which adults were injected with known doses of an emulsion containing the insecticide.

The reproducibility of the results obtained with the above methods is briefly discussed. It was found that in the case of the skin-application and injection methods the regression line did not deviate significantly from linearity. The same was true for the contact method if the results obtained with the smaller doses were not taken into consideration.

External characters enabling the sexes to be distinguished readily in the adult Anobium punctatum (Deg.), popularly known as the common furniture beetle, have been described by Kelsey & others (1945) but no account has yet been published of the external sex characters of the pupae of this Anobiid. In the course of research at the Forest Products Research Laboratory on the biology of this species, a series of larvae in the prepupal stage and of pupae have been examined to determine whether the sexes can easily be recognised in the immature stage. Sex determination, before the adult stage is reached, is of great value for expermental work on breeding techniques and other projects.

The Spinach Stem Fly Hylemyia echinata (Séguy), is an important pest of spinach (Spinacia oleracea) grown in the east and south-east of England for canning and freezing. Attack by the larvae results in the blackening and distortion of terminal shoots and the splitting and discoloration of petioles and mid-ribs, and some larvae may be present in the crops when they are harvested.

The eggs are laid in May on the upper surfaces of the leaves and among the leaflets of the terminal and axillary buds. The larvae penetrate the epidermis and tunnel through the mesophyll until they reach mid-ribs, petioles or stems where they feed on the hollow inner surfaces. The puparia are usually found in the soil but may occur in the feeding sites. The second generation emerges in June and July, and further emergences occur in August and September. Larvae are present in the crops from May to October.

Eggs and larvae are described and illustrated so that they can be distinguished from those of the Mangold Fly, Pegomyia betae (Curt.), which are often present on spinach at the same time. The flies are described and the characters which distinguish them from the Bean Seed Flies, Delia cilicrura (Rond.), are noted.

Observations were made chiefly in the southern Sudan, particularly at Mvolo where human onchocerciasis is common. The country and climate are briefly described.

Methods are described at some length.

The distribution of S. damnosum and places where it is known to be abundant are shown on a map. It does not appear to exist at the Fola Rapids.

Changes in certain organs were studied, chiefly in relation to the approximate estimation of age and (particularly in the case of the mid-gut and peritrophic membrane) to the movements of microfilariae. Recently emerged flies can frequently be readily detected by the clarity of the halteres (in which glycogen has not yet been stored) and the presence of abundant fat body, and by less conspicuous features such as the absence of an old peritrophic membrane. The oesophageal diverticulum often contains plant sugars and particles of grit but never blood.

The peritrophic membrane is formed at the time of a blood meal by the epithelium of the expanding part of the mid-gut. It is a laminated chitinous envelope completely surrounding the blood and remains unbroken for 24 hours or more. When very large numbers of microfilariae are ingested they appear to prevent the completion of the membrane so that blood quickly passes to the hind-gut.

The primary object of the work which is the subject of this paper was to clarify the confusion that has existed for many years in the nomenclature and taxonomy of certain important Agrotid borers of graminaceous crops in Africa.

The genera involved are Spcia, Sciomesa, Poeonoma, Conicofrontia, Bussecla and Sesamia, and of these the first three are new and are described and the others are redescribed. A key to the genera and keys to the species of Sciomesa, Poeonoma and Sesamia are given. The genus Speia is erected for Phalaena vuteria Stoll; the name vuteria Stoll has been wrongly applied to the important pest of sugar-cane in Mauritius, which is, in fact, the well known Sesamia calamistis Hampson. Sciomesa is erected to contain three species previously included in Conicofrontia. Poeonoma also contains three species, of which one is Phragmatiphila serrata Hampson and the other two are new. Hampson's species Conicofrontia sesamoides is redescribed in Conicofrontia and is the only species of that genus dealt with in detail; Phragmatiphila bipartita Hampson is synonymised with it. In the genus Busseola, only the well known pest, B. fusca (Fuller) is described.

This work was undertaken to unravel past confusion concerning the identity of certain economically important species of Cryptophlebia. It involved the study of several other species of the same genus and has resulted in the recognition of three new species and the transfer to Cryptophlebia of several species hitherto placed in other genera, mainly Argyroploce.

The three new species are described and 14 species are redescribed. The distribution of each is given and the food-plants are listed where known. The adult female and the male and female genitalia of each of the new species and certain others are illustrated.

The larvae and pupae of the following Lepidoptera, all of which are of economic importance in Mauritius and most of them elsewhere also, are described:—

The Agrotids, Sesamia calamistis Hamps. and S. inferens (Wlk.); the Crambids, Proceras sacchariphagus Boj. and P. indicus Kapur (larva only); and the Olethreutids, Argyroploce schistaceana (Snell.), A. leucotreta Meyr., Cryptophlebia peltastica (Meyr.) and C. williamsi Bradley.

The mean size of the males of the three tsetse species Glossina pallidipes, G. morsitans and G. swynnertoni is negatively correlated with the mean 2 p.m. saturation deficit of 2 months before.

The correlation is highest (—0·90) for G. pallidipes, the largest species, and lowest for G. swynnertoni, the smallest. The variation coefficient of mean vein length also is highest for G. pallidipes and lowest for G. swynnertoni.

The reason for the apparent 2 months' lag in the effect of saturation deficit on size of flies is that the mean male pupal period is 35 days in Shinyanga (23°C.) and the mean age of males measured is 3–4 weeks. If 1 month's lag is tried, the correlation for G. pallidipes drops from —0·90 to —0·32, and with no lag at all it is —0·24. The correlation with maximum temperature of 2 months earlier is insignificantly lowerthan that with saturation deficit; it is —0·79 for G. pallidipes.

An account is given of a survey of the sandfly fauna of Iraq made in 1949 and 1950. Two new species, one of which has been previously misidentified, and two new varieties are described, and brief notes are given on all the 12 species of Phlebotomus and Sergentomyia taken in the survey. A description is given of a male of P. palestinensis taken in Baghdad, as it differs from the male described from Jericho. Keys to the Phlebotominae in Iraq and neighbouring territories are included, together with a Table showing their distribution.

Relationship between distribution of human dermal leishmaniasis and the species of Phlebotomus is shown on a map, supporting the belief that P. sergenti is the principal, if not the sole, vector of oriental sore in Iraq.

The distribution of Sergentomyia is given in another map indicating that, in contrast to Phlebotomus, the individual species of Sergentomyia are confined to one or other side of the boundary between the Saharo-Sindian and the Irano-Turanian zoogeographical regions.