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.

This paper presents a key to the larvae and pupae of 28 species of Culicoides found in Britain and to larvae and pupae of the genera Stilobezzia, Serromyia and Ceratopogon including the subgenera Ceratopogon and Isohelea. The keys are supplemented by descriptions of the larvae and pupae, including photographs of the fourth instars and figures of the so-called “hypopharynx” —the true epipharynx—of most of the larvae and by figures of specific characters of the pupae. Twenty-eight species of Culicoides larvae are described:—C. albicans, C. chiopterus, C. circumscriptus, C. cubitalis, C. cunctans, C. delta, C. fascipennis, C. grisescens, C. halophilus, C. heliophilus, C. impunctatus, C. lupicaris, C. maritimus, C. nubeculosus, C. obsoletus, C. odibilis, C. pcdlidicornis, C. pictipennis, C. pseudochiopterus, C. pulicaris, C. punctatus, C. riethi, C. salinarius, C. scoticus, C. simulator, C. stigma, C. truncorum, and C. vexans. The descriptions of the pupae include all the above, with the addition of C. parroti.

An analysis has been made of the breeding preferences of Culicoides and it was found that species could be placed in one of six groups depending on the larval habitat. The six categories were:— (i) Bog, (ii) Fresh Water Marsh, (iii) Swamp, (iv) Mud, (v) Salt Water Marsh and (vi) Dung.

The vertical distributions of seven species of Culicoides larvae are given. There are marked differences between the species in this respect.

The preponderance of males in tsetse-fly catches is an interesting fact that has not been understood in the past. Attention is drawn to the importance of the agefactor. Teneral flies are nearly always taken in equal numbers whereas non-teneral A.G.I flies and A.G.2 flies have the highest male/female ratio. In A.G.3, the ratio drops, indicating a decline in reproductive capacity. Females become fugitive about seven days after emergence, at the time when the first egg is almost due to descend into the uterus, i.e., at the end of the teneral stage. This is the mating phase par excellence. Mating is prolonged, vigorous, and frequent, and this accounts for the early appearance of the mating scars. As the uterus lies under and between the mating cushions, it is unsafe for females with eggs in the uterus or young larvae to mate. Third-instar larvae are safer as the highly chitinized polypneustic lobes take the brunt of the pummelling from the claspers. Safe periods also occur during the hiatus between larvipositions when the uterus is empty. There are, of course, other factors influencing the ratio, but the age factor is considered paramount, and failure to recognize this in the past has resulted in a good deal of confusion.

Cacoecia histrionana Froel. a European relative of the North American spruce budworm, Choristoneura fumiferana Clem., was found in several localities on the north-eastern frontier of Bavaria in 1949, but was not abundant anywhere.

Details are given of its biology based upon observations made during large-scale collecting in the summer of 1949, which yielded approximately 2,100 larvae of C. histrionana.

An important characteristic of the species is the great variation in the stages of larval development present at any given time, which is apparently caused chiefly by the absence of diapause as a synchronising factor.

Approximately 4°C. was found to be the lower temperature limit for movement and feeding of larvae ready for overwintering.

Three samples of larvae taken in favourable localities showed that 0-15 to 0-70 larvae were present per metre length of spruce forest edge from ground level to a height of 2 metres. An estimate of the minimum population is made for a limited and well searched area.

From 1803 C. histrionana larvae collected in the field, 15 species of primary parasites and four of hyperparasites were bred. Combining the result of three samples taken at different times the minimum reduction of the population after hibernation is calculated to be 66-8 per cent., the parasitism of pupae at least 13-5 per cent. Egg parasitism occurred.

Nine of the 20 parasites, known hitherto from C. histrionana, have been bred from other hosts of the same animal community.

The most important larval parasite was Meteorus ruficeps Nees which completes 2-3 generations in one generation of C. histrionana. A proportion of the population also overwinters in other Microlepidoptera, concentrating on C. histrionana in summer. Details of its life-history are given.

Occasionally some larvae were found that had probably died from disease but disease, as a mortality factor, was of little consequence in the observation area in 1949.

Mortality caused by parasites proved to be very important in affecting changes in the population density. This result does not agree with Eidmann's theory that the scarcity of C. histrionana is due to climatic control.

The effect of piperonyl butoxide (PB) on the toxicities of allethrin, DDT, and BHC in a heavy oil base to Tribolium castaneum beetles has been tested. PB synergised allethrin and BHC both in films and direct sprays. It antagonized DDT in films, but left the toxicity of DDT unchanged in direct sprays.

The effect of PB on the joint toxicity of BHC and pyrethrins to T. castaneum was also investigated, applying the materials as direct sprays. The data were not so conclusive as had been hoped, but they indicated strongly that in a mixture containing all three materials the PB synergised each insecticide as though the other were absent, i. e., it synergised both simultaneously.

The experimental findings of the present paper are examined in conjunction with the findings of Hewlett and Plackett (1950). It is shown that there is an underlying similarity between the film and direct spray results for the joint toxicities to T. castaneum of pyrethrins, DDT, BHC, and PB, taken in pairs.

Twenty-five species of Simuliids are listed with indications of their relative abundance, importance as pests of man, seasonal appearance, temperature requirements, and larval habitats in Labrador. Seven of these are undescribed species. The most important species are Simulium venustum Say and Prosimulium hirtipes (Fries).

A circular area of 200 square miles around Goose Bay airport was surveyed for important breeding sites. Of 163 streams and rivers investigated, 77 were suitable as larval habitats, and larvae were virtually eliminated from them in June, 1950, by applications of a 10 per cent, solution of DDT in fuel oil at the rate of 1–5 p.p.m.- minutes from a helicopter, conventional aircraft, or boats, or by hand application from the ground. Methods of application are discussed.

The repopulation of the area by black flies was studied, and deductions are made concerning the flight habits of the most important species. On the basis of averages throughout the season, a great reduction in numbers of black flies at the centre of the area was obtained, and a worth-while reduction to a distance of between 4 and 6 miles from the centre. Even near the centre of the area, however, black flies were sometimes troublesome late in the season.

It is suggested that, where P. hirtipes is the important species, relief for at least one season could be secured by eliminating larvae within a radius of 2 miles; for S. venustum, 6 miles is suggested as a suitable radius. No adverse effects on useful animals were recorded.

The course of embryonic development of S. gregaria under controlled conditions of temperature and humidity is described, with special attention to the water requirements of the developing egg. The development of the egg is interrupted if contact water is lacking and is resumed when the egg is moistened. This occurs at the stage of late anatrepsis, which is the stage at which the embryo of some other locusts and grasshoppers undergoes diapause.

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.

During a study of the natural enemies of mealybugs that transmit a virus causing swollen shoot disease of cacao, R. G. Donald submitted specimens representing a new species of the gall midge genus Coccomyza. This species is here described to provide a name for use in connection with the biological work.

Further studies were made of G. medicorum and G. fusca using the resting-haunt technique.

During 5½ collecting days, 200 G. medicorum and G. fusca were taken by the resting-haunt technique ; over this period, only one fly was taken by the normal, human bait technique.

Out of 119 G. medicorum 45 per cent, were females, and out of 73 G. fusca, 44 per cent, were females ; the resting-haunt technique yields a good cross-section of the tsetse population.

Out of 15 recently gorged G. medicorum and eight G. fusca examined, all contained mammalian blood. Gorged flies were very numerous, so that it should be possible to ascertain the wild hosts by the precipitin test.

From the evidence available, it is believed that at the end of the rains both G. medicorum and G. fusca feed only during the twilight hours, or when the forest is fully illuminated by the moon.

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.

The control methods used to protect new-crop groundnuts stored in Kano against insect attack are described.

The main method used was the spraying of aqueous suspensions of DDT directly on to the sacking of piles stored in the open and on the walls of warehouses before the nuts were stacked. The solutions were applied with a slow-moving orchard power sprayer, and 50 per cent, wettable powder applied at the rate of 360 mg./sq. ft. was found satisfactory. The BHC wettable powder applied at about 12 mg./sq. ft. was cheaper and equally as good and has now been found safe. Treatment markedly reduced the Tribolium population but had little effect on Trogoderma. Sprays of oil solutions were little used and were not very satisfactory.

The damage caused by the Cotton Jassid to the Egyptian-type cottons in the Gezira and White Nile areas of the Sudan is very considerable. Realisation of this fact has been greatly aided by chemical control of the pest in small-scale experiments, followed by large-scale work with tractor-drawn sprayers and with helicopters fitted with spraying equipment. This paper deals primarily with examination of available records pertaining to the cotton crops in the four seasons from 1946/47 to 1949/50, preceded firstly by an introduction which emphasises the importance of yield records in the appraisal and interpretation of losses from pests, and secondly by an account of certain aspects of the pest in the Gezira Scheme.

Large-scale spraying to control the pest started in the Gezira in the crop season 1945/46; yield increases from about 1,250 feddans (acres) sprayed with 0·1 per cent. DDT emulsion were very satisfactory. In succeeding seasons increasing areas were sprayed; in 1947/48 spraying was extended to the cotton farms along the White Nile between Khartoum and Kosti; in 1949/50 the total area sprayed in the Sudan was over 150,000 feddans. Material and also methods and dates of application varied considerably.

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.

Collections of Cactophagus spinolae (Gylh.) were made in Mexico in 1946, 1947, and 1948 to supplement the biological control of prickly pear (Opuntia spp.) in South Africa. During these three years, 862, 1,396, and 15,584 adults, respectively, were dispatched to South Africa. The weevils were sent by air express in specially designed containers, and arrived in excellent condition.

This paper includes information on the distribution, life history and food preferences of C. spinolae. The need is stressed for anticipating the effects of transit conditions upon living insect material transported by aircraft.

Factors affecting the persistence of deposits from aqueous suspensions of insecticides have been studied.

There is an inverse relationship between particle size of insecticides and the initial contact toxicity to mosquitos. The influence of particle size on effectiveness decreases as the intrinsic toxicity of the insecticide increases. The compounds investigated can be arranged in order of immediate contact toxicity to mosquitos (Aëdes aegypti): dieldrin ≥ gamma-BHC > aldrin > DDT.

An account is given of an investigation made of the life-histories of Oscinella frit and its parasites in Ontario, Canada, with a view to the possible introduction of suitable parasites into England. The various Chloropid species associated with O. frit in North America are discussed.

The life-history of the frit-fly in Ontario is similar to that in England except wheat, not oats, is attacked, and that there appears to be no regular grain-infesting generation, but the insect is never a major pest in Canada.

The life-histories of the following six species of parasites are described : Hexacola sp. n., Polyscelis sp. n., Loxotropa sp., Cyrtogaster sp., Callitula bicolor and Spalangia drosophilae. Other hosts from which these parasites have been reared include Chloropids associated with O. frit in wheat, namely O. carbonaria, O. soror, O. minor and Meromyza americana.

A brief account is given of the control exerted by these parasites on the population of frit-fly in Ontario and a comparison is made between the Canadian and English parasite complexes. From this it is concluded that S. drosophilae might exert some control of frit-fly if introduced into England.

The surfaces of bags containing fumigated cocoa were sprayed with the macrodosage of 956 mg./sq. ft. DDT applied as a 5 per cent, suspension of wettable powder in water.

After exposure to an infestation of Ephestia cautella and Tribolium castaneum, no appreciable effect was obtained in preventing an attack by E. cautella, though the larvae appeared to choose unusual pupation sites on the surface of the bags. T. castaneum were rapidly affected and prevented from entering into the sacks.

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.

An arsenic-resistant tick was first noticed in the East London district of South Africa in 1938–39. It was a strain of the one host blue tick, B. decoloratus. BHC was very toxic to the tick, as 50 p.p.m. of the gamma isomer killed adult females in in vitro experiments. Field results in 1946–47 were equally convincing. Weekly dippings in BHC washes containing 50 p.p.m. gamma isomer brought the arsenicresistant tick under control.

In March 1948, BHC was found to be ineffective against blue ticks at “Burnside”, “Mistley” and “Gulu”, farms in the East London district. Later, ticks at “Tharfield” and “Elmhirst” in the Bathurst area survived regular weekly dippings in BHC preparations. In vitro experiments showed that adult female blue ticks taken from these localities could withstand high concentrations of gamma BHC, while females of the same species from other areas were readily killed. Not even 1,000 p.p.m. would give 100 per cent. control of ticks from resistant areas, and different sources of gamma BHC were equally ineffective. Laboratory experiments further indicated that the ticks were still arsenic-resistant. Indeed arsenic resistance appears to be associated with BHC resistance, as no BHC-resistant tick has been found that is not arsenic-resistant. The chlorinated cyclic hydrocarbons toxaphene and chlordane were ineffective against BHC-resistant ticks, but controlled BHC-sensitive ticks in the laboratory. DDT gave moderate in vitro results against both resistant and sensitive ticks.