The principal object of this work was to elucidate the swarming behaviour of Aëdes cantans and other mosquitos, Chaoborus crystallinus and certain Chironomids. In addition, ancillary studies were made of the general ecology of these species. The swarms were found to consist entirely of males and to bear no direct relationship to mating or to the search for food. There was no noticeable difference between the swarming habits of the different species of mosquitos and even the differences between the Culicids and Chironomids were very slight. Swarming was observed to take place at about sunset in the evening and sunrise in the morning. The evening swarms appeared to be formed in response to decreasing light intensity and to disperse at a light intensity of about 7 Lux. Low temperatures may delay the start of swarming. The morning swarms started at about the same threshold of light intensity and at this time also their duration was reduced by low temperatures. Below about 50°F. they were not formed at all. Atmospheric humidity appeared to be of minor importance.

Experiments were carried out to investigate the persistence of toxicity to tsetse of hessian, impregnated with DDT, exposed to the normal weather conditions of the Inland Savanna Region of the Gold Coast; also, to establish a satisfactory method of estimating the loss or change in its toxicity, and to study the effects of impregnation with DDT on the efficiency of tsetse traps.

Hessian was impregnated by being soaked for ten minutes in a filtered saturated solution of commercial DDT in kerosene which gave 4·4 g. DDT per sq. ft. and tests were made at intervals with batches of Glossina tachinoides at 15- and 60-second contacts. The comparison of the survival times of these flies compared with those of controls showed an appreciable residual toxicity after 20 weeks  full exposure to the weather including 4·26 ins. of rain, a slight toxicity after 30 weeks, and a negligible toxicity after one year including 34·35 ins. of rain. The same preparation could still produce toxic symptoms in tsetse after 15-second contacts when exposed for one year to wind and daylight, but protected from rain and direct sunlight. There was no great difference on the whole between the results from 15-second and 60-second contacts.

It was found that survival times lengthened in October when the humidity was high but were shortened in December when the conditions became hotter and drier.

A further experiment was carried out with hessian carrying 4·4 g. DDT per sq. ft. and super-impregnated hessian with 7·4 g. DDT per sq. ft. Samples of both were exposed to the weather and others kept as controls. All samples were tested by 30-second contacts with G. tachinoides.

It was shown that contact with the super-treated cloth was invariably fatal; the standard cloth had an 82 per cent, toxicity but the flies that received a lethal dose took longer to die on the whole. It was found to be the survival time and not the toxicity that varied with seasonal conditions.

A full analysis of the survival times from the exposed samples in relation to those from the control samples showed that exposure to weather during late rains followed by dry season conditions caused only a slight but progressive deterioration of the killing power of exposed DDT-impregnated hessian. This amounted to 10 per cent, in 3–4 months including 7·42 ins. of rain in the case of standard cloth, and 10 per cent, in six months with the same amount of rain in the case of the super cloth.

Hessian impregnated with 25 per cent., 50 per cent, and neat DDT emulsion was found to be highly toxic and to retain its efficiency satisfactorily for at least 12 weeks' exposure in the dry season.

Hessian freshly impregnated with DDT in kerosene solution caused flies to die more quickly as long as traces of kerosene persisted but moisture, on the other hand, interfered with the action of DDT unless kerosene was also present.

An “animal” tsetse trap covered with standard impregnated hessian showed a 40 per cent, superiority in the numbers of G. palpalis and G. tachinoides taken over a period of 20 weeks. Corresponding to the results of the laboratory tests this superiority was lost in October but reappeared in December.

Comparisons of catches made by traps covered with standard impregnated hessian and hessian sprayed with 25 per cent. ATSO emulsion showed that, although the emulsion might initially give much better results, its superiority relative to the standard impregnation tended to diminish, especially during the wet season.

The increased efficiency of an impregnated trap is more than the measurable amount of the increased catches since flies which have investigated the trap, but have not been caught, are likely to have received a lethal dose of DDT.

The application of DDT to traps represents an economical use of the insecticide which can conveniently be applied in sufficient concentration to ensure that brief contacts will be fatal to tsetse over a period of several months.

Comparative tests have been carried out in the laboratory to assess the relative toxicities of Chlordane, BHC and DDT to the leather beetle, Dermestes maculatus. The method used was simple enough for routine industrial purposes when comparisons of new, untried contact insecticides are required, and consists in a measurement of the toxicities of solid films produced by a blood-smear technique on glass photographic plates from standard solutions of insecticide.

Among factors influencing the application of the method, the most important were size of insect and size of crystal clusters as influenced by the volatility of the solvent used to form the film. From LD50 measurements, BHC and Chlordane proved, respectively, 140 and 600 times as toxic as DDT to the leather beetle. DDT had comparatively little effect on eggs, larvae or adult beetles.

Under the conditions prevailing at Kilifi G. pallidipes is evenly distributed throughout all vegetation types with the exception of cultivation from which it is at all times almost entirely absent. There is a preference for the denser vegetation in the dry season from which the tsetse spread out into the lighter vegetation in the wet and humid seasons. There is never at any time any concentration of G. pallidipes along the edges of extensive thicket or forest.

The distribution of G. austeni is similar to that of G. pallidipes except that there is no tendency to spread into lighter vegetation in the wet season.

There is some reason to think that G. brevipalpis prefers thicket of medium density and does not share with G. austeni a preference for tall heavy thicket.

G. pallidipes was the only species staged for hunger, except for austeni in the Sokoke forest. Males are replete at all seasons. G. austeni showed a remarkably large proportion of recently fed males.

Pupae and pupal cases of G. pallidipes were found on the floor of the coral rag thicket and forest. G. austeni and G. brevipalpis showed a preference for the undersides of large logs.

♂ (Type). Antennae somewhat longer than the head and pronotum together. Frontal ridge flat, punctured, gradually narrowed to the apex, its margins obtuse. Fastigium of the vertex slightly concave, oval, with rounded apex and almost smoothed lateral carinulae. Occiput with a scarcely distinguishable median carinula.

The status of the Mediterranean fruit fly in Israel is reviewed briefly. Apricots, peaches and guavas are the most severely attacked of the summer fruits.

The ecology of the various stages of the insect is discussed. It is pointed out that, in addition -to temperature, the type of food influences the length of development of the larva. The threshold of development in the temperature development hyperbola has been calculated and found to be between 10–11°C.

The threshold of development of the pupae was found to be close to 11CC. A daily exposure of the pupae for six hours at a temperature of 32–37°C. caused no injury, but a similar exposure at 42°C. brought about a heavy mortality. At 46°C. one hour's exposure resulted in considerable injury whilst three hours' exposure killed 80 per cent, of the pupae. This explains the very high mortality of the pupae in the groves during June, July and August.

A study of the development of the eggs in the ovarioles at various degrees of temperature indicated that at 18–22°C. no appreciable development took place and at 23–25°C. it was still retarded. The optimum development temperature was found to be 27–29°C, whilst 33–34°C. was actually detrimental.

A study of the length of life of the adult showed that survival was longest between 16–19°C. at which temperature it took 100 days to reach 50 per cent, mortality and 200 days a 100 per cent, mortality.

The fluctuation of the fly population in Israel is discussed in detail. It is pointed out that the prevalence of host fruits is one of the great factors responsible for these fluctuations. An analysis of the climatic conditions month by month and its influence upon the fly population is discussed. The curve depicting the fluctuations of the fly in the coastal plain has two depressions, one between December and January, and the other in July and August. In the Upper Jordan Valley, the summer depression was more clear-cut than in the maritime plain, and the spring population reached a much greater height than that in the autumn.

The fly appeared about two months later in the hills than in the plain, namely towards early June, and it disappeared also earlier, presenting a single peak in July and August.

Observations have been made on the life-history and habits of C. cilicrura. The flies came to moist, freshly turned soil at all times from April to October, particularly in warm bright weather, but the number of flies seen on observation plots was affected by the area of damp and disturbed soil nearby. Both males and females were attracted and some females laid eggs within a few minutes of their capture. When isolated in phials and fed on dilute sugar solution, captured flies lived up to 79 days. Captured females spent varying periods up to 44 days before laying eggs. The eggs were usually laid in batches of less than ten at irregular intervals over periods extending up to 28 days, and 53 eggs per fly was the highest number recorded. Parasitism by the nematode, Heterotylenchus aberrans Bovien, occurred.

Eggs were found in soil crevices and on vegetation in contact with soil. The observed incubation period was 2–4 days according to the temperature.

The duration of the larval instars was affected by temperature; in captivity, the larval feeding period was 8–16 days in May-June and 15–24 days in October-November. The pupal stage lasted from 16–21 days in May-June and from five weeks to five months in autumn and winter. A few flies emerged during January and February in the insectary.

In captivity first-instar larvae found food buried at a depth of 6 ins. and they were able to reach maturity on fragments of vegetation buried in sand. It is suggested that they are primarily scavengers on organic matter in the soil.

Larvae of P. fugax have been found in the stems and crowns of turnips and swedes, and in cabbages, cauliflowers, lettuces and brussels sprouts. A study of their habitat shows that they occur in decomposing vegetation.

Eggs have been found about various brassicas. Their incubation period was 2–4 days. Larvae were reared in decomposing vegetation. Pupation takes place in the soil and in the feeding sites. Adults have been taken from May to October. The life-cycle from egg to adult occupied 4–5 weeks in spring and the winter was passed in the pupal stage.

Regular surveys were carried out from May to July to find out where Jassids live during the cotton close season.

A list of host plants on which Jassids can breed, or feed only as adults, is given; they exhibit preference for certain plants.

The movement of Jassids to cotton was recorded. The initial infestation of cotton is very small but is rapidly built up within the cotton crop. Gardens are shown to be the chief sources of infestation and cotton fields nearest them show larger initial numbers.

Attempts to exterminate Jassids in these gardens by spraying all plants with 0.1 per cent, or 0.5 per cent. DDT emulsion during the summer dead season were not successful. It is thought that reinfestation came from adults which had been present on the tops of Acacia arabica trees and had not been reached by the spray.

The Gezira Scheme is divided into three areas according to the incidence of the Cotton Jassid, Empoasca lybica.

1. The Northern area of normal abundance.

2. The Central area of occasional abundance.

3. The Southern area of possible abundance.

The causes for this difference in the number of Jassids in the three areas were studied and rainfall in showers over 10 mm. in July and August was found to be the important factor. A definite correlation was found between the number of Jassids on cotton and the amount of this rainfall.

Some experiments were carried out which proved that the effect of rain was due to the splashing of mud from the soil on to the lower side of the leaves. The rain could therefore be effective if it is heavy enough to produce mud splashing.

It was shown by a simple apparatus that mud splashing hardly rises more than 30–40 mm.

The correlation between the number of Jassids and the amount of rainfall in July and August might be used as a basis for forecasting the extent of Jassid attack on cotton every year.

An account is given of observations made in two rooms of a warehouse during 1945 and 1946. In 1945 fortified flour was stored in a single tier of upright sacks, whilst in 1946 the rooms were empty except for 50 small experimental bags of wheatfeed.

Before the flour arrived in 1945, no insects were found except a few larval Ptinids in a bag of sweepings. Adult Ptinus tectus soon appeared on the sacks of flour and, in one room, the numbers on the sacks increased steadily to 6,000 by the time the flour was removed in November. In the other room, where the ecological conditions were obviously variable, the increase was erratic, but there were 4,500 adult Ptinus on the sacks by the time the flour was removed. The numbers on the experimental bags in 1946 rose from zero to 5,000 by the end of September. The weekly figures varied with temperature, falls in numbers coinciding with colder weather. In both years a steady 30–40 per cent, of the total Ptinus on the sacks or bags were fcund at the bottom except for the early months of 1946 when 80 per cent, were at the base of the bags until April.

In empty premises it was obvious that many adult beetles hid in the fabric of the building, a rough estimate of 150,000 being obtained following the use of traps and marked beetles. There were indications that the main hiding place in this building was at the junction of walls and floor. After the sacks of flour had been removed in 1945, it was estimated that the flour covering the floor of Room 70 contained about 7,000 larvae. These would normally be removed by sweeping and vacuum cleaning, but this treatment left behind about a further 10,000 larvae in the floor cracks of each room. No estimate of larvae inside the sacks was possible, but in eight months in 1946, about 1,500 eggs were laid in each small bag of wheatfeed. An average of at least 300 eggs per day were laid in the room in 1946.

Ptinus tectus has two complete generations a year. All stages may survive the winter so that overlap of generations is complete.

In a stack of sacks of flour, adults are most abundant on the sacks at the edge of the stack especially on those near the corners. Draughts, wetness and sunshine caused local changes of distribution. There was some suggestion that Ptinus preferred to rest upon cotton sacks rather than on jute. Larvae are normally present only in the outer layers of flour in a sack and spin cocoons on the inside surface of the sacking. The adults emerge through the sacking to the outside.

The activity of Ptinus in a warehouse is greatest during darkness. Hence it is fairly continuous in dark premises and periodic in light places. In the latter, beetles emerge from their hiding places at dark and return at dawn. If dark crevices are provided artificially they act as traps, for some of the beetles will use them as daytime hiding places. Activity is reduced by low temperatures but does not stop altogether until it is as low as 2°C.

Two methods are suggested for actual estimation of insect numbers without too much labour. One for estimating the numbers on the sacks is based on the fact that most of the insects are found on outside sacks, and involves the counting of the insects on several representative groups of contiguous sacks. Over half of the estimates made by applying this method to the data from one of the rooms in 1945 were within 20 per cent, of the correct values as indicated by total counts of the population. The combination of traps with the release of marked beetles is suggested for estimating the resident population of empty premises.

The different instars of Agriotes sputator larvae cannot be distinguished by measurements of total length or of various parts of the wireworm.

The number of teeth on the mesothoracic and abdominal spiracles increases with age, and an examination of 700 wireworms showed that the average numbers of teeth on the two thoracic or on all the abdominal spiracles fell into eight groups. These criteria were valid for populations collected at different times of the year.

The number of teeth on the thoracic spiracles of a larva in any particular group approximates to that on the abdominal spiracles of a larva in the next larger group.

The eight groups formed by counting either the thoracic or the abdominal spiracle teeth represent growth stages and not necessarily instars.

The larvae may sometimes moult without growth, a phenomenon probably caused by an inadequate supply of food. At such an ecdysis the number of spiracle teeth does not increase.

The larvae pupate after attaining an optimum size, and reach this size in seven or eight growth stages.

A quick method of determining the growth stage to which a larva belongs is given, whereby more than 80 per cent, of the larvae are placed in their correct growth stages by counting the teeth on one spiracle only ; for less than 1 per cent, of the larvae is it necessary to examine as many as five spiracles ; an accuracy of more than 97 per cent, can be maintained.

The possibility of determining the relationship of growth stage and age is discussed.

The division of the larvae into those which will pupate after seven, and those which will pupate after eight growth stages is apparent at a very early stage in the life history. One larva was found which appeared to be in its ninth growth stage.

The cause of this difference in growth stage number is unknown. It may be due to the size of the egg, to the time of the year at which hatching occurs, or to heredity.

The geographical distribution in the African Continent of very few of the species of Ixodoidea has been fully determined. Rhipicephalus sanguineus (Latr.) and certain species of Boophilus are known to be widely distributed, while others, such as R. duttoni Neum., have been recorded from only one or two localities. The present study was primarily undertaken to determine the genera and species of ticks occurring in Nyasaland, but it is hoped it will contribute to the wider problems of the distribution in Africa of the several species.

While investigating the biological control of certain Hepialids, a very interesting Ichneumonid parasite, Alomya debellator (F.) was reared from the pupae of the Swift Moth, Hepialus lupulinus (L.).

The systematic position of this parasite has been thoroughly investigated and the members of the special sub-family, Metopiinae, to which it has been assigned, are characterised by the possession of only one trochanter on each foreleg. A. debellator is the sole representative of the tribe Alomyini.

After extensive collecting, and a thorough search of the literature, the conclusion has been reached that the distribution of this parasite is fairly local, but its range in Great Britain and certain other European countries is wide. As a result of the present study H. lupulinus has been definitely proved to be the host of A. debellator.

A fairly full account of the life-history of the parasite has been worked out, and amongst other things, a point of special interest is the arrest in development which occurs in the first-instar larva. Possible explanations of this phenomenon are discussed.

The morphological and anatomical structure of the larva have been fully investigated and described, and useful diagnostic characteristics both for the primary and mature larval stages, have been discovered.

The paper concludes with a discussion on the potential value of A. debellator as a factor in the control of H. lupulinus, and other allied species belonging to the genus Oncopera in Australia. It is maintained, on the evidence collected, that this parasite in some areas is probably the most important single factor of biological control. A note on the feeding habits of Hepialids, and a few remarks about the collecting of parasitised material are appended. Altogether some 7,000 specimens of H. lupulinus larvae and pupae many of which were parasitised by A. debellator were collected from the Willingham area of Cambridgeshire.

This paper deals with the aerial curtain method of spraying flying swarms of locusts with insecticide from aircraft.

Equations are developed for calculating the dosage deposited on locusts in single spraying runs under idealised conditions. Graphical methods of solving the equations are described together with a simple method for obtaining the summed effect when a number of spraying runs are carried out in a regular sequence to form an aerial curtain.

There is an optimum combination of spray droplet size distribution and spraying height according to the depth and density of the swarm, but good performance can be obtained with a single fixed droplet size distribution. A fine spray is recommended for the attack of flat-topped, shallow swarms, but a coarser spray is required to penetrate adequately into deeper and denser swarms.

The efficiency of application of the insecticide solution, calculated as the proportion of lethal doses actually applied to those potentially available, may be as high as 10 per cent., but varies rapidly with spray droplet size and swarm characteristics.

The numerical values given may need some modification in the light of further experimental and field data, especially in regard to locust airspeed in the swarm and the effect of droplet size on mortality.