Experiments were carried out in West Bengal to ascertain whether the Paddy Stem Borer, Schoenobius incertulas (Wlk.) could be controlled by “Tetrax” 1, a systemic insecticide containing technical schradan equivalent to approximately 42 per cent, octamethyl pyrophosphoramide + approximately 25 per cent, triphosphoric acid pentadimethylamide.

In a preliminary experiment, treatment had little effect on the damage caused by the borer but the yield of grain was higher from a treated plot than from a control plot.

A further experiment was carried out, the following year, in which the seed was soaked in a 0·1 per cent, water solution of “Tetrax” 1 for eight hours before sowing in the seed beds. The seedlings were lifted about 2½ months later and steeped in 0·1 per cent. “Tetrax” 1 for eight hours before transplanting into two plots, each 32 ft. × 32 ft. About three weeks later the plants were sprayed with a solution of the same strength. Two plots of similar size, in which the paddy had received no treatment, were maintained as controls.

Again there was very little difference, between the treated and untreated plots, in the damage caused to the ear heads by the pest, but the treated plots produced 108·68 lb. of grain as against 77·27 lb. for the untreated plots. The increase was largely due to an increase in the number of ear heads per plant.

The incidence of the borer was too low in both experiments to determine whether “Tetrax” 1 exercised any appreciable control, but the treatment did give rise to a higher yield of grain under the conditions of the experiments.

This paper presents the results of an investigation of certain processes taking place when flies of the species Phormia (Protophormia) terraenovae R.-D. are exposed to finely particulate deposits. Information is advanced concerning the precise sites of uptake of particles on the tarsi and pretarsi, the effects of “cleaning” reflex movements on the location and retention of particles and the influence of lipoid solubility (a fundamental property of contact insecticides) on the adhesion of dry particles to the lipophilic surfaces of insect and leaf cuticle.

A technique for the controlled exposure of active blowflies of the species P. terraenovae to particulate deposits is described.

The possibility of controlling the human body louse, Pediculus humanus humanus L., through the development of clothing which is inimical to it on physical rather than chemical grounds was investigated. Claw size in lice was shown to be related to diameter of host hair. The grip force of lice on fabrics made of fibres of various diameters and compositions, some spun and some unspun, and of various weaves largely dictated by availability, was measured with an apparatus of which the essential parts were a torsion balance and a kymograph motor. The force was found to be a maximum at fibre-diameters approximating that of human hair. The ability of lice to grab hold of a fabric when dropped on to an inclined surface of it was also measured and found to vary with fibre-diameter in a similar manner to grip, but less strongly. The number of eggs laid on fabrics when no choice was offered was also found to vary with fibre-diameter in a similar manner. While this physical method of louse control is not promising for immediate practical application, it has possibilities which may be enhanced by developments in textile technology.

Two of the species in Callosobruchus, C. maculatus (F.) and C. analis (F.), are compared and redescribed, together with a description of the male and female genitalia of both species. The species Bruchus vicinus Gylh., B. ornatus Boh., B. ambiguus Gylh., B. sinuatus Fhs. and B. quadrimaculatus F. are shown to be synonymous with C. maculatus (F.). Bruchus jekeli Allib. and B. glaber Allib. are almost certainly synonyms of C. analis (F.), but this could not be verified as no type specimens are available.

Continuous trapping of winged Aphids was carried out with Moericke trays and a suction trap for two years at a site at 6,850 ft. above sea level in Kenya, and with Moericke trays, for four months only, at a site at 1,200 ft. in southern Tanganyika.

The trap data show a marked seasonal periodicity of flight (three-quarters of the annual catch in two months) at the Kenya site. The large catch is a reflection of a large increase in population following the rains. A similar relation between size of catch and the period of the rains is indicated by the data from Tanganyika.

Successive hourly catches with a suction trap show no distinct diurnal double peak of aerial density such as occurs in Europe.

Reactions of 3-day-old first- and fourth-instar hoppers of Schistocerca gregaria (Forsk.) of phase gregaria, to three physical factors, namely to relative humidity, temperature and light have been studied in an alternative chamber apparatus designed to give an enclosed space with gradients of humidity. The responses to each factor independent of the others, and to the interactions of these factors, were considered.

It was found that both the first- and the fourth-instar hoppers respond strongly to humidity. They are agitated by low, and even more by very high, humidities, but become more quiescent within a zone of 60–70 per cent. R.H., where they spend more time. Within this zone they hop and turn less and this decrease in activity appears to be a response which is independent of both temperature and of light intensity. This zone of decreased agitation has been called “the zone of minimum activity”. However, the speed of walking in contrast to the other types of activity, increased progressively with humidity.

Increase in light intensity raises the level of activity at all humidities, i.e., it increases the duration of activity within the limits of experimental time and the speed of walking. With rise in temperature there is an increase in hopping, in klinokinesis and orthokinesis.

The population of the Makonde plateau, Newala district, Tanganyika, underwent a severe epidemic of a virus disease in 1952–55, and during an investigation of the epidemic the opportunity was taken to define the biting activity cycle of Aëdes (Stegomyia) aegypti (L.), a mosquito that was extremely common in native huts on the plateau.

Continuous baited catches, lasting for 49 hours, were made by teams of four native catchers, inside a hut and on its verandah. The intensity of attack is expressed as the geometric-mean numbers of A. aegypti alighting on such a team per hour. The catches are recorded on a 24-hour system in which sunset is near to 1800 hr.

The two isomers demeton-O and demeton-S which occur as a mixture called demeton in the commercial insecticide Systox act on Aphis fabae Scop. as contact and systemic insecticides and as fumigants.

When applied as a contact insecticide or systemically via the roots from solution or from soil, demeton-S was about ten times as toxic to Aphis fabae on broad beans as demeton-O. Using demeton-S containing 32P it was shown that, when applied to the roots, radioactive material passed to all parts of the plants and that the concentration in the aerial parts was higher than in the roots. Leaf samples were more active than stem samples. By radioassay and by the cut tap-root technique it appeared that the lethal dose of demeton-S was equivalent to about 1·0 mg./kg. of fresh plant tissue. The lethal dose of demeton-O by the cut tap-root technique was 3·0 mg./kg. From solutions, the plants first absorbed demeton-S preferentially, then water preferentially. Demeton-S was more rapidly absorbed from sand than from soil.

Both isomers were translocated from older to younger leaves of broad beans usually in sufficient quantities to kill Aphids but the results were more consistent with demeton-S. The quantity translocated downwards was small. A low light intensity before and after treatment reduced the quantity of demeton-S translocated. There was also a reduction in the quantity translocated when the plants were only shaded before treatment. One day of shading was sufficient to cause the maximum reduction.

Solutions of the two isomers gave off toxic vapours and plants treated via the roots gave off toxic vapours from the foliage.

The range of Thyridanthrax abruptus (Lw.), a widespread puparial parasite of Glossina morsitans Westw. in East Africa, is now extended to British West Africa where this species has been found parasitising a Calliphorid fly, Rhyncomyìa pìctìfacìes Big. Puparia of R. pictifacies were collected in the stream-bed sand of dry-season breeding sites of Glossina palpalis (R.-D.) and G. morsitans submorsitans Newst. at the following localities in Northern Nigeria: Gamagira, Zaria Province; Mando Road (25 miles NNW. of Kaduna), Zaria Province; Rahama, Bauchi Province. All were collected during January and February 1957. During February, eight adults of Thyridanthrax emerged from a total of 33 puparia of R. pictifacies found at Rahama.

A method is described by which a continuous supply may be produced, efficiently, of large numbers of adults of Drosophila melanogaster Mg. of known age and sex for microbioassay tests.

Equal numbers of male and female flies were introduced into breeding jars containing a nutrient medium and maintained at 24–25°C. and 60–80 per cent, relative humidity. They were removed ten days later, just before the emergence of their progeny.

It was found that the physical conditions in the culture jars exerted an appreciable influence on several aspects of the breeding of Drosophila. Thus, in trials in which the surface of the nutrient medium was flat and unbroken, with a pad of cotton-wool laid on it to provide suitable sites for pupation, and with or without a layer of cotton-wool beneath it, or in which the medium was broken with irregular lumps, laid on a layer of cotton-wool and arranged with a space, filled with cotton-wool, at the centre, the best results were obtained with the last modification.

Under these conditions, emergence of adults began earlier and reached its peak earlier, a most constant sex-ratio and a higher number of progeny per female, and consequently a higher yield of flies per culture jar, were obtained.

A special device, which takes advantage of the positive phototropism of the flies emerging from a group of culture jars enclosed in a darkened box with an exit funnel leading into a collecting jar, made it possible, by daily replacement of the collecting jar, to remove practically all newly emerged flies within 24 hours, so that the known age of any batch is accurate within the limit of one day.

Male flies have been found to be twice as susceptible as females and give a greater response to differences in dosage of toxicant. For this reason male flies only are to be preferred for use in bioassay experiments.

Using another device, the flies were therefore sexed, and the required number of batches of males collected. This device consists of a glass-covered container through which a gentle continuous stream of CO2/air is passed over the flies, which have already been anaesthetised with CO2. The male flies are taken up individually with a small aspirator and passed direct into test tubes where they are collected in batches.

The responses of females of Aëdes aegypti (L.) to beef blood have been investigated. Paired comparisons were made of the numbers of mosquitos attracted to test and control materials.

Vapours emanating from the heparinised blood were found to be significantly more attractive than water vapour in an olfactometer. When the blood vapour was passed through an aqueous solution of Ba(OH)2 this attractiveness disappeared.

Exposure of heparinised blood on filter paper proved it to be two to four times as attractive as water or washed corpuscles suspended in saline. Plasma proved to be 4·7 times as attractive as water, indicating that the attraction of blood lies entirely in the plasma.

Treatment of blood with BaCl2 and a vacuum, thus rendering it incapable of evolving CO2, removed its attractiveness to mosquitos. Treatment with vacuum alone, which may be expected to remove the volatile substances, did not completely remove the attractiveness; nor did the treatment with BaCl2 alone, which removes the bicarbonates in the blood.

The attractiveness of blood was completely removed by desiccation and was not returned by remoistening. No attractive substance was isolated in an ether extract of blood.

When CO2-freed blood was treated with gaseous CO2 its attractiveness was significantly increased. When the treatment was such as to restore the normal CO2-producing capacity, the attractiveness was one-half that of whole blood. The attractiveness of whole blood was not increased by adding excess CO2.

It is concluded that the CO2 in beef blood is a definite element in its attractiveness, though probably not the most important one.

The structure of the shell of eggs of Pieris brassicae (L.), together with changes in it and associated membranes during embryonic development, have been investigated in relation to the penetration and toxicity of simple chemicals. The rigid outer shell consists of two proteinaceous layers, covered externally by a relatively hydrofuge cement, by which the egg is attached to the leaf surface. The egg has respiratory pores over its surface, and a single apical micropyle penetrating these layers. The inside of the rigid shell is lined with a layer of unsaturated oil—an unusual feature for an insect egg. When the egg is first laid, the vitelline membrane is directly applied to the inner surface of the solid shell over the region immediately around the micropyle, but within four hours this contact is broken, and the oil layer flows into this region also, and becomes complete. As development proceeds, the vitelline layer is replaced by membranes of embryonic origin, but before eclosion both these epembryonic layers, and also the oil, are resorbed.

The egg is remarkably resistant to water-soluble poisons which have no oil-solubility, except during the first four hours of development. This resistance is attributed almost entirely to the oil layer, and the early susceptibility to its absence over the micropylar region. These changes are not reflected in the effect of oil-soluble poisons or fumigants. The solid portions of the shell do not seem to be of great importance in restricting the entry of liquid poisons, even though the cement is comparatively hydrofuge; from experiments with wetting agents and with eggs immersed in poisons under vacuum, it does not appear that the respiratory air spaces in the shell are preferential channels of access; rather, the poisons penetrate through the solid portions of the shell. This penetration, even of oil-soluble materials, is slow, for they can be effectively washed out of the shell again, some considerable time after dipping. On the other hand, non-volatile oily materials can interfere with the respiration of the egg by blocking the air spaces in the shell.

The secretion of epembryonic layers does not appear to change the resistance of the egg to water-soluble materials; this is to be expected, for they do not contain lipoid. On the other hand they do add appreciably to the resistance to oil-soluble materials. There is no evidence that poisons are accumulated in these epembryonic membranes, and released during the pre-eclosion period. Experiments with covalent compounds, such as mercuric chloride, suggest that their oil-solubility accounts for their toxicity, whereas electrovalent compounds containing similar heavy metals are only effective while the direct micropylar path of entry is available to them.

The present world distribution of six species of Cryptolestes found in stored produce is delineated from the evidence of specimens collected from a small number of countries and from specimens collected from produce examined in ships at British ports.

It is concluded that C. ferrugineus (Steph.) is worldwide, being found in temperate and tropical areas and in humid and dry zones. The range of C. minutus (Ol.) is limited by low temperature and low humidity but it is more abundant than C. ferrugineus in the wet tropics. C. pusilloides (Steel & Howe) is at present confined to the southern hemisphere but may be spreading slowly. It seems unlikely that this species entered stored products handled by the shipping trade much before 1944. C. turcicus (Grouv.) has been identified from Europe, North and tropical Africa, Turkey, North America, Uruguay and Argentina, and C. spartii (Curt.) only from Europe, North Africa and Turkey. C. ugandae Steel & Howe is rare, being found only from Uganda, Nigeria and Ghana.

By means of a laboratory spraying technique, ten comparisons were made of the resistance to rotenone of samples of adult apterous viviparous parthenogenetic females of the Pea Aphid, Acyrthosiphon pisum (Harris), reared on broad bean and on clover, respectively. In nine of the tests, the Aphids from clover were more resistant than those from broad bean, the ratios ranging from 1·1 to 2·5. These differences were not all significant. In the remaining test the Aphids. from broan bean showed a very small increase in resistance over the Aphids from clover which was not significant.

The Aphids from the clover were generally smaller than those from broad bean. Figures are given to show that while the total amount of poison retained by the larger individuals from broad bean was more than that retained by the smaller individuals from clover, the amount of poison retained per unit body weight was greater with the smaller individuals. It appears, therefore, that while the results obtained might be due, at least partially, to the greater total weight of poison retained by the larger individuals from broad bean, the difference in resistance between the insects from broad bean and clover, respectively, might be even greater if the poison were applied on the basis of equal weight of poison per unit of body weight. Since the difference in resistance between the Aphids from the two host-plants did not appear to depend primarily on difference in size, the assumption might be made that it is due to difference in nutrition. It was found that Aphids reared on clover had a significantly higher proportion of dry matter in their composition than those reared on broad bean, which may be taken as evidence that differences due to nutrition are being produced. These may lead to differences in resistance.

Previous work has shown that, under natural conditions in the Lake District, larvae of Phyllopertha horticola (L.) hatch in early July and feed actively on the roots of pasture plants during the next 3½–4 months, undergoing two moults. They then empty the gut and enter hibernation, pupating the following spring. Stores of organic material in grass roots are at their highest level during this autumn feeding period. It has also been shown that the egg production depends almost entirely on the weight of the hibernating larva or of the pupa, which thus plays an important part in determining the reproductive rate of the population, and studies were accordingly made on larval growth and certain factors affecting it.

Newly hatched larvae were cultured at 15°C. in moistened plaster-of-paris containers filled with a mixture of soil and germinating grass seeds. They moulted at about 20 and 45 days after hatching, and stopped feeding and entered hibernation at about 100 days. When the seeds were scattered on the soil surface, larval growth was slower. The mean larval weight, plotted against age, gave a sigmoid curve; in the. first instar and most of the second, the rate of increase in weight was proportional to the weight, but thereafter, up to the time of hibernation, it was more or less constant. The rate of growth of the individual larva was irregular, being slower at the moults and variable even in the middle of the instar.

Larvae cultured under semi-natural conditions in pots of growing grass in the open moulted about 3–4 and 7–9 weeks after hatching and entered hibernation at 100–120 days. Growth is possible on a wide variety of food plants, larvae cultured on 13 species of pasture plants grown in pure stands surviving to the hibernation stage on all but two of them.

During hibernation, the larva loses 20–25 per cent, of its weight, mostly in the first few weeks. The pupal weight is almost constant and does not appear to be affected by the temperature treatment of the hibernating larva. It is thus a useful index of effective larval growth.

The mean and (in brackets) range of the weights of all pupae collected in two fields in the Lake District between 1950 and 1953 were 139·3 mg. (65–242) for males and 171·3 mg. (72–310) for females. Field samples of hibernating larvae and of pupae show considerable variation in weight from place to place, from year to year and within apparently homogeneous areas.

Variation in the time at which larval growth takes place is a major cause of variation in pupal weight. The growth period of larvae in a field at Buttermere was three weeks earlier in 1952 than in 1950, though of the same duration, and the resulting pupae in 1953 were heavier than those in 1951. Two lots of larvae of similar parentage, grown in adjacent plots of grass out of doors, one of which both hatched and entered hibernation three weeks before the other, likewise showed a difference in weight at hibernation, the earlier lot being the heavier. A series of weighed samples of larvae taken from part of a field at Ambleside in 1953 at weekly intervals during the period when they were entering hibernation showed that heavier individuals did so before lighter ones, and males before females. Factors inducing mortality during this period thus operate selectively against females, because these are exposed to them for longer.

Field-collected larvae fed in the third instar on roots of lettuce produced pupae the following spring that were significantly heavier than those from larvae fed on roots of either ryegrass or clover.

There is no evidence to show that population density affects the weight of the hibernating larva or the pupa. On the other hand, larvae from soil from which the damaged turf had been stripped by birds were significantly lighter than those from the surrounding undisturbed sward.

When moving through the soil, larvae may meet and fatally injure each other by an undirected “ snapping ” reaction. This mechanism may limit population density. In an experiment in which larvae were reared in loose soil on grass roots, the mortality rate was seen to increase with the size and activity of the larvae, and also with the larval density.

Females of Simulium ornatum Mg. were found to contain abundant fat-body on emergence from the pupa. Unengorged individuals fed on sucrose solution in the laboratory at 16–18°C. and 22–23°C. showed depletion of the fat-body until little remained after 14 days. Females engorged on cattle in the field and kept in the laboratory at 16–18°C. became gravid in 4–5 days, when virtually no fat-body remained.

Field and laboratory studies on the water-velocity preferences of the larvae of Simulium monticola Fried, and S. variegatum (Mg.) show that both species occur in velocities of 0·5–2·5 m./sec. but aggregate in the velocity range 1·0–2·0 m./sec.

The velocity range that the larvae of different species of Simulium can withstand indicates that current speed plays an important part in governing the distribution of blackfly larvae, and perhaps isolating different species along watercourses.

A technique for dividing populations of Anopheles gambiae Giles into three age-groups, on the basis of the degree of ovarian development and on the presence of sporozoites in the salivary glands, has previously been described. Using this method, the proportions of the three age-groups amongst females feeding during the three periods into which the night was divided were established for this mosquito in the coastal region of Tanganyika. The feeding activity of newly emerged females followed fairly closely that of older mosquitos, in which entry into experimental huts reached a peak in the period between 2200 and 0200 hr. but remained high from 0200–0530 hr. The younger females were, however, slightly more active in the period before 2200 hr. No difference in fertilisation rate was observed amongst newly emerged females caught in different periods of the night. Infective females were caught in all three periods of the night.

It is not considered that the main features of the biting cycle in A. gambiae can be explained in terms of the differential activity of the age-groups recognised in this paper.

This paper deals mainly with species of Tanytarsus (CHIRONOMIDAE) at Khartoum, particularly the very common T. lewisi Freeman. These midges are a serious pest there, usually between November and April, causing great annoyance by swarming in vast numbers around lights during the first few hours after sunset and thus interfering with work and pleasure in the riverain area. They are probably responsible for a considerable amount of asthma and other conditions due to allergy. Little information is available about the biology of CHIEONOMIDAE in Africa, so reference is made to the Palaearctic T. mancus Walker, to which T. lewisi is closely related. Studies of Chironomids from the health point of view elsewhere have little relation to the Khartoum problem, but work on Chaoborus (CULICIDAE) is of interest.

The conditions under which these midges occur at Khartoum and the methods of study are described.

At least 26 species of CHIRONOMIDAE, including four of Tanytarsus, occur at Khartoum. The respiratory organs of some pupae are figured, and a key, based on the characters of these organs, is given for some of the species.

Observations on the biology of all stages are recorded, particularly on the vertical movements and drifting of larvae and pupae and the time of emergence. Many larvae and pupae drift downstream at night, and T. lewisi emerges mainly in the early morning.

Some exploratory field trials of larvicides were carried out. The results were inconclusive, and the difficulty of assessing them is pointed out. Thorough control by anti-larval measures would be extremely difficult owing to the large size of the river and the drift of pupae from upstream. It is believed that it might be possible but prohibitively expensive, and would have to be repeated annually, perhaps throughout the midge season. Various protective measures are discussed. It is considered that riverside dwellers who can do so should move inland, and that a barrier of trees parallel to the river would protect houses away from the river front. People who must be near the river in the evening can achieve considerable protection by clearing some vegetation, fogging with insecticide, or using air-cleaning or air-conditioning equipment.

An experiment has been undertaken in Northern Nigeria to ascertain whether the felling of the trees forming the overhead canopy and the deliberate blocking, with trash, of the stream-bed to obstruct the tsetse's flight-line, would result in the eradication of Glossina palpalis (R.-D.).

Obstructive clearing was employed on approximately 3¾ miles of stream. The results suggest that, provided the experimental reaches are adequately isolated, obstructive clearing does lead to the eradication of G. palpalis.

It is noteworthy that if, owing to inadequate isolation, the cleared stream becomes re-infested in the rains, conditions for at least the first two dry seasons are so unfavourable that flies cannot persist.

The immediate effect of obstructive clearing is to increase greatly the hunger of the few surviving flies.

Records suggest that obstructive clearing leads to a considerable reduction in the number of human hosts visiting uninhabited parts of the stream, presumably because of the destruction of forest produce. The duiker (Sylvicapra and Cephalophus) population also becomes greatly reduced, especially in the vicinity of hamlets. The hunger observed in the surviving fly population may therefore be in part due to an actual reduction in the number of hosts, as well as to the altered environment, which prevents free movement, under shade, of the hungry tsetse that is searching for food; instead, the tsetse is forced out into the open, where the climate in the dry season is intolerable, and presumably the unsuccessful fly rapidly succumbs from water-loss.

The effect of obstructive clearing on the vegetation is as follows. Within a few weeks the mound of trash is overgrown with creepers, Mucuna pruriens becoming dominant. In the first year's heavy rains the mound of trash tends to sink down in the stream-bed; on larger streams, spates do some temporary damage to the creeper growth and gaps may appear in the obstruction. The impression gained is that the blockage will persist for many years on small tributaries, but will disintegrate within a few years on larger streams. In very hilly country, with a rapid run off, the obstruction is likely to be displaced. In perennial streams of the type dealt with, the annual fires make only small inroads into the obstruction.

The technique evolved for the obstructive clearing of streams is described. The cost of this method worked out at 390 man days per mile, which is about half the cost of the present methods.

Should large-scale undertakings in the field confirm the efficacy of this new method, the biggest saving will be the elimination of the present necessity to re-slash streams that have been partially cleared. Observations will be continued to ascertain how long it will be before the vegetation again becomes suitable for G. palpalis.