A description is given of the hair structures associated with the spiracles of the adult worker honey bee, Apis mellifera L.

The surface hairs around the spiracular orifices vary in size, density and arrangement and with the exception of those of the third, fifth and sixth abdominal spiracles appear to be capable of holding back particles greater than 30 microns.

When living bees were exposed to dust clouds of charcoal and cuprous cyanide, no particles were found in any internal part of the respiratory system beyond the spiracles except in the case of the trachea of the first thoracic spiracle which contained charcoal particles less than 5 microns.

The mechanism of tracheal ventilation was considered and evidence accumulated to suggest that all spiracles could have an inspiratory function.

In the coastal region of British East Africa three ant species, Anoplolepis custodiens, A. longipes and Pheidole punctulata may destroy the ant Oecophylla longinoda which is a valuable predator on the coconut pest Theraptus sp. (Coreidae). The three first-named species do not prey on Theraptus, which may severely damage palms occupied by them.

Nesting habits of the three ant species and their behaviour towards O. longinoda and certain other insects are described.

O. longinoda has been exterminated in the limited areas occupied by the two Anoplolepis species. P. punctulata is widespread and is usually common in areas occupied by O. longinoda and is also present, though relatively less common, in A. longipes areas.

The distribution of the Anoplolepis species, particularly A. custodiens, is correlated with sandy soils bearing a sparse ground vegetation. Where there are heavy soils or a thick ground vegetation of grasses and creepers the Anoplolepis species are absent and O. longinoda is usually present. It is suggested that the Anoplolepis species are limited by the relatively low temperature of soils shaded from sunlight by thick vegetation.

The geographical ranges of Sahlbergella singularis and Distantiella theobroma overlap, and the Gold Coast lies in the zone common to both. The respective northern limits remain to be determined, and should be investigated to the north of the main cacao belt, from Kintampo to the Afram plain.

The same area should also yield information on the possible importance of alternative hosts in the dispersal of cacao Mirids, as the small stands are well separated from each other.

Earlier records, that D. theobroma is confined to seedlings and S. singularis to mature trees, are erroneous. D. theobroma is found on pods and, particularly, chupons. The feeding range of S. singularis includes fan branches in addition, but breeding is confined to chupons and pods.

Observations suggest that there is competition for breeding sites on chupons. Of the many chupons in an area only a small number is available to Mirids, and the proportion of nymphs reaching maturity is limited by their sedentary habit and the destructiveness of their feeding.

Co-existence of the two species is possible by their slightly different habits. S. singularis produces more eggs, but is more diffusely distributed. D. theobroma is virtually restricted to chupons, but can quickly build up a large population in favourable areas by its greater rate of egg production.

In Nigeria, the rate of egg production by D. theobroma is less than that by S. singularis, and this, together with the sparsity of chupons, may account for the unimportance of D. theobroma in that country.

The systemic insecticide Hanane (mainly bisdimethylamino fluorophosphine oxide) is readily absorbed by the trunk of a coffee tree and translocated to the foliage when the bark is lightly scraped and the chemical applied in solution on a pad of absorbent material covered with a waterproof skin to prevent evaporation.

Smaller dosages of Hanane are required to give equivalent control of Planococcus kenyae (Le Pelley), or to cause a similar degree of phytotoxic damage, by this method than by soil treatment.

Abrasion or removal of the bark before application enables a greater absorption of the chemical but leads to serious phytotoxic damage by a comparatively low dosage.

The colour change and formation of green pigment in Mantis, Acrida, Locusta, Schistocerca and Dixippus are studied.

There is no background reaction to green and brown or yellow colour in these species.Usually the young nymphs of Mantis are green; some ofthe old nymphs and adults have a tendency to lose the green pigment. Phytophagous nymphsbecome green only when fed on fresh or growing grass. Green individuals may be obtained in darkness on this food (Locusta). The green pigmentdisappears on a diet of dry grass.

The colour change from non-green to green, or vice versa, is dependent on the formation or disappearance of the blue component (bile pigment-protein) of green pigment. The blue pigment generally appears first in the blood and is deposited in the integument at the following moult; it does not appear to be a breakdown product of chlorophyll or haematin. It is probably synthesised from a colourless precursor in the peripheral fat body.

Observations made on the pericardial cells of Locusta suggest that the blue pigment may be converted into insectorubin.

The resistance to a 5 per cent. DDT powder of 36 species of adult and larval Coleoptera which infest stored products has been determined. The species are grouped according to the time required to effect 95 per cent. kill. In the data for adults, the slopes of the probit regression lines were not significantly correlated with the log-times for 50 per cent. kill. No obvious connection could be seen between the degree of resistance to the insecticide and size, activity, hairiness, etc., but larvae tended to be much more resistant than the corresponding adults.

The two species of Mirids, Sahlbergella singularisHagl. and Distantiella theobroma (Dist.), are important pests of cacao (Theobroma cacao L.) in the Gold Coast. The damage sustained by the cacao is due, in part, to the direct effects of feeding by these insects, but more to the subsequent invasion of the resulting lesions by the weakly pathogenic fungus, Calonectria rigidiuscula (Berk. & Br.) Sacc.

In the field, Mirid damage may be classified into three categories. “Blast” is the result of light diffuse attack and is so named because of its similarity to fire damage. “Stagheaded cacao” is more severe, the trees showing numeroussmall crown branches but forming a poor canopy. “Mirid pocket” describes severe damage, normally limited to a small area, the trees losing the crown completely and the polelike trunks bearing numerous lateral chupons. In general, stagheaded symptoms are more prevalent where cacao is grown without shade, and pockets where cultivation of cacao utilises shade trees.

Consideration of the factors associated with Mirid damage shows that it is correlated with breaks in the cacao canopy. Evidence is brought forward to suggest that such breaks normally precede, rather than result from, Mirid attack. The canopy itself is unsuitable for the development of either species, the major part of the population being confined to the sub-canopy levels. The initial causes of the breaks are, most frequently, the die-backs associated with swollen shoot or with adverse water relations. The falling of shade trees causes a number of breaks, and, where cacao is grown without shade, the Mirids themselves may be a cause.

The most important single factor influencing the form of the cacao canopy, and thus the course of Mirid attack, is the amount of overhead shade, particularly that provided by trees little taller than the cacao itself. Shade which is too dense causes etiolation of the cacao and thus renders it susceptible to attack, the resulting damage generally taking the form of a pocket. Shade which is too sparse does not shield the cacao from the adverse effects of exposure. The Mirid damage in such areas generally assumes the stagheaded form.

It is suggested, from field experiments, that the invasion by Mirids of areas suitable for colonisation is not by random movements, but is determined by the change in some physical factor resulting from the broken canopy. Changes in light intensity are the most obvious results of such breaks, but further experiments are needed to determine which is the operating factor.

Degraded cacao is prevented from recovery, not by Mirid attack alone, but by the interaction of it with the presence of C. rigidiuscula, and by increased exposure.

The sampling methods employed are described, and the bearing of the results upon control measures is discussed.

A simple, but reliable, technique is described for the study of the acceptability to locust hoppers of poison baits under field conditions.

This was applied to the study of a number of vegetable materials which might be used for the manufacture of wet baits to destroy hoppers of the Desert Locust.

The materials tested could be divided into five classes of acceptability, and consideration of these indicated that heavy lignification detracted from acceptability while the presence of starch added to it.

It was shown that molasses adds to the acceptability of only the least acceptable materials unless very large amounts are used.

Simple tests showed that acceptability was not correlated with water-absorbing properties, that the rate of drying of bait was dependent on the amount of water initially absorbed, and that molasses influences the rate of drying only when large amounts are added.

Sinoxylon senegalense is essentially the wood borer of felled Acacia seyal Del. in the Sudan, damage due to other beetles being contributory in a very small degree.

The life-history of the Bostrychid is recorded. The period from egg to adult is about eight weeks, but the complete life-cycle is considerably longer. The larval tunnels are superficial and only a few inches in length. The damage is almost entirely due to the adult, which remains boring within the logs for nearly 10 months. A predacious Clerid, Cylidrus fasciatus, and Braconid parasites, a species belonging to genus near Doryctes and Platyspathius pictipennis, were recorded.

Destruction of the timber is very rapid and control methods should be undertaken as soon after felling as possible. Insectaries were prepared containing the timber treated in various ways and the behaviour of the insect noted in each instance. The chemicals used in the experiments were sodium arsenite, boracic acid and pentachlorophenol. The latter, used as a spray on barked logs, was found to be the most effective.

A review of the literature is given which shows that changes in the susceptibility ofinsects to insecticides occur during development when the poison is applied as a fumigant, as a stomach poison and as a contact poison.

The assessment of changes in susceptibility to contact poisons is discussed. The basis of assessment may be the concentration required to kill a given number of individuals, or the amount of poison required to kill unit weight of insect material. The great majority of the earlier work used the former basis of assessment, but where the insect is changing in size and shape during development and hence changing in the proportion of surface area to body weight, this method has limited significance when the poison is applied as a spray of constant deposit evenly over the surface area. A mathematical method is given for transforming the results obtained in terms of concentration to kill a given number of individuals into weights of poison to kill unit weight of insect material. Rearingmethods are outlined which enable batches of various stages of Diataraxia oleracea (L.) (tomato moth), Tenebrio molitor L. (meal worm) and Periplaneta americana (L.) (American cockroach) to be obtained at a known age and stage of development.

Experimental results are given for a spraying technique using DDT and the pyrethrins as insecticides on the comparative resistance of the eggs, larvae and pupae of D. oleracea, the larvae, pupae and adults of T. molitor and the nymphs and adults of P. americana.

On the basis of the concentration of insecticide required to kill a given percentage of individuals, it is shown that great differences can occur in the resistance of different instars of one species and considerable differences may occur within the instar. If the data for the larval and nymphal instars are considered on the basis of the weight of poison required to kill unit weight of insect material, differences still exist but are much reduced.

When toxicity is estimated on the basis of the concentration of poison in a constant spray deposit required to kill a given percentage of individuals the overall variations of resistance during development measured for DDT in terms of median lethal concentrations were: —D. oleracea eggs and larvae fifty times (0·002 per cent.–0·1 per cent. w/v), the pupa proved resistant to 0·5 per cent, w/v; T. molitor larvae, pupae and adults thirty-seven and a half times (0·0008 per cent.–0·03 per cent, w/v.) and P. americana nymphs and adults eight and a half times (0·0035 per cent.–0·03 per cent. w/v). The figures for pyrethrins were: D. oleracea eggs, larvae and pupae thirty-seven times (0·0027 per cent.–0·1 per cent. w/v), T. molitor larvae, pupae and adult forty times (0·005 per cent.–0·2 per cent. w/v), and P. americana nymphs and adults ten times (0·00031 per cent.–0·003 per cent. w/v).

The figures show that the range of variation of resistance during development may be very large, over 250 times in the case of DDT and D. oleracea, where the pupa, is resistant. The maximum variation that was found within an instar was 16·6 times where the resistance to pyrethrins of the 1-day old pupa of T. molitor was compared with that of the 4-day old pupa. The data show that the amount of variation in resistance that can occur varies with the test species and with the insecticide. Furthermore that the order of resistance of the developmental stages of any given species will differ with the insecticide and that with any given insecticide the order will vary with the species.

It may be inferred from these data that any comparison between insecticides on one stage of development of one instar of one species will not necessarily hold true of any other stage of development of that species or of any other species.

Observations were made on the action of the insecticides on the various instars and the symptoms of poisoning are described. It was observed that DDT at the highest concentration used (0·075 per cent. w/v) failed to prevent the development of the embryo inside the egg-shell and death only occurred after the fully developed embryo had eaten the egg-shell which it normally does prior to emergence. Pyrethrins on the other hand if applied at sufficiently high concentrations could prevent embryonic development although at lower concentrations a high percentage of eggs formed fully developed embryos.

At the highest concentrations used neither DDT (0·5 per cent, w/v.) nor the pyrethrins (2·5 per cent, w/v.) were able to prevent pupal development, and partial emergence often occurred before death. DDT differed from the pyrethrins in that it was ineffective on the pupae of D. oleracea.

Using data given in the literature and from some preliminary experiments on respiration rates, it was possible to deduce some correlation between metabolic rate and susceptibility, and changes in the permeability of the cuticle and chorion and susceptibility, but the evidence is unsatisfactory and the causes of the changes in susceptibility await further detailed investigation.

The period of digestion of the blood meal of 10 different blood-sucking arthropods which had been artificially and naturally fed on known hosts was studied by means of specific precipitin tests.

A large proportion of positive feed (80–100 per cent.) was found with midges and mosquitos up to 24 hours, whether naturally (Anopheles aquasalis) or artificially fed (A. maculipennis atroparvus, Culex molestus, Culicoides nubeculosus, Aëdes aegypti).

Tsetse flies showed greater differences between the rate of digestion of captive flies (Glossina morsitans), which showed 90–100 per cent. positive feeds at 3 days after the experimental blood meal, and wild flies (G. swynnertoni) which showed only 28 per cent. positive meals after a similar period of digestion. Arachnids showed both the longest period of digestion, more than 6 months for Ornithodoros moubata and also the shortest period as represented by Bdellonyssus bacoti (about 1 day).

Cimex lectularius showed 90 per cent. positive feeds after 10 days.

Kumasi is a rapidly expanding township of about 80,000 inhabitants. This has led to an extensive building programme which has followed the ridges in the vicinity of the town, leaving the valleys in between potentially dangerous isolated habitats of Glossina. The danger from these isolated habitats is enhanced by the large numbers of itinerant labourers.

The topography of the town and its surroundings is hilly; the vegetation is of semi-deciduous rain forest type, but with very thick secondary bush along most of the valleys in which the farms had been abandoned.

The climate is remarkably equable with the rainfall showing periodicity but the percentage relative humidity is high and even throughout the year.

The experimental clearing of an isolated habitat of Glossina in the Dechem valley was commenced in July 1950 and finished in March 1951. The clearing was of a discriminative nature, with cutting, stumping and burning of a strip of bush up to 20 ft. high and 250–300 yards wide along the stream, and a high reduction of fly population was achieved. This reduction was such that further clearings were planned.

The reduction in fly population was assessed from fly-boy catches and from trap catches. These records showed that rainfall affected the catches.

At the time of writing, about a sixth of the protective clearings planned around Kumasi have been completed, the fly population being reduced between about 80 per cent. and complete eradication.

Lumsden's “standard sunset” period observations have been repeated with the three commonest species of Anopheles occurring in Trinidad. The method was modified to yield data on the ovarian and fertilisation states of these three species over a period of ten months which included the dates of the latest and earliest sunset at 10°N.

A. aquasalis comprised nearly 95 per cent. of a total catch of 8,592 specimens. Just over 18 per cent. of those that attacked were newly emerged, and no more than half of these were fertilised. Relict eggs, denoting a second or later gonotrophic cycle, were found in February, June and July. The 40 minutes from sunset + 20 minutes yielded nearly 80 per cent. of the total of the first two hours of activity, this period comprising nearly half the estimated total night's attack. From one hour after sunset the proportion of newly emerged specimens that attack is well below the mean. The second hour after sunset therefore provided the greatest infection risk when age, not numbers attacking, is considered.

The larval characters of 33 species (largely Palaearctic) of the genus Apanteles have been examined and studied in relation to the division of the species of the genus into four major groups on the characters of the adults. Ingeneral, the larval characters indicate a grouping of the species which is very similar to the grouping of the adults. Groups S and U contrast sharply with groups A and F on the form of the mandible. The form of the mandible also allows group A to be distinguishedfrom group F. The relationships of four aberrant and some other species are discussed.

I wish to thank Mr. J. F. Perkins of the British Museum (Natural History) and Professor G. C. Varley of the Hope Department of Entomology, Oxford, for permission to study material. Mr. G. E. J. Nixon's advice on the relationships indicated by the characters of the adults of the species of the genus Apanteles has been invaluable.

In Trinidad A. aquasalis swarms over open areas, mostly grass, and over drains and not over scrub vegetation.

Swarming commences at a light incidence not exceeding 5 foot,-candles.

Mating has been observed in 54 per cent. of the swarms, the fertilisation index of females captured in them being 65 per cent.

The lag between the first sight of a swarm and the first observation of a mating pairaverages 6·5 minutes, the light incidence at commencement of mating being no higher than an average of 0·8 foot-candles.

Of the various methods for the eradication of G. palpalis that have been tried in Kenya, hand-catching has the most limited application.

Total and discriminative bush-clearings of the river banks have been used on a considerable scale and progress on the Yala, Magori, and Nyando rivers is reviewed. The decrease in fly-populations caused by these clearings is gradual, but complete eradication may be achieved. Maintenance of the clearings is however difficult, the initial cost varied from £200 to £300 per mile and labour was often difficult to obtain in sufficient numbers.

The use of 5 per cent. DDT sprays on the fringing vegetation along 20 miles of the Mbogo river gave dramatic results and G. palpalis was eradicated at a cost of £42 per mile. The rate of application was 15 to 20 lbs. of DDT per acre and the residual effect lasted for at least 14 days during dry weather, but was rapidly lost during the rains.

Spraying along the Ainamotua gave equally promising results.

Areas under treatment, either by hand-catching, bush-clearing or spraying with DDT, must be properly isolated from other tsetse-infested areas if quick results are to be achieved.

Between December 1947 and May 1949, six colonies of body lice from various sources were cultured in the laboratory. Three of the strains originated from natural infestations in England and the others came from laboratory cultures in Hamburg, Basle and Tunis. After being bred for at least one generation in the laboratory, these lice were subjected to a standard test for resistance to DDT. Only one strain showed any evidence of abnormal resistance; this was the strain from Tunis where it had been laboratory-cultured for over 12 years.

Colonies of Aëdes aegypti from Karachi, Poona and Delhi were being cultured at the Virus Research Institute, Lagos, together with a local Nigerian strain. Extensive tests showed no difference in average susceptibility of the four strains to DDT, though there was some evidence of differences in the spread of resistance through the various populations.

A colony of A. aegypti was started with larvae taken from Ilaro, a Nigerian town which had been regularly sprayed with BHC for 2½ years. Comparative tests showed no difference in resistance to γ BHC between this colony and a laboratory culture at the Malaria Service Laboratory, Lagos.

Colonies of house-flies were initiated and maintained at Lagos. Tests with insecticides gave the following results:

(a) M.d. vicina from Ilaro were much more resistant to γ BHC than similar flies from Yaba, near Lagos, or M.d. domestica from England.

(b) The M.d. vicina from both Lagos and Ilaro were considerably more resistant to DDT than M.d. domestica from England. This is surprising, as no DDT-spraying has been done at Ilaro and, so far as can be ascertained, virtually none in Lagos.

(c) The M.d. vicina flies from Lagos were considerably more susceptible to γ BHC and dieldrin than M.d. domestica from England. M. sorbens was much more susceptible to γ BHC and to DDT. These differences could be explained by the smaller average sizes of the two susceptible species.

Seventy species of Tabanids occur in the Sudan. Many of the inhabitants are pastoralists, and the Tabanids have a profound effect on them, largely by causing them to remove their animals from infested areas in the rains and to undertake extensive annual migrations. New problems will arise when economic development involves permanent settlement of certain infested areas. This paper sets out the problem, and satisfactory control measures have yet to be devised.

The country is briefly described.

The section on individual species consists mainly of lists of localities which are shown on maps.

In a general discussion of distribution faunal areas are designated for discussing Tabanids in the Sudan. The composition of the Tabanid fauna, which is mainly Ethiopian, is described. Types of habitat are indicated, and distribution is discussed in relation to systematic position. The area in which Tabanids are abundant, and their seasonal prevalence, are indicated.

There are brief references to habits, particularly the attraction to inanimate objects and the fact that some species bite man on some occasions and not others.

The economic effect, namely, the direct effect of bites and probable role of the flies in the transmission of cattle and camel trypanosomiasis and human loiasis, are described, mainly from published sources.

The effect of Tabanids on the distribution and annual migrations of pastoral tribes is described. Attacks by flies on domestic animals and the search for pasture and water are the main causes of the very extensive rainy season migrations which are shown on a map.

The problem of control is very briefly discussed.

Additional information on some of the foregoing subjects is given in notes on faunal areas.

Ptinus tectus occurs on a large range of foodstuffs in all types of storage places, in warehouse refuse and in the nests of birds. It is widely distributed in cool and temperate areas but is very rarely found in hot climates. In Britain it can survive the winter when exposed in a Stevenson screen to outdoor shade conditions. P. tectus is seldom found on imported cargoes inspected aboard ship, but many British warehouses carry a population of the species resident in the fabric of the premises.

The larva is able to bore through cellophane, card and textiles and can also make impressions on wood. The fully fed larva spins a cocoon on the fabric of containers and buildings. Holing of packages and contamination by silk of high grade produce form the chief economic losses caused by the species, but occasionally large populations are found, sufficient to reduce the food value of produce. Unlike the larvae, adult beetles cannot penetrate sound linen bags, but lay eggs through the meshes.

In a series of consecutive experiments, performed identically as far as possible, variations in the length of developmental period and in emergence weight of adult beetles were greater than would be expected by chance. The variations could not be related to any single observed or suspected inconsistency of technique or environment. It is desirable therefore to conduct comparative experiments simultaneously.

The paper describes the construction, calibration and performance of an electrolytic hygrometer based on the principle of the “Gregory” hygrometer, but considerably smaller. Its dimensions are about 6×6×10 mm.

The element consists of two platinum-clad nickel-iron electrodes, holding a spiral of continuous fibre-glass wool yarn which is impregnated with a solution of calcium chloride. The water content of this hygroscopic salt varies with humidity, so that the resistance between the two electrodes also varies. In order to measure this resistance, alternating current of a known voltage is used, and the current is measured in terms of micro-amperes. A suitable circuit is described. Air temperature is measured by a fine thermocouple permanently attached to each element.

Long exposure to air above acid and water mixtures damages the elements so that calibration is best carried out without acid. An apparatus in which this can be done is described. A stream of air with a high water vapour content is cooled to a precisely known temperature which is below its saturation point, and then raised to the temperature required for calibration, so that its relative humidity is known as it passes over the element being calibrated. Finally the dew-point is again found as a check. Temperature affects the resistance of the elements, and calibration must therefore be carried out at three different constant temperatures.

Curves obtained by means of this apparatus show that one element will give readings from 50 to 98 per cent. R.H. within ±2 per cent. Another element with more hygroscopic salt must be used for humidities between 60 and 10 per cent. R.H.

There is an ageing process whereby the resistance of each element increases for some time after it has been constructed. This period can be shortened by exposing the elements to alternating high and low humidities for a few days. Elements which have received this treatment can be calibrated and used after six weeks, and will remain in calibration for at least a fortnight.

Subsequent calibrations can be made in a simple apparatus (which is described) involving acid-and-water mixtures, but the use of filters and exposure of the elements for no more than 15 minutes avoids damage.

The hygrometer equilibrates in a new humidity within ten minutes.

The instruments possess certain advantages: they are small, they can be read or recorded at a distance, and they do not depend upon evaporation of water, so that disturbance of the natural environment is minimised. The main disadvantages are that they cannot be exposed to saturated air without going out of calibration and that each instrument must be calibrated individually—they cannot easily be standardised for mass production.