An investigation has been made into the distribution and bionomics of Ornithodoros moubata (Murr.) in East Africa in relation to the incidence of relapsing fever, and a survey has been made of the infestation in over 4,600 African huts, together with the temperature and relative humidity conditions.

In Kenya Colony, relapsing fever is endemic in the high rainfall areas of Meru, Nyeri and Taita Districts. These habitats are cool and wet with a mean microhabitat temperature of 71°F. and a relative humidity of 86 per cent. Tick infestations were relatively sparse and were rare in the hot and dry climate of Embu District, the base of the Taita Hills and generally over all such country in Kenya.

In Tanganyika Territory, relapsing fever is widespread, and the most striking difference was the relatively much greater abundance of the tick, especially in the dry central areas. It is pointed out that although relapsing fever is most prevalent in the north-west, endemicity is at a lower level than in Kenya, and decreases towards the south-east, indicating that the degree of incidence of the disease does not conform with that of the vector.

In the Digo District, south of Mombasa on the Kenya coast, ticks showed a reversal in their choice of microclimate from those in the cool highlands and were numerous in hot, moist conditions. The incidence of the disease was very low.

O. moubata was widespread in the Usambara Mountain area of Tanganyika. Ticks were most numerous in the cool, wet conditions above 4,000 ft., but were also abundant in the hot, moist foothills and plains, whereas they were absent in hot and dry country at the base of the Taita Hills in Kenya 80 miles to the north.

As humidity appeared to be a foremost factor affecting the distribution of O. moubata it was not possible to evaluate clearly the effects of temperature. It is suggested that all the conflicting evidence of the relationship of the tick populations to microclimate and the incidence of relapsing fever may be explained only by introducing a hypothesis of biological variation in the tick itself. It is shown that there are two peaks of greatest abundance, at relative humidities of 86 and 67 to 68 per cent. respectively, and it is suggested that these two peaks represent the distribution of two hypothetical hut-haunting biological forms.

An examination of the blood-meals from pooled catches by the precipitin test showed that in the cool and wet habitats of the Kenya highlands and the north-west of Tanganyika, 94 per cent. of the recognisable feeds were on man and only 2 per cent. on fowls. In the hot and moist habitats of Digo and the low-lying area between Digo and the Usambara Mountains, 18 per cent. were on man and 78 per cent. on fowl. In the mainly warm and moist habitats of the Usambara Mountains and the area bordering the south-east of Lake Victoria, 73 per cent. were on man and 22 per cent. on fowls.

It is therefore suggested that there are two biological forms of O. moubata found in huts, one feeding on man and the other feeding on fowls. The former is found in huts at high altitudes in areas having a cool and wet climate; it is essentially a human parasite showing a marked preference for the blood of man while ignoring the presence of fowls however numerous or available. It occurs in greatest abundance at a relative humidity of about 86 per cent. It is found at relatively low temperatures from 67° to 75°F. It is absent in areas where the microclimate is consistently over 90 per cent. R.H. and may not occur where it is consistently lower than about 74 per cent.

The form that feeds on fowls appears to possess a tolerance to a wide range of temperature and R.H., occurring in greatest abundance at 67 to 68 per cent. R.H. It is found at temperatures from 68° to 87°F. It is more resistant to starvation than the form that feeds on man.

Among a number of insects sent in for identification by Dr. J. J. H. Szent-Ivany, of the Department of Agriculture, New Guinea, were several species of weevils that are reported as causing serious injury to cacao and coffee plants. Four of these are described below, and the types have been deposited in the British Museum (Natural History).

The earliest reference to the occurrence of Helopeltis in Ceylon was made by the French entomologist, Signoret (1858), when he described Helopeltis antonii, the so-called “Mosquito Blight”. Helopeltis attacking cacao in Ceylon was first recorded in the year 1880 or 1881 in the Matale district (Green, 1901), the damage to the young leaves and stems having attracted the attention of cacao planters. Populations of Helopeltis occurring on cacao today, however, favour the pods, damage to young leaves and stems being relatively rare and generally associated with poor shade over the cacao plant. This apparent change of feeding habits prompted a careful and critical examination of the existing species of Helopeltis in Ceylon. Extensive collections of Helopeltis from the major cacao-growing areas in the island, including the Matale district, have not provided any specimens referable to Helopeltis antonii. The new species described below was the only species of Helopeltis found on cacao at Teldeniya, Kundasale and in the Matale district, which may be regarded as representative of the major cacao-growing areas of Ceylon.

The duration of the aquatic stages of the mayfly, Povilla adusta Navás, in Lake Victoria, Uganda, has been determined by analysing larval samples from the stomachs of an insectivorous fish, Mormyrus kannume Forsk., and by culturing eggs in vitro. Emergence shows a well-defined lunar rhythm and, since adults live for only about one hour, duration of the aquatic stages must be an integral number of lunar months. Results indicate that a generation is usually completed in four or five months. Approximately the first two weeks of this period are spent in the egg.

The periodicity of reproduction imposes a feeding rhythm on certain species of fish in Lake Victoria. Some biological implications of the need for synchronisation are briefly discussed.

The paper includes a review of the published literature on the biology of the Cigarette Beetle, Lasioderma serricorne (F.). A list is given of foods on which this species has been found breeding. Information on the duration of the various developmental stages is tabulated and the data on oviposition are summarised. Observations are collected together on the rate of increase of the species in warehouses, on the number of generations per year, on sex ratio, on the use of traps to catch adults and on the spread of the pest and the damage that it causes. The lengths of exposure to various high and low temperatures that are required to give a complete kill of the species are tabulated, and the known natural enemies are listed.

Original work includes a morphological comparison of L. serricorne and the closely related common storage species Stegobium paniceum (L.). The experimental work consists of a study of the life-cycle of L. serricorne on wheatfeed over a wide range of combinations of constant temperature and humidity. Development was possible from just under 20°C. to 37·5°C. at favourable humidities. Larvae died at 90 per cent. R.H. at 37·5°C. The lower humidity level for development was under 25 per cent. R.H. at 30°C. but change of temperature, both up and down, raised the lower humidity limit so that, at 20°C. and 37·5°C., all larvae died at 40 per cent. R.H. When fed on foodstuffs such as groundnuts, which contain less water than wheatfeed at all humidities, the effects of low humidity are more rigorous. The effect of a number of foodstuffs on the length of the developmental cycle was investigated. The duration of larval instars on wheatfeed at 30°C. and 70 per cent. R.H. was found. The adults obtained in the experiments were weighed. The heaviest insects were obtained at 25°C. and 100 per cent. R.H. Higher temperatures and low humidities reduced weight. Females were heavier than males. The sex ratio was unity.

The oviposition rate was investigated at 70 per cent. R.H. over a wide temperature range. Under all conditions the eggs were laid quickly. At this relative humidity, no fertile eggs were laid at 37·5°C. and few pairs laid at 20°C. The total number of eggs laid per female at 20°C. was low, otherwise temperature had little effect on the number of eggs laid, but the rate of oviposition was increased by high temperature. The theoretical rate of increase at 70 per cent. R.H. was calculated for several temperatures and shown to increase with temperature up to 35°C.

The conclusions on the distribution and multiplication of the species which can be drawn from the laboratory results are discussed.

The varieties of the banana plant (Musa) on the Kenya coast, with particular reference to Aëdes simpsoni (Theo.), a species concerned with the transmission of yellow fever in East Africa, are described, and the species of mosquito larvae found in their leaf axils are recorded. A. simpsoni was virtually the only species present.

Details are given of the proportion of leaf axils that contain water and the percentage of these that produce larvae. Breeding was found to take place in all varieties, but to a much lesser extent in that known as Kibungala than in the others. Although there was often more water in the lower and upper axils than in the middle ones they produced less larvae individually than did the latter. Larvae were also found in old axils at the base of the stems in spite of the fact that these sites seldom appear to provide direct access for an ovipositing mosquito. Water was present throughout the year in the upper axils only.

It was found that the water content of axils varied from day to day and from morning to evening during dry periods and that the axils were often apparently dry for days at a time although the larvae were able to survive. It is suggested that the larvae are able to survive in the water film at the base of the axils, but that such unfavourable conditions may account for the retarded growth that has been observed.

The relationship between water content and number of larvae per axil is discussed, and the conclusion is reached that unless all measurements of water content for all varieties are made simultaneously each day, a comparison of average water content becomes impossible, and therefore no connection can be established from the data so far available.

Busseola fusca (Fuller) is a serious pest of maize and sorghum in Tanganyika where it occurs mainly at altitudes of 4,000 ft. and over.

Laboratory work on the life-cycle and on the diapause of the larva is described. Diapause is terminated by contact with water.

Field work at Nzega, Western Province, indicates that the first sowings, made within two to three weeks of the beginning of the rains, are likely to be heavily attacked by larvae of the first generation. These are the progeny of a “raininduced” flight of adults of Busseola derived from diapause larvae in the maize and sorghum left in the fields from the previous season, the larvae being induced to pupate when the stems are wetted by rain.

The number of generations in the main crop season, November–June/July, is two. A third generation occurs in sorghum tillers produced after June/July.

No alternate hosts of importance comparable with maize and sorghum have been found.

Cultural control by burning the crop residues left in the field after harvest, in order to destroy the diapause larvae, is not practicable in peasant agriculture as these residues are required for such purposes as palisading, building of contour banks and for grazing cattle and goats during the dry season.

Chemical control of the first generation of Busseola in young maize can be achieved by the application of a dust containing 2·5 per cent. DDT into the funnel of the plant. In 13 experiments on peasant-owned plots at Mbeya, in which a dust containing 2·5 per cent. DDT was applied four times, at weekly intervals, beginning about 18 days after germination, and at the rate of 10 lb. per acre, the average weight of maize cobs from 100 plants was increased from 12·46 to 22·82 kg., an increase of 83·1±19·0 per cent. Factors other than Busseola which affect the yield are discussed and it is suggested that control measures would probably be worthwhile only where a combination of a suitably fertile soil, early planting and adequately distributed rainfall obtains.

An instrument is described that will brighten and dim a light source and control its “on” and “off” timing.

The periods of brightening and dimming and the period of full illumination are both adjustable.

The instrument is being used successfully for studying the effects of changing light intensity and photoperiod on the activity and development of insects.

The quantitative study of Tyroglyphid populations involves their separation from the food material, for which existing methods are not entirely satisfactory A new method is described which depends on chemical treatment to remove the bulk of the flour. It is made quantitative and independent of moisture-content variation by application of the lycopodium-spore method of Wallis. A techniqul for determining the numbers of hatched and unhatched eggs per unit weight of flour is described. It provides information on the rate of increase or decreas in the number of eggs (natality rate per unit time) and hence on the ability the species to survive in a particular environment. The egg distribution in an undisturbed culture of Tyroglyphus farinae (Deg.) is found to be uneven. The technique is applied to the study of a population of Thyreophagus entomophagus (Lab.) under controlled conditions of temperature and humidity and the results discussed.

Results are given of investigations on the effects of five post-treatment temperatures on the mortality of adults of Tribolium castaneum (Hbst.) sprayed with five or six concentrations of each of six insecticidal formulations, emulsified solutions of DDT, γ BHC, toxaphene, chlordane and parathion and a suspension of DDT.

With both emulsified solutions and suspensions of DDT and emulsified solutions of γ BHC the mortality of the insects decreased with the rise of temperature from about 14° to 30°C. and increased when the temperature increased from 30° and 40°C. On the other hand, with emulsified solutions of toxaphene, chlordane and parathion, the mortality of the test insects increased continuously with increase of temperature from 14° to 40°C. As a possible explanation for such divergent results with different insecticides it is tentatively suggested that whilst the inherent physiological resistance of Tribolium to DDT and γ BHC formulations which appear to increase with increase of temperature up to a certain point has been demonstrated, the technique has not been sufficiently critical in the case of the other formulations, and it is thought that physiological resistance has possibly remained masked by other factors and that the values of LC50 are not a true index of physiological resistance in the ease of these insecticides.

An essential similarity between the curve obtained by plotting values of LC50 against temperature in the case of DDT and γ BHC and those relating temperature to other physiological activities (published by various workers) has been stressed, implying a similarity between the resistance of the insect to insecticides on the one hand and its other physiological activities on the other.

The genus Pseudodoniella was proposed by China & Carvalho (1951) for the species pacifica from Keravat, New Britain. Recently two more species have come to hand, from Lae, New Guinea and Popondetta, Papua. They are new and are described and figured here. It has been found that in the genus Parabryocoropsis China & Carvalho (1951), two of the species then described, cheesmanae from Kokoda, Papua and duni from Keravat, New Britain, were incorrectly placed and should have been assigned to Pseudodoniella.

Sixteen varieties of Rubus, comprising four species, were tested with the Aphid, Amphorophora rubi (Kalt.), which is a vector of virus diseases of Rubus in Europe and N. America, to establish the range of resistance to the development of populations of the insect. The phenomenon of resistance was then further investigated from the aspect of fecundity, reproductive rate, length of life, growth rate and behaviour of the Aphid. In these latter investigations only four varieties of raspberry were employed. The varieties Malling Promise and Lloyd George showed no resistance. Malling Landmark proved to be highly resistant but showed a slight reduction in resistance in the autumn. Newburgh appeared to occupy an intermediate position between Malling Landmark and the other two varieties. There were indications, however, that under field conditions its degree of aphid resistance may be greater than was observed under experimental conditions. Resistance seems to involve a slowing down of the reproductive rate, a shortening of the length of life of adults and prevention of development of the nymphs. The practicability of using aphid-resistant varieties of raspberry to minimise virus spread is discussed.

Fourteen species of SIMULIIDAE (of which one occurs in two forms) are recorded from Northern Nigeria. Localities for each species are given on distribution maps. Most of the species are of fairly general occurrence in the Ethiopian Region, although Simulium kenyae De Meillon is recorded for the first time from West Africa. No new species was found in an extensive survey of about 200,000 square miles.

Some notes are included on the breeding habits of the species, particularly the type of breeding site preferred, the altitudes at which breeding occurs, and the months in which immature stages have been found.

Some discussion is given of the distribution of SIMULIIDAE in Northern Nigeria and the factors which appear to influence it, partly illustrated by maps. The most important factor is thought to be the geology of the country, which determines the areas of rivers suitable for breeding. Other factors such as climate, altitude, or vegetation zones, seem to play little part, except in the far north.

Observations on the behaviour of Culex pipiens fatigans Wied. were made in 24 huts built and occupied by Africans on a sisal estate near Tanga, Tanganyika Territory. Catches were made in four huts each day, an exit trap being fixed on the window from 2 p.m. to 6 p.m. (evening trap) and replaced by another from 6 p.m. to 8 a.m. next day (morning trap), when a spray catch was made of the mosquitos still in the hut. Each hut was used only once a week, for 31 weeks, from December 1952 to July 1953. The females caught were sorted according to the stage of the gonotrophic cycle, as judged by external examination. The stages used were: I, no blood, no visible ovaries; II, stomach full of blood, ovaries small; V, little or no blood, ovaries fully developed; III and IV, intermediate between II and V.

An analysis of variance was performed on the results. Catches of both sexes showed a significant variation with time, which was not, however, correlated with rainfall. Significantly different numbers were taken in the traps and in the huts. Females were significantly most numerous in the hut catch, and males in the morning trap, the former result suggesting that most females spend more than one day in a hut. There were significant differences between the numbers of females in the different stages of the gonotrophic cycle, stages I and II together accounting for 80 per cent, of all females caught. The high proportion of stage I is attributed to delay between emergence and feeding, and of stage II to the taking of more than one meal during the gonotrophic cycle, later meals obscuring the state of ovarian development. There were significant differences between huts as regards the numbers of females caught, but not as regards males, and it is concluded that this is due to variations in the attractiveness of the inhabitants of the huts.

Females in stage I were most numerous in the morning trap, those in stages II–IV were taken only rarely in traps, but there was no significant difference between numbers of stage V caught in huts and in the two window traps. These results arse attributed to restlessness in both hungry and gravid females, and sluggishness in fed ones. All stages except III were significantly more numerous in some weeks than in others and this might be due to variations in either rate of reproduction, or rate of loss of mosquitos from huts. There were significant variations in behaviour in different weeks. For females, this is attributed to changes in the proportions of the stages with time and the dependence of behaviour on stage. For males, there is some evidence of a relation between behaviour and humidity outside the hut. For females, the distribution of stages between different places of capture changes with time, stages II and III being most consistently associated with hut catches, while the most variable behaviour is shown by stage V.

The necessity for behaviour studies on mosquitos in the field is pointed out, especially in relation to field trials of residual insecticides.

Ephialtes brevicornis (Grav.) has been found to parasitise the prepupal stage of Plutella maculipennis (Curt.) under laboratory conditions.

A general description of the life-cycle of E. brevicornis on P. maculipennis is given and it is found to occupy 16 days from egg to adult at 20°C. and a R.H. of 60 per cent. Comparative descriptions are given of the five larval instars. The egg is also described.

Estimations have been made of the weight of material accumulated by adults of Phormia (Protophormia) terraenovae R.-D. from deposits of DDT and other lipophilic particles on different types of substrate on which the flies were exposed.

Uptake of dry DDT particles is shown to be similar to that of dry lipophilic dye particles of similar size so that conclusions on the contamination of insects by dry lipophilic dyestuff may be extended to contamination by DDT dust.

The presence of oil greatly reduces the uptake of DDT particles from a fibrous substrate, the uptake decreasing logarithmically with increase in the amount of oil applied to the substrate. The viscosity of the oil has no more than a very small effect on the uptake of lipophilic particles from oily deposits and the solubility of the particles in the oil has no significant effect.

A reduction in the uptake of dry lipophilic particles from filter paper and from a hard, waxy substrate occurs when a wetting agent solution is applied immediately before the particles. When the particles are applied after the drying of the wetting agent on the substrate, a reduction in uptake also occurs on the non-absorbent, waxy surface, but is not so large as when the particles are applied before drying of the wetting agent. No reduction in uptake occurs on the absorbent substrate under these conditions.

On the basis of the experimental results the variations in the adhesion of lipophilic particles to substrates are discussed.

While differences in the affinity of particles for substrates of different types cause variations in adhesion, the physical structure of the surface may be more important in determining the amount picked up from it. The presence of oil or wetting agent on the surface increases adhesion, probably by increasing both the affinity of the lipophilic particles for the substrate and the area of contact between the particles and the substrate.

Two tons of cocoa, in 32 bags, stacked in a typical cocoa store in Ibadan, Nigeria, were sampled from December 1953 to the end of April 1954. The weekly catches on “ até “ strands hung round the stack suggested that Ephestia cautella (Wlk.) was the most numerous insect on cocoa, but spear samples of the beans, taken from the sacks every two weeks, showed that the actual population of this species in the beans was small throughout the season, with no sign of build-up. Lasioderma serricorne (F.), on the other hand, was shown to be the most serious pest, the population in the beans increasing steadily from an extremely low level. It is estimated that on the average it is not safe to store initially good cocoa for more than 25 weeks in the main crop season.

Athalia lugens subsp. proximo (Klug) is a pest of cruciferous crops, and shows special preference for turnip. In the matter of selection of food, smell and taste of the food and the age of the plant are important factors. Epilachna vigintioctopunctata (F.) is a pest of solanaceous plants, particularly brinjal. In this insect only smell and taste are important factors in the selection of food.

The hydrogen-ion concentrations of the salivary gland, foregut, midgut and hindgut of the larva of Athalia are 6·4–6·6, 6·4–6·8, 6·6–6·8 and 7·0 and of the adults 6·2–6·4, 6·4–6·6, 6·4–6·6 and 6·6, respectively. The hydrogen-ion concentration of the salivary gland, foregut, midgut and hindgut of the larvae of Epilachna are 5·4, 6·4–6·8, 6·0 and 6·0 and of the adult 6·6–6·8, 6·2, 6·0 and 5·4–5·7, respectively.

The foregut and hindgut of the larvae and adults of Athalia and Epilachna do not secrete enzymes; the salivary glands of both larva and adult of Athalia secrete amylase, the midgut epithelium of both larva and adult of Athalia secretes amylase, maltase, invertase, lactase, lipase and protease. The salivary glands of the larva of Epilachna secrete amylase, but those of the adult do not, and the midgut epithelium of both larva and adult secretes amylase, maltase, invertase, lactase and protease. The midgut of both larva and adult of Epilachna secretes lipase also, although in the adult no more than traces are detectable. The proteases in both insects act in slightly acidic media.

The method of measuring relative humidity by matching the colours of tissue paper impregnated with cobalt thiocyanate has now been made more convenient by the commercial production of impregnated paper and coloured glass standards.

Although the method as used straightforwardly is not at all precise, it is especially useful for the measurement of humidity in small or relatively inaccessible spaces, e.g., cracks in floors, air spaces in stored grain, under bark, or inside small tubes, etc., and for general use when elaborate equipment cannot be employed.

A piece of the paper is exposed to the humidity to be measured, preferably for two hours, then mounted on white opal glass in oil (liquid paraffin) and matched, in a simple comparator, against the coloured glass standards. When matching is done at a temperature other than 20°C., corrections are required as tabulated.

Tables of error are given, showing the range of variation from different causes, with estimates of 95 per cent, confidence limits. To cover all the sources of variation normally affecting the measurements under various conditions, limits up to ±5 are allowed for relative humidities down to 70 per cent.; these limits increase at lower humidities to a maximum of ±15, about 30 per cent. Various ways of avoiding errors are described, and it is shown that if special precautions are taken the method can be used with considerable accuracy, particularly at relative humidities above 65 per cent.

The quantities of lipophilic dyestuff picked up by specimens of five insect species, namely Vespula vulgaris (L.), Feronia madida (F.), Rhagonycha fulva (Scop.), Dysdercus fasciatus Sign, and Notostira erratica (L.), in their first few steps on a dust deposit of the dyestuff have been estimated. The uptakes per step by insects of different size and structure were shown to differ only slightly. While the uptake was found to be greater for the larger insects, the smaller insects picked up more particles per unit body weight at each step.

The ratios of the actual amounts (estimated by a colorimetric method) picked up by the different pairs of legs are similar for all the insects that have been studied and in all cases the hind legs were shown to pick up an amount at least equal to the sum picked up by the fore- and middle legs.