The problem of insect infestation of stored export food commodities in southern Nigeria is discussed, and a list of insects is given. At the ports there is considerable cross-infestation between commodities produced in northern and southern Nigeria awaiting shipment.

Old sacks used for the storage and transit of groundnuts are responsible for the spread of insects to palm kernel and cocoa marketing centres in the south. After bulk shipments of a portion of the groundnut crop, sacks are repaired and distributed for the shipment of palm kernels and some of them may be used by fanners and brokers as service bags for the marketing of cocoa and local food commodities. The importance of disinfestation before distribution is realised, and a small fumigation plant is in operation at port.

Ephestia cautella and Lasioderma serricorne are the major pests of stored cocoa beans. Both originate in farmers' and brokers' stores which are rarely cleaned, and in which small parcels of low-grade beans may be retained for mixing with a following crop to conform with an exportable grade. Ephestia cautella also infests palm kernels, and the early abundance of adult moths in cocoa stores up country during the marketing season is considered to be largely due to the storage of palm kernels in the vicinity. The development of Ephestia larvae can be completed on the outside of cocoa beans, only germinated or damaged beans being penetrated.

A previously published method for determining the physiological age of female Lucilia cuprina (Wied.), based on a linear relationship between their rates of ovarian development and temperature, was tested under field-cage conditions. It was found that ovarian development was more rapid than that predicted by thermal summation based on ambient temperature. A re-examination of the rate of development-ambient temperature relationship, over a wider temperature range that that used previously, showed that the development threshold temperature was 8·2°C rather than 11·3°C. Thermal summation using the revised threshold also fell short of the observed day-degree totals. An effective temperature for ovarian development (ambient temperature plus a temperature excess proportional to the incoming solar radiation intensity) was fitted to the data from the field cage. This relationship gave accurate predictions of ovarian development (±8%) for flies that were released into the field.

Experiments were made at three different sites in Malaya between 1952 and 1957 to compare the numbers of mosquitos attracted to man, calf or goat under the same conditions. The baits being compared (either two men and one calf or two men and two goats) were exposed simultaneously in two net traps placed about 50 yd. apart. This procedure is referred to as comparative trapping.

The total number of mosquitos caught with each bait showed calf to be much the most attractive, followed by goats and then men. However, there were three species, the dark-winged form of Anopheles barbirostris Wulp, Aëdes albo-pictus (Skuse) and Culex pipiens fatigans Wied. that were attracted in larger numbers to man than to calf, and six species attracted in larger numbers to man than to goat.

To compare the host preferences of the different species as between man and calf, the numbers of each caught with man and with calf have been expressed as a ratio (the man: calf attraction ratio). For most species the ratios from the different sites were much the same, showing that the method produced repeatable results. The data from the three sites were therefore combined.

On the combined data the ratios range from 3·4:1 in favour of man for the dark-winged form of Anopheles barbirostris to 1:82 in favour of calf for A. vagus Dön.

As might be expected, the ratios show that the vectors of malaria, filariasis and virus diseases are among the more anthropophilous species.

Attraction ratios have been calculated from suitable data published by various authors for ten different species in five countries. The ratios obtained place the Anophelines in an order that agrees well with their status as vectors of malaria.

It appears that if the results of comparative trapping are expressed as attraction ratios, this offers a method of comparing the host preferences of mosquitos of the same or different species, at different times and places in a country, or even in different countries.

Chrysomya megacephala (Fabricius) is shown to be a principal cause of loss of salted-dried fish in south-east Asia. Field and laboratory work conducted in 1982–1989 was aimed at reducing these losses. Field work at a small–scale fish processing site in Cirebon, West Java, showed that fully gravid C. megacephala females were highly differentially attracted to fish at the salting stage, which means that the salting tanks must have properly designed fly-tight lids to prevent infestation. C. megacephala counts and ovary examinations showed that females with various stages of immature ovaries (stages I–IV) were predominent during the drying stage after the fish had been removed from the salting tanks, with numbers usually greater on the first day of drying than the second. C. megacephala counts were high during the dry season, although numbers fluctuated enormously depending on weather, among other factors. Physically screening fish during the initial drying period effectively controlled infestation, although problems associated with the screen design were identified. In laboratory cultures adult sex ratio was approximately 1:1 and longevity in both sexes, over three generations, ranged from 47 to 55 days (maximum induced longevity, 98 days) at c. 29°C, 30–60% r.h.; under similar conditions, 10% of females had mature (stage V/VI) oocytes after one week, 40% after two weeks and 90% after three weeks. Mean number of ripe oocytes in gravid flies was 221 (range 151–228).

A wide variety of abiotic and biotic factors act on insect pests to regulate their populations. Knowledge of the time and magnitude of these factors is fundamental to understanding population dynamics and developing efficient pest management systems. We investigate the natural mortality factors, critical pest stages, and key mortality factors that regulate Chrysodeixis includens populations via ecological life tables. The total mortality caused by natural factors was 99.99%. Natural enemies were the most important mortality factors in all pest stages. The critical stages of C. includens mortality were second and fourth instars. The key mortality factors were predation by ants in the second instar and predation by Vespidae in the fourth instar. The elimination of these factors can cause an increase of 77.52 and 85.17% of C. includens population, respectively. This study elucidates the importance of natural enemies and other natural mortality factors in C. includens population regulation. These factors should be considered in developing and implementing C. includens management strategies and tactics in order to achieve effective and sustainable pest control.

The examination of the armature of the males of all the hitherto described species of the genus Glossina, with the exception of G. maculata, Newstead,* has not only revealed some very striking morphological characters, but has led to the discovery of three new species† and the re-establishment of Bigot's G. grossa.‡ One of these new species, G. submorsitans, Newstead, has hitherto been overlooked through its striking similarity to G. morsitans. Morphologically these two species are separable chiefly by the small but important organs herein described as the median lobes; these characters will be best understood by reference to the accompanying figures (figs. 15ml, 16ml), in which the difference is as well marked as that between the holoptic and dichoptic heads found in certain groups of Diptera. G. palpalis, R. D., and G. tachinoides, Westw., are also very closely allied in the general form of the armature of the males, but they are easily separable by the minute differential characters of the inferior claspers (figs. 9ic, 11ic).

In France, during the summer, cattle in mountainous pastures can be highly exposed to tabanid bites. The persistent biting behaviour of tabanids not only causes disturbance, but is also responsible for transmitting diseases, such as bovine besnoitiosis. The purpose of this study was to better identify the level of tabanid annoyance on cattle by means of insect trapping and direct observation of cows. Tabanids were active during the entire daily observation period (10:00–16:00), except for Haematopota sp., which were less active in the morning. The tabanids collected in Nzi traps were generally representative of those that landed on cattle, except for Haematopota sp., as Nzi traps were not very effective for these species. The preferred feeding sites for most species appeared to be cow's legs or udder. Leg stamping was the defensive reaction most related to a tabanid alighting on a host. Generalized linear mixed models showed that the parameters associated with tabanid landings on hosts were related to weather and altitude, but not to landscape structure. Increased landings were mostly associated with the higher temperatures and lower wind speeds at midday, but some differences were observed between species. The results indicate that cattle-protection measures should be taken during the peak of tabanid abundance when climatic conditions favour intense biting activity. Nzi traps set close to livestock were very effective to catch tabanids and could help in reducing the annoyance caused by horse flies.

Populations of Culex pipiens fatigans Wied. were exposed to infection by Plistophora culicis (Weiser) by allowing eggs to hatch in water containing a known concentration of spores. At 26°C–28°C (mean 27°C) exposure of newly hatched larvae to a concentration of 6 000 spores/ml resulted in a 12–9% reduction in the net reproduction rate, and exposure to a concentration of 12 000 spores/ml to a reduction of 24·0%. These reductions were due to an increase in the rate of female mortality and an increase in the number of eggs laid which were non-embryonated and hence did not hatch. At 33°C–35°C (mean 34°C), although the spores of the microsporidian were not killed, development of P. culicis in the mosquito was inhibited. At 19·5°C–20·5°C (mean 20°C), the net reproduction rate of a population exposed as newly hatched larvae to a concentration of 1 890 spores/ml was reduced by 35·6%, due to a greatly increased rate of female mortality. P. culicis, with the inocula tested, is not considered of practical use against C.p. fatigans; more infective spore inocula are not feasible with the present methods of propagating the parasite.

The essential oil (EO) of Piper aduncum Linnaeus, known as ‘sireh lada’ to locals Malaysian, has the potential to be used as an alternative to synthetic insect repellents such as N,N-diethyl-meta-toluamide. However, the EO's efficacy as a repellent decreases after application due to the high volatility of its active ingredients. A number of studies have showed that optimizing the formulation of plant-based EOs can improve their efficacy as repellents. The present study sought to evaluate the effectiveness of 10% P. aduncum EO in ethanol and in three different semisolid formulations: ointment, cream and gel. These formulations were tested on Aedes aegypti under laboratory conditions. Each formulation was applied to the subject's hands, which were then inserted into a cage containing 25 nulliparous A. aegypti. The number of mosquitoes landing on or biting each subject's hand was recorded, and the repellency percentage, landing/biting percentage and protection time for each of the formulations were compared. There were no statistically significant differences between the semisolid EO formulations with regards to the repellency percentage and the landing/biting percentage at 4 h post-application. All three semisolid EO formulations were able to repel >65% of the A. aegypti at 4 h post-application. The EO ointment formulation provided a protection time (182.5 ± 16.01 min) that was statistically significantly longer than that associated with the EO gel formulation (97.5 ± 14.93 min). Meanwhile, the EO cream formulation provided a protection time of 162.5 ± 6.29 min. As the EO cream and ointment formulations displayed better repellent properties than the EO gel formulation, they appear to be the most promising P. aduncum EO formulations to be developed and commercialized as alternatives to synthetic repellents.

In a continuation of studies of diurnal and seasonal feeding activity of Glossina pallidipes Aust. in thick riverine vegetation at Rekomitjie, in the Zambezi Valley, Southern Rhodesia, flies attracted to a stationary black ox were allowed to become engorged, then caught, marked and released. More flies fed per day in the late dry season (November), and fewer during the rainy season (February), than at other times of the year. The proportions of females amongst flies feeding, and of marked flies recaptured, were greatest in May (77·6 and 20·0 per cent., respectively) and least in November (59·2 and 7·7 per cent., respectively). The diurnal pattern of feeding activity was similar in all seasons, there being a well-marked peak of activity at or shortly before sunset.

The trypanosome infection rate was obtained by dissecting flies caught near the experimental site and was combined with figures for the number of flies attacking the ox to give an estimate of the seasonal trypanosome risk (mean number of infected flies that fed on the ox per day); this was greatest in November and smallest in February.

From comparison of catches off a moving and a stationary ox, two stationary oxen standing together, and two standing out of sight of one another, in each case one being red and the other black, it appears that colour of the bait-animal is not of great importance as an attractant to G. pallidipes unless a definite choice is presented, when flies show preference for feeding on a dark surface.

The distribution of cholinesterases hydrolysing acetyl- and butyrylthiocholine in the brain and thoracic ganglion of Musca domestica L. was examined histochemically in untreated flies, and in flies poisoned with diazinon (O,O-diethyl 0–2–isopropyl–4–methyl–6–pyrimidinyl phosphorothioate) of both susceptible and resistant strains.

The inhibition of cholinesterase after poisoning was, to a greater or lesser extent, confined to the peripheral region of the ganglia, and to other specific areas such as the suboesophageal ganglion and lamina ganglionaris. The extent of inhibition increased with increasing doses of poison, and increasing time after treatment. The degree of inhibition could be broadly correlated with the condition of the fly; badly affected or moribund flies having less active cholinesterase than living and unaffected flies. Together with these areas of more or less complete inhibition were other areas, especially in the neuropile or synaptic regions, in which there remained large amounts of active enzyme. Active enzyme was still present in these areas 24 hours after apparent death of the fly. Total inhibition of cholinesterase throughout the central nervous system was rarely seen, even after very high doses of diazinon causing over 99 per cent. kill.

Inhibition did not occur in the ganglia of living flies of a diazinon-resistant strain after a dose which caused inhibition and death in the normal susceptible strain. With 25 times this dose, causing approximately 99 per cent, kill in the resistant flies, cholinesterase was inhibited in them also, although to a somewhat lesser extent than in the susceptible flies given a comparable lethal dose.

The data provided strong evidence that if death is caused by inhibition of cholinesterase of the nervous system it is due to local inhibition and not to generalised inhibition.

Large colonies of holocyclic Rhopalosiphum padi (L.) were sampled in May-June in 1985 and 1986 from the principal host, Prunus padus, in various parts of Britain, mainly in the south-east. They were tested electrophoretically using nine enzymes representing 14 putative genetic loci. Only two loci (14%) were polymorphic (GOT, glutamate-oxaloacetate transaminase, and SORDH, sorbitol dehydrogenase), the remainder being monomorphic. Allele and genotype frequencies at each locus were generally similar both spatially and temporally, and genotype frequencies were close to Hardy-Weinberg expectations. The low level of genetic variability may reflect population bottlenecks which have purged most of the variation and which have been imposed by the distribution of P. padus, especially in the south of Britain where the tree is generally scarce. In addition, it is probable that adverse climatic conditions directly affect winter survival of anholocyclic populations of the aphid and thus also reduce variability. In the long term, such bottlenecks would tend to preclude the maintenance of effectively neutral enzyme variants that arise within populations. The similarity of allele and genotype frequencies may reflect the highly migratory behaviour of R. padi. Thus, in southern Britain, where P. padus is generally much rarer in comparison with the north of the country, R. padi inter-population gene flow is still sufficient to alleviate the influences of genetic drift and possible directional selection on the allelic variation that remains.

The association between weather and light-trap catches of Spodoptera exempta (Wlk.) was examined for four traps in East Africa, using whole–night catches and several years' data. Large increases in trap catch were found to be (1) significantly associated with rain at all four traps for the period December–March, but not for later in the season; (2) significantly associated with light wind periods at Muguga for December–May, but not later in the year, and not at Nakuru, due to the very high overall frequency of light winds there; and (3) not significantly associated with windshifts at either Muguga or Nakuru. These results suggest that high densities of flying moths, which may give rise to caterpillar outbreaks early in the year, often occur where the rather infrequent early–season rains fall.

The three species of Laemophloeus commonly associated with stored products have been shown, by a survey of recorded information, to be cosmopolitan and to occur on a large variety of foodstuffs.

The egg, four larval instars and pupa of L. minutus have been described briefly and the life-history outlined.

Mated females of Laemophloeus minutus lay eggs continuously throughout their long life at the rate of about 0·5 eggs per day at 17°C. rising to 4·0 eggs per day at 30°C. Humidity changes over the range 55–90 per cent. R.H. have little effect on the rate of oviposition. Oviposition is stimulated by the constant presence of the male.

The attraction of several adult predators, genera Elatophilus, Hemerobius and Sympherobius, to the sex pheromones of pine bast scales, Matsucoccus Cockerell, has already been demonstrated. Here, the hypothesis that the larvae of these predators are similarly attracted to the host prey sex pheromone is tested. The response of predators was tested in field trials using pine tree arenas baited with the sex pheromones of M. josephi Bodenheimer & Harpaz, M. feytaudi Ducasse and M. matsumurae Kuwana. Experiments were conducted in Israel in stands of Pinus halepensis infested by M. josephi and in Portugal in stands of P. pinaster infested by M. feytaudi, respectively. The selectivity of larvae for the three sex pheromones was tested in Petri dish arenas in the laboratory. In the field, the larval stages exhibited similar modes of attraction to those of the conspecific adults: Elatophilus hebraicus Pericart in Aleppo pine forest, E. crassicornis Reuter and Hemerobius stigma Stephens in the maritime pine forests. Laboratory choice tests confirmed the kairomonal selectivity of larvae. Both forest and laboratory tests demonstrated the response of a coccinellid of the genus Rhyzobius to the sex pheromones of M. feytaudi and M. matsumurae. A unique chemical communication system among several taxa of predators of Matsucoccus spp. was highlighted that may be attributed to their coevolution on a geological time scale.

Sex pheromonal components of the tephritid fruit fly Bactrocera dorsalis (Hendel), 2-allyl-4,5-dimethoxyphenol and (E)-coniferyl alcohol, are biosynthesized from a highly potent male attractant, methyl eugenol, then sequestered and stored in the rectal gland prior to their release during courtship at dusk. These sex pheromonal components have been detected in the haemolymph and crop organ. Hence, attempts were made to separate and identify the haemolymph fractions which contained the sex pheromonal components. Identification of these bioactive fractions in methyl eugenol-fed male flies using gel filtration column chromatography and biodetection using live male flies showed two fractions as highly attractive to conspecific males. These fractions show a significant increase in protein absorbance in the elution profile of haemolymph from methyl eugenol-fed males compared with that from methyl eugenol-deprived males. The molecular mass of these bioactive fractions as determined by using gel filtration was in the peptide range of 3.3 to 5.5 kDa. Subsequent gas chromatography–mass spectrometry analyses further confirmed the presence of the pheromonal components in the bioactive fractions. The presence of these methyl eugenol-derived sex pheromonal components in specific haemolymph fractions suggests the involvement of a sex pheromone binding complex.

General Growth.

Generally, females have higher rates of growth than males. The phases, however, do not show appreciable differences in the rate. The pronotum has for increase in length the highest values which decrease throughout the instars (whereas the constants for the other parts remain fairly stable up to the fifth instar).

Dyar's rule was applied for the growth in length of the middle femur and the width of the head, and it was found that the rule holds good for these parts.

Przibram's rule, as modified by Bodenheimer, holds true for the growth in length of the different parts and shows the occurrence of latent cell-divisions varying from one (width of head and of pronotum) to four (length of pronotum). The number of latent cell-divisions keeps fairly constant in both phases.

For wet weight Przibram's principle is inapplicable, owing to the large percentage of differences between the actual and calculated values.

Gregarious males are heavier than solitary males up to the third stadium ; gregarious females are heavier than solitary females up to the third stadium ; fourth, fifth and adult stadia being characterized by higher values in wet weight for solitary females than for gregarious females. Females have higher rates of increase in wet weight than males. No significant differences exist in the rates of increase between gregarious and solitary individuals. In the fifth-adult stadium all the rates decrease except in gregarious females, which show a rise.

Gregarious insects have higher values in dry weight than solitary insects, except solitary females in the adult stadium. The coefficients are higher for females than for males.

The rates of increase reach the highest values in the second-third stadium of gregarious insects and solitary females, whereas solitary males have their highest value in the fourth-fifth stadium.

With the exception of solitary females, all the rates of growth in dry weight decline in the fifth-adult stadium.

The rates of growth of the hind legs obtained from the cube-roots of their wet weights are compared with the rates of linear growth of the hind femora. Their variation throughout the instars seems to be in opposite directions. Therefore it is suggested that the rates of growth in wet weight of the hind legs and the rates of growth in length of the respective hind femora are independent of each other.

Growth of the parts.

The application of the exponential allometry formula y=bxα to the data on dimensions of the parts of Locusta shows the existence of negative, positive and almost isometric growth.

The pronotum has the highest value for the growth in length relatively to the growth in length of the middle femur ; the lowest value pertains to the growth in width of the head.

Males have higher values than females ; phase gregaria exhibits higher growth-ratios than phase solitaria.

With the exception of the hind femur the growth-ratios decline throughout the instars. The greatest decline pertains to the growth in length of the pronotum.

A growth-gradient exists in Locusta with the highest value in the pronotum. The middle femur divides the growth-gradient into two parts : an anterior part with values decreasing with the growth of the insect, and a posterior part whose values increase with its growth.

Effects of the amputation of the hind tibiae on crowded locusts.

The effects obtained by mutilating both hind tibiae of three hundred first instar hoppers of Locusta migratoria migratorioides and placing them in a crowded condition are compared with the effects obtained by crowding a batch of the same number of first instar unoperated insects.

The insects with their hind tibiae cut off did not develop as far as those of the control batch ; the differences in dimensions are greater for the hind femur than for the other parts of the body.

In the experimental batch the hind femur, as a consequence of its useless condition, became extremely short as compared with the elytra, bringing the ratio E/F to a high value (over 1·950), thus leading to a false interpretation.

The occurrence of the black-orange coloration in both batches suggested that both developed towards phase gregaria. This coloration was stronger and more uniform in the control batch than it was in the experimental batch. Thus the control animals developed into a better gregarious type.

Attention is again drawn to the presence of mating scars in G. palpalis. They vary in degree and are caused by the superior claspers. The function of the inferior claspers is described and a function for the vermiform appendices is suggested. Flies mated under certain laboratory conditions may fail to develop scars, for reasons given. There are no mating scars in the two other tsetse-flies found in Sierra Leone, viz., G. longipalpis and G. fusca owing to the character of the claspers in those species. For this reason it is likely that the scars are confined to flies of the palpalis group. A suggestion is made concerning the physiology of the production of the scars and attention is called to their bionomic importance. The results of spermatheca dissections of unscarred and scarred females are tabulated. From these it is concluded that the absence of mating scars provides a fairly reliable index of the rate of emergence at any particular time.

The toxicities at 25°C and 70% RH of methyl bromide at about 4 mg/litre and phosphine at about 0·24 mg/litre were determined for large populations, including all developmental stages, of a number of strains of seven species of stored product beetles from 29 countries for a range of exposure periods. The species tested were Oryzaephilus surmamensis (L.), Rhyzopertha dominica (F.), Sitophilus granarius (L.), S. oryzae (L.), S. zeamais Motsch., Tribolium castaneum (Hbst.) and T. confusum Duv. With both fumigants, some individuals of certain strains of S. oryzae and T. castaneum survived a concentration × time product twice that sufficient to kill every individual of other strains of these species, and this was also true for R. dominica with methyl bromide and T. confusum with phosphine. With methyl bromide, some individuals of six species survived the longest exposure used. For the two species of Tribolium, this was 48 h, and for the three of Sitophilus and R. dominica it was 32 h. With phosphine, individuals in many strains of S. granarius, S. oryzae and S. zeamais survived for 8 days. In several of the species, there was some correlation between the tolerances of immature stages and of adults for both fumigants. Many strains were tolerant to both fumigants.

A combination of historical, geographical, and epidemiological studies has given sufficient insight into the ecology of sleeping sickness to enable the main factors influencing the development and spread of an epidemic to be traced.

The evidence shows that in West Africa sleeping sickness is not primarily a disease of the forest, where tsetse flies are most abundant, but belongs essentially to the dry country in the north of the savanna woodland zone, where the earliest occurrences and severest outbreaks have been located.

The first mention of sleeping sickness comes from the upper Niger and dates back to the 14th century. By the beginning of the present century intense though localised epidemics were devastating parts of the Mossi, Grounsi and Lobi country of the upper Volta rivers. At this time the disease was unknown on the coast and of sporadic occurrence only in the forest. A severe trans-Volta epidemic covering 60,000 square miles, developed between 1924 and 1940, but was confined to the north of the inland savanna zone with nothing comparable in the forest.

The epidemic spread in three principal ways : (1) Outwards from original foci of infection because of the dynamic nature of the disease. This produced a concentration of infection around headwaters, a feature characteristic of advanced epidemics. (2) Through the agency of travellers, originally from north to south but subsequently in both directions : a rapid method of spread producing linear distribution of infection along trade routes. The tempo was greatly increased on the pacification and development of West Africa after 1900. (3) A gradual southward shift in the main epidemic zone appears to be resulting from a long-term change in the African climate which is combining with man's activities to produce a southerly extension of xerophytic vegetation types and a regression of forest.

The most important spread was that caused by the trading caravans, more especially the cola traders, who have been coming down to the cola-nut areas in the Ashanti forest from the big markets on the Niger and Upper Volta since the 11th century. The caravans were formerly very large, up to one or two thousand strong, and were frequently made up of Mossi and Grounsi from the territory that was so heavily infected by the beginning of the present century. It is certain that a continuous introduction of infection would have been taking place into the forest ever since trypanosomiasis was prevalent in the north, that is for 100 years at least. And infection has been known in the forest for about that period, yet always to a mild degree, never reaching epidemic form. It has been sought for, because conditions in the forest, with the vector Glossina palpalis in contact with every village and path, appeared to be ideal for the transmission of infection and this drew the particular attention of the early workers from 1908 onwards. But the most that could be found was a threatened epidemic in north-west Ashanti, very significantly centering on the big cola markets which formed the termini for the northern traders.

This historical evidence and the reasoning from epidemiology lead to the conclusion that conditions in the forest are not conducive to the development of epidemic sleeping sickness and that the low state of endemicity found there is maintained by the constant introduction of infection from the true epidemic areas in northern savanna.

From this conclusion arises a practical point of the greatest importance. If the sources from which infection is introduced into the forest could be eliminated the disease there should eventually die out and the tsetse, from the human point of view, would be harmless. Tsetse control in the forest may prove difficult and expensive, and if it is attempted by clearing this might end in the literal destruction of the forest. Such measures would be hard to justify, so many other factors of possibly greater importance than trypanosomiasis are involved, both the intrinsic value of a forest for its products and the wider value through its influence on climate, soil and water.

In formulating a plan for the control of sleeping sickness, the habits of both vectors, human as well as insect, should be considered. The tsetse plays a major role in the development of the high infection rates characterising the epidemic outbreaks in northern savanna ; the human vector distributes infection from these sources along trade routes and into the forest. The elimination of the disease at its source, in true epidemic centres, which can be most effectively accomplished by eradication of the tsetse, will check the distribution of infections to the secondary areas of lighter infection which could then be cleared up by quite minor control measures or might even disappear spontaneously.

This plan is now in operation in the Gold Coast. The validity of the arguments on which it was based is being shown by the results that are already apparent : the high rates of reduction in the epidemic areas and the pronounced lowering of infection in neighbouring, uncontrolled areas, more particularly in the forest region of north-west Ashanti where it is entered by a trade route coming from the previously heavily infected country.