A detailed study of the bionomics of Glossina longipalpis, Wied., was undertaken at Takoradi, the principal port of the Gold Coast in West Africa, and lasted from February to September 1931.

The topography of this country is undulating; the vegetation is of Transition Forest type, intermediate in character between Rain Forest and Savannah Forest, and of an exceedingly dense, homogeneous nature, with a few small glades in the forest, and interrupted by large open marshes on the lower and flatter ground.

The climate is remarkably equable, with a low mean annual rainfall between 40 and 45 inches, but constantly high humidities, owing to the moisture-laden sea-winds. There is a double rainy season, the main rains from April to July, and a second shorter period of rainfall in October and November.

There is a rich mammalian fauna, with the exception of the larger game animals.

Three species of Glossina occur: G. longipalpis, Wied., the commonest, evenly distributed throughout the bush, and the only species dealt with in this paper; G. palpalis, R.-D., confined to water-courses and the edges of lagoons; and G. medicorum, Aust., rarely met with.

Two isolated fly-belts, identical in every way, were studied. In one, section A, flies were caught and killed daily; in the other, section B, the control area, the flies were liberated after noting the catches. By September, the tsetse population of A had been reduced to less than one-third of that of B, presumably the effects of catching and killing.

The main food hosts of this species were the bushbuck and duiker, ubiquitous in this forest. When these small game animals were driven out of a third fly-belt, section C, by farming and wood-cutting, the fly quickly and completely disappeared. This species was never found to feed on reptiles, although they were common in the fly-belts.

Meteorological observations in the open country and in the fly-belts showed a consistently lower temperature and higher humidity in the latter, as well as its greater equity in these factors. The movement of the fly into the open was apparently governed by humidity, the greatest movement taking place when the humidity of the open was within the normal range of fly-belt humidity.

By statistical methods, coefficients of correlation were determined for the fly's density-activity and various climatic factors of the fly-belt. The fly showed a high positive correlation with temperature, and a lower correlation with humidity, of which saturation deficit was a better index than atmometer evaporation. There was a significant correlation with sunshine, but none with rainfall. This correlation with humidity was mainly a temperature effect, as was also the correlation with sunshine. Temperature was evidently of major importance. There was a significant negative correlation between fly and relative humidity, measured with a wet and dry bulb hygrometer in a screen in the open.

All correlations were greatest when considered direct, the fly catches with simultaneous climatic readings, indicating that these factors influence the activity of the fly in this way, rather than its density. The fly was found to be inactive at temperatures below 74°F., with high humidities of 80 or 90 per cent. or over. This explains the major influence of temperature, shown by the methods of correlations. The temperature range in the fly-belt, during the period of observations, was close to the temperature significant for the fly's activity, and therefore variations produced marked reactions; the humidity range was much closer to the fly's optimum and therefore better tolerated.

There is marked daily rhythm in the fly's activity, which is only influenced by climate under extremely unfavourable conditions of temperature or humidity.

The distribution of G. longipalpis in the Gold Coast is dependent upon the humidity of the ecoclimate, rather than upon temperature. It occurs in three main vegetational types—Transition Forest, Inland Savannah Forest, and Coastal Savannah— where the range of humidities is between 50 and 80 per cent. R.H., and temperature between 75° and 85°F. It does not occur in the Rain Forest, where the relative humidity is constantly above 80 per cent., or in northern Savannah, where the humidity is as low as 30 per cent, in the dry season.

The main breeding season was from March to July with its maximum in May, at the height of the rains.

This species was found infected with Trypanosoma gambiense, T. congolense, and T. vivax at Takoradi, and is probably second in importance to G. palpalis as a vector of sleeping sickness in the Gold Coast, but at present of less importance than G. palpalis or G. tachinoides in the transmission of trypanosomiasis of stock.

The receding of the Ashanti forest and the present development of the Colony may cause even greater contact between this species of tsetse and man. The main policy for control should lie in improving and controlling the natives' methods of cultivating the bush. Farms should be as close to the village as possible, contiguous, and kept under cultivation, if possible, permanently. Clearings should be made of at least 100 yards width round bush villages, and of at least 200 yards width round important towns. Small clearings and isolated farms are considered a danger.

In a previous paper (Pospelov, 1926a) I pointed out that adult locusts (Locusta migratoria migratoria, L.) kept in a cage at a constant temperature of 35–38°C. (95–100°F.) and at sufficient humidity attained sexual maturity in a month, while those kept at 20–30°C. (68–86°F.) failed to mature even after three months.

1. The number of egg-tubes and the number of eggs in each tube varies in accordance with the food and the climatic and microclimatic conditions of each habitat. The majority of Siberian grasshoppers have adaptations in the ovaries which enable them to take full advantage of the available heat.

2. In the species possessing 10 or more egg-tubes, their number varies in different parts of the distribution area. It decreases towards the centre of the area with increasing warmth and dryness, and increases towards the colder and more humid margins of that area (e.g., in the Far East and in Western Europe).

3. The potential fertility is more or less stable in different species of grasshoppers, and in the species studied it fluctuates between 84 and 388 eggs per female.

4. There is no correlation between the potential fertility and the abundance of the species in nature, for the greatest fertility is met with in those species which occur but rarely. The injurious (i.e., very numerous) grasshoppers have a medium, or somewhat less than a medium, potential fertility.

5. The actual fertility is greatly dependent on the environment and has a wide range of fluctuation.

6. Lack of food in reservations was observed to lower the fertility of grasshoppers by 30–40 per cent. The parasites (Blaesoxipha spp., Mermis spp.) greatly reduce the degree of fertility of the Siberian grasshoppers. However, the percentage of infestation by these parasites is low, but in the reservations it is somewhat higher than outside. Thus, the actual fertility in reservations is rather lower than outside.

7. The outbreaks of the Siberian grasshoppers are determined by the climatic and microclimatic conditions. The fluctuations in fertility never have any real importance in causing the outbreaks. Lack of food, parasites, predators and diseases are of minor importance; among the latter the main factors are the diseases of the egg-pods, which again depend on the microclimate.

Methods have been devised and applied to an intensive study of the course of illworm activity on numerous rain-grown and irrigated crops. These were developed the first instance to enable accumulation of data considered essential for evaluating eusefulness of certain egg and larval parasites when released experimentally. and they have now been extended to the point of providing continuous, quantitative data on bollworm-food-plant relations. This work has been placed on a routine basis. The information that is supplied comprises:—

1. The course of oviposition in point of duration, magnitude and time of occurrence in the life of a host crop. This serves well to indicate the true course of moth activity on different food-plants, the relative attractiveness of these and to reveal if such matters are maintained under different conditions and bear definable relations to growth stages of a food-plant.

2. The identity and activity of egg and larval parasites under natural conditions.

3. The identity and activity of insects predatory on the eggs and larvae, as occurring in the varied insect communities associated with different crops.

4. Comparative mortality of larvae in the different crops where oviposition has been recorded.

Continuous records of egg-laying by the American bollworm, H. obsoleta, F., have been taken at the Cotton Station, Barberton and on several farms in the neighbourhood. Cotton and maize were the principal crops, but the surveys included a number of other food-plants. Egg-laying was found to be very closely associated with the period of bud and flower production, and its duration on different hosts thus varies according to the flowering habit.

In the case of maize, egg-laying hi quantity commences when the tassels (stam-inate flowers) are extruding, and the peak of the oviposition is passed before silks (pistillate flowers) are abundant. This is at variance with the generally accepted view that the plant is most heavily oviposited upon during the silking period. The typical course of oviposition on maize here lasts for two to three weeks only.

Numerous instances were observed where oviposition by Heliothis occurred on maize in tassel to the practical exclusion of neighbouring cotton in freely fruiting and healthy condition, and the possibilities of exploiting this relationship are discussed.

As regards winter-irrigated vegetable crops and citrus orchards, data are given showing that the American Bollworm breeds extensively in these crops, particularly so a month or two prior to the appearance of rain-grown cotton, maize and tobacco.

The irrigated crops in the Barberton and contiguous districts are regarded as a main source from whence bollworm on cotton is derived. Citrus orchards of which there are relatively large acreages may be of particular importance in this regard.

The methods of obtaining information on the course of moth emergence are described. Data are given that explain the course of moth activity in winter crops and indicate when moths enter rain crops from winter breeding areas.

The only larval parasite of importance under natural conditions is Sturmia inconspicua, but this fly does not parasitise young larvae. There is a scarcity of insects parasitic on American bollworm larvae, and the question of importing them should be considered. Breeding and experimental releases of a larval parasite, Microbracon brevicornis, are discussed.

Two important egg parasites are a species of Phanurus and Trichogramma lutea.

An Anthocorid bug, Orius sp., destroys large numbers of bollworm eggs and probably also young larvae, and this insect and certain species of ants are the most important agents in natural control.

As regards the red bollworm, Diparopsis castanea, Hmps., it is concluded that the use of trap crops should be discouraged for general adoption as a means of controlling it owing to the danger, through inattention to the trap crops, of breeding this boll-worm in them. Its incidence in former years is briefly reviewed. Of late years the annual infestation has diminished greatly in some districts but not in others. The variations in this regard are attributed mainly to the presence or otherwise of ratooned cotton, particularly in mild winters and to seasons of very late planting.

Records of stainer infestation in cotton have been taken at the Cotton Experiment Station, Barberton, South Africa, since 1931, and in 1933 a uniform system of recording stainer populations in cotton by sampling 10-acre blocks was extended to four farms in the Barberton district, three farms in Swaziland and the Cotton Experiment Station at Magut, Natal.

The records so obtained show that stainers normally appear in plant cotton in late February or early March. D. intermedium, Dist., is present in comparatively small numbers throughout the season; D. nigrofasciatus, Stål, and D.fasciatus, Sign., are very variable in relative abundance. In 1933 the latter species was practically absent from cotton at all points save those in the vicinity of ratoon or standover cotton, but in 1931 and 1932 it appeared in numbers equal to those of D. nigrofasciatus and bred up a very much larger population in the crop.

Where normal migration occurs, all three species of stainers pass through two and a partial third generation in the crop; at the end of the season part of the adults migrate from the crop and the remainder, together with the bulk of the nymphs, may be destroyed by appropriate clean-up measures.

Extensive surveys of the Transvaal Low Veld and rapid tours of portions of Swaziland, Zululand and Portuguese East Africa, indicate that the principal wild food-plants of stainers in these regions comprise the genera Abutilon, Gossypium, Hibiscus and Sida in the Malvaceae, Melhania and Sterculia in the Sterculiaceae and Adansonia in the Bombaceae.

The Malvaceous host plants and Melhania are all herbaceous or shrubby species and upon these D. nigrofasciatus is frequently found. It is possible that colonies of these plants existing in sheltered situations may provide overwintering grounds for this species.

Two species of Sterculia are known, S. rogersii and S. murex. The former is wide-spread and abundant throughout the Low Veld and probably constitutes the main breeding-ground of all species in the early summer. The latter species is rarer, and its status as a food-plant is not yet fully investigated.

The Baobab occurs in large numbers in the Northern Transvaal, but it has not yet been proved to be a winter food-plant. The latest information shows that during the summer it may commonly be infested with D. fasciatus.

In conjunction with stainer population records in the crop, weekly systematic records of damage to the crop have been obtained from samples of bolls which have been examined for puncturing and graded for degree of staining. The number of punctures per boll and the percentage staining are strongly correlated, but it has proved difficult to correlate these with stainer population, except where young bolls are examined.

Internal boll disease, particularly early in the season, may be due to bacterial organisms transmitted by species of Hemiptera other than stainers. Later in the season the infection of the crop is more definitely due to Nematospora spp., of which N. gossypii is commoner than N. coryli.

All species of stainers collected on cotton have been found to transmit Nematospora, though they are not efficient vectors until the fourth instar is reached. Adult stainers collected on wild food-plants (Gossypium herbaceum var. africanum, Hibiscus spp., and Sterculia rogersii) have been shown to be infected with N. gossypii.

The etiology of the disease produced by both species of Nematospora has been followed in inoculation experiments, using pure cultures. The rate of spread of the disease varies with the age of the boll at the time of inoculation, being slower when the boll has passed middle age. In neither species does staining extend beyond the foculus in which infection starts, nor does the fungus occur within the seed except lollowing direct puncturing of the seed.

The fact that the staining is not co-extensive with the region occupied by the fungus, but goes far beyond it, and that a pathological condition indistinguishable from that due to the living organism may be produced by injecting a sterilised suspension of the fungus, suggests that the death of the lint hairs, producing staining, is due to a toxic substance liberated by the developing fungus.

1. From a block of country of four square miles, infested by Glossina swynner-toni and a few G. pallidipes, grass-fires have been excluded for three years in succession. The tsetse-population has decreased in that time by nearly nine-tenths (from 9.4 to 1.0 flies per 1,000 yards of transect). In a block of two square miles it has decreased in two years without burning to the same average of one fly per thousand yards of transect from a high previous figure unmeasured. Two “barrier” strips following roads that previously were highly infested have also been unburned for three and four years respectively and have become similarly inhospitable to the flies.

2. In a control block of only 1¾ square miles, the grass has been burned in the ordinary native fashion annually during the same period. The average fly-catch per thousand yards of transect has increased since this was done from 4.2 to 13.1.

3. In each of these blocks game is about as plentiful as it was at the first. The 4-square-mile block shows a slight gain.

4. In the four experimental blocks and strips, but not in the controls, extensive thicket is growing up everywhere in the grass as a result of the exclusion of the fires. Thus the previous marked difference, both spatial and seasonal, between the respective densities of the different vegetational communities is commencing to disappear. Much grass-country remains but its average condition is one of long grass rising from a mulch, thick or thin and sometimes absent, of the previous year's grass that keeps the soil damp after rain—the more so since run-off is checked. Longer and denser grass is encroaching into the previously very open concentration sites of G. swynnertoni, which are also being invaded by thicket.

5. The contrasts between burned and unburned country are especially strong in the short wet season. At this time in burned country the flies have just gone through a period of intense desiccation, short hunger cycle and hardship, and the population is at its annual minimum. The ground, however, is very open and visibility of the other sex and of food animals and breeding-places is unimpeded. Conditions are suddenly made ideal by the advent of the rains. Humidity is added to temperature; the hunger cycle is lengthened; the openness and insolation of the ground now probably play a further beneficent part by preventing an excess of humidity. The flies are active, they breed freely, the shade conditions enable them to spread, and the density curve soars upward.

On the unburned ground the water-content of the soil is increased in the early rains, dampness is retained between showers, the temperature is lowered, evaporation is reduced, and light intensity in the grass becomes less (Scott, 1934). The activity and breeding of the flies is quite likely affected. The striking increase in the population that characterised unburned country in the early rams and short dry season is absent, and the density, having failed to rise at this time, continues low or falls further.

6. In two cases (G. morsitans, Nash 1933, at Kandaga; G. swynnertoni in Block 11 at Shinyanga) the second annual impetus to breeding, associated normally with the advent of the long dry season, duly produced its usual effect on the tsetse-populations of country that was in its first year of no burning. In the case of the block that has been unburned for three years this effect has been slight.

7. That the conditions, though deteriorating, are as yet not lethal through hunger, due to poor visibility or otherwise, is suggested by the fact that the very small fly populations referred to maintain a nearly stationary balance in at least the larger experimental block and do not show special hunger or other sign of distress. It is possible that most of the diminution hitherto has been caused merely by emigration to better conditions, for the blocks are not yet fully isolated. On the other hand, were the main effect on the breeding, distress would not be detected and the result might take place independently of any emigration. Reduced visibility of food animals may become operative later.

8. It is suggested by the results so far on the tsetse and by the present appearance of the country in these four experiments that with the further advance of the vegetational succession towards its natural climax the remaining fly population will probably dwindle further and disappear—at least if the areas are isolated; the growing homogeneity in the density of the whole vegetation will reach a point at which it is unlikely to satisfy the daily and seasonal needs of an insect which for food, breeding and regulation of moisture and temperature, has a separate and vital use for each of the three densities furnished by thicket, savannah wooding and nearly open hard-pan and vlei.

9. The concentration sites of G. swynnertoni combine in a small space the types of vegetation the flies need, both the denser and the more open. They are important at all times but especially as refuges from unfavourable conditions elsewhere and as meeting-grounds of the sexes when the population is reduced. They are operative all the year round, and an effective change in these refuges alone in either the wet season or dry should be a shrewd blow at the fly. In experiments elsewhere in Shinyanga the clearing of the thickets at these places has quickly brought down the fly-population through its dry-season effect. In Blocks 4A and 10A the cessation of grass-burning is apparently already affecting these sites by hemming them in with areas presenting unfavourable conditions—probably mainly through excessive shade and over-humidity in the rains. The cessation of burning might even suffice if confined to these concentration sites and their neighbourhood.

10. As regards the probable effect of not burning the grass on other species of tsetse, it is considered that the method may prove useful against G. morsitans under moderately extensive vegetational conditions, though it may in this case take much longer and may not apply to large areas. Berlinia-Brachystegia wooding went to thicket in the writer's early experiments in a specially high rainfall area in Rhodesia, and (under lower rainfall) the exclusion of fire for five years at Itundwe (Central Province, Tanganyika) has produced strong densification in the Berlinia. In the Kikore plots (5 years protected) savannah type seedlings are being suppressed by the new conditions, but the flourishing state of the few shade-tolerating thicket plants suggests that all that is wanted is the introduction of a suitable seed-supply. This will be necessary in any case in all places without natural regeneration.

11. In an observation by Nash (Kandaga, Central Province) G. morsitans reacted initially in much the same way as G. swynnertoni, but the experiment was interrupted. In Itundwe G. morsitans and its pupae are much less numerous in the unburned Berlinia than in the burned.

12. The reaction of G. pallidipes, as distinguished from that of its habitat, is uncertain but so far has been promising under Shinyanga conditions; but the new conditions at Itundwe look as though they might favour this fly. G. brevipalpis is definitely likely to be favoured by the effect of not burning the grass.

13. The increase in humidity and lowering of the temperature produced by not burning the grass may be expected to be specially effective towards the wet side of a tsetse-fly's range. Towards the dry side it might even at first assist the fly.

14. Experiments to test the possibility of success against morsitans are being taken in hand, as are experiments on larger pieces of country infested by swynnertoni and pallidipes.

15. The control of grass-fires offers difficulties, but our experience over a wide area and many years shows that with determination and organisation it is quite possible, though an occasional minor set-back must be expected. The advantages of this measure from other points of view than that of tsetse extirpation, and the means of restoring the pasture, are referred to on p. 425.