Projects undertaken on the biological control of insect pests in Bermuda since the first introduction of Bufo marinus in 1875 and including those still in progress are discussed. Work on 15 pests or groups of pests has been undertaken involving the introduction of over one hundred species of beneficial organisms.

Icerya purchasi Mask. is considered to be under excellent control as a result of the introduction of the Coccinellid, Rodolia cardinalis (Muls.), and the fly, Cryptochetum iceryae (Will.). Pseudaulacaspis pentagona (Targ.), a serious pest of oleanders, was brought under control about 1922 by the introduction of Aphytis diaspidis (How.). However, in recent years heavy infestations have periodically developed. In addition to A. diaspidis, the Aphelinids, Aspidiotiphagus citrinus (Craw) and A. lounsburyi (Berl. & Paoli), the Coccinellids, Lindorus lophanthae (Blaisd.) and Chilocorus cacti (L.), and the Nitidulid, Cybocephalus sp., now attack it.

Comstockiella sabalis (Comst.) at one time causing severe injury to the endemic palm, Sabal bermudiana, was brought under control by the introduction of Physcus sp. Bracon gelechiae Ashm. has been established on the potato tuber moth, Gnorimoschema operculella (Zell.), but satisfactory control has not resulted.

Two cedar scales, Carulaspis minima (Targ.) and Lepidosaphes newsteadi (Sulc), have decimated the stands of Juniperus bermudiana despite an extensive programme of biological control. C. minima, which proved to be the more serious, is attacked by the Aphelinids, Prospaltella sp., Aspidiotiphagus lounsburyi, A. citrinus, probably introduced with the scale, and the Coccinellids, Lindorus lophanthae and Microweisia suturalis (Schwarz), which were liberated in large numbers. The predacious mite, Hemisarcoptes malus (Shimer), and the fungus, Myiophagus ucrainica, were established on Lepidosaphes newsteadi which for unknown causes became very scarce.

Damage by Calpodes ethlius (Cram.), a pest of ornamental cannas, is less serious since the introduction of Ooencyrtus sp. and Trichogramma sp.

Several parasites were liberated to control various species of mealybugs. Pseudococcus adonidum (L.), serious on a number of ornamentals, is under satisfactory control as the result of the establishment of the Encyrtids, Tetracnemus peregrinus Comp. and Anagyrus fusciventris (Gir.). Planococcus citri (Risso) is now attacked by the introduced Encyrtids, Leptomastidea abnormis (Gir.) and Pauridia peregrina Timb., as well as by Leptomastix dactylopii How., which was present at the start of the investigation. Acerophagus pallidus Timb. has been recovered from the mealybug, Phenacoccus gossypii Tns. & Ckll.

The Encyrtid, Microterys kotinskyi (Full.), and the Coccinellids, Azya luteipes Muls. and Cryptolaemus montrouzieri Muls., have been effectively established on the soft scale, Pulvinaria psidii Mask. Tree lizards, Anolis spp., which feed readily on Azya and Cryptolaemus, are considered undesirable and accordingly the passerine bird, Pitangus sulphuratus, has recently been liberated in an attempt to reduce their numbers.

Several species of parasites and predators were liberated against the soft scales, Saissetia oleae (Bern.), S. coffeae (Wlk.) and Coccus hesperidum L. Aphycus stanleyi (Comp.) is well established on Saissetia spp.

Although the Braconid, Opius humilis Silv., was established on the Mediterranean fruit-fly, Ceratitis capitata (Wied.), for a number of years it has now disappeared.

Parasites and predators introduced against Nipaecoccus nipae (Mask.), the onion thrips, Thrips tabaci Lind., and the red spider mite, Oligonychus ununguis (Jacobi), did not become established.

Projects at present in progress to control tree lizards, Anolis spp., and snails cannot yet be evaluated.

In the discussion a number of factors which may have contributed to the failure of establishment of some beneficial organisms are mentioned.

Certain species of COCCIDAE that excrete honeydew and are attended by ants or enclosed in their nests are quite prevalent on tea bushes and seed trees in the plains of Assam and West Bengal but those which are not attended by ants are kept under considerable check by the activities of their natural enemies. In Darjeeling, where the natural enemies are fewer, a number of species occur abundantly and are often responsible for serious damage to tea.

From the studies of the relative population of the ant, Crematogaster dohrni Mayr and the Coccid, Saissetia formicarii (Green), occurring on tea bushes it is doubtful if more than a small portion of the food requirement of the vast ant population in the nests which contain sexual forms could be met from the honeydew excreted by the small number of Coccids enclosed therein. The major part of food must, therefore, come from other sources. Insects attacking or visiting the tea bushes and tea seed trees or even those found on the ground appear to constitute the major part of the food of the ants, C. dohrni and Oecophylla smaragdina (F.).

Several factors are responsible for the decrease in the population or disappearance of the Coccids in the absence of attendant ants. In the plains, Eriochiton theae Green, Coccus hesperidum L. and S. formicarii entirely disappear in the absence of attendant ants either due to the activities of their natural enemies or by contamination with honeydew accumulation or both. Parasitism may be slightly higher in ant-free colonies, but no estimation was possible since, in the absence of ants, the Coccids are quickly destroyed by predators.

The ants do not protect the Coccids from Hymenopterous parasites; but their active movements hinder the parasites in their efforts to oviposit, and this leads to a reduction in the rate of parasitisation.

In the presence of the ants, O. smaragdina and Crematogaster dohrni, predators are rare; they are destroyed as are any other insects or any foreign bodies that happen to be near their nests, whether they constitute food or not. The larvae of predators which have a protective covering or which resemble Coccids, if they happen to have gained access to the Coccid colonies, are not attacked by the ants, because they are not recognised as different from the Coceids.

O. smaragdina does not normally transport Coccids, though young nymphs of E. theae and Coccus hesperidum may be aided in their dispersal, but Crematogaster dohrni and Crematogaster sp. are primarily responsible for the dispersal of S. formicarii and this takes place when an occasion arises to remove the Coccid to more favourable sites.

O. smaragdina does not destroy the nymphs and sedentary form of Coccus hesperidum for food, but sedentary forms which are unable to establish themselves on transfer from withered leaves to a new nest are eaten.

With the control of the attendant ants, the honeydew-producing Coccids disappear or at least they become rare. Conversely, where the Coccids are controlled, the ants automatically disappear.

Two field trials of obstruction (‘ obstructive clearing ’) as a means of control of Glossina palpalis (R.-D.) in locations representative of the Northern and Southern Guinea Savannah zones of Nigeria, are described.

In neither case was complete eradication achieved, pockets of G. palpalis remaining from the beginning at certain points on the main stream. Greater success was obtained in the smaller tributaries, which lent themselves more to obstruction. There was little penetration of G. palpalis for any great distance into obstructed reaches from natural ‘ reservoirs ’ left abutting on to the obstruction, but a trial of the ‘ protective ’ value of obstruction failed, owing to complete penetration in some strength of 300 yd. of obstructed stream on either side of the point to be protected. In neither case was immigration of flies from elsewhere into the trial areas an important factor. Although, at first, the surviving fly population was very localised, there were later indications that dispersal was beginning to take place.

Some accidents which may happen to obstruction are described, with their effects on its ultimate appearance. Consequent to these, a number of factors which limit the wide application of obstruction are stated. The more important of these are: the dimensions of the river-bed, which may be too large to permit of successful obstruction; the presence of wide swampy forest through which G. palpalis ranges freely; alternatively, the presence of shallow rocky stretches with low eroded banks that may be devoid of all but certain characteristic trees, where adequate obstruction is impossible; the rate of run-off of water in the catchment area, rapid run-off leading to spates which disrupt the obstruction; human interference with the obstruction in quest of firewood.

No technical difficulties were encountered in carrying out obstruction, and costs were from 40 to 50 per cent, cheaper than comparable partial clearing.

Considering the subsequent appearance of originally obstructed stream, and its frequent resemblance to partial clearing, the suggestion of ‘ destructive ’ clearing is put forward, in which the top canopy would be destroyed, but no effort made either to create obstruction or to clear away the fallen trees. Instead, reliance would be placed on the action of the various agencies encountered in these trials, which brought about the disruption of the obstruction, to produce the desired end-result.

It is concluded that successful obstruction depends too much on specialised conditions, difficult to fulfil in large-scale tsetse control schemes, and that it is unlikely to become a normal method of control of G. palpalis in the savannah zones of Nigeria.

This part of the study of the garden chafer, Phyllopertha horticola (L) in the English Lake District deals with the reproductive state of the females during the flight season. Total egg-production depends entirely on stores (fat-body) accumulated in the final larval instar. On the average, the fat-body enables about 16 or 17 mature eggs to be manufactured per female, the usual range being 9–32. Rate of reproductive development is the same in the largest and smallest female adults. The outstanding mass features of the flight season are the two roughly equal and half-overlapping Phases: Phase 1, swarming over the grass sward, followed by Phase 2, swarming on the surrounding bracken, hedges and trees. Mass aspects of the female reproductive state throughout the two Phases are as follows.

At primary emergence on the grass sward, females always contain some fat-body together with some fully developed and/or immature eggs. On the average they have about one-third of their full complement of eggs matured, the range being from none (with about 50% of the original fat-body still remaining) up to four-fifths (with about 10% of the fat-body). Since primary emergences in a homogeneous population extend over about a fortnight, females taken from the grass sward throughout Phase 1 are in various reproductive states. Thus after the first few days of the Phase and until the last individual makes its primary emergence, sample females may have half their fat-body and no eggs yet fully matured or no fat-body and all their eggs actually laid, or any intergrade between these extreme states. Towards the end of Phase 1 (which finishes about a week after the last primary emergence), females have no fat-body remaining and have already laid most or all of their eggs; and a small proportion of them now has food in the gut.

In Phase 2, about 99 per cent, of females on bracken, hedges and trees contain no fat-body and therefore cannot manufacture any more eggs. On the average they have two mature or very nearly mature eggs left (range 0–26). This egg content is much the same as at death. The remaining 1 per cent, of females are aberrants with some fat-body still unconsumed. ‘ Bee-liners ’, the females which shoot out bullet-like from the bracken, hedges or trees to alight comparatively far afield, either have some fat-body remaining, or, if not, considerable numbers of eggs (mean about 9 as compared with the general mean of 2). Thus bee-liners are the phase-2 individuals with most eggs still unlaid. Obviously they are a minority.

Deductions as to individual behaviour are made from the mass aspects of the reproductive state and are to be examined in the next paper of this series.

Since females of the garden chafer have already laid all or most of their eggs before appearing on hedges and trees, gardeners will not control this pest by killing all they find on their hedges and trees.

A survey of the populations of eggs and larvae of Heliothis armigera (Hb.) was made on the Cotton Research Station, Namulonge, in Buganda Province, Uganda, over the four-year period, 1954–57 inclusive, on cotton, maize, groundnuts, beans and, in one year, sunflower. The populations encountered were low in comparison with some other cotton areas in Africa. The oviposition rate on each crop closely followed the flowering cycle, and there was no indication of the population from one crop influencing that on a subsequent crop, even when their flowering cycles overlapped. Under the normal crop sequence there is a sufficient gap between the attractive phases of successive crops to cause dispersal, possibly to wild host-plants, of the moths emerging from pupae bred in the preceding crop.

The variation in population from year to year on a given crop was no greater than that between different localities in any one season. Maize and sunflower did not prove successful when tested as trap crops grown adjacent to cotton.

Earias spp. and Argyroploce leucotreta Meyr. were less abundant than Heliothis and together constituted only 27 per cent, of the total population of Lepidopterous larvae on cotton.

A method is described for breeding H. armigera, in the laboratory, in which the mean duration of the various stages was: egg, 4 days; larva, 24·8 days; pupa, 22·9 days; preoviposition period, 3·1 days; and oviposition period, 10·4 days. The mean number of eggs laid per female was 751·6, of which 71·4 per cent, hatched. Larval diets consisting of differing species and parts of food-plants caused significant differences in larval and pupal periods, the former being least (21·8 days) on maize silks and greatest (33·6 days) on sunflower corolla and receptacle, and the latter least (19·7 days) after larval feeding on three-week-old maize cobs and greatest (26 days) after seven-week-old cotton bolls. Pupae developing from larvae collected from the field did not exhibit any diapause or resting stage.

Two egg parasites and 15 larval parasites (three of which were probably secondary) were bred from material of H. armigera collected in the field, but the degree of parasitism remained low throughout the year. A nuclear polyhedral virus disease of the larvae was also recorded.

It is concluded that under the climatic conditions encountered, H. armigera is active throughout the year because wild or cultivated food-plants are always available and no resting stage of the insect is induced; this continuous activity is accompanied by biologically controlling factors that maintain populations stable at a relatively low level.

An examination of the records from 1930 onwards shows that a very high level of Lake Rukwa is correlated with small numbers of the red locust, Nomadacris septemfasciata (Serv.), in the Rukwa Valley outbreak area in Tanganyika. When the lake level is not very high, the size of the adult locust population (taken as that present in the middle of the dry season) is correlated negatively with the total rainfall of the last but one wet season (broadly, November–May), positively with the size of the preceding parental population (taken as that present at the time of oviposition) and possibly also with the rainfall of the preceding October–December, but not significantly with the date of the drop in temperature that is thought to be associated with the start of ovarian development.

Three tentative explanations of the correlation between adult population and rainfall are offered. First, if the water-table is high because of heavy rain in the previous season, the early rains may make the soil unsuitable for successful egg-laying and incubation; second, after a season of heavy rainfall the grass cover may be particularly dense at the end of the following dry season and the consequent reduction of the oviposition sites may make breeding unsuccessful; third, parental mortality may be high during a dry season following heavy rains. These possibilities are being further investigated.

It is suggested that by using a multiple regression equation incorporating the correlations that have been established, the size of the adult locust population can be forecast in time for the scale of hopper control measures to be appropriately modified and economies thereby achieved.

In the British Solomon Islands Protectorate, the incidence of immature nutfall of cococuts that is caused by the Coreid bug, Amblypelta. (chiefly A. cocophaga China), depends indirectly upon certain species of ants, some of which protect the palms against Amblypelta, whilst others do not. There is evidence that populations of the ants can sometimes change quite rapidly, and that local fluctuations in nutfall are largely dependent on such changes.

Observations on ant populations were maintained over a period of 2½ years (1954—1956) to find out if such changes are of common occurrence and to attempt to explain their cause.

An account is given of ideas, current at the beginning of the author's investigation, on the effect of vegetation and other factors on changes in ant populations, and in particular of the cover-crop or creeper theory, the advocates of which suggest that the presence of such vegetation, prevalent in plantations during and after the war, provided conditions favourable to beneficial species of ants.

The actual progress of recorded changes in ant populations is described and discussed. Rapidly changing populations usually involve the ants, Pheidole megacephala (F.), Oecophylla smaragdina (F.), and sometimes also Anoplolepis longipes (Jerd.); more stable populations usually involve Iridomyrmex myrmecodiae Emery, and occasionally Oecophylla and Anoplolepis. An account is given of the ‘battles’ which often occur during replacements of one species by another.

An account is given of the vegetation found in coconut plantations in the Solomon Islands, with special reference to the plant communities associated with each of the four species of ant of special importance in immature nutfall, and also with mixed ant populations. It is concluded that heavy creeper growth is not particularly associated with O. smaragdina (as was thought by supporters of the creeper theory), nor with the other beneficial species A. longipes, but rather, if anything, with P. megacephala, a non-protective or harmful species; there is thus no good reason to suppose that a growth of creepers will encourage beneficial species. Iridomyrmex myrmecodiae is the only species of the four which tends to be associated with a characteristic type of vegetation, including several species of epiphytes and often heavy creeper growth. But there are exceptions even to this, and there is evidence that the epiphytic vegetation may to some extent be the result rather than the cause of the presence of Iridomyrmex. There are, in fact, exceptions to every rule, and it is concluded that vegetation is not an important factor controlling ant distribution, except in so far as heavy growth of creepers and other plants may encourage a more mixed ant population in general, including several indigenous species which are not normally conspicuous in well-maintained plantations; if there is any effect on the four ‘major’ species, it is to encourage Pheidole and Iridomyrmex at the expense of Oecophylla and Anoplolepis.

An account is given of two experiments which involved control of creepers and other vegetation by repeated cutting down or ‘brushing’ in marginal zones between areas occupied by two different ant species, to see if this practice would alter the course of changes in population that were already taking place. One experiment involved a marginal zone between I. myrmecodiae and A. longipes, and the other between O. smaragdina and P. megacephala. It was found that in both cases there was no appreciable difference in the course of events between ‘brushed’ plots and plots adjacent to them in which the vegetation was not controlled. This bears out the previous conclusions that the presence or absence of creepers and other vegetation has little, if any, effect upon changes in ant populations.

At Rua Vatu, where an extensive replacement of P. megacephala by O. Smaragdina was taking place, accompanied by recovery from a condition of heavy nutfall, detailed studies revealed that this replacement was not a direct one, but that, at all events for the most part, a succession of normally unimportant ‘transition’ species first replaced Pheidole, and were in turn replaced by Oecophylla. The details of this succession are described and discussed. Evidence is produced to suggest that a similar succession may have been involved in recorded examples of recovery from nutfall in other places, notably in that which occurred in the Kukum/Lunga/Tenaru group of plantations after the second world war. These conclusions present a picture not so much of direct antagonism between Pheidole and Oecophylla, but rather of the initial disappearance of Pheidole owing to unknown intrinsic factors, followed later by the infiltration of Oecophylla in the wake of a variable succession of indigenous ‘transition’ species, which have been allowed to increase in numbers temporarily during the interim period when the area is not dominated by either of the two major species. In view of this, it is not so surprising that a factor such as vegetation should have little or no direct effect upon the change as suggested in terms of the creeper theory.

As regards the reverse change, the replacement of Oecophylla by Pheidole, there is little evidence to go on, but such as there is suggests that the replacement in this case is more in the nature of a direct one.

The fact that recovery from nutfall took place recently at Rua Vatu, at a time and place where insecticides had not been applied, contradicts the theory that the earlier and similar recovery in the ukum/Lunga/Tenaru group of plantations was the result of a differential effect upon ant species of the application of insecticides during the war for mosquito control.

Observations on the population density of Amblypelta cocophaga China on coconut palms in the Solomon Islands are described. Although the figures are somewhat larger than those previously reported for the related Coreid, Pseudotheraptus wayi Brown, in Zanzibar, the densities are still very low.

Observations were made on the oviposition habits of A. cocophaga. The principal oviposition site, contrary to previous observations, was found to be on the undersides of the fronds, in the basal recesses of the leaflets. The first-instar nymphs on hatching have to make their way to the spadices in the centre of the palm crown; this explains why first-instar nymphs are themselves only rarely found on the spadices, and also why a single treatment with insecticide is not completely effective, since the oviposition sites escape the treatment. Observations on the number of eggs on coconut palms are recorded.

Anastatus axiagasti Ferrière was found to be a common egg-parasite of Amblypelta cocophaga in certain plantations of Guadalcanal. Rates of parasitisation on coconut palms ranged from 15·5 to 55 per cent, with an average of 33·3 per cent. The percentage of successful hatching of Amblypelta eggs ranged from 19 to 38 per cent., with an average of 31·3 per cent.

Investigation of the area of Baunani plantation in Malaita, where the Tachinid parasite, Trichopoda pennipes (F.), had been released in 1949, indicated that it has not survived there, or, if it has, is exercising no control over A. cocophaga.

Observations are recorded on two predators of interest with regard to immature nutfall.

In the Sudan Gezira, some 240,000 feddans of Egyptian-type cotton (Gossypium barbadense) are grown annually by gravity irrigation from the Sennar Dam, and this is sprayed with DDT, 6–10 weeks after sowing, in order to control the cotton jassid, Empoasca lybica (de Berg.), which is considered to reduce the yield. The seasonal yield response to DDT was estimated by comparing the yields of single sprayed and unsprayed 90-feddan fields, pairs of which were selected in each of the 40 (now 44) Blocks into which the cotton estate cropped by the Sudan Gezira Board is divided for administrative purposes. In order to establish that this estimate adequately represented that of the estate as a whole, it was necessary to show the validity of three assumptions: that the sample was representative; that the unsprayed plots, though surrounded by sprayed cotton, were sufficiently large to behave in respect of yield as if their environment had not been sprayed; and that the selection of the fields was effectively at random.

Examination of the yield history of the fields that were sprayed showed that there had been a slight bias towards the selection of fields that yielded better than the mean of the locality, and although this bias did not change from place to place or year to year, it did increase with level of yield. It is not, however, considered big enough to invalidate the first assumption.

The second assumption was tested by a special experiment reported elsewhere, which produced no evidence to suggest that a 90-feddan field would be affected in respect of yield and insect pests by proximity to a differently treated neighbouring field.

The third assumption cannot be proved, but during two seasons when fields were selected by a random procedure, the results did not differ seriously from those in years when the choice was not completely random. Moreover, when the yields of fields selected for treatment in one year were examined for the season when the fields were last cropped with cotton, and spray treatments were identical, they were found not to differ significantly, although the differences were increased and became significant in the year when sprayed and unsprayed treatments were applied.

Accordingly, the yield of the unsprayed sample is taken to indicate what the yield of the whole estate would have been had all the cotton been unsprayed.

The yield response to DDT spray of Gezira cotton, as thus estimated over the period 1949–50 to 1956–57, was shown to vary from season to season. A highly significant part of this variance was correlated with the amount of ram falling in July, some six weeks before the crop was sown, but the response was also significantly affected by both seasonal and site effects that were also correlated with this early rain. A series of experiments in 1956–57 showed that Domains Sakel cotton, which is grown in the drier, northern part of the Gezira, tended to give an increased response to DDT spray at higher levels of nitrogenous fertiliser, and that a very highly significant part of this response was due to the control of jassid, E. lybica, and thrips, (Caliothrips spp.). X1730A, grown in the wetter, southern part of the Gezira, gave no over-all response to spraying, nor was the response to nitrogenous fertiliser affected by spraying. When the yields of these varieties were examined separately over eight seasons, it was found that Domains Sakel gave a mean yield response to spraying of 1·11 kantars of seed cotton per feddan, which did not vary significantly from season to season, but that X1730A gave a yield response which was less when pre-sowing rains were good and nitrogenous fertiliser was applied. Although the regression on July rains and on fertiliser of the response of X1730A to spray failed to reach significance at P = 0·05, it is considered that further data should enable a prediction of yield response of X1730A to DDT spray to be made by examination of these two factors.

Since 1935–36, yields of cotton in the Sudan Gezira have been positively correlated with the amount of rain falling between 1st July and 15th August of the year of sowing. Comparison of the coefficient of regression of yield on this rainfall in the period (1935–36 to 1947–48) before sprays or fertiliser were applied, with that of a more extended period (1935–36 to 1954–55) including six seasons in which sprays and fertiliser were applied, shows that the latter is only about one half the former. After allowing for differences in varietal response to spraying and fertiliser, it can be shown that this decrease in the deleterious effect of a deficiency in pre-sowing rains, is almost exactly accounted for by the beneficial effect of DDT spray.

It is concluded that at least half of the deleterious effect of poor pre-sowing rains on Gezira yields is a pest effect which can be eliminated by DDT spray.

The study thus provides a means whereby DDT spray may be applied selectively to those areas of the Sudan Gezíra where its effect is likely to be most profitable and suggests, moreover, that such a policy would reduce the considerable seasonal fluctuations in cotton yields which in the past have characterised cropping in this area.

A population of Glossina longipalpis Wied. was studied in southern Nigeria, in derived savannah of the Southern Guinea, zone type, between November 1953 and December 1956. Regular fly-rounds were carried out, using man as bait, and during the third year also using an ox as bait. Meteorological records were taken in the savannah woodland and within a forest island; the latter is cooler and more humid than the former.

The forest-island type of vegetation, with dense thicket under high shade, is the permanent habitat of the fly, although the inside of the forest apparently becomes too humid in the heavy rains, when the flies move out to the edge. Seasonal pools in the savannah, encircled with rather thicker vegetation, form temporary habitats during the rains and early dry season. Transition forest and woodland savannah, when in association with permanent habitats, are used as feeding grounds. During the dry season, the flies concentrate in and around the forest island, and evacuate the woodland savannah, which they recolonise in the early rains.

Fly concentration appears to be associated with saturation deficits (S.D.) reaching 7 mb. or over in the savannah, whereas dispersal is associated with an S.D. dropping to 6 mb. or below. When the mean monthly temperature is compared with the mean fly densities in that and the succeeding month, the value associated with the greatest density is about 77°F. The optimum saturation deficit, similarly judged, is 4–5 mb.; values below 2 or above 7 mb. appear to be relatively unfavourable. These observations suggest that laboratory cultures of G. longipalpis should be kept at 77°F. and 85 per cent, relative humidity.

Fly catches are at a minimum in the early rains (April). They then increase rapidly, level off in the mid-rains, and increase again rapidly to reach their peak in the early dry season (November). The decrease in catches during the dry season represents the adverse effect of high temperature and low humidity on the population, but the continuing decrease during the early rains is believed to represent the effect of fly dispersal, and not a further decrease in population.

In general, catches from the ox fly-round showed the same seasonal fluctuations in fly population as those from the man fly-round, although female flies constituted 39 per cent, of the total catch from the former and only 1·9 per cent, of the total from the latter. The catch is larger from an ox, which attracts more hungry flies (7·9 per cent, of all those caught, against 2·7 per cent, on man). The catches from the ox are higher, in relation to those from man, in the conventional feeding grounds, such as transition forest and woodland savannah, than in the permanent habitat. The proportion of hungry flies amongst non-teneral males caught from man is a maximum in the late dry season and early rains, after the grass fires; good visibility then facilitates hunting activity by man, and the consequent disturbance of the game may cause the fly to lose touch with its hosts. Conversely, flies are least hungry in the early dry season, by which time they have established intimate contact with the game, whose movement, like that of man, is limited by dense elephant grass, 10–15 ft. high.

Precipitin tests on 44 blood-meals, collected over a long period from gorged examples of G. longipalpis, suggest that bushbuck (Tragelaphus scriptus) provides the bulk of the meals, but that the red river hog (Potamochoerus porcus) is also of importance. Of 4,360 males of G. longipalpis dissected, 939 (21·5 per cent.) showed mature infections of trypanosomes (768 of Trypanosoma vivax group, 170 of T. congolense group, and one of T. brucei group, comprising 81·8, 18·1 and 0·1 per cent., respectively, of the infections).

Pupae of G. longipalpis were found under logs in the forest island, together with pupae of G. medicorum Aust., G. fusca (Wlk.) and G. palpalis (R.-D.). The pupae could be found throughout the dry season and early rains, but not during the heavy rains, when the soil is sticky.

It is suggested that since G. longipalpis becomes concentrated in islands and riverine strips of forest when the mean monthly saturation deficit exceeds 7 mb., It might be eradicated by partial clearing of such habitats, except towards the southern, humid limit of its range, where rapid regeneration of the vegetation would make maintenance too costly.

A population of Glossina palpalis (R.-D.) was studied for three years, between February 1954 and January 1957, at Ugbobigha, on the northern edge of the main rain-forest belt of southern Nigeria. A fly-round was laid out along the banks of a forested stream, running northwards from the forest belt into the savannah woodland, and was divided into four sections representing farmland, wide fringing forest, narrow fringing forest, and the edge of forest.

No major seasonal movements of the fly population from one section to another could be detected; it was found that open farmland and the edge of forest with good visibility always yielded the highest catches, whereas catches inside dense forest were always low. Data from other sources showed that at all seasons of the year G. palpalis may be found in small numbers throughout the savannah woodland, even in the absence of water. This species also occurs in very small numbers within the main forest belt, and in village clearings lying within this belt.

Apart from an increase in the second and third months of the rains (March–April) and a fall during the fourth and fifth months, the population tends to remain steady at a low level throughout the year. The increase in population is associated with a mean temperature of 79–80°F. (26·1–26·7°C.) and an average saturation deficit of 5·5 mb. These figures agree closely with those found to be optimal for G. palpalis by other workers. The decrease in population is associated with a falling temperature, but more especially with a mean saturation deficit that has dropped below 3 mb. These results agree closely with those found near the northern limit of the range of the species in Nigeria. The favourable period for increase during the wet season lasts for four months in northern Nigeria, but only two at Ugbobigha: this is believed to account for the much lower fly density found in the humid south.

Dissections of females showed no seasonal trend in the proportion that were pregnant, nor any cessation of breeding in the heavy rains (August–September). Of 3,130 flies caught, 45·5 per cent, were females, and of the 1,040 females dissected, only 3·6 per cent, were found to be virgin; in northern Nigeria, the comparable figures were 49·1 and 4·0 per cent., respectively. At Ugbobigha, there is no seasonal trend in the percentage of females amongst flies appearing to man. Among the non-teneral males caught, the mean monthly proportion that was hungry ranged from 8 to 22 per cent., but showed no seasonal trend, whereas comparable figures from northern Nigeria ranged from 24 to 43 per cent.; this suggests that G. palpalis requires food less often in the humid conditions of Ugbobigha, or possibly that game is more numerous.

Of 1,635 examples of G. palpalis dissected, 2·1 per cent, were found to have mature infections of trypanosomes; of the latter, about two-thirds belonged to the Trypanosoma vivax group and about one-third to the T. congolense group. There was no difference in the infection rates of males and females.

Very few pupae were found, owing to the low fly population and the extensiveness of the breeding sites under the equable climatic conditions. The temperature of the pupal environment is considerably higher here than in northern Nigeria.

The diurnal rhythm of activity of G. palpalis was investigated both in the dry season and the wet. In both, activity increases steadily between 7 and 10.30 a.m., as the temperature rises, and falls steadily between 3.30 p.m. and dusk; peak activity occurs at various times between noon and 3.30 p.m. The numbers caught before 11 a.m., expressed as a percentage of the day's catch, increases at seasons when the temperature is higher. The flies are equally active in overcast weather and full sunshine, but rain reduces activity by more than a half.

Observations were made on Glossina tabaniformis Westw., G. fusca (Wlk.), G. nigrofusca Newst. and G. medicorum Aust., which all occur near the field station of the West African Institute for Trypanosomiasis Research at Ugbobigha in southern Nigeria. Identification of these species by the use of external characters has not been found possible between the females of G. tabaniformis and G. fusca, but is fairly simple between males of these two species and between both sexes of G. nigrofusca and G. medicorum. A simple key, based on external characters, is given. When necessary, females of G. tabaniformis and G. fusca were separated by dissection. G. tabaniformis, G. fusca and G. nigrofusca usually rest in a vertical position, with the head downwards, at a height of 4–6 ft. above ground (possibly lower for G. nigrofusca), on tree trunks, climber stems, etc., having a diameter of 5 in. or less.

A fly-round was started using a Zebu bull as bait. G. tabaniformis and G. fusca were caught in good numbers, G. tabaniformis forming 83 per cent. of the catch. There appears to be a decrease in population in the late dry season (January and February) in both these species. Females comprised 56 per cent. of the total catch of G. tabaniformis and 47 per cent. of that of G. fusca.

The vegetation of the fly-round, which is typical secondary rain-forest as found in southern Nigeria, was analysed; both G. tabaniformis and G. fusca prefer old forest with an absence of a lower stratum, beneath a continuous middle stratum and good upper stratum, that is to say, where visibility beneath the trees is good. G. nigrofusca comprised only 1·1 per cent. of the catch on the fly-round, although at first it was believed to be common in the area. G. medicorum does not inhabit the main forest belt, but is confined to riverine vegetation and forest islands in savannah.

G. tabaniformis is unlikely to be of economic importance, since the rate of infection with trypanosomes is low (3·7%) and this fly is confined to the forest. G. fusca and G. medicorum are both of economic importance, since their infection rates are high (14·9 and 15·4%, respectively) and they travel out into the savannah grassland. G. nigrofusca has a yet higher infection rate (26·7%), but it is confined to the forest at Ugbobigha; where, as in Ghana, it frequents the savannah, it is potentially dangerous. Females of G. tabaniformis and G. fusca are more heavily infected than males.

Females of G. tabaniformis were examined (by dissection) for pregnancy; 82 per cent. of the females were pregnant and 4·3 per cent. unfertilised. No seasonal fluctuations in the rate were apparent.