The limitations of the use of apparent density in estimating trypanosomechallenge are discussed, and it is concluded that such estimates should be based on the feeding portion of the tsetse population, its activity in relation to a given host, the total period of feeding activity (or parts thereof) as the unit of time, and the trypanosome infection rate.

A method of investigating the diurnal feeding activity of Glossina pallidipes Aust. in the late dry season at Eekomitjie, in the Zambezi Valley in Southern Rhodesia, is described. A black ox was tethered daily under a large tree from before dawn until after dusk. Only flies that engorged on the ox were caught; the time of capture and sex of each fly was recorded, and the fly then marked and released. Catches were made on 15 separate but not consecutive days between 21 October and 30 November, 1959.

Diurnal activity extended from 0445 to 1845 hr., there being a small earlymorning peak, reduced activity over the midday period, and a comparatively large evening peak. Climatic factors were recorded but no conclusions could be drawn about their separate effects on activity.

The distribution and biology of two related species of mosquito, Mansonia (Mansonioides) africana (Theo.) and M. (M.) uniformis (Theo.), have been compared. M. uniformis is found from China to Africa, whereas M. africana is restricted to the continent of Africa. The two species do not interbreed although mating, but no insemination, is possible in the laboratory. Strains of M. uniformis from Africa, Ceylon and Malaya are interfertile, but crosses between the African and the other strains, especially, showed a reduction in fertility of the eggs produced and thus some evidence of speciation.

The two species show the same adult behaviour at mating, feeding (both in the field and in the laboratory) and during oviposition. Both species are stenogamous and mate readily in small cages. The first blood-meal is taken approximately 24 hours after emergence and immediately after each oviposition, 3–5 days after the previous blood-meal. M. uniformis is more active directly after the blood-meal.

Because the lettuce root aphid, Pemphigus bursarius (L.), is gall-inhabiting on poplar in spring and lives underground on lettuce during summer, its naturalenemy complex differs from that associated with foliage-feeding aphids. It suffers little from parasites and only fundatrices have been found attacked. The only species reared from parasitised individuals was the Pteromalid, Pachyneuron sp., which is assumed to be hyperparasitic. When the galls open at migration time, Syrphid larvae and Anthocorids can enter and attack the contents. Anthocoris nemorum (L.) and A. nemoralis (F.) are the main predators at this stage. Before they begin feeding, they kill all the aphids within a gall extremely quickly and efficiently. It is suggested that the aphids may be killed by a secretion from the stink glands of the Anthocorids working as a fumigant within the confines of the gall. Several Staphylinids and Carabids are frequently associated with subterranean colonies of P. bursarius and are almost certainly predators. The larvae of the Chloropids, Thaumatomyia glabra (Mg.) and T. notata (Mg.), are common predators of P. bursarius in the soil. The sexuparae, both before they leave the lettuce plants and on their arrival on poplar, are attacked by three species of Coccinellid.

The life-cycle and immature stages of the Eulophid, Syntomosphyrum albiclavus Kerrich, a pupal parasite of tsetse flies (Glossina), are described. Measurements of the widths of the cephalic skeletons of larvae of all ages fell into four well separated groups, and confirmation that these represented the existence of four larval instars was given by Dyar's law, the application of which in this instance is not invalidated by the disproportionate length of the fourth instar or the effects of overcrowding, which do not become apparent before that stage.

A convenient and accurate measure of size is necessary for studies on the physiology of tsetse flies (Glossina). Residual dry weight (i.e., dry weight minus fat) is adequate as regards the larva, pupa and teneral fly, but cannot be used for flies that have taken their first blood-meals. A linear measurement provides an index of size that remains constant throughout the life of the fly, but the use of the length of the middle part of the fourth longitudinal vein in the wing has certain disadvantages, and a measure of surface was thought preferable. That finally adopted was a function of the dorsal thoracic surface; details of it are given and a close correlation was demonstrated between it and residual dry weight for females of G. morsitans Westw. bred in the laboratory from puparia maintained at 28°C.

The relation between this measure and the weight of the newly emerged fly is affected by the temperature at which the pupal stage is passed; above approximately 25°C. the surface area of flies of any given residual dry weight decreases quite sharply, so that puparia of a given weight produce smaller but relatively heavier flies at 30 than at 25°C. This holds good also for G. pallidipes Aust. and G. swynnertoni Aust. The dependence of surface area on the temperature at which development has taken place unavoidably complicates the use of this measurement in work on transpiration; it also limits the application of the theory that stresses acting on the pregnant fly may be gauged from the size of flies two months later, and suggests that where the mean temperature of pupal sites is likely to exceed 26°C, any inference should be based on puparial rather than adult size.

Anthores leuconotus Pasc., indigenous in East, South-East, South and South-West Africa, is an important ring-barking and wood-boring pest of the main stem and root of arabica coffee. The duration of the life-cycle ranges from 12 to 25 months, with most individuals requiring 16–20 months. Thus beetles developed from eggs laid during the long rains (April–June) of one year will mostly emerge during the short rains (Nov.–Jan.) of the following year, with some appearing during the rains preceding and others during the ensuing rains.

If the mean life-cycle is taken to be 18 months, the approximate duration of each stage is as follows:— eggs require 21–23 days for eclosion; larvae in the first five instars ring-bark the tree for 4 months, and those in the final two instars bore into the wood for 12 months; the pupal period lasts about 4½ weeks, and the beetle remains in the tree for a further two weeks before emerging.

In the course of a recent preliminary revision of the MIRIDAE of the subfamily BRYOCORINAE in the British Museum (Natural History), the results of which will be reported in a paper now in preparation, the genus Pseudodoniella China & Carvalho was examined. The investigation revealed that the two species, P. laensis and P. szentivanyi, both described by Miller in 1957, are definitely conspecific. Because of the importance of the species as a pest of cacao in New Guinea and Papua, a short note is published here in advance in order to clarify this problem and make available a name for biological work.

A population of Glossina swynnertoni Aust., at Shinyanga, Tanganyika, has been studied in respect of size and fat content of non-teneral males by monthly samples over a period of 13 years.

Flies are large from February to July and small from August to January, and this change in size suggests an effect of the wet season (December to May) and dry season (June to November) upon the parent females, allowing for the time-lag of two months representing pupal development and mean age of adult males at capture. Male flies have more fat in the rains and less in the dry season and it is possible that similar changes in the nutritional status of females are responsible for the observed size changes.

The correlation found in earlier work between the size of male flies in any month and saturation deficit two months earlier is confirmed, but reasons are given for rejecting a simple causal interpretation of this correlation.

Since 1951, there has been a progressive decrease in size of G. swynnertoni in the area studied, more especially as regards those produced in the dry season.

Basic laboratory investigations have been carried out on a method for giving house-flies, Musca domestica L., relatively large doses of insecticide, with a view to possible applications in controlling, or preventing the appearance of, resistant strains of flies. The principle is that a relatively large drop of mineral oil will hang on the lower end of a thin vertical or near-vertical wire (e.g., a drop of up to 3 μl. on a wire 0·3 mm. in diameter), and a fleeting contact of a fly with the drop will generally transfer to the surface of the fly a substantial volume of oil. For investigational purposes pins were inserted obliquely into rods (e.g., about 700 pins into a rod 60 cm. long), and drops of up to about 1 μl. were formed on the ends of the pins by dipping the pin-bearing rods into solutions of insecticide in oil. In a typical experiment a rod with suspended drops was hung vertically from the ceiling of a chamber into which flies were released; flies then collected doses of insecticide when attempting to alight on the rod.

An apparatus and technique are described for handling, immobilising by suction, and individually dosing house-flies, Musca domestica L. The apparatus consists of a suction platform connected to a vacuum cleaner, a specially designed cage and a measured-drop apparatus. The suction platform consists essentially of a circle of terylene gauze, on to which the flies are drawn from the cage and held by suction during treatment. The cage can be made to contract, so that the flies may be crowded together near the special emergence hole through which they are to be withdrawn. The technique avoids the use of cooling and anaesthetics, which affect the metabolism of the flies, and is therefore especially suitable for measuring knockdown, although it can equally be used to estimate toxicity. Some factors likely to influence the results are examined and discussed, and an example is given of two experiments with house-flies, to show that the method gives reproducible results.

The extent of pigmentation of the abdominal bands of Glossina pallidipes Aust. was studied in specimens emerging in the laboratory from puparia maintained at constant temperature and a range of relative humidities and derived from females collected in the field at Shinyanga, Tanganyika. An index of pigmentation was obtained by regarding the bands as consisting in all of 15 zones, each carrying a score of 1.

The index was closely dependent on the humidity experienced during pupal development, almost full pigmentation being produced in saturated air and almost complete suppression of it in dry air; it is inversely related to size and little affected in nearly saturated air by temperatures below 28°C. during pupal development, although still higher temperatures reduce it quite sharply.

In flies collected in the field throughout the year, most of those taken towards the end of the rains (March and April) fell into the darker pigment categories; as the dry season advanced the distribution tended to become bimodal, with the darker mode relatively steady at an index of about 12 and the paler mode moving progressively down the scale, reaching an index of about 5 in October and then disappearing. December and January collections (rainy season) were again unimodal, resembling those of March. It is suggested that these changes reflect the use of two types of larviposition site, the darker mode representing pupae from the evergreen thickets along the drainage lines and the lighter mode those from semi-deciduous thickets on the eluvial slopes, and that during the dry season the soil-space humidity in the latter sites may reach levels inimical to survival.

The depth to which larvae of G. pallidipes burrow appears to be related to the temperature, and perhaps the humidity, obtaining at the time of larviposition.

The possible effect of humidity on coloration was tested in four other species of tsetse fly, namely G. swynnertoni Aust., G. morsitans Westw., G. palpalis fuscipes Newst. and G. longipennis Corti. Only G. swynnertoni gave indications of some slight effect.

A survey of the parasites of aphids that occur on lettuce was made in two localities, in the Midlands and northern England, respectively, and a list of these parasites compiled.

A study was made of the Braconid parasite, Monoctonus paludum Marshall, in relation to its host, Nasonovia ribis-nigri (Mosley), on lettuce. Techniques for observing the parasite's behaviour towards various species of aphids are described and methods of conducting experiments on breeding success in species other than N. ribis-nigri are given.

Trials in East Africa (chiefly in Tanganyika) are described to show that the time taken for first-instar larvae of Busseola fusca (Fuller) to reach the more closely packed young leaves in the central axis of the maize plant is about ten days, and that insecticides are effective up to the end of this period. Results show that the best time for control is as near hatching of the eggs as possible, but with more persistent insecticides such as endrin, economic control is possible up to five days later.

A method of testing insecticides as residual deposits, by allowing first-instar larvae to walk on them, is given, and it was found that isodrin, DDT, endrin and γ BHC are highly effective as residual films. The MLD's for one minute in contact are 1·8 mg./sq.m. for isodrin, 4–7 mg. for DDT, 8·3 mg. for endrin and about 20 mg. for γ BHC. Derris emulsion has no residual effect after drying and is only effective in the liquid state after contact with larvae for several minutes.

In a series of field trials over three years, increases in yield of up to 2·6 times the control yields were shown to be possible, and averaged twice the control yield. Endrin was the most consistently effective insecticide, applied as a 2 per cent, dust and as a 0·03–0·04 per cent, emulsion spray. Two applications of endrin at an interval of two weeks were effective, but, for DDT, three applications of an emulsion containing 0·05 per cent. DDT at nine-day intervals were more effective than two while one may be of little value. An application of 2·5 oz./acre of DDT can be effective for 7–10 days, while 1·5 oz./acre of endrin can be effective for 14 days. In general, however, rates per application should not fall below 3·5 oz. DDT or 2 oz. endrin per acre, overall.

The superiority of a 5 per cent. DDT dust over one of 2·5 or 1 per cent, makes it more economical in a high-yielding, heavily attacked area. Diazinon and malathion in emulsion sprays are less persistent than DDT.

Trials with 4 per cent, malathion dust and 0·15 per cent, malathion emulsion spray were inconclusive on account of heavy damage by Spodoptera sp.

Attempts to increase the persistence of malathion and γ BHC by the addition of chlorinated terphenyl resins were also inconclusive, but DDT in emulsion, with resin, appeared more effective than DDT alone.

The economics of successful control measures at the prices obtaining at the time are discussed under the various trials.

Chemical estimations of the deposits of insecticides retained on the plants showed that between 1·4 and 3·7 per cent, of the quantity applied per unit area can be recovered in this way.

In a discussion of the significance of the results in control, it is suggested that spraying the stems only is half as effective as spraying the whole plant.

The conditions and results relating to two aerial spray trials are given.

The place of control of Busseola in agricultural practice is described, and some of the present results are quoted to show that yields can be increased by good farming practice as much as by control of Busseola.

Earlier work in Nyanza Province, Kenya, had led to the conclusion that riverine communities of Glossina palpalis fuscipes Newst. were permanently hungrier than lake-side communities. This was based on analysis of catches (percentage of teneral flies in the whole catch, and percentage of females among non-teneral flies) and on a behaviour criterion (percentage of non-teneral males caught on the party), but subsequent observations in the two types of habitat, in which a different area was used to represent the lake side, showed the lake-side flies to be slightly smaller than the riverine flies and not to differ in fat content, and a further investigation was accordingly made.

Puparia were collected on three dates between January and March 1958 and their surface area measured. A measure of the thoracic surface and fat content was taken of all adults emerging. Non-teneral flies were collected, for comparison, about two weeks later than the puparia.

In all samples, the riverine puparia were significantly larger than those from the lake side, and flies that emerged showed a comparable difference in size, but not in fat content corrected for size. Non-teneral riverine flies were slightly larger than lake-side ones but the difference was less than half that shown by the puparia and the teneral flies obtained from them. Evidence is adduced to show that this discrepancy is due to elimination of the lower size-groups in the lake-side community. Estimates of fat content of non-teneral flies support the conclusion that the lake-side community was under stress as compared with the riverine one, and analysis of available fly-round data from the lake side also suggests stress conditions.

The lake-side results are at variance with those from the site used in the earlier work. Available meteorological data show that the average temperature during February and March is 2°C. higher at the present site than at the former; such difference may directly cause the stresses that appear to be operating in the present instance.

The results suggest that the percentage of non-teneral males caught on the party has a real meaning in terms of nutritional status, and that it is also a very responsive indicator, but that the proportions of tenerals and of female nontenerals may not be simply related to the nutritional state as had hitherto been supposed.

In an area of sleeping sickness due to Trypanosoma rhodesiense in Uganda, Morris's ‘ animal ’ traps were used to study the activity and the relations with habitat and hosts of the vector, Glossina pallidipes Aust., a tsetse difficult to sample by conventional fly-round methods.

This type of trap was found to give samples both numerically greater and more truly representative of the tsetse population present than did either fly-boys or Chorley's bicycle screen.

Black traps showed an over-all superiority to brown traps, greatest during the rains and disappearing in the dry season, and this was related to the tsetse being attracted by the trap as representing a natural host.

A method is described for the large-scale rearing of Pseudotheraptus wayi Brown, the Coreid causing immature nutfall of coconuts in East Africa.

Adults were kept in cages with sides of thick white drill and wire-gauze, in an outdoor insectary at Matuga, near Mombasa, Kenya, and were provided with freshly collected fallen nutlets from which the bracts had been removed. Eggs were normally laid on the walls of the cage. The nutlets were replaced every two days, and all newly hatched nymphs removed and placed in other cages supplied with fresh nutlets every second day. There was some mortality in the first- and second-instar nymphs due to the handling entailed when nutlets were replaced, but in the later nymphal stages it was very low. Under these rearing conditions, the life-cycle from egg to adult was completed in from 35 to 40 days.

The toxicities to Pseudotheraptus of dieldrin, DDT, γ BHC, malathion and pyrethrins in a solvent were compared by topical application of measured-drop doses from an Agla micrometer syringe in a range of five concentrations (except for DDT, where eight concentrations were used). The mortality counts at 72 hr. were taken as the measure of toxicity.

Analysis of the log dosage/probit regression lines indicated that dieldrin was markedly more toxic than DDT to Pseudotheraptus, and that the toxicity to this insect of pyrethrins was of a very low order.

In a supplementary experiment to determine whether the addition of resin improved the toxicity of DDT when applied topically, batches of adults were treated with measured drops of a solution of p, p'DDT (0·5 per cent, for females, 0·25 per cent, for males) and others with the same concentrations of DDT to which coumarone indene resin at one-tenth of the DDT content had been added. The toxicity of the DDT was not enhanced.

Reasons for the large day-to-day variations in the numbers of nymphs and adults of the Coreid bug, Pseudotheraptus wayi Brown, taken in the crowns of coconut palms in Zanzibar by the searching technique over a period of six years were investigated in 1957–58. Data are given showing the results of searches (each occupying less than 20 minutes) carried out on two young palms at different times of day and night and in different weather conditions. For each successive 2-hour period between 6.0 a.m. and 2.0 p.m. (in the case of nymphs) or 4.0 p.m. (in the case of adults) the proportion of searches in which P. wayi was observed was significantly greater on dull days than on bright, sunny days, but there were no such differences that were significant in respect of any other 2-hour period for which comparisons could be made, except 4.0 to 6.0 p.m., when the proportion of searches disclosing nymphs was greater on bright days. During the hours of bright sunlight, the adults and nymphs hide in crevices and in the debris found in the leaf axils, but both remain in the open from dusk to dawn. During heavy rain they take shelter in dry crevices and niches.

It is pointed out that this behaviour must be taken into consideration if the searching technique is used to assess the result of an application of insecticide.

It has previously been shown that the sexual maturation of males of Scliistocerca grcgaria (Forsk.) is accelerated by crowding with other individuals of similar or greater age, and that the maturation of males kept in single pairs with older mature males is accelerated as compared with that of isolated males or males kept in single pairs with other young males or females of their own age. The effects of these groupings on the levels of feeding and excretion are investigated in the present work.

Crowded males ate and excreted more than isolated ones during the first ten days of adult life. Five males in a 9-litre cage are sufficient to induce almost the full effect of crowding, and marked effects are shown when only two males are present in such a cage.

After the second or third week, the level of feeding declines. This occurs earlier in early-maturing individuals, so that for a short period the crowded males eat little more or even less than the isolated ones. When the isolated males in their turn become mature their feeding again falls slightly below that of the crowded ones. When all males are isolated, there is a significant tendency for those males which eat least from the beginning of adult life and which increase their weight least to become mature earliest.

The proportion of the food utilised was not affected by density. It was higher during the early period of maximum consumption than it was after the level of feeding declined.

A general description of mass behaviour of the garden chafer, Phyllopertha horticola (L.), in the flight season was given earlier in this series (Milne, 1958). The outstanding features are two roughly equal and half-overlapping phases of activity: Phase 1, the swarming of the beetles over the grass sward, followed by Phase 2, the swarming on the surrounding bracken, hedges and trees. Investigation of sex proportions and mass reproductive state in the two phases permitted some deductions as to individual male and female behaviour (Milne, 1959a, b). In the present paper, further details of behaviour are given, and study of the flight season is concluded with a brief general discussion.

The black rice bug, Scotinophara lurida (Burm.), is widely distributed in Ceylon in areas where rice is grown under irrigation. It first became a serious pest in 1940 and, periodically since, it has assumed epidemic proportions in the Southern Province where two crops of rice are grown annually. Each crop takes from 3½ to 4 months to mature, the fields lying fallow in the intervening periods. During these periods the insects aestivate, in the adult or late nymphal stages, in cracks in the bunds in the rice-fields or on neighbouring higher ground. They remain motionless for the most part during aestivation, are gregarious and occur as much as 2 ft. below ground-level.

The adults leave the aestivation sites in April and May and settle in the first crop when it is two to three weeks old, and a subsequent aestivating population behaves similarly in November and December for. the second crop. There is at first considerable flight activity at dusk, and at night, and after feeding for about a week on the rice seedlings copulation takes place and oviposition commences about ten days later.