This part of the study of the garden chafer, Phyllopertha horticola (L.), in the English Lake District covers the flight seasons 1948–1952. Annual sex ratios in the population of pupae (just before ecdysis to adult) ranged from 34·6 to 46·9 per cent. females.

The flight season begins with the emergence of some adult males upon the sward. If the weather continues favourable, the earliest females appear on the second or third day of the season. Unsuitable weather delayed the advent of females until the sixth day in two seasons. In a homogeneous population, primary emergence is complete in just under a fortnight, at the end of which time numbers of beetles seen on the grass sward are at their peak. Phase 1, swarming over the sward, continues, with dwindling numbers, for just over a week more (overlapping Phase 2, swarming on the bracken).

The female/male ratio rises throughout Phase 1 except for a tendency to fall in the last day or two. But generally for most and sometimes the whole of Phase 1, the proportion of females above ground is far below the true population ratio. This is partly because population emergence in the female is 1–2 days behind emergence in the male; but much more because after primary emergence the male is fully involved in above-ground activity every day until the beginning of Phase 2 or end of Phase 1 (depending on whether he emerges earlier or later), while the female is not.

In the same way, there are no females present on the bracken until after the first day of Phase 2, but the proportion of females rises more quickly and to a higher level than in Phase 1. By the middle of Phase 2, the proportion is close to the true population ratio. Since males are now confined to the bracken, this means that mass oviposition is more or less complete. During the last week of the season the female proportion rises steeply. This is because females live a few days longer than males besides being 1–2 days behind males in their original emergence.

After primary emergence, the average female lives about a fortnight, the male rather less. Approximately the first half of adult life is spent in the grass sward area, the second half on the surrounding bracken (or hedges or trees).

As Phase 1 proceeds, the pairing rate of females decreases. This is partly because the proportion of males is falling and therefore fewer males are available to search for each female over the grass sward, and partly because of a change in mating behaviour of the female as she ages. On the other hand, pairing rate is at its highest (average 82%, maximum 95%, of available females) in Phase 2 when the proportion of males is at its minimum (actually the true proportion in the population). This is because on the bracken the beetles are confined to a much smaller area than on the grass and therefore males find females more readily.

In flying weather, the proportion of beetles in the air at any moment is at best no more than about 70 per cent.; usually it is less than 50 per cent. On the whole males are very much more given to flying than females.

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.

Since the sharply defined biting cycle shown by outdoor populations, in Uganda, of Aëdes aegypti (L.), which closely resembles oviposition and general activity rhythms, could not be reconciled with the ill-defined patterns found in domestic populations, on the Kenya coast, in the absence of knowledge of the composition of the population involved there, 24-hour baited catches were made at Ganda on the Kenya coast, and the abdominal colour pattern of each individual was noted. In the series there was gradation from the darkest to the palest.

Of 427 females taken biting, 82·1 per cent, were of var. queenslandensis (Theo.) in the generally accepted sense, 14·5 per cent, of the type form and 0·9 per cent, of subsp. formosus (Wlk.). The material of var. queenslandensis was further divided into two groups in which the lateral spots on the abdominal tergites were of silver and matt white scales, respectively.

Very similar biting cycles, with the main peak in the hour before sunset, occurred both inside a hut and within an adjacent compound, although catches were not concurrent and were made under different seasonal conditions.

The distribution of the various colour forms in the total catch was independent of the hour of capture.

There is a resemblance between these cycles and those reported in comparable situations in Nigeria, where, with the exception of the paler forms, the population of A. aegypti is similar to that at Ganda. It is concluded that the main biting peak is shortly before sunset. Subsidiary peaks, when present, occur with increasing intensity as the day progresses.

The relationship of biting activity to other aspects of general activity is discussed, and it is concluded that several aspects require further investigation.

The following hypothesis is offered to account for the various patterns of biting cycle observed in different situations. It is suggested that A. aegypti possesses an endogenous multi-peaked diel rhythm of activity. Activity impulses occur in a cycle of waves of increasing intensity from dawn onwards, reaching a maximum at the end of the daylight period, and a biting peak will result when such an impulse coincides with environmental conditions within the range between upper and lower thresholds of activity.

The identification of spider beetles found in storage premises, especially of species of Ptinus s.l. and Mezium has frequently been incorrect. The inadequacy of the present descriptions of genera and subgenera of spider beetles is pointed out. Grouping of the storage species by adult and larval characters corresponds well. The recorded world distribution of species is shown in a Table.

Species of spider beetle considered to be native to Britain are Ptinus lichenum Marsham, P. palliatus Perris and P. subpilosus Sturm, which are not found in storage premises, and P. fur (L.), P. sexpunctatus Panz. and Tipnus unicolor (Pill. & Mitt.), which may be found in warehouses. Eight species and a gyno-genetic form have been imported into Britain and have succeeded in becoming established, Mezium affine Boield., Gibbium psylloides (Czenp.) and Niptus hololeucus (Fald.), early in the nineteenth century, Ptinus clavipes Panz. and also its triploid form mobilis Moore (= P. latro, auct.) later in the nineteenth century, Ptinus tectus Boield., Trigonogenius globulus Sol. and Ptinus pusillus Sturm about the turn of the century, and finally Pseudeurostus hilleri (Rttr.) about 20 years ago. The status and distribution of each species is discussed. Only Ptinus tectus is a widespread pest in Britain.

The wide variety of food suitable for scavenging species which will utilise substances of both animal and vegetable origin is stressed. Spider beetles are especially attracted to moisture and excrement and as a result will occur in the protected nests of other species of animal. Published records of associations of spider beetles with nests are summarised in a Table. Animal droppings and dead insects enable spider beetles to grow rapidly. Wool, hair and feathers, textile fabrics, old wood and a number of apparently non-nutritive substances are damaged by spider beetle larvae which seem to be able to grow on some of these substances.

Damage caused by spider beetles is mainly indirect, contamination due to frass, silk and fragments of dead insects, the boring of holes in containers and spinning of cocoons on the containers. Actual loss of weight due to feeding is small unless the beetle population is enormous.

A large proportion of the adult spider-beetle population of a warehouse inhabits cracks in the floors or walls and spreads from there to the peripheral part of stacks of produce where eggs are laid, producing a superficial infestation. Adult spider beetles are chiefly active at night. Parasites and predators recorded as attacking spider beetles are listed, and methods of culturing species are described.

Spider beetles usually have three larval instars, but adverse conditions may increase their number. The total developmental period is long compared with other families of warehouse beetles. Most spider beetles have a normal life-cycle but some species of Ptinus have a facultative larval diapause and an adult dormant period preceding emergence from the cocoon. The diapause and dormancy enable adults of these species to emerge in the autumn regardless of the weather during the previous season. Adults live from 6 to 15 months. At constant temperature, eggs are laid at a steady rate, the number being laid varying from under 50 in some species of Ptinus to nearly 1,000 in P. tectus.

The influences of temperature, humidity, food, population density and of diapause and dormancy on the rate of increase of spider-beetle species is discussed. The most rapid increase possible for these species in Britain is doubling in three weeks by P. tectus. It is concluded that P. tectus is unlikely to be superseded as the most important spider beetle of cool temperate areas and that, elsewhere, spider beetles will not attain the importance of this species.

Grouping the species on their biological features corresponds with the taxonomic relationships of the family.

A study has been made of the rate of oviposition, on parboiled milled rice, of the small strain of the rice weevil, Calandra oryzae (L.), under normal laboratory conditions of temperature and relative humidity (means 27°C., 80% R.H.) in Sierra Leone, and of the utilisation of grains for oviposition.

On the average, a female laid 68 eggs in all, over an oviposition period of 71 days, the peak of egg-laying being reached during the third week. Only 13 per cent, of grains were utilised. Differences between the results obtained and those recorded by previous workers are discussed.

The mean length of life of male and female weevils was found to be 113 and 97 days, respectively.

During the winter months, when larval populations of shoot flies (Diptera, Acalypterae) are relatively static, pure clumps of grasses in southern England were sampled. The tillers were dissected and the shoot-fly larvae removed and identified to determine what species were present and how and in what numbers they were distributed within the species of grasses. Concurrently, a permanent pasture was sampled in which the grasses were closely intermixed, and it was found in the two cases that the same host preferences of the insects were broadly maintained. Those preferences are due to the selectivity of the ovipositing female rather than the dietary requirements of the larvae, which are facultative parasites of most grasses and cereals.

A Table is given of the relative abundance of the larvae of 17 species in 16 different grasses and indicates the degree of host specificity of each insect. For example, Oscinella frit (L.), the frit fly of oats, is found in 11 of the common grasses but not in Dactylis glomerata whereas O. albiseta, (Mg.) is found only in this grass.

Horizontal migration of larvae from tiller to tiller can take place; vertical migration may also take place from ploughed-in grasses to cereals sown above. It is shown that migration is mainly limited to autumn and spring when soil temperatures are above the thermal threshold of activity of the larvae.

An experimental laboratory study of the deposition of droplets on dead house-flies (Musca domestica L.) was made, using a spinning-top sprayer to produce a spray of uniformly sized oil droplets and a cascade impactor to measure the concentration of the spray of droplets, which were dyed. The deposits obtained on a dead house-fly and a cascade-impactor slide when these were exposed in turn to a wind of 1 m. per sec. in a wind tunnel were compared colorimetrically, and determinations thus made of the collection efficiency of the flies, defined as the volume of liquid deposited on an object expressed as a percentage of the volume that would have passed through the same cross-section as the object had that not been there.

The measured collecting efficiency of a fly varied from about 70 per cent. (droplet dia. 27μ) to about 200 per cent. (droplet dia. 75μ), and was approximately twice that of a sphere with a cross-sectional area twice the projected frontal area of the fly. From theoretical calculations of the filtering effect of different elements of the vegetation, it is concluded that the optimum droplet diameter for deposition on flies in woodland is 20–40μ.

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 were made on the red locust, Nomadacris septemfasciata (Serv.), between October 1957 and February 1958 in an area of grassland, six miles long by one mile wide, marked out by beacons and divided lengthwise by a line of beacons down the centre, in the Rukwa Valley of south-west Tanganyika.

One half of the plot had been burnt off completely in the latter part of the dry season; the other half was unburnt and carried in part a four-year accumulation of growth and in part an area of standing grass that had regenerated after a damaging fire during the previous wet season and then, for the most part, flooded. Vegetation profiles were made along the whole length of the plot, and rain gauges, soil thermometers and soil tensiometers were installed at regular intervals along the three lines of beacons. Assessments of the population and distribution of adult locusts within the plot were made from Land-Rover or on foot in mid-October, mid-December (ten days after the onset of the rains) and early in January. A systematic search was made for egg-pods, starting at the end of December, along furrows ploughed down the middle of each of a number of narrow strips mown in the grass in sets near each beacon and sampling equally the burnt and unburnt halves of the plot. The first hoppers were seen on 3rd January, and assessments of hopper populations were carried out four times during January.

The primary object of the work was to study the effect on choice of oviposition site and on incubation success of the type and condition of the grassland (whether burnt during the previous dry season, at an earlier date, or left unburnt) and its possible bearing on control of the species in an outbreak area. Data were also obtained on the conditions of air temperature, soil moisture, soil temperature and rainfall in which eggs are laid and incubated; and the effect of variations in these factors on oviposition and on incubation success was examined.

It was observed that, in the hot, dry conditions of mid-October, adult locusts were completely absent, from the recently burnt-over ground, and were found almost exclusively in that part of the standing grass that had suffered a wet-season burn. By mid-December, the locusts had spread out from the unburnt into the burnt-over zone, where the grass had put out fresh growth, but many were still to be found hi the former, with a concentration along the line of contact with the latter. By early January, the size of the population had been greatly reduced and it was evenly distributed over the whole plot.

The distribution of egg-pods snowed that the locusts had laid almost exclusively in the burnt-over zone, about 50 per cent. being found within 0·1 mile of the line of contact with the unburnt zone.

The hoppers were likewise almost exclusively confined to the burnt-over zone, and with numbers significantly higher in the ¼-mile band next to the contact line than in the band at ¼–½ mile from it. The numbers of hoppers in the unburnt grass was significantly lower than might have been expected from the results of the egg-pod survey, suggesting that survival was lower there than under fresh grass following a dry-season fire. A subsidiary experiment, in which adult locusts were confined in cages placed on the lately burnt-over zone, the early-burnt and unburnt areas, respectively, suggested that, where there was no choice of oviposition site, the greatest number of surviving egg-pods occurred in the first zone, almost as many in the second and about half as many in the third.

During the incubation period, the soil under the unburnt grass was significantly colder, and tended to be moister, to moisten more slowly and to dry out less rapidly than that which had been burnt over. No significant correlation was found between incubation success in the burnt-over zone and total rainfall, mean recorded soil temperature or soil moisture.

It is concluded that, since these observations show that, for oviposition, adults of N. fasciata exhibit a very significant preference for ground that has been burnt over in the previous dry season, the burning of selected strips should lead to the concentration of oviposition and, consequently, of hoppers, thus making chemical control of the latter easier and cheaper.

There was some evidence, also, that when locusts could not move to bare ground, either oviposition or egg-pod survival (or both) were least successful where the grass cover was thickest.

Several collections of pupae and adults of Simuliid Diptera were made in British Honduras between 9th January and 18th February 1958. Samples were collected in the Mountain Pine Ridge and El Cayo areas in the west, and along the highway traversing the eastern part of the country between Caves Branch and Stann Creek.

Thirteen species of Simulium were found, nine of which are named, including S. quadrivittatum Lw. and S. metallicum Bellardi which are very annoying biters. A, few observations on distribution and habits are recorded.

Of the two anthropophilic species of Simulium found, one is known to be a vector of onchocerciasis, if only of secondary importance, and the capability of the other to transmit the disease is unknown. The disease has apparently never been established in British Honduras and is present in Guatemala. The risk of infection to settlers moving into territory near Guatemala cannot be assessed without detailed knowledge of the epidemiology of the disease in Central America.

This paper presents further observations on the continued persistence of larvicidal treatments applied to small plots (10 yd. × 10 yd.) on Soutra Hill, Midlothian, to control larvae of the biting midge, Culicoides impunctatus Goetgh. Before doing so, consideration is given to the nature of the observed fluctuations in larval population encountered in the untreated plots. Evidence is produced which indicates that this is not due either to delayed hatching of eggs (this, if it occurs, is of minor importance), to change in technique or to the application of insecticide to neighbouring plots, but is due to the larvae responding to an oscillating factor (or factors) in the breeding site. It is suggested that one such factor might be soil water level. Therefore, it follows that changes in the untreated larval population must be taken into account when assessing the degree of control achieved by treatments, especially when the larval population is declining.

As regards insecticidal persistence three years after application: —

(i) Nine of the eleven DDT treatments (wettable powder, water-miscible concentrate and dust at 12, 50 and 200 mg. p,p′DDT/sq. ft.) gave 100 per cent. control. The other two (both wettable powder at 12 mg./sq. ft.) produced 75 and 22 per cent. reduction.

(ii) Only one of seven γ BHC treatments (wettable powder at 50 mg. γ BHC/sq. ft.) gave complete control and one treatment (w.p. 12 mg./ sq. ft.) was completely ineffective.

(iii) DDT retained its superiority to γ BHC as a larvicide against Culicoides, achieving 93 per cent. control compared with 55 per cent. for γ BHC.

(iv) The lowest dosages of dieldrin (3 mg./sq. ft.) and chlordane (6 mg./ sq. ft.) had begun to lose their larvicidal power, control declining from 76 to 53 per cent. and 67 to 29 per cent., respectively. There was no change at 6 mg. dieldrin/sq. ft. but the other treatments (12 and 25 mg. dieldrin and 12, 25 and 50 mg. chlordane/sq. ft.) had improved. Dieldrin at 12 and 25 mg./sq. ft. and chlordane at 50 mg./sq. ft. attained complete control.

The spray-volume treatments, now in their second year, showed an increase in activity. This was most marked in the wettable-powder treatments at 25 mg. p.p′DDT/sq. ft. which a year ago were completely ineffective and now five out of six trials gave complete control and the other 97 per cent. Improvement in the treatments at 50 mg./sq. ft. was less (from 43 to 83%) due in the main to the complete failure of one treatment (10 gal./acre).

It is confirmed that spray volume in itself is unimportant in larvicidal applications providing the coverage is adequate.

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.

The term drift spraying denotes a method of applying an insecticidal spray whereby it is released at a height above the ground and allowed to drift with the wind while it gradually sinks; if the source of emission is moved in a line across the direction of the wind, insecticide will be deposited at a distance downwind of that line. The method has been used for vegetation baiting, a term meaning the application of stomach poisons to natural vegetation for control of locusts; this may be more economical than the application of contact insecticides to the insect itself.

Spray particles emitted from a point source have a mean trajectory downwind inclined to the horizontal at an angle of tan−1 (f/V), where f is their terminal velocity and V the windspeed, and they are dispersed by wind eddies to all sides of this mean axis so as to form a conical plume; if the source is moved across the wind, horizontal dispersion normal to the wind tends to cancel out and only the vertical component of the dispersion need be considered. The concentration of spray drops is a maximum on the plume axis and decreases with distance from it. The spray cloud from such a source thus occupies a wedge-shaped space as it drifts downwind, and it reaches the ground over a band whose width depends on the height of the source and the degree of dispersion. The point at which the plume axis strikes the ground is determined by its declination and by the height of the source; the density of the spray deposit, whose overall value is determined by width of the band sprayed and by the quantity of spray emitted from the source per unit distance travelled across wind, is a maximum upwind from this point and diminishes more steeply towards the upwind edge of the band than towards the downwind one.

Large drops will fall faster and hence be deposited nearer the line of emission than will small drops, but in practice, in day-time, the effects of dispersion by wind eddy tend to exceed and mask those due to the range of drop size and it is thus a valid simplification to consider the spray cloud as composed of drops all of one size. The behaviour of heterogeneous sprays is best characterised by the assumption that all drops are of a diameter equal to the surface-volume mean diameter. At moderate wind speeds, the drop diameter used should be of the order of 100μ, and an oil of low vapour pressure is needed if the tendency of such small drops to evaporate before reaching the target is to be prevented.

The angle of dispersion probably depends on the degree of wind turbulence. Experimental measurements of the concentration of drops within a spray plume, relative to that on the axis and at different angular deviations from the latter, enable the fraction within each sectpr to be known, and suggest that for normal atmospheric conditions, when the lapse rate is adiabatic, 95 per cent. of the spray is contained within ± 7° of the plume axis in the vertical plane.

The calculated densities of deposits on a horizontal surface at varying distances downwind, related to a source whose height and rate of emission are unity, are shown as graphs for different values of the declination of the plume axis (predictable from the wind speed and drop size) and are compared with experimental measurements. Using these data, the conditions that will afford any desired deposit density can be selected. Since the interest of drift spraying for locust control lies mainly in the deposits on the nearly vertical stems of grass, similar data are given for values of the deposit density on an exposed vertical surface, which can be shown to be n times that on a horizontal one at the same distance downwind, when the latter is expressed as a multiple, n, of the source height.

Previous work on strains of Amphorophora rubi (Kalt.) is discussed and evidence is presented to show that the form on European raspberry can be divided into three strains. These are designated European raspberry strain 1, 2 and 3. The distribution, abundance and importance of the strains in relation to plant breeding for resistance to A. rubi is discussed.

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.

Walnuts grown and shelled in the Dordogne and adjacent regions of France are exported to Britain and other countries. The inspection of cargoes arriving at Liverpool between July 1955 and July 1958 has shown that they may frequently be infested by a number of species of insect pests. Of the 20 species recorded, six occurred regularly. These were Oryzaephilus surinamensis (L.), Aphomia gularis (Zell.), Plodia interpunctella (Hb.), Cryptophagus subfumatus Kraatz, Nemapogon granella (L.) and Enarmonia sp. During that period, changes occurred in the levels of infestation on parcels and the relative abundance of the species. In particular, there was a considerable increase in the occurrence of O. surinamensis. Though the general levels of infestation were light, parts of 58 per cent, of the cargoes had to be fumigated to prevent pests being distributed to factories, bakeries and shops in Britain and on transhipped parcels to Canada, U.S.A. and the Eepublic of Ireland. Though many of the species found are already established in those countries where conditions are suitable for their development some are still limited in their distribution. These include A. gularis, a serious pest of nuts, dried fruit and cereals. If the further spread of this and the other pests is to be prevented there is need for a more general application of control measures in the country of origin with strict control and possibly fumigation of cargoes before shipment.

Studies of the physical and biological factors involved in the application of concentrated involatile oil solutions of a persistent insecticide (dieldrin) in the form of a fine spray to the low-density vegetation typical of the breeding areas of the desert locust, Schistocerca gregaria (Forsk.), have led to a technique of control of the locust hoppers with a dosage as low as 0·30 litres per hectare (approximately ⅕ pint per acre). A simple device for producing such a spray has been designed to work off the exhaust system of a light four-wheel-drive motor vehicle. Successful control of hoppers has been obtained under a wide variety of weather conditions in both desert and bush typical of locust breeding areas, using ‘target’ and ‘barrier’ spraying techniques. Both techniques involve the spraying of vegetation which it is judged will be subsequently eaten by the hoppers, but target spraying is done on or near a known hopper band, whereas barrier spraying is done, not necessarily in sight of hoppers, across an area known to be highly infested. Examples of such successful attacks are described from the Eritrean coast, Tripolitania and Ethiopia. The methods can replace the well established technique of poison-baiting individual bands, and have the additional advantage of producing highly persistent toxic swathes which can be exploited by the barrier technique for treating locust egg-fields and for creating widely spaced barriers for the control of extensive infestations.

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.

The Pentatomid bug, Scotinophara lurida (Burm.), is a serious pest of the rice crop in certain areas of Ceylon. Five or six generations develop on the two annual rice crops, and that which attains the adult stage at the time of harvest of either crop ‘aestivates’ and does not become sexually mature until later. The generations that become adult earlier in each crop season become sexually mature forthwith, and mate and oviposit.

In 1952, laboratory experiments to ascertain the susceptibility of adults of S. lurida to a range of modern organic insecticides, and field experiments on insecticidal control, were initiated. The insecticides tested were DDT, BHC, endrin, dieldrin, malathion, Chlorthion, Guthion, Dipterex, diazinon and parathion.

In the laboratory, freshly emerged, sexually mature and aestivating bugs were tested separately by topical application on the abdomen, and it was found that the insecticides could be arranged in the following descending order of toxicity, based on the LD50, against the sexually mature adult:— γ BHC, endrin, dieldrin, parathion, Dipterex, Chlorthion, diazinon, Guthion, malathion, DDT. The adults of the aestivating generations, at least prior to becoming sexually mature, were markedly more resistant to all the insecticides tested than were sexually mature bugs of uninterrupted development, the resistance ranging from two-fold to nineteen-fold that of the latter.

There is some indication that tolerance to every insecticide does not necessarily increase with increasing age and sexual maturity of the normal adult bug. Thus, whereas with the organophosphorus insecticides increasing sexual maturity is associated with an increase in tolerance, with DDT and endrin the bugs appear to become more susceptible with increasing sexual maturity, while with γ BHC and dieldrin there is little change.

The chlorinated hydrocarbon insecticides DDT, toxaphene, chlordane, aldrin, dieldrin, endrin, isodrin and γ BHC and the organophosphorus insecticides malathion, diazinon, Dipterex, Chlorthion, Guthion and parathion have been tested as emulsion sprays against S. lurida in the field. DDT and toxaphene gave the poorest results with about 85 per cent, control of the pest in 24 hours when applied at and above a concentration of 0·045 per cent, active ingredient. The other insecticides are arranged thus in descending order of efficacy against the pest considering the minimum dosage required to give 100 per cent, or near 100 per cent, control within 24 hours of application of the treatment: —parathion 0·02 per cent.→ endrin 0·03 per cent. = Chlorthion 0·03 per cent.→ Dipterex 0·03–0·04 per cent.=Guthion 0·02 per cent.→ dieldrin 0·06 per cent.= malathion 0·06 per cent.= γ BHC 0·06 per cent. → diazinon 0·07 per cent. Aldrin and isodrin were of about equal effectiveness giving about 90 per cent, control of the pest within 24 hours when applied at a concentration of 0·06 per cent, active ingredient.

Of the dusts tested, both γ BHC at 1·3 per cent, and dieldrin at 2·5 per cent, gave 100 per cent, control of the pest in 24 hours when applied under still and dewy conditions obtaining in the morning. Under dry, windy conditions however, γ BHC at 1·3 per cent, and 3 per cent, gave better control of the pest than did dieldrin or aldrin dusts.

Parathion, dieldrin, endrin, Metasystox and Ekatin were tested for residual action against S. lurida on the rice crop. Parathion was the most effective residually for a period of two days with dieldrin coming next in order of residual effectiveness.

Metasystox and Ekatin were tested for their systemic action against S. lurida on three-week-old and ten-week-old rice plants as foliar sprays and as root treatments. Systemic action of a low order of effectiveness against the pest was demonstrated in all cases but the poor results achieved and the high rates of application involved did not warrant their consideration for practical field use.

One exceptional instance of a mycosis, with epidemic character, in white grubs has been studied in Southern Rhodesia.

The hosts were the larvae of Anomala exitialis Pér. and Schizonycha profuga Pér., which are tobacco pests, the entomophagous fungi being Torrubiella sp. (most prevalent), Beauveria bassiana (Bals.) Vuill. and Metarrhizium anisopliae (Metsch.) Sorokin.

Soil with an abnormally high content of nitrogenous organic matter favours the breeding of the two insects but at the same time provides a suitable medium for the survival and development of a high degree of virulence in the cryptogamic pathogens.