In an outdoor population of Aëdes (Stegomyia) aegypti (L.), mainly consisting of subsp. formosus (Wlk.), in Uganda, a series of ten 24-hour catches has shown a sharply-defined biting cycle which corresponds closely to an observed diurnal cycle of flight activity. A main peak of activity occurs one or two hours before sunset, and a lesser peak two or three hours after sunrise.

Comparison with recent work in Kenya suggests that, in comparing the behaviour of populations out of doors with those indoors, a distinction must be made between ssp. formosus and the other two forms of A. aegypti, in which no similar cycle has yet been demonstrated.

Ssp. formosus, which is presumed to be the wildest form of A. aegypti, is shown to have a cyclical behaviour very similar to a related forest species. A. africanus (Theo.).

Nausibius clavicornis (Kug.) is a cosmopolitan Cucujid that has frequently been recorded from sugar. It is commonly found in this commodity in Trinidad, where it has not been collected from any other.

The adult and other stages are described, and an account is given of the life-history on Haydak's formula at 85°F. and 75 per cent. R.H. Development has also been studied on two types of unrefined sugar.

Copulation can take place within one day of the emergence of either sex and the female may begin laying within four days of copulation. The average number of eggs laid was 275 and the overall viability was 85 per cent. The average incubation period was just under five days.

The larvae of both sexes may undergo only five moults in development, but the more usual number for females is six. When larvae are disturbed during development, both sexes tend to have six larval instars. Severe disturbance may induce a seventh moult. The mean development period from oviposition to the emergence of the adult was 30 days when there were five larval instars; when there were six, development took about two days longer. Larval mortality on Haydak's formula was low.

Ovipositing females lived for up to 163 days under controlled conditions, but males tended to outlive females by about 50 days.

On unrefined sugars (e.g., raw or yellow-crystal sugar), adults lived for almost as long (73:99) as on Haydak's formula, but oviposition was greatly reduced and the viability of the eggs was much lower. Larval mortality was high, especially in the first instar, and the total development period was greatly increased.

It is unlikely that N. clavicornis could multiply rapidly in raw or unrefined sugar, and any deterioration in stored sugar directly attributable to it would probably be small in comparison with that caused by other factors.

An investigation was made to determine the factors governing the distribution pattern of the larvae of certain species of Melolonthids and Tenebrionids; these are known to be serious pests of tobacco plants in Southern Rhodesia.

Observations were made on mixed populations of the white grubs, larvae of Anomala exitialis Pér. and Schizonycha profuga Pér. (MELOLONTHINAE), on the one hand, and on those of the false wireworms, larvae of Psammodes similis Pér. and P. scrobicollis (Fhs.) (TENEBRIONIDAE), on the other.

It was found that the habitats favoured by white grubs had a higher clay, silt and organic matter content than those favoured by false wireworms. This was indicated by the darker brown colour of the soil; the clay ratio of the soils of the two types of habitat was as 1 to 0·725 and the nitrogen ratio as 1 to 0·524, respectively.

Heavy infestations of tobacco fields are associated with 60,000 white grubs or 1,500 false wireworms per acre. The white grubs complete their life-cycle in one year, the larvae obtaining the food requirements necessary for their develop ment in the 4 to 5 months of the wet season. The false wireworms have a two-year life-cycle, the active feeding stages of the larvae being spread over 18 to 21 months, comprising both wet and dry seasons.

The infestations by the two classes of insect do not overlap in space to any great extent but are governed by the nature of the soil, the white grubs favouring areas in which the soil has a higher nutrient value and the false wireworms areas where the soil is poorer.

Reference is made to parasitisation of white-grub larvae in two areas, where the soil had an abnormally high nitrogen content, by a species of Tiphia in the one area and by entomogenous fungi in the other.

False wireworms have not been found to be similarly attacked under field conditions.

The red spider, Oligonychus coffeae (Nietn.), is the most widely distributed and probably also the most serious pest of tea in north-eastern India, and also occurs on tea in other parts of India and in other countries. It attacks jute, Corchorus capsularis, in India and has been recorded on a wide variety of other plants in India and other countries.

The life-history of O. coffeae in north-eastern India is described. The duration of the life-cycle varies with the season depending on the temperature and humidity.

In May and June the life-cycle is completed in 9·4–12 days outdoors, while in the cold weather it may take as much as 28 days. The maximum length of life of a female has been found to be 29 days indoors. The males usually die within four or five days. Parthenogenetic reproduction may take place under induced conditions, the progeny being all males.

Red spider normally attacks the upper surface of the mature leaves in which the sap is not flowing freely. In a severe infestation, particularly under conditions of dry weather, the lower surface and the young leaves are almost equally attacked. The affected leaves turn brown, then bronze, and may eventually dry up and fall off.

The red spider mites live under a cover of web that they spin as a protection against inclement weather. The pest occurs in severe form from March to June but with the monsoon rains it practically disappears. A second, light, attack may, however, develop in September or October.

During the cold weather, the mites are present in very small numbers on a few old leaves of the tea bushes, and with the rise in temperature in the spring, they multiply rapidly, resulting in subsequent heavy infestations.

Various factors influence the incidence of red spider and the intensity of its attack. Pruned bushes properly cleaned out are less affected. Bushes defoliated after pruning, and medium pruned tea remain practically unaffectsd. Prolonged dry weather during the early part of the flushing season normally increases the red spider incidence. It prefers bright sun and unshaded areas are more severely attacked.

The red spider spreads from bush to bush by crawling. Dispersal is also effected by various agencies such as wind, cattle, goats and labourers.

A number of predatory insects attack eggs and other stages of the red spider, often keeping it considerably in check.

The fly-round has for long been regarded as the most satisfactory way of following fluctuations in populations of tsetse flies (Glossina) and locating areas of concentration. It consists of a path cut through bush so as to traverse the principal vegetation communities and is divided into sections, corresponding to the latter, on each of which the flies are caught. A modification now widely used but not previously described in detail is termed a line transect or transect fly-round; this follows an arbitrary course along straight lines that may be orientated with regard to the topography and is divided into numerous short sections of equal length terminating at posts at which flies are caught. In its simplest form it follows a straight course, but various patterns are used including an angular spiral. It facilitates the collection of quantitative data on tsetse density and the factors (such as vegetation) that affect it, and their analysis is possible in more detail than was the case when the fly-round was laid out according to a pre conceived notion of vegetational relationships. This is illustrated by data from a fly-round at Shinyanga, Tanganyika, consisting of six sides, each of 2,000 yd., of two diagonally adjoining squares, that was divided originally into nine sections of varying lengths representing the floristic communities traversed, and subse quently into 120 sections each 200 yd. long. Comparison of the catches of non-teneral males of G. swynnertoni Aust. grouped according to the two methods emphasises the much greater detail provided by the second of them. The transect fly-round is easy to lay out and operate and is thought likely to be particularly useful in connection with reclamation work.

The effect of varying the section length was investigated for G. swynnertoni at Shinyanga, G. pallidipes Aust. in Nyanza Province, Kenya, and G. austeni Newst. in Zanzibar. With the first, progressively fewer flies of all categories except teneral males were caught as the section length was increased progressively from 50 to 200 yd.; with the other species a similar tendency was apparent, but not significant. The results emphasise a point long recognised but often neglected, that data from fly-rounds reflect, in part, the reaction of tsetse populations to the behaviour of the catching party. That this reaction, termed the availability, is itself inconstant is shown by catches of G. pallidipes on a fly-round done daily for a month, in which differences between catches on consecutive days, sometimes exceeding 3:1, must represent changes in availability, not in absolute population.

Data from the transect fly-round can be analysed so as to indicate sections where the catches deviate significantly from those expected on the assumption that they are distributed according to a Poisson series, and where there may thus be presumed to be areas of concentration of the population, or the reverse. A Table is provided to facilitate such analysis.

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.

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.

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.

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.

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.

In laboratory studies of Dysdercus fasciatus Sign., populations were exposed to constant temperatures of 15, 20, 25, 30, 35 and 40°C. and a relative humidity of 60 per cent., and to 28°C. and 70 per cent. R.H. After hatching, the insects were supplied with cotton seed as food and water to drink. Development of eggs was incomplete below 25°C., of nymphs below 20°C., and of both above 30°C. To allow comparison of growth and rate of reproduction at temperatures outside the embryonic range, this stage was ignored in calculating values of the intrinsic rate of increase, r, and the mortality rate and length of life were measured from the time of hatching, the eggs being incubated under optimum conditions (those at 28°C.) and the freshly hatched nymphs then moved to the appropriate temperature. The value of r was found to increase with increasing temperatures up to 30°C., and to do so more rapidly between 25 and 28°C. than between 20 and 25°C. The age-schedule of deaths for populations living at 28°C. showed a distribution of deaths that was almost ideal, in that their highest frequency did not occur until the reproductive period was advanced. The principal deviation from this ideal was due to the high mortality rate found in the first instar. At 20°C., the death rate approached constancy throughout the life-span of the population. The interval between generations decreased with increasing temperature, the rate of decrease being approximately 4·6 days per 1°C. rise in temperature.

Further analysis of r was made by considering separately the growth and reproductive characteristics of the insect, and the effect of temperature upon them.

The rate of post-embryonic growth, as measured by live weight, increased with temperature, within the range of 20–30°C. At 15°C., growth did not proceed beyond the third instar, or beyond the fifth instar at 35°C. The principal cause of the increase in growth rate was the decrease and eventual disappearance of the periods between initial ecdysis and start of growth, and between the end of growth and final ecdysis, the rate at which growth actually took place differing but slightly.

The size of the insect just after the final ecdysis had an important effect on r because the number of eggs laid by small insects (mean weight 68·6 mg.) was only about half that of large ones (mean weight 100·2 mg.). Any decrease in size observed with increasing temperature was slight compared with that produced by restricting the insect's access to drinking water.

Copulation and oviposition occurred in adults maintained at any of the temperatures except 15 and 40°C. The percentage of females that laid eggs differed according to the temperature, the highest recorded being 90 per cent, at 28°C. and the lowest 30 per cent, at 20°C. The total time spent in copulation also varied with temperature, being least (9 days) at 28°C. and most (26·3 days) at 20°C. The change of weight of the female after moulting largely represented growth of the ovaries; at 15°C., this is slow and not completed before the female dies; at 40°C. the ovaries do not mature; at other temperatures tested (20–35°C.) growth is fairly rapid, the ovary being full grown in about four days.

The fertile female lays her eggs in batches, the maximum observed being six batches, at approximately three-day intervals. A few females survived the laying of the sixth batch of eggs by a period longer than their interoviposition period. At 28°C., the preoviposition period and the time spent in copulation were less, more egg-batches, and hence more eggs, were produced and a higher proportion of females mated, than at any other temperature. In the unmated female, the average life was twice that of the mated one, the preoviposition period was the same, the interoviposition period approximately three times as long, the egg-batches half as numerous, and the number of eggs per batch nearly the same. All fertile females were observed to lay eggs, but only 20 per cent, of the unmated ones did so. At 35°C., mated females produced one or two batches of eggs; unmated ones produced none, and although the ovary matured normally up to the fourth day, the yolk was subsequently reabsorbed, this process being complete by the 14th day.

These studies have indicated that in D. fasciatus the decrease in the value of r with decreasing temperature is caused by a rise in pre-reproductive mortality and a fall in reproductive capacity, as well as by the increase of the generation length, which other workers have found to be of predominating importance in the case of other insects.

The development of the khapra beetle, Trogoderma granarium Everts, and the cycle of movement of insects between the food and hiding places has been studied at 30°C. The results have been correlated with observations at maltings, its chief habitat in Britain.

In populations at 30°C., many larvae delay pupation and enter diapause, the remainder spending most of their time in the food and completing development quickly. The diapause larvae leave the food in the fourth and in later instars in search of hiding places. Disturbing the food stimulates the larvae to leave it a little earlier. Larvae resting in diapause moult occasionally, and at long and irregular intervals they emerge, presumably to replenish their food reserves by feeding, after which some pupate and the rest hide again.

The hidden diapause larvae can persist for a very long time; in cultures, 16 per cent, remained after four years. Apparently, as the food stored in the fat-body is depleted, they become readier to emerge from the crevices to feed. Replacing stale food by new food causes some larvae to emerge and the effect of disturbing the larvae is variable. After feeding, some of these larvae complete development and the resulting adults breed, presumably producing both quick developing and diapause larvae among their offspring.

When denied a hiding place, the diapause larvae remain inactive in the food without increasing their rate of pupation. However, they feed more, producing heavier beetles, an effect also obtained by regularly providing fresh food.

It is concluded that when a malt store is loaded, some diapause larvae remain in the fabric of the store and others emerge and feed; after feeding, some larvae re-enter crevices and others complete development and breed; the offspring contain some diapause larvae, which accumulate in the crevices and on the walls just below the malt surface; after the malt is unloaded, diapause larvae may persist in empty stores for a number of years, because they can restore their food reserves by occasionally eating grain residues.