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.

Cattle were treated with cypermethrin and flumethrin pour-ons to determine possible adverse effects of residues in dung on the survival, fecundity and fertility of Euoniticellus intermedius (Reiche). Dung from both cypermethrin- and flumethrin-treated cattle was collected 1, 2, 3, 5, 7, 14, 21 and 28 days after treatment, with an untreated control for each. Mortality of adult E. intermedius exposed to dung collected from cypermethrin-treated cattle two to seven days after treatment ranged between 80% and 100%. Cypermethrin had no effect on adult and immature survival or on fecundity and fertility of E. intermediusexposed to dung collected 1, 14, 21 and 28 days after treatment. Dung collected from flumethrin-treated cattle had no apparent effect on adult survival, egg production, immature survival, adult emergence, fecundity and fertility of E. intermedius, except at seven days after treatment, when fewer brood balls were produced and consequently fewer adults emerged from dung from treated animals compared with the control.

The ability of the foreign grain beetle, Ahasverus advena (Waltl), a reputed mould feeder, to breed on various foods under conditions not conducive to mould growth was investigated in a series of culturing experiments. At 25°C., on a diet of rolled oats and dried yeast, the lowest relative humidity at which successful breeding occurred was 65 per cent., although a few adults were produced at 60 per cent. R.H. Wheat germ proved a satisfactory food under these conditions and the addition of yeast or germ to cereal products enabled the species to breed in the absence of visible mould growth, which it failed to do on. the cereal products alone. Although thriving larval cultures developed with crushed, dead grain weevils (Sitophilus granarius (L.)) as food, they invariably died out without producing pupae. On oilseeds at 70 per cent. R.H., moderate breeding occurred on groundnuts, which remained free from visible mould, but little or none on copra, cocoa or palm kernels in the absence of mould.

It is concluded that most stored foodstuffs are deficient in some factor, present in adequate quantity in dried yeast or wheat germ, that A. advena requires for successful breeding and that, in the field, this requirement frequently limits the species to mouldy products, although direct damage to groundnuts at 30°C. and 70 per cent. R.H. is possible in the apparent absence of mould.

The departure of the newly emerged adults of the salt-marsh mosquito, Aëdes taeniorhynchus (Wied.) from the breeding sites was studied in Florida. The departures, which are presumed to be the initial stage of the migratory flight, have been observed to take place only in the dark period of the 24 hours, and, the vast majority of individuals being ready to take off at dusk, spontaneous mass departure took place at that time.

Samples of the resting population of mosquitos were taken at intervals before and after the mass departure, and from the departing migrants. The average age of the males in each sample was estimated by the proportion in different stages of hypopygial rotation, from which it is concluded that migratory activity begins when the insects are six or more hours old. The end of the migratory period is not yet known. In all of 21 female departing migrants examined, the ovaries were immature and the spermathecae empty.

The within-row dispersion characteristics of larvae of Antitrogus mussoni (Blackburn), A. parvulus Britton, Lepidiota crinita Brenske, L. negatoria Blackburn, L. noxia Britton and L. picticollis Lea in sugarcane were determined in studies in southern Queensland, Australia. The Poisson distribution, negative binomial distribution, Iwao's regression model and Taylor's power law analysis were used to determine the relationship between mean and variance of larval counts. All methods examined showed that the larvae were slightly aggregated. Taylor's power law generally gave equivalent or better fits to the population dispersion compared with the other models. The power law relationship for L. picticollis differed from those of the other five species, and a common relationship for those five species was determined. Relationships to determine sample sizes for fixed levels of precision and fixed-precision-level stop lines for sequential sampling were developed for both L. picticollis and the other five species. There were functional relationships between the variance and mean of untransformed population counts for all species, and the suitability of transformation functions is discussed.

Genetic variation among 14 populations of Plutella xylostella (Linnaeus) from USA (Geneva, New York), Brazil (Brasilia), Japan (Okayama), The Philippines (Caragan de Oyo), Uzbekistan (Tashkent), France (Montpellier), Benin (Cotonou), South Africa (Johannesburg), Réunion Island (Montvert), and five localities in Australia (Adelaide, Brisbane, Mareeba, Melbourne, Sydney) were assessed by analysis of allozyme frequencies at seven polymorphic loci. Most of the populations were not in Hardy–Weinberg equilibrium and had a deficit in heterozygotes. The global differentiation among populations was estimated by the fixation index (Fst) at 0.103 for the 14 populations and at 0.047 when populations from Australia and Japan, which differed most and had a strong genetic structure, were excluded from the analysis. By contrast, the populations from Benin (West Africa) and Brazil (South America) were very similar to each other. Genetic differentiation among the populations was not correlated with geographical distance.

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.

In preparing the part dealing with the Diprionidae in a synopsis of the British sawflies I came upon several morphological characters that, if used or made more use of, would greatly facilitate the naming and classification of this economically important group of insects. A comparison between Neodiprion and Diprion (s.l.) revealed at once striking differences in the shape of the meso-scutellum, the sculpture of the abdomen and the anal cell in the hindwing, characters easily visible in the field and therefore of great importance to the economic entomologist. Diprion pini, L., and similis, Hartig, were found to differ from the other Diprion species, among other things, in their small cenchri, a character easily visible in the field, and the genus has been divided.

Ten economically important species belonging to the Tephritidae have been recorded in Union of the Comoros (an island nation off the coast of East Africa). Little is known about the distribution of these species and how they are affected by climatic factors in the Comoros archipelago. The main objectives of this study were to characterize: (i) the population dynamics of tephritid fruit flies in relation to season and host fruit availability and (ii) the geographic distribution of tephritids in relation to temperature and rainfall. The study was conducted during 2 years at 11 sites on three islands (Grande Comore, Anjouan, and Mohéli) in the archipelago. The site elevations ranged from 55 to 885 m a.s.l. At each site, flies were collected weekly in eight traps (four different lures, each replicated twice). Fruit phenology was also recorded weekly. The dominant tephritid species detected was the invasive Bactrocera dorsalis Hendel followed by Ceratitis capitata Wiedemann. Tephritid species were generally more abundant during the hot and rainy seasons than during the cold and dry seasons. Bactrocera dorsalis numbers were higher on Grande Comore than on the two other islands. On Anjouan and Mohéli, B. dorsalis numbers were very low in 2014 but sharply increased in 2015, suggesting a recent invasion of these islands. Abundances were significantly related to the fruiting of mango, strawberry guava, and guava for B. dorsalis and to the fruiting of mango, guava, and mandarin for C. capitata. Bactrocera dorsalis was more abundant in hot and humid low-altitude areas, while C. capitata was more abundant in dry medium-altitude areas, suggesting the occurrence of climatic niche partitioning between the two species.

Larval diet quality and rearing conditions have a direct and irreversible effect on adult traits. Therefore, the current study was carried out to optimize the larval diet for mass rearing of Aedes aegypti, for Sterile Insect Technique (SIT)-based applications in Sri Lanka. Five batches of 750 first instar larvae (L1) of Ae. aegypti were exposed to five different concentrations (2–10%) of International Atomic Energy Agency (IAEA) recommended the larval diet. Morphological development parameters of larva, pupa, and adult were detected at 24 h intervals along with selected growth parameters. Each experiment was replicated five times. General Linear Modeling along with Pearson's correlation analysis were used for statistical treatments. Significant differences (P < 0.05) among the larvae treated with different concentrations were found using General Linear Modeling in all the stages namely: total body length and the thoracic length of larvae; cephalothoracic length and width of pupae; thoracic length, thoracic width, abdominal length and the wing length of adults; along with pupation rate and success, sex ratio, adult success, fecundity and hatching rate of Ae. aegypti. The best quality adults can be produced at larval diet concentration of 10%. However, the 8% larval diet concentration was most suitable for adult male survival.

We tested the enemy hypothesis for gall morphology on a model system comprising two Diplolepis rose gall wasp species and their associated parasitoids. The enemy hypothesis predicts both that gall traits will influence parasitoid attack rates within species, and that galls with contrasting morphologies will support different parasitoid communities. This hypothesis is supported by studies at both intraspecific and broader taxonomic levels (i.e. between genera), but patterns remain to be explored in closely related species. Our aims were to explore the relationships between aspects of gall morphology (number of larval chambers, overall gall size and thickness of the gall wall) in each of Diplolepis mayri and D. rosae, and to explore correlations between these traits and both the presence/absence (=incidence) and attack rates imposed by parasitoids. We found in both galls that chamber number is positively correlated with gall size. In galls of D. mayri, parasitoid incidence was negatively correlated with thickness of the wall of the larval chamber, but there was no significant correlation between parasitoid attack rates and overall gall size. In D. rosae galls, parasitoid incidence was positively correlated with chamber wall thickness, but parasitoid attack rates were negatively correlated with gall size, suggesting that selection may favour the induction of galls containing more larval chambers. These results confirm that gall extended phenotypes can significantly influence enemy attack rates, consistent with the ‘enemy hypothesis’. Further, differences in gall morphology between the two Diplolepis species may underlie differences in their associated parasitoid communities – further research is required to test this hypothesis.

Male pupae of the tobacco hornworm, Manduca sexta (Linnaeus), were exposed to γ–radiation from a 60Co source. This treatment induced mortality and malformations in the emerging adult insects. The incidence of these adverse effects of radiation declined with increasing pupal age at the time of treatment. Within any one age class, the effects of radiation treatment increased with increasing dose. When 16 d old pupae were irradiated, the resulting adult male insects exhibited adverse effects on mating behaviour and fertility when tested against unirradiated females. These effects were dose dependent in the range 0–30 krad. The major cause of reduced fertility was the failure of eggs to hatch. These eggs mostly showed no sign of embryonic development. F1 progency of moths given substerilizing doses of radiation showed significantly elevated larval mortality, pupal and adult malformations, and a slightly prolonged developmental period, but nevertheless a high proportion of the F1 insects survived to adults. The sex ratio of the F1 generation was markedly skewed in favour of males. When F1 insects, male or female, were mated with normal insects of the opposite sex, they were significantly less fertile than the irradiated parental (P1) generation. The F1 male moths transferred spermatophores to normal females only slightly less well than normal males, but the F1 females were much less successful than controls in mating with normal males. Examination of spermathecae of normal females mated with F1 males showed that both eupyrene and apyrene spermatozoa were successfully transferred from the spermatophore in all cases where the P1 insects had received 10 krad, but there was a slight reduction in the cases of higher doses. There was a dose-related decline in the number of eggs laid per mated female, and a dose-related reduction in hatching rate for the matings of both male and female F1 insects, but the effect on males was more severe than on females. The longevity of both F1 males and F1 females was reduced. The reduction in fertility of the F1 insects was in part due to a reduction in the number of eggs laid, but also to an increase in the number of eggs which failed to hatch. In contrast to the P1 generation, the reduction in hatching success of eggs laid by F1 insects was due mostly to the death of partly developed embryos.

Landscape genetics have been particularly relevant when assessing the influence of landscape characteristics on the genetic variability and the identification of barriers to gene flow. Linking current practices of area-wide pest management information on pest population genetics and geographical barriers would increase the efficiency of these programs. The woolly apple aphid, Eriosoma lanigerum (Hausmann), an important pest of apple orchards worldwide, was collected on apple trees (Malus domestica Borkh) from different locations in a 400 km north-south transect trough central Chile. In order to determine if there was population structure, diversity and flow were assessed. A total of 215 individuals from these locations were analysed using Inter Simple Sequence Repeat (ISSR) markers. Four ISSR primers generated a total of 114 polymorphic loci. The percentage of molecular variation among locations was 18%. As the algorithm used by structure may be poorly suited for inferring the number of genetic clusters in a data set that has an IBD relationship, the number of genetic clusters in the samples was also analyzed using a Bayesian clustering method implemented in software Baps version 4.14. We inferred the presence of four genetic clusters in the study region. Clustering of individuals followed a pattern explained by some geographical barriers. Using partial Mantel tests, we detected barriers to gene flow other than distance, created by a combination of main rivers and mountains. Although landscape genetics are rarely used in pest management, our results suggest that these tools may be suitable for the design of area-wide pest management programs.

The seasonal variation of adult populations of Haematobia irritans Linnaeus was monitored at Santa Fe, Argentina from August 1992 to August 1994 by weekly counts of flies on grazing heifers. Each year, flies were recorded at a density of more than two flies per heifer from August/September to the following June, with peaks of abundance in mid to late spring and late summer to mid autumn. The seasonal trend of fly numbers was best correlated with the mean temperature 4 weeks prior to each fly count (correlation indices of P<0.01 in six of the nine fly periods) followed by the previous 4 week mean saturation deficit. Rainfall and relative humidity correlated poorly with the seasonality of H. irritans. Temperature appeared crucial at the beginning (late winter) and at the end (early-mid autumn) of the fly season while its relevance diminished in the middle of the season. The percentage of heifers that were infested decreased from 80–100% in the fly season to 0–55% between fly seasons but H. irritans never disappeared from the heards, indicating that if diapause occurs at the latitude of the study area, part of the fly population was not sensitive to diapause inducing factors.

In an attempt to isolate yellow fever virus from Aëdes (Stegomyia) africanus, Theo., an intensive series of catches was carried out during 11 weeks of 1945 in 2 forest areas in Bwamba County, Uganda. Most of the work was carried out on platforms in trees during the sunset period, since the main biting activity of A. africanus occurs in the forest canopy just after sunset. Virus was not obtained during the course of this work.

The results confirmed that A. africanus is the dominant arboreal Culicine of the sunset period. In catches carried out actually in the canopy it formed 69 per cent. of the total Culicines taken.

Cyclodiene insecticide resistance persists in field populations of Drosophila spp. at a frequency of approximately 1% (0.01), despite the withdrawal of most cyclodiene type insecticides except endosulfan. However, we have previously documented that resistance-associated amino acid replacements in the gene Rdl, a γ-aminobutyric acid receptor, can significantly affect several channel functions of the integral chloride ionophore. We were therefore interested in investigating if different resistance-associated replacements confer significant fitness disadvantages and whether the use of endosulfan could be maintaining selection for cyclodiene resistance in the field. Using PCR amplification of specific alleles (PASA) within 3000 individual flies, we report that neither the alanine302 > serine (allele 1) replacement in Drosophila melanogaster Meigen nor the alanine302 > serine (allele 1) or alanine302 > glycine (allele 2) replacements in D. simulans Sturtevant showed any reduction in frequency in cage experiments run for one year in the laboratory in the absence of selection. Further, repeated applications of endosulfan selected significantly for cyclodiene resistance in the field. Thus the apparent absence of fitness cost, combined with the continued use of endosulfan, may maintain cyclodiene resistance at this relatively high frequency in field populations.

Experiments were conducted to investigate oviposition and host selection by Stenobracon deesae (Cam.), a Braconid parasite of certain Lepidoperous borers of sugar-cane, maize and sorghum in India. The fecundity and sex-ratio of this parasite and the duration of its life-cycle were also studied.

Chilo zonellus (Swinh.) and Corcyra cephalonica (Staint.) were used as hosts. The former is one of the principal hosts in the field, but the latter is not normally a host of this parasite.

The femal Stenobracon normally avoids laying eggs on hosts that are already parasitised by its own kind when unparasitised hosts are available; but in the absence of healthy hosts or when these are too crowded, parasitised hosts are attacked by it.

At a temperature of 26°C. and relative humidity of 75 per cent., the life-cycle of the parasite was completed, on an average, in 23·3 days, but under laboratory conditions at Delhi it took 14·1 days in June-July and 43·7 days in November-December. The average duration of adult life of females in June-February, mainly in ordinary laboratory conditions, was 35·7 days, and single females lived as long as 122 and 128 days. The adult male lived for 42·7 days on the average.

In the laboratory, the female lays about 24 eggs on an average, but only about one-third of them yield adults.

Males predominate. The sex-ratio appears to vary according to the host; among adults reared on Chilo larvae, 28·8 per cent. were females, but among others reared on Corcyra larvae, only 6·2 per cent. were females.

The phenomena of discrimination between parasitised and unparasitised hosts and of the change of sex-ratio with change of host are discussed. It is suggested that the ovipositor enables the parasite to recognise the host and that the stimuli received by the ovipositor from the host influence the functioning of the spermatheca which in turn controls fertilisation and finally the sex of the progeny.

It is known that the females of some species of parasites can distinguish hosts that have already been parasitised and refrain from ovipositing in them. A study was made of the extent to which Spalangia drosophilae Ashm. avoids superparasitism of the puparia of Drosophila melanogaster Mg. by means of these two steps, which are termed discrimination and restraint, respectively.

Host puparia 0–24 hours old were stuck on paper, with water, equidistant ¼ in. from each other and placed in 4½ in. × 1 in. glass vials into which females of Spalangia were introduced for different periods. A series of experiments was set up, in which 25, 10 and 5 puparia were exposed to attack by 1 unmated or 1, 2 and 5 mated parasites for 24, 48 and 72 hours. In this way a wide range was obtained of the parasite-host (P/H) ratio, computed as the ratio of the number of female parasites, multiplied by the number of 24-hour periods for which they were used, to the number of host puparia exposed. Each treatment was replicated ten times, thus entailing a total of 360 experiments. The sequence of events associated with oviposition consisted of examination of the puparium by the females, stinging, followed sometimes by feeding on the fluid that exuded, and finally, but not invariably, oviposition. At the end of the experiment each puparium was examined and the number of eggs present, or the occurrence of stinging only, was recorded. The chance of a puparium being attacked was unaffected by its position on the paper and there was no significant difference between the total number of eggs that virgin and mated females laid under the same conditions.

The results were assessed by comparing the observed distribution of parasite eggs amongst host puparia with the probable random distribution calculated from a formula that is given. The divergence between these distributions was greatest at the lower P/H values, and very little superparasitism occurred unless these exceeded 3/25, at which point total parasitism reached about 60–70 per cent. As the P/H value increased, so did the total parasitism and the degree of superparasitism, and the deviation of the observed from the random distribution of eggs diminished, although even amongst experiments in which parasitism reached 91–100 per cent., superparasitism was still avoided in 15·6 per cent, of them.

The degree to which females of Spalangia can restrain themselves from ovipositing in hosts that have been parasitised was estimated by plotting the percentage of experiments in which restraint was observed to break down, against the level of attack, and comparing the distribution of the points so obtained with the curves that would relate these two functions if the power of restraint was to break down when the female was confronted with 2, 3 or 4 successive puparia that had already been attacked. It is concluded that the assumption that restraint breaks down at about the third successive unsuitable encounter gives the best fit with the observed data.

Contributory evidence that females of Spalangia can distinguish parasitised hosts was obtained by direct observation of their behaviour, which indicated that, on the average, females took about 3½ minutes to examine an unparasitised host before deciding whether to attack or not, but, in the case of hosts already parasitised, either rejected them in half that time, or only accepted them after unduly prolonged examination.

When individual mated females were supplied daily for 16 days with a single puparium, then for 3 days with 25 puparia, then again for 8 days with a single puparium and finally for 8 days with 25 puparia, the number of eggs laid daily was restricted to less than two when only a single host was available, but rose to about 9–11 on the first day an excess of hosts was provided and then fell to a normal output. The females thus adapt their egg-laying to some extent to the number of hosts available.

It was hoped that this elucidation of the combination of perfect discrimination but imperfect restraint exhibited by Spalangia. when ovipositing, together with the data previously obtained on its biology, would make it possible to predict the fluctuations of a population of Spalangia in the field and its effect on the natural host, Oscinella frit (L.), but the factors involved, and their interactions, are too complex, particularly when weather effects are considered, and it is concluded that any predictions of population must be deduced empirically from field observations over a number of years.

When studying the biology of the house-fly or any other fly annoying to man and domestic animals with a view to practical control, it is obvious that a correct knowledge of the breeding-places of the species is perhaps the most important problem which the investigator has to solve. As to the common house-fly (Musca domestica, L.) it is generally held that this problem has been completely cleared up by several workers years ago, but recent observations in Denmark have convinced the writers that this is not the case. We have arrived at conclusions regarding the chief breeding-places of the house-fly differing from those generally found in text-books.

Our work has not been limited to Musca domestica, for we have as far as possible studied the breeding-places of other flies occurring in houses or connected with domestic animals, first and foremost the stable-fly (Stomoxys calcitrans, L.). The knowledge of the biology of the stable-fly in Europe is surprisingly meagre, though the practical interest of this species as a tormentor of cattle and horses and a possible vector of infectious diseases is generally recognised.

As our observations may be of some interest to workers in other countries we have collected them in this paper, which constitutes the third of a series containing the main results of our investigations into the fly problem started under the auspices of the Health Organisation of the League of Nations and the Danish Committee of Rural Hygiene and with the support of the Danish Ministry of Agriculture and several private funds.

The writer was able to make a field and laboratory study of Leucoptera coffeella, Guér. (white coffee-leaf miner) when serving as Entomologist in Kenya Colony.