The genus Diparopsis Hmps. is confined to Africa. During the present century, an insect always identified hitherto as Diparopsis castanea Hmps. has become a serious pest as a bollworm of cotton in many parts of that continent. Until recently, the genus was thought to consist of only two species, D. castanea Hmps. and D. tephragramma B.-Bkr., but differences in the structure of the frontal process of the adult suggested that the former comprised two or more distinct sub-species or species. The present study was undertaken to determine the status of these different forms. It is based on the material in the collections of the British Museum (Natural History) and on additional material obtained through the courtesy of the Government Entomologist, Anglo-Egyptian Sudan, and the Commonwealth Institute of Entomology.

The development of Ptinus fur (L.) and P. sexpunctatus Panzer at 70 per cent. R.H. and several temperatures has been studied.

The optimum temperature for rapid development of P. fur is about 23°C., at which temperature it completes its development in a mean period of 132·1 days on fishmeal. For P. sexpunctatus the optimum temperature for rapid development is slightly below 30°C., development being completed in approximately 111 days on wheatfeed at this temperature.

Eggs of P. sexpunctatus, but not those of P. fur, hatch at 30°C., which is near the maximum temperature for development of P. fur.

Larvae of P. fur normally moult three times at 23°C. on fishmeal, but some have an extra moult.

Well defined diapause as mature larvae in cocoons occurs at low temperatures in some individuals of P. fur ; at 23°C. this lasts about 220 days after normal larvae have pupated ; the period at 20°C. is about 280 days. Diapause at this stage also occurs in P. sexpunctatus. In experiments, the development periods of the diapausing and non-diapausing larvae overlapped to form a continuous series.

Some P. sexpunctatus pass through a period of quiescence as mature adults in cocoons ; at 23°C., this lasted 43·5 days on fishmeal and 103·0 days on wheatfeed (mean periods). In P. fur the pre-emergence period is 30 to 60 days, considerably longer than that of other warehouse Ptinids studied.

Of the foods, wheatfeed allows the quickest development for both species, but fishmeal produces the heaviest beetles.

The adult beetles live for several months. They require food and drinking water. Egg output is small, the mean number of eggs laid per female at 25°C. being 38·6 for P. fur and 21·3 for P. sexpunctatus.

P. sexpunctatus was able to overwinter in an unheated outbuilding and could possibly become a pest on some foods.

P. fur is unlikely to occur in large numbers, owing to its long development period, small egg output and tendency to larval diapause.

An experiment is described in which three light traps were tested for relative efficiency by having three locations in a wood and moving the traps each day so that over a period of three nights each trap had been once in each position. The actual number of moths caught were converted to a logarithmic scale and the mean log. (i.e., log. of the geometric mean catch) was used for comparison. By analysis of variance it is possible to show what portion of the differences between the catches is due to the difference between the locations, to the difference between the nights, and the difference between the traps.

All varieties of sweet corn, in the seedling stage, are susceptible to frit fly attacks in England.

Different open-pollinated, hybrid and inbred varieties differ in susceptibility to damage by frit, indicating a possible genetical basis for resistance. Some breeders have produced less susceptible types than others.

Susceptibility is not associated with adaptability or maturity (i.e., comparative earliness when whole rows were ready for picking) of varieties but there is indication that seed origin is of some importance.

Sowing sweet corn at different dates influences the severity of attack. Peaks vary according to variety and year but generally sowings late in May are preferable.

Distribution of attack on a crop is at random, although there is a suggestion that plants in stringers from a central mass are mere damaged in the direction of the prevailing wind but there is no regular decrease in incidence with distance from the central mass.

Methods of tackling the frit fly problem include growing sweet corn in frit free areas, timing sowing dates, using prophylactic measures and breeding more resistant strains on genetical principles.

Field and laboratory studies were made of the mosquitos of the Wuhan area, central China, between June 1947 and March 1948.

The following species were collected : Anopheles hyrcanus var. sinensis, Mansonia uniformis, Armigeres obturbans, Aëdes albopictus, Culex fuscanus, Culex vagans, Culex fatigans, Culex pipiens and Culex tritaeniorhynchus. A brief account is given of the topography and other environmental features of Wuhan.

The seasonal incidence and feeding habits of the adults, and the breeding sites favoured by the various species are recorded.

Monthly mean figures for rainfall, temperature and humidity are examined in relation to incidence of malaria and abundance of adults and larvae of Anopheles hyrcanus var. sinensis. The peak of malaria incidence coincides with that of Anopheles population which occurs two to three months after the peak of rainfall at an average relative humidity of 66 per cent.

A chemical analysis of waters from different types of breeding sites was made. Both the total organic nitrogen, and the amount of dissolved oxygen were considerably greater in the breeding site of Armigeres obturbans than in those of other genera. A sample of water from a site in which no mosquito breeding was observed contained very much smaller amounts of organic substances and minerals than samples from known breeding sites.

Other ecological factors affecting the early stages in their breeding sites are briefly referred to.

1. A warm object is more attractive to the female yellow-fever mosquito than a cooler object, such that the numbers touching a ball warmed to 100° or 110°F. were twice as great as those touching a ball 20°F. cooler. This attractiveness was reversed when the temperature of the warmer ball reached 120°F.

2. This response is eliminated by the insertion of an air-tight window of thallium bromoiodide, despite the fact that it allows almost all of the radiation to filter through. It is therefore concluded that heat convection, which is eliminated by the air-tight window, is the factor which makes a warm object attractive to the mosquito.

3. The several faces of a warm cube, differing in their radiant emissivity but identical as to surface temperature, exhibited attractancies to Aëdes which were not significantly different one from another (except in the case of black enamel, which will be explained in a later paper). These results may be interpreted to indicate that radiation plays no part in the attraction of the mosquitos to the warm face.

4. It is concluded that the failure of Parker (1948) to obtain a positive response of Aëdes mosquitos to a warm dry object was due to the fact that his apparatus allowed only the radiant heat but not the convective heat to reach the insects.

5 Since the response of Aëdes aegypti to heat is eliminated by a window transparent to infra-red radiation, the theory of olfaction proposed by Beck and Miles (1947) evidently has no application to this species of mosquito.

Methods of preparing solutions of graded density for the accurate control of atmospheric relative humidity are described, and some pitfalls in their use and in the use of saturated salt solutions are indicated.

For graded solutions of potassium hydroxide and of sulphuric acid, data from the International Critical Tables or more recent sources are used as the basis of tables giving the concentrations (wt.%) and densities corresponding to relative humidities in steps of 5 per cent. R.H. Sources of similar data for calcium chloride, sodium hydroxide, sodium chloride, and glycerol solutions are given.

As an addition to the compilation of the available data on humidities in contact with various saturated salt solutions by O'Brien (1948), some more recent figures are quoted.

Conwentzia psociformis (Curt.) and Conwentzia pineticola End. differ as adults in only two characters, and since there are variable and intermediate forms occur, reliable determination is sometimes impossible. In the past, these two species have often been regarded as two forms of the same species.

The immature stages of C. pineticola are, however, very different from those of C. psociformis and show that the two are distinct species and can readily be separated on larval characters. The larval stages and egg of C. pineticola are described for the first time, and an account of its life history given.

The feeding habits of these two species are described, and mention is made of two other Coniopterygid species that occur in orchards.

Owing to the courtesy of Miss H. Dombrowski (E. V. Dombrovskaya) of the Zoological Institute of the Academy of Science, Leningrad, U.S.S.R., it is now possible to describe a sixth species of gall midge belonging to the genus Trisopsis Kieffer. Males, females and larvae of this species were received from Russia in April, 1937. The larvae had been found during the previous winter preying on the Flour Mite, Tyroglyphus farinae (Deg.) during laboratory observations on the predaceous mite, Cheyletus eruditus (Schr.), which had been kept with the flour mites in paraffin wax cells at the Institute for Plant Protection, Leningrad (Sorokin, 1938).

Whilst the status of Capnodis as a pest in Israel has been considerably reduced by the control measures that have been adopted, it was considered desirable to test the new synthetic contact insecticides, in particular DDT and BHC.

Techniques for the determination of the effect of insecticides on neonate larvae of Capnodis are described and the results discussed.

It is shown that BHC and DDT are ineffective as fumigants against the boring larvae.

Used as a contact insecticide against the larvae, a high degree of mortality is obtained with 5 per cent. BHC over a period of 50 days. DDT is far less effective. BHC, dieldrin and methoxychlor remained effective for over a year if left undisturbed in the ground.

Against adult Capnodis, BHC gave results comparable to those obtained with cryolite and retained its activity for at least twelve days after application.

1. The responses of adult mosquitos, consisting of several Canadian species of Aëdes, were investigated under field conditions by employing heated and clothed robots.

2. Moisture increased the attractiveness of a warm body two to four times when the air temperature exceeded 60°F. ; at cooler temperatures, surface moisture decreased the attractiveness.

3. Warmth increased the attractiveness of a body, so that a robot at 98°F. attracted three times as many mosquitos as one at 50–65°F.

4. It may therefore be concluded that moisture is the major attractant factor when the air temperature exceeds 60°F., and warmth when the temperature is less than 60°F.

5. Carbon dioxide vapour emitted from an artificial head almost doubles the attractiveness of a warm body.

6. The vapours of ether and gasoline were significantly attractive. A sweat-soaked jerkin was more attractive than a water-soaked one.

7. Light colours were less attractive than dark ones, and luminescent dyes decreased the attractiveness of cloths. Green is less attractive than red or blue.

8. Glossy satins were less attractive than matt broadcloths. Greenish-khaki nylon cloth was much less attractive than khaki drill or cotton.

9. There was no evidence of interspecific differences in the responses of the mosquitos investigated.

Simuliid flies are a well known feature of riverain land in the northern Sudan during months of low Nile. They have been discussed in detail by Lewis (1948). Two species occur, Simulium damnosum Theobald, and S. griseicolle Becker. The former is larger and darker in colour. The latter is smaller with characteristic grey shoulders and is usually much more numerous. S. damnosum bites humans readily, especially round the ankles. S. griseicolle is usually less effective in its attempts to bite humans but susceptible persons may be badly bitten. It commonly attacks the head and shoulders and may cause great irritation by invading the eyes, ears, nose and mouth. Temporary protection for up to four hours can be obtained by rubbing the skin with di-methyl phthalate which acts as a repellent against both species.

1. The reactions of Xenopsylla cheopis Roths, to uniform and alternative relative humidities have been investigated.

2. X. cheopis aggregates in the dry side of the alternative chamber. There is an indication that the intensity of aggregation increases with increase in percentage difference between the alternatives and that it is also high when the alternatives are high in the scale.

3. Locomotor activity and speed of movement increase with rise in relative humidity.

4. Males kept at 90 per cent. relative humidity for five days aggregate intensely in the drier of the alternatives 65 and 85 per cent. R.H. Similar fleas kept five days at 70 per cent. relative humidity react weakly.

5. There is greater activity after five days' exposure to 90 per cent. relative humidity than after exposure to 70 per cent. R.H. for fhe same duration.

6. One concludes that high activity in wet air contributes towards aggregation in the dry side and that the intensity of aggregation is affected by the difference in activity which occurs in the fleas at different relative humidities.

7. The intensity of aggregation to the alternatives 80 and 90 per cent. relative humidity is unaffected by sex, or by the remains of a blood meal.

8. A high klino-kinesis may occur in X. cheopis.

9. Nosopsyllus fasciatus reacts in the same way as X. cheopis to uniform and alternative humidities, but there is no evidence of a high klino-kinesis.

10. When a roll of lint is dropped into a vessel infested with X. cheopis the number which jump on to it increases with relative humidity. The number which jumped on to a month-old rat did not show a clear relationship to humidity. Relatively more females than males jumped on to the roll of lint and rat.

11. A colony of 25 buck rats was infested with X. cheopis. In relation to size of flea population the flea index increases with rise in relative humidity. The proportion of each sex on a rat, to its respective number in the bedding material, does not appear to bear a simple relationship to humidity.

12. Humidity receptors are not confined to the distal three segments of the maxillary palps if indeed there are any there.

Attention is again drawn to the presence of mating scars in G. palpalis. They vary in degree and are caused by the superior claspers. The function of the inferior claspers is described and a function for the vermiform appendices is suggested. Flies mated under certain laboratory conditions may fail to develop scars, for reasons given. There are no mating scars in the two other tsetse-flies found in Sierra Leone, viz., G. longipalpis and G. fusca owing to the character of the claspers in those species. For this reason it is likely that the scars are confined to flies of the palpalis group. A suggestion is made concerning the physiology of the production of the scars and attention is called to their bionomic importance. The results of spermatheca dissections of unscarred and scarred females are tabulated. From these it is concluded that the absence of mating scars provides a fairly reliable index of the rate of emergence at any particular time.

The garden chafer, P. horticola (L.) is widely distributed in England and Wales but is more abundant in the western half of the country. Its natural habitat is poor quality permanent grassland characterised by a diversity of species of flowering plants and a high proportion of weeds. The soil of the infested areas is invariably light, the land is usually hilly and the rainfall relatively high.

Adults emerge suddenly in May or June according to the weather. Males emerge some days before females. Daily activity increases during the flight period which lasts 3–4 weeks. Beetles only fly in warm sunny weather.

The females lay an average of 14 eggs each. Fecundity is correlated with weight and is related to the food supply of the larvae. In nature, the weight of the adults may be limited through the exhaustion of the food supply of the larvae. Females will mate and lay fertile eggs without feeding. In general, feeding by the adult does not affect fecundity but in one experiment beetles fed on salad burnet produced and laid more eggs than beetles fed on bracken, blackberry, grass or kept without food. Over 90 per cent. of the eggs are fertile ; fertility decreases with the age of the adult. The incubation period of the eggs is about 22 days in the laboratory but about 28 days in the field.

The spatial distribution and seasonal changes in population of P. horticola have been studied within an infested field on the Tickenham Ridge, Somerset. The eggs are laid in groups from which the larvae disperse. At the end of the feeding period the larvae may be distributed at random but there is some evidence that regrouping at feeding sites occurs. Most of the eggs are laid in the top 3 ins. of soil. The larvae feed in the root zone but go deeper in the soil in winter to hibernate. The population fell in successive years within the area studied. Initially there was a higher infestation in part of the field where the turf was damaged by the larvae but the relative intensity of infestation changed and subsequently more eggs and larvae were found in part of the field where the turf was undamaged. There was a higher mortality among larvae in the damaged part of the field. These population changes have been related to a number of environmental factors which may account for them, in particular to dispersal of the adults, density of the vegetation, consolidation, soil moisture and predators. In a field at Alton Pancras, Dorset, predation by birds reduced the larval population by 50 per cent. between 1st September and 1st November.

A study of the effect of infestation upon the vegetation showed that damage was largely due to the destruction of the grasses. Weeds were unaffected and there was no evidence of an increase of weed area by colonisation of bare patches resulting from damage. Brachypodium pinnatum resisted attack owing to its tough rootstock. Dactylis glomerata and Lolium perenne were relatively resistant, Poa spp. and Festuca spp. were damaged but regenerated when feeding stopped and the population declined. Salad burnet, a favoured food plant, was more abundant in damaged areas and its distribution may influence the distribution of P. horticola.

When infestation is severe and the grass roots are destroyed, the soil aggregates are broken down. The soil structure was restored when the grasses regenerated, and by consolidation.

Field populations were reduced by ploughing and by reseeding. Dusting with 3·5 per cent. benzene hexachloride at 70 lb. per acre during the flight period gave promising results when applied in favourable weather.

Arising out of a routine mosquito survey, carried out in a coastal district of the Gambia in 1946, it was discovered that specimens of typical A. gambiae showed a variation in maxlllary indices, suggesting the possible differentiation of the species into two races distinct from the known variety “ melas ”.

Material from catching stations, considered beyond flight range from possible breeding places of “ melas ”, was subjected to statistical analysis as were also collections of adults emerging from different categories of fresh-water breeding places.

The analysis showed that the maxillary indices of the samples obtained from control house catches were distributed in an abnormal manner and were therefore unlikely to have been drawn from the same population. At the same time, the samples collected by window-traps and spray-catches were found to differ significantly in their means, and this supported the view that a mixed population was being sampled. The samples obtained by trapping emerging adults from different categories of breeding places, where any adulteration by “ melas “ was a physical impossibility, showed significantly different mean maxillary indices. It was therefore very unlikely that they could have been drawn, by random sampling, from a pure population. When the samples, obtained by trapping over-breeding places, were divided according to their mean indices, it was found that those falling into the group with a mean index of 13·107 were taken from collections of water which could be classified as casual and those falling into the group with a mean index of 15·33 were collected from permanent pools.

Preliminary research on the micro-flora of fresh-water pools has shown that certain distinct phases, marked by dominant plants, can be distinguished. The distinction between casual water and permanent water is capable of more accurate definition by reference to the dominant species. It has been observed that, within the limits of statistical differentiation, the race having the larger mean maxillary index is never found in water where photosynthesis, and hence chlorophyll, is absent whereas the race with the smaller mean maxillary index is never found in water where photosynthesis has been established amongst the micro-flora.

The apparent difference in behaviour between the two races, as shown by the predominance of the 13·107 index group in the window-traps, and the predominance of the 15·33 index group in the spray-catches, cannot it is thought, be accepted as evidence unless the existence of a fatigue factor, accounting for house-resting habits in members of the latter group which have travelled far and exhausted their energy reserves, can be excluded.

It is considered that the results of the work described in this paper may be of value in permitting control house catches to be analysed. From such analysis it should be possible to assess the proportion of adults which had originated in casual water and the proportion coming from more permanent breeding places. If, of course, it should be proved that the apparent differences in adult behaviour are, in reality, linked with differences in mean maxillary indices, it will be necessary to take this into consideration in assessing the value of residual insecticides and mass spraying. It is further argued that, even if the differences in behaviour can be explained on the fatigue factor hypothesis, it will still be necessary to take them into account in attempting to assess the value of mass spraying technique.

It is considered that the method of statistical analysis could be more widely utilised in exploring many problems arising in the field, and that other variations, apart from those of maxillary dentition, might prove even more fruitful as a basis for analysis, although they would call for more time and labour than can usually be spared.