The methods used to investigate the properties of dusts are described and, in a theoretical section, the relevance of the various physical properties to insecticidal action are considered.

In order to investigate the effect of toxic and non-toxic dusts on insects the experimental procedure was simplified to eliminate all difficulties associated with the formation of uniform dust clouds and deposits. In problems relating to the adherence of the dusts to insects the actual quantity of dust was measured either by weighing the insects before and after dusting or by dyeing the dust with Sudan III and determining the quantity colorimetrically. The experiments were all conducted under known conditions of temperature and humidity.

Non-toxic dusts killed insects by causing them to lose water. Not all non-toxic powders were equally effective when conditioned to the same relative humidity. All were without effect at saturated humidity and became progressively more rapid in action as the humidity at which the test was carried out was decreased (p. 32).

The non-toxic dusts caused the insects to lose water by abrading certain areas of the cuticle ; the more extensive the abrasion the more quickly the insects died (p. 27).

To be effective as an abrasive the dust must be hard and finely ground and, perhaps also, sharply angular. Thus materials which ranked high in Moh's scale of hardness were in general more effective than soft materials and hard materials became quite ineffective unless they contained material below about 10 μ, diameter. Presumably the coarser materials could not gain access to the articulations, etc., where abrasion usually occurred. This effect can be seen clearly with carborundum powders. Sharply angular glass was more effective than the same powder converted into rounded spheres (pp. 25–31).

Mosquitos continue to enter occupied, untreated native huts throughout the night, with peak periods of entry at dusk and dawn. Early morning mosquito catches do not give a true picture of the numbers entering and leaving huts during the night.

In a series of catches 63 per cent. of 5,576 mosquitos and 79 per cent. of 506 Anopheles gambiae were caught resting on the underside of the thatch roof.

By using five traps inserted in apertures one foot below the top of the wall, the numbers of mosquitos attempting to leave a hut were determined. Of 1,014 mosquitos entering huts before 10 p.m., 63 per cent. remained inside until 6.30 a.m., that is for 8½ hours. Catches to estimate numbers entering and leaving at different times during the night were also made.

Treatment of huts with DDT wettable powder and DDT-kerosene solution did not interfere with the normal behaviour of mosquitos as far as entry was concerned. Biting occurred in the treated huts.

The DDT wettable powder appeared to be more effective than the DDT-kerosene solution.

Some mosquitos entered the treated huts, fed and then left before acquiring a lethal dose. After making contact with treated surfaces mosquitos became restless but, under the conditions existing in the huts during the experiments, activation did not result in more leaving the treated huts than the untreated one. Unfortunately there were few A. gambiae and the predominant species entering the huts was Taeniorhynchus fuscopennatus.

Some of the female A. gambiae released into unoccupied DDT-treated huts escaped into the traps before acquiring a lethal dose. Although there was a tendency for more to enter the traps of a DDT-treated hut than those of an untreated hut, the data are insufficient to show a significant difference.

The majority of mosquitos entering the traps did so within one hour of their release.

No mosquitos were still alive 12 hours after their release in huts treated 17 weeks previously with DDT wettable powder or DDT-kerosene solution, or in the hut treated 12 weeks previously with "“Gammexane” wettable powder.

The paper describes field and laboratory investigations on the bionomics of Cephalonomia waterstoni, a Bethylid parasite of Laemophloeus spp. A table is given in which are listed all the Bethylids attacking insect pests of stored products to which reference could be found in the literature.

An infestation of Laemophloeus, associated with two “hot spots” in Manitoba wheat, which supported a large population of Cephalonomia is described.

A simple technique for the laboratory culture of Cephalonomia is described.

The life-cycle of C. waterstoni with Laemophloeus ferrugineus as host has been worked out.

The lengths of egg, larval and cocoon (prepupal and pupal) stages at combinations of 25°C, 30°C. and 60 per cent., 80 per cent. R.H. are given. The egg and larval stages are short, lasting for about six days at 25°C. and four days at 30°C.

Within the limits used, the relative humidity appears to have no effect on the duration of development at any stage. On the other hand, temperature exerts a considerable influence; the life-cycle at 30°C. is completed in two weeks but at 25°C. it takes three weeks.

Again within the limits used, the mortality appears to increase with decrease in saturation deficit. Mortality ranged from 9 per cent, at S.D. 12·7 mm. to 36·5 per cent, at S.D. 5·0 mm.

Without food or water at all combinations of 25–30°C. and 60–80 per cent. R.H. adults live for about four days, with a range of 0·5–9·5 days. There is no difference between the sexes. Unexplained contradictory results were obtained in two experiments.

With normal or paralysed host larvae available at 30°C. and 80 per cent. R.H., males live no longer than when no food or water is available but females live for about five weeks at 25°C. and 80 per cent. R.H. and for about four weeks at 30°C. and 80 per cent. R.H.

Males fed with sucrose solution at 30°C. and 80 per cent. R.H. live for several days longer than when starved : females live for the same length of time as when fed with host larvae.

The pre-oviposition period at 25°C. and 80 per cent. R.H. is about five days; at 30°C. and 80 per cent. R.H. about one and a half days.

Fecundity. At 25°C. and 80 per cent. R.H., Cephalonomia lays about 40 eggs on 30 host larvae : at 30°C. and 80 per cent. R.H., about 65 eggs on 40 larvae.

Cephalonomia females readily oviposit on larvae that have been paralysed some time previously, and can be induced to oviposit on larvae already bearing eggs.

Virgin females produce only male offspring (arrhenotoky).

Eggs are laid in groups of one, two or three (rarely four) per larva. Single eggs produce mainly females ; pairs produce mainly one male and one female ; trios produce mainly one male and two females. At 25°C. and 80 per cent. R.H. more single eggs are laid than pairs ; at 30°C. and 80 per cent. R.H. more pairs are laid than singles. This results in the production of a higher proportion of females at 25°C. than at 30°C. The incidence of trios at both temperatures is low.

C. waterstoni is equally viable on L. minutus, L. ferrugineus and L. turcicus but shows a marked preference for L. ferrugineus.

Two strains of a virus disease, “A” and “B,” which possibly may be two distinct viruses, occur on cacao in Trinidad. These are compared with the more virulent “swollen-shoot” and related viruses that are widespread in West Africa.

The most important resemblance between the Trinidad and the West African viruses is that both are carried exclusively by mealybugs of the family Pseudococcidae. There are also points of similarity in the symptoms, which in the Trinidad virus consist mainly of a transient red vein-banding, with or without a more or less discontinuous yellow vein-flecking (which does not disappear when the leaf matures) and, on certain varieties of cacao, red-mottle on the pods. Swellings on the shoots, a conspicuous symptom of most of the strains of the West African viruses, have not been observed in Trinidad.

Four species of mealybugs are definitely known to be vectors: Pseudococcus citri, which is the commonest and undoubtedly responsible for most of the natural spread of the disease; P. brevipes; a species near P. brevipes but almost certainly distinct; and Ferrisia virgata. Certain other mealybugs have been found on cacao in Trinidad but the virus has not yet been transmitted by them.

Most transmission experiments have been made with mealybugs bred up on potato tubers and with Posnette's technique of feeding potential vectors, after infection-feeding, on cacao beans from which one of the cotyledons has been removed, so that the insects can feed on the convoluted surface of the remaining cotyledon or on the radicle. Notwithstanding some drawbacks to this method it has many advantages over using young growing plants as tests.

The “latent period” of the virus in the test plants grown from dissected beans has varied between 20 and 123 days, though the symptoms most commonly appear from 30 to 50 days after infection of the bean. The symptom of red vein-banding has appeared much more often than that of yellow vein-flecking, irrespective of the symptoms on the virus source plant. When both symptoms appear the red veinbanding almost always shows up first.

All three immature instars, and young adults, of all four vector species are probably almost equally efficient as vectors, except that there is some indication that P. brevipes may be slightly more efficient than the other three species.

Starvation of the mealybugs before infection-feeding does not increase their capacity to transmit, though it usually helps to make them settle and feed more readily on the source plant.

The time for which the mealybugs feed on the virus source plant has little if any effect on their capacity to transmit the virus. Mealybugs have become infective in just over one half-hour infection-feeding, though the proportion of transmissions obtained when the infection-feeding time has been between one-half and two hours is rather less than that for over two hours, probably because in the former tests some of the insects had not actually fed.

The duration of feeding on the test bean is probably also immaterial, provided of course that the mealybugs do actually feed. The shortest test-feeding time that has resulted in transmission is 90 minutes, but this included a considerable “settling” time.

Transmission may be effected whether a mealybug feeds on the cotyledon or the radicle of a test bean.

Mealybugs can still transmit the virus if they are starved after infection-feeding for a period up to 22½ hours, but no transmission has yet been obtained when the post-infection starvation has been over 23 hours. It is not yet known whether a short period of feeding after infection-feeding renders the mealybugs incapable of transmitting, but post-infection feeding for 66 hours does so.

A transmission rate of just under 14 per cent, has been obtained with single mealybugs to each test bean but with larger numbers the rate has not risen in accordance with the mathematical expectation. A possible explanation for this might be that there are “active” and “inactive” races of P. citri, but so far practically no evidence for this has been obtained.

Mealybugs can become infective by feeding on the symptom-free parts of flush leaves showing symptoms in other parts, on entirely symptom-free flush leaves from infected trees, on the stem of a young infected plant, and on the leaves of a young infected plant after the disappearance of the transient symptoms of red vein-banding. It appears, however, that they pick up the virus more readily from flush leaves actually showing symptoms, and these have been used as the source of the virus in most of the experiments.

Few experiments have yet been made with strain “B” of the virus, but this strain has been transmitted with P. citri and P. brevipes.

All stages of P. citri, but especially young adults, often wander about of their own accord and are thus capable of spreading the virus, particularly to trees actually in contact with an already infected tree. The transport within a plantation of cacao pods during harvesting is thought to be a likely cause of isolated new infections.

Coccids on cacao have received much attention in recent years in connection with the transmission of swollen-shoot disease in the West African cacao belt and many papers on them have been published by British entomologists.

The best method of assessing the wetting powers of liquids is to measure the contact angle formed with a particular solid surface. In order to study the wetting of insects by spray liquids, it was necessary to measure, as rapidly as possible, the contact angles of very small droplets on restricted surfaces (such as portions of the insects). The apparatus used projected a greatly enlarged image of the drop, the outline of which could be traced very quickly and used for subsequent calculations.

Under practical conditions, spray droplets impact on insects with some relative velocity either due to drift of the spray particles or to flight movements of the insect.Measurements were therefore made of the contact angles formed by droplets of water of known size falling on to insects (or to a beeswax surface) at a known speed. It was found that with rather large drops (5 mm. diameter) the contact angles formed were somewhat lower than the normal advancing contact angle. With small droplets (0·1-0·5 mm. diameter) there was no difference. Biological tests were made with 30 species of insects, differing widely in the nature of their integument and habitat. The resistance to wetting was found to vary greatly, not only from species to species but also on different parts of the body of a single insect. In general, most of the insects were readily wetted by oils and unwetted by water. Insects withhard cuticular lipoids, such as Tenebrio, were more hydrophobic than the Blattidswith greasy cuticular waxes. A few species were both lipophilic and hydrophilic (larvae of Mamestra, Polia, Musca). Apart from the chemical nature of the cuticle, irregularities and the presence or absence of hairs were important. Increased roughnesslowers the contact angles of liquids with good wetting powers, but has the opposite effect with liquids with poor wetting powers. Measurements were made of thecontact angles formed on individual hairs of Arctia caja larvae by spray droplets. The contact angles formed on these hairs by plain liquids were strongly correlated with the angles formed on smooth Tenebrio cuticle or on an artificial beeswax surface; but there was only very rough correlation between the three sets of data when aqueous solutions of wetting agents were tested.

The test liquids included saturated and unsaturated hydrocarbons, mineral oils with varying aromatic contents, organic esters, alcohols and aqueous solutions. Among the hydrocarbons, members of the aliphatic series wet insect cuticle more readily than the aromatic group. The aromatic contents of the oils did not, however, affect their very high wetting powers.

The effects of adding surface active agents to aqueous sprays were investigated. Of the samples tested, the most effective wetting agents were those with neutral un-ionised molecules.

A method based upon Yeager's technique is described permitting the study of the surviving heart of Periplaneta americana under varying conditions for several hours.

Rotenone causes diastolic contractions, decrease of frequency and cessation in diastole, threshold <0·0000005 per cent. Presumably it produces an inhibitory action on the neurogenic automatic cardiac centre.

The latent period of the rotenone action is dependent upon the concentration. Using this principle a method is developed for quantitative estimation of the activity of derris preparations.

Tetraethyl pyrophosphate has a strongly accelerating action on the frequency of the heart and increases the amplitude; in this case there is no latent period. Threshold 0·000008 per cent. Presumably TEPP activates the neurogenic heart automatism by its vigorous anticholinesterase activity.

The purpose of this note is to illustrate the importance of searching for resting tsetse when making a fly survey. Highly experienced entomologists and fly boys, who are accustomed to making surveys for G. palpalis (R.-D.), G. tachinoides Westw. and G. morsitans Westw., get into the habit of expecting tsetse to be attracted to themselves or to screens or to bait animals, and may easily fail to detect the less common species unless they appreciate that these should be searched for in their resting haunts.

The wings of male Glossina morsitans appear to become frayed in the rainy season at about the same rate as in the dry season, and their brittleness seems directly related to age. The law of diminishing returns does not appear to apply, perhaps because of the weakening of portions of the trailing edge between indentations fairly near together.

The Epilachninae constitute one-sixth of the known species of the family Coccinellidae. They are herbivorous and include a number of well known pests of cultivated plants in different parts of the world. Their adults present a great uniformity of external structure, with the result that nearly all the known species have been placed in one genus, Epilachna Hope. Their identification is made more difficult by the employment of characters such as the elytral markings and spots which may vary a great deal in one species or be almost identical in two quite unrelated species. Lately, there has been a tendency to split the genus by employing more reliable morphological characters, including genitalia. A greater knowledge of the biology and morphology, including that of the immature stages, particularly the larvae, is necessary to evolve a natural classification. Relatively little was known of the larvae. This paper deals with 14 species belonging to six different genera.

In addition to discussion of the relationship of this subfamily with other Coccinellidae in the light of the extensive larval material examined, it is observed that larvae belonging to different genera, including those recently erected or revived, show considerable morphological differences that support a division of Epilachna (s.l.) based on adult characters. A study of the larvae of nine species that are still retained in the genus Epilachna shows that they are separable into several groups, which may well indicate where further division of the genus may be made.

In a search for the forest vector of yellow fever, catches of biting Diptera have been made by various methods in forest trees in Bwamba County, Uganda. The work here reported concerns Tabanids taken in catches made during the period 1944–45.

Three species of Tabanids have been taken in trees during these catches, and one of these, Chrysops centurionis, has proved to be mainly arboreal.

Observations on C. centurionis have shown that its main biting-activity begins just before sunset and reaches a peak during the hour after sunset. Thereafter the numbers taken diminish rapidly, but some activity continues throughout the night.

In the wet-season catches, this species was most prevalent in the forest canopy at heights of 50 to 60 feet above ground. In the dry season the most favourable level was lower, at 20 to 30 feet above ground.

It is suggested that monkeys are the natural hosts of C. centurionis, and that C. centurionis may be the vector of filarial infections among wild monkeys.

It is shown that there is a very close correspondence between the biting-behaviour of C. centurionis and that of the mosquito, A ëdes africanus.

Evidence of nocturnal activity has now been obtained in the case of one species of Tdbanus, three species of Haematopota and two species of Chrysops. It is suggested that there may be some connection between the remarkable eye colours of Tabanids and crepuscular or nocturnal activity.

Records of other Bwamba Tabanids are given.

The status of the species of Hypoderma that attack goats, and related species, is discussed. The Oriental species, H. crossi, and the Mediterranean species, H. aeratum, are shown to be distinct. H. aegagri is known in the larval stage only, but as this is identical with that of H. aeratum, the latter becomes its synonym.