The present paper is the result of studies begun privately by the writer shortly after his return from South America in February 1930. The subsequent continuation and conclusion of the task was made possible through the authorities of the Imperial Institute of Entomology, to whom, especially the Director, Sir Guy A. K. Marshall, C.M.G., F.R.S., the writer is gratefully indebted for his appointment, in a temporary capacity, at the Farnham House Laboratory, as from 1st August. It was considered that a final revision of the American forms of the groups here considered would be a useful contribution to the West Indian investigations on sugar-cane insects being conducted on behalf of the Institute by Dr. J. G. Myers. At the laboratory the writer found conditions ideal for the prosecution of such work, and he desires to acknowledge his appreciation of the continuous help and encouragement received from the Superintendent, Dr. W. R. Thompson, and his colleagues there, among whom Dr. G. Salt deserves a special word of thanks for his never-failing generosity in offering friendly advice and practical aid, both of which, it must be confessed, have been frequently needed.

Beattie & Howland's recent studies of the bionomics of some tree-hole mosquitos emphasize the importance of the food factor, total organic nitrogen, and the apparent lack of correlation between hydrogen ion concentration and larval incidence. In Queensland mosquitos selecting such breeding-places are with a few exceptions distinctly arboreal, and the presence of domestic mosquitos in tree-cavities is dependent upon proximity to human habitations. It is a curious fact that when this is the case both Aëdes argenteus and Culex fatigans will breed in smaller accumulations of water than Aëdes notoscriptus does.

Appended herewith are the results of a recent survey made in midsummer of trees situated within the Brisbane Area of 385 square miles. Pine trees and gum trees do not lend themselves to the production of cavities and therefore offer very little opportunity for breeding.

The poincianas hold the highest actual percentage, but on account of the far greater number of figs containing potential breeding cavities, the latter constitute a greater actual menace. The amount of water contained in each cavity varies considerably with the time of year.

Erythroneura lubiae, sp. n.

Colour :—Pale green covered with a whitish pruinosity ; middle of pronotum and apices of tibiae, tarsi and ovipositor of ♀, slightly darker green ; a spot at middle of apical margin of pronotum and a broad stripe down middle two-thirds of scutellum, opaque white. Eyes dark greenish grey, apex of rostrum brown. In some female specimens the head and pronotum are uniformly greenish yellow and the white spots are obsolete. Tegmina more or less hyaline, the veins, clavus, brachial and suprabrachial areas, sub-opaque, suffused with pale green or greenish yellow ; the membrane infuscate towards apex and along inner margin ; claval commissure very narrowly and extreme inner margin of membrane beyond apex of clavus, dark brown ; costal plaque distinct, pallid. Wings whitish hyaline, faintly infuscate towards apex, veins white. Abdomen pale whitish green, basal tergite and anal segment greenish yellow. Tibial spines white.

Structure :—Ocelli absent ; head as wide across eyes as pronotum across humeral angles (47 : 47) ; seen from above slightly less than half as long in middle as wide between eyes (13 : 27), only slightly longer than length at eye (13 : 11) ; face (including clypeus) about 2·25 times as long as wide between antennae (50 : 22) ; frons three times as long as clypeus (36 : 12), which is apically sub-angulate. Pronotum about half as long as wide across humeral angles (23 : 47).

The larval stages of two species of Syrphid flies, namely, Eumerus tuberculatus and E. strigatus, are frequently found in rotting narcissus bulbs, in iris and tulip, and in vegetable roots, such as parsnip. The writer has shown that frequently the decay, at least in the narcissus, is directly attributable to the presence of these larvae and that they must therefore be considered to be primary pests. It was further shown that, contrary to current opinion, the predominant species at the time of writing was E. tuberculatus. In passing it may be recorded that this predominance has, in each subsequent year, become more marked, until at the present time E. strigatus has ceased to rank as a bulb pest, at least in South-West England, Holland, and probably the Irish Free State. The larvae of the two species are very similar to one another, and it has not been found possible to separate the species, with any great degree of accuracy, during the immature stages. In the adult form, as shown by Collin, separation is easily effected. In the course of experimental work with these flies a third, and superficially somewhat similar Syrphid, namely Syritta pipiens, L., was frequently bred from decayed narcissus bulbs.

The following data have been gathered over a period of about one year (January to December 1929) in the Nairobi District, Kenya Colony.

It was thought that the organic content of natural waters would certainly offer some indication of their suitability for the breeding of Anopheline mosquitos and that an investigation might suggest some definite line of approach to this intensely complex problem.

During November and December 1928, certain water sources were selected by one of us (C. B. S.), in widely separated parts of the district, for weekly sampling. In each separate area some four to eight places were chosen for routine searches for Anopheline larvae ; thus in the Q area (Table II) seven places were searched every week and in the B area (Table I) six places. From the places in each area two were chosen for routine oxygen absorption tests, one with Anopheline larvae and one without, water from these same two places being sampled and tested weekly. Thus in the Q area, spots Q 5 and Q 6 were used for this purpose, and in the B area B 3 and B 5. It is necessary to emphasise the fact that these places were separated from one another by distances of 50 to 150 yards. The choice of the source of water to be sampled was made purely on the presence or absence of Anopheline larvae at the beginning of the work.

Many of the Aëdes larvae commonly met with in Nigeria have been described by Ingram & Macfie, who have made extensive studies on the Gold Coast. Wesché described larvae of seven species of Aëdes that he studied in Lagos in 1910. In 1912 Edwards published keys to the then known larvae of the African Culicinae, but many of the species of Aëdes that are plentiful in this area are not included in Edwards' key. Therefore it was thought that an additional comparative study would be of value.

The larvae dealt with in this paper by no means represent all the species that can be found in this area. They merely include the commoner ones in the vicinities of Kano, Ibadan, and Lagos, and some additional specimens of species found in Nigeria, which were lent by Mr. F. W. Edwards, of the British Museum, and Dr. V. B. Wigglesworth, of the London School of Hygiene and Tropical Medicine.

Rhaconotus mahensis, sp. n.

♀♂. Black ; scape and all legs red testaceous ; ovipositor bright red ; flagellum red-brown, possibly rather darker at apex ; wings hyaline, the setae with a distinctly fulvous tinge, and the stigma hyaline (at least not darkened).

♀♂. The integument is not coriaceous throughout, and is only sparsely clothed with setae (except on the flagellum and possibly the legs). Head smooth and highly shining, not coriaceous, impunctate, the vertex and occiput almost entirely devoid of setae ; antennae longer than head, thorax, and abdomen together ; flagellar joints in ♀ 29–33, in ♂ 26–28. Thorax : mesonotum dully shining, coriaceous ; the notauli well marked, joining slightly before reaching the posterior margin of the mesonotum ; propodeon with five longitudinal carinae, one in the middle and two on each side, these latter rather more closely placed to each other than to the median carina ; this median carina is discernible as such only in the basal half of the propodeon, thereafter becoming lost amongst the reticulate wrinkles with which the apical half of the propodeon abounds ; the lateral carinae, on the other hand, are discernible more or less throughout their length, particularly the inner pair which can generally be traced to the median apex of the propodeon where they join each other ; the integument of the basal half of the propodeon coriaceous on each side of the median carina as far as the first lateral carina, thereafter wrinkled as in the apical half.

Like Mauritius, many other cane-growing countries in the world are suffering severely from the ravages of Lamellicorn beetle grubs. In some of these countries, such as Australia, India, South America and the West Indian Islands, these insects are indigenous, whilst in others, such as Hawaii and Mauritius, some of them have been accidentally introduced.

Through intensive cultivation of sugar-cane, which in some places is the staple industry, these so-called white grubs have found an abundance of food and an adequate environment, so that they have become, even in their country of origin, a major pest of sugar-cane ; whilst in places where they have been introduced, the damage done, in some cases, is a serious menace to the sugar industry.

Heavy annual losses are being sustained in the Philippines, Queensland and Porto Rico ; at present the damage in Porto Rico is estimated to be 3 million dollars yearly.

In order to cope with such a state of affairs, all possible effort is nowadays being made in most of these countries to try to control the pests by rational and scientific methods. Though many important points have been solved by research workers engaged thereon, there still remain many unknown factors upon which enlightenment is required.

During work on mosquitos in Uganda a certain number of hitherto undescribed larvae have been found ; advantage has also been taken of the opportunity to redescribe from fresh material some species of which the published descriptions are (in the light of our increased knowledge of mosquito larvae) found to be inadequate.

Unless otherwise stated all larvae are from the neighbourhood of Kampala. All descriptions are of fourth-stage larvae, and in every case identification of larvae has been made by comparison with the cast skins of isolated specimens from which adults have been bred. The nomenclature used for the head-setae is that proposed by Edwards & Given ; measurements of the head are always maxima. As the setae of the thorax and abdomen do not appear usually to be of much value for purposes of specific identification descriptions of them have in most cases been omitted.

For determination of adults and other assistance the writer is greatly indebted to Mr. F. W. Edwards, of the British Museum.

The sandflies of the two largest Italian foci of visceral leishmaniasis, Naples and Catania, were studied.

The following species were found : P. papatasii, P. perniciosus, P. sergenti, P. vesuvianus, sp. n., P. parroti var. italicus var. n.

P. papatasii and P. perniciosus are the commonest sandflies in the areas examined.

Out of 1,547 ♀♀ dissected none showed a natural infection with Leishmania.

P. papatasii was infected with Italian strains of L. infantum by feeding on cultures through membranes. The infection rate was low, but in contrast to Indian strains of L. donovani in the same sandfly, the infection once established did not die out.

The following descriptions axe based on material collected or reared by the author, together with specimens reared from host-plant material collected by colleagues to whom the author's thanks are due.

From the descriptions it will be further evident that the generic location of new species is still difficult, but this state of affairs can only be remedied by a monographic revision of the African Trypetidae. It is felt, however, that although the author has such a work in progress, it is not desirable to hurry publication. Delay is advisable, especially in view of the number of new species continually being found, and the frequent need for the formation of new genera.

Types of the new species are in the author's collection ; paratypes so far as available will be placed in the British Museum.

Eurytoma verbena, sp. n.

♀♂. Black ; abdomen sometimes a little reddish on the sides. Antennae dark brown ; pedicel slightly yellow below. Wings whitish, with the veins very clear yellow. Legs with coxae and femora black, the latter sometimes a little reddish ; tibiae red in the middle, often mixed with black, especially at the hind tibiae ; knees, base and tip of tibiae, and the tarsi whitish.

♀. Head rugulose, face covered with white ciliae, with a carina between the base of antennae and the clypeus, and weaker striae diverging from the mouth. Antennal furrow rather deep, bordered by a carina and reaching almost to the median ocellus. Cheeks as long as half the length of the eyes, finely rugulose. Antennae inserted in the middle of the face ; scape short, reaching very little beyond the top of the antennal furrow ; pedicel not longer than broad ; annelli very small ; funicle joints longer than broad, the 1st almost twice, the 2nd about 1·5 times longer than broad, the following gradually shorter.

Thorax more strongly sculptured than the head, reticulate. Scutellum protruding a little above the postscutellum, which is hidden, and the propodeon ; this latter, seen from the side, has the posterior margin almost vertical. Mesopleurae finely punctate, with some short horizontal striae ; episternum transversely striate, but the striae not reaching to the hind margin, along which it is punctate, like the mesopleurae.

(1) A. elutus females in Palestine show seasonal variations of fertility, but these do not appear to explain fully the distribution of adults throughout the year.

(2) Females of the overwintering generations show low fertility. This depends probably on conditions of larval life.

(3) The seasonal changes in the egg of A. elutus in Palestine are due to temperature variations. It is suggested that these changes are protective adaptations against cold in winter and excessive heat and irradiation in summer.

(4) The entering of the hibernation stage of A. elutus in Palestine cannot be considered as a pure consequence of the low temperature in autumn, since spring activity begins at a much lower temperature.

(5) During hibernation the females feed, but do not bring eggs to maturity ; the blood is used for fat accumulation.

(6) During the second half of the hibernation period the females lose their reserve materials.

(7) Full fat females starved in the laboratory lose their fat-body reserves, and simultaneously their ovaries develop to stage 2. Under the prevailing temperature the process requires about 3 weeks.

(8) A slow development of the ovary is going on during hibernation, but never proceeds beyond the second stage. The ovaries in a large percentage of females reach this stage at all times when reactivity occurs at the end of the hibernation period.

In the great majority of organisms, the reproducing individual does not engender all of its progeny simultaneously. Between the beginning and the end of the reproductive period there is usually a certain interval of time, during which the production of offspring continues in a manner depending, on the one hand, upon the specific characteristics of the organism, and on the other, upon the conditions under which it lives. From this simple fact follow some interesting consequences.

If the successive generations are separated by a long interval of time and conditions during this interval are of such a nature that the organism is inactive and in the condition of obligatory dormancy, known as diapause, then, in spite of the increase of the population, the generations will remain separate and distinct, and a comparison of the total populations in the successive reproductive periods will enable us to determine the rate of increase.

On the other hand, if the interval between generations is short and favourable to activity and the organism does not pass through a period of obligatory dormancy at this time, then, as the species increases, the successive generations will come to overlap, and the amount of overlapping will increase progressively as time goes on.

This is primarily due to the fact that when there is reproduction over a period of time-intervals, in a typical individual of the species, and conditions remain constant then the number of time-intervals during which births occur will increase from generation to generation.