During the years 1925–7 an investigation was made of the Culicine mosquito fauna of Singapore, mainly with the object of learning which species were responsible for the local mosquito plague, and where they bred. In the course of this work numerous species were reared, the larvae of which have never been described, and descriptions of these are presented in this paper; these are supplementary to the descriptions published recently by Edwards (Bull. Ent. Res. xvii, pt. 2, 1926).

During the last few years a number of papers have been published by entomologists in connection with the hypothesis known as the “ Hopkins host-selection principle.” This principle, as defined by Dr. A. D. Hopkins himself, is that an insect species that breeds in two or more hosts will continue to breed in the host to which it has become adapted. Thus, according to this author, the mountain pine beetle, Dendroctonus monticola, will destroy mountain pine, yellow pine, lodgepole pine and sugar pine, but if it becomes established in one species of pine through many generations, the beetles on emergence show a decided preference for the species in which they have bred and will not, in fact, attack any other. In 1922 Craighead published a paper giving the results of experiments carried on during a number of years with about a dozen species of Cerambycids. He states that in practically all the species studied the adults show a marked predilection for the host in which they have fed as larvae, provided that they are not deterred by other factors. Continued breeding in a given host is said to intensify the preference for that host. With some beetles whose larvae can be transferred to another species of plant and successfully reared therein, this association with the new host for a year, or even less, during the latter part of the larval life is said to determine a preference for this in the resulting adults. The author believes that his experiments may indicate the mode of origin of certain closely related species or varieties. The conclusions at which he has independently arrived were long ago suggested by Walsh. That new forms do not thus arise more rapidly in Nature, Craighead considers to be due to the high mortality of the young larvae in the new hosts.

While engaged as entomologist to the Central Aguirre Sugar Company, owners of some 12,000 acres of sugar-cane lands situated on the south coast of Porto Rico, the writer continually recommended the importation into that island of certain larval parasites of Diatraea saccharalis, Fabricius (sugar-cane moth borer), as the one species indigenous to Porto Rico—Lixophaga (Euzenilliopsis) diatraeae, Townsend (Tachinidae)—alone, does not effect a sufficiently high percentage of control of the island's major sugar-cane pest.

The examination of a collection of fleas, obtained during the last two years in the course of the investigation of plague amongst the rodents of the South African veld, has resulted in the finding of three new species of Xenopsylla, which are described below.

My thanks are again due to Dr. K. Jordan and to Dr. G. A. K. Marshall for advice and help kindly given to me.

(1) An effort has been made to find an explanation for certain problems involved in the selection of breeding-places of mosquitos in Queensland.

(2) Many of these problems must remain unsolved until it is possible by patient study of local conditions to bring all the factors involved into play.

(3) In order to explain the reason for the avoidance of natural water, where it exists, it is suggested that the soils that underlie them should first be taken into consideration, and that the waters should be examined with reference to their physical and chemical conditions.

(4) Observations and experiments, spread over a period of eighteen months, confirm the findings of previous authors that Characeae do not in themselves possess larvicidal properties.

(5) That food is the main determining factor in the choice of preferential breeding-places seems to be borne out by actual results obtained, and that when such are not available, mosquitos will resort to breeding-places of compulsion, such places being usually observed to be entirely or partly devoid of food supplies.

(6) It is suggested that the salts of alumina and iron in the ferrous state tend to destroy food organisms, and that where these conditions exist, the water is not selected preferentially.

(7) The presence of algae leads to the appearance of Anopheles annulipes.

(8) That Cladophora holsatica inhibits larval growth seems to be experimentally established.

(9) Bacterial scums are mainly due to B. subtilis and have a tendency to produce a slight alkalinity.

Microbracon hancocki, sp. n.

♂♀. Black; the front legs completely, the middle legs except the coxae, hind trochantines, hind femora, basal third of hind tibiae, mouth-parts largely, all ventrites, the lateral membranous margins of the 1st tergite, about each lateral quarter of the 2nd and succeeding tergites, bright red testaceous.

In summarising, the following points are to be noted:—

1. The thermal death point of the blow-fly was definitely influenced by the factor of humidity.

2. Saturated and dry air had the effect of lowering the thermal death point.

3. Relative humidities from 60 per cent. to 80 per cent. were more favourable, while relative humidity of 70 per cent. actually was found to be an optimum point.

4. From the weighings it may be concluded that death in saturated air was due to the inability of the flies to regulate their heat by evaporation.

Like other species of its genus in different parts of the cotton-growing areas of the world, Dysdercus sidae is a serious pest of cotton, not as has been stated from staining the lint by its excrement or being crushed in the gins, but from being the agent by which internal boll-rot fungi enter the green cotton boll.

Many anti-malarial workers have recorded the larval habitats of Anopheline species, and while their records usually reveal a variety of types of breeding-places for the same species even in one and the same country, the characterisation of the breeding waters usually lacks precision. This is hardly surprising, since descriptions are based upon naked eye observations, and only physical aspects of the breeding-places, or in addition only the most striking characteristics of the associated forms of vegetation are recorded, more or less casual information being given concerning the depth, clear or muddy character, and stagnation or currency, of the water, together with even more incomplete statements relating to the plants growing in or near it. The statement, not unimportant in itself, is, for example, often volunteered that larvae of a particular species are found in streams or pools with grassy margins, while information is usually lacking relating to the species of even the more conspicuous plants which grow in the water itself, and which are characteristic of it or of the presence of particular Anopheline larvae. For example, it has been found that in Malaya in ricefields on the flat coastal plain, the presence of the floating plant Utricularia flexuosa is widely associated with larval associations in which Anopheles sinensis predominates over A. barbirostris, other Anophelines being generally absent (Williamson, 1925). It seldom if ever happens, however, that an aquatic plant has the same range of adaptability as the associated mosquitos. For example, in the case quoted, U. flexuosa abounds over many square miles in the Krian rice-fields, from which all Anopheline larvae are absent, despite the proximity of their breeding-grounds; and conversely, A. sinensis and A. barbirostris are very commonly found unassociated with Utricularia.