The construction of a spraying tower for obtaining even deposits of insecticide of known weight is given, and the method of adjustment of this apparatus and procedure adopted during spraying are described.

To determine the weight of deposit obtained with different liquids under various conditions of spraying, a colorimetric method of estimation was adopted. Deposits of dye solution were collected on test-papers disposed at different positions on the area sprayed, the dye dissolved in 50 cc. of solvent and the concentration of dye in this solution measured by means of the Spekker Photo-electric Absorptiometer. By this method estimations of the weight of dye deposited on each test-paper were made to 0·01 mg. with great rapidity. The solutions of dye used in these experiments were 1 per cent. wt./vol. solution of “Oil Golden Yellow 13777” in petroleum distillate and a 1 per cent. wt./vol. aqueous solution of “Orange 60506”.

Series of tests were carried out with both the petroleum distillate and the aqueous dye solutions to determine the replication and distribution of deposits obtained with the spraying tower. It was found that the Standard Deviation of the mean weight of deposit per test-paper for the two spray liquids, both from one test to another and between different positions on the area sprayed in any one test, fell between ±0·8 per cent. and ±3·0 per cent. of the mean under the most favourable conditions for spraying.

In my recent paper on “Lygus simonyi, Reut., as a Cotton Pest in Uganda”*, I referred in the introductory notes to the fact that I had studied the male genitalia and other characters of about 20 species of Lygus in order to determine reliably all specimens collected in the course of the field work on which I was then engaged. In the present paper all of these species are described. Only a few of them occur commonly on cotton, and only one, which must now be called L. vosseleri, Popp., is a major pest of cotton, but the others were encountered, in most cases very frequently, in connection with an investigation of the alternative host plants of the cotton-frequenting species, and two are common on coffee (with L. coffeae, China, which belongs to a different group of species and is therefore not included here). Some of them bear a very close resemblance to L. vosseleri and often occur with it on the same plants and in the same localities; consequently considerable confusion had existed previously as to the identity of the various species collected.

In connection with field work it is often necessary to identify large numbers of specimens rapidly and without adequate facilities for the examination of genitalia. Consequently, the object of my study of the external genitalia of the males was not only to separate the species on the basis of these structures but also to test by means of them the reliability for diagnostic purposes of the few differences, such as those of colour and markings, that occur in both sexes and are readily visible with a hand lens. I concluded that the male genitalia afford the best characters for determination whenever they can be examined, but that colour and markings can suffice in both sexes for this purpose, despite the great variation which occurs in most species. The only other characters that are of value for the separation of species, within the group with which I have dealt, are size and (occasionally) length of rostrum. There is, in fact, a remarkable uniformity throughout this species group, so that in the absence of males or of facilities for examining genitalia, determination must depend upon a combination of a few simple characters, two of which, colour and markings, are variable, often difficult to describe, and can be utilised satisfactorily only after experience has been gained of many species and specimens from numerous localities and plants.

The species described in this paper constitute what may be called the simonyi group of Lygus and have the following features in common:—

1. A smooth, semi-shiny appearance (never very shiny because of slight pubescence and minute punctation).

2. The whole of the dorsal surface, including the hemelytra, and also the ventral surface, rather sparsely covered with very fine, short decumbent hairs directed backwards.

3. The whole of the dorsal surface, including the hemelytra, indistinctly and minutely punctate; the scutellum and (to a lesser extent) the pronotum very slightly rugose transversely.

Rothschild in 1917 (Novit. Zool., 24, p. 355) stated that the above name, which had previously been accepted as the “Brown-tail” or “Cul brun”, really represents the “Gold-tail” or “Cul doré”. Although this opinion was discussed and agreed to by such writers as Barnes and Benjamin in 1924 (Proc. ent. Soc. Wash., 26, p. 213) and Joannis in 1928 (Encyc. ent., Sér. B III, Lep. 3, p. 99), the great majority of systematic works since published in Europe still adhere to the interpretation of P. chrysorrhoea as the Brown-tail.

1. The original purpose of the present work was to confirm a previous finding that, in unfed adult Xenopsylla, longevity varies according to the humidity during the cocoon period, and to find whether this is due to differential loss of water during the prepupal period. The previous finding has been confirmed, but the cause is shown to lie in loss of water during the pupal and not the prepupal period.

2. Prepupae are shown to gain in weight by the absorption of water vapour from the air if kept at 24°C. and any relative humidity from 50–90 per cent. If kept below 45 per cent. R.H. they rapidly dry and fail to pupate.

3. During this period (about three and a half days from cocoon spinning to pupation at 24°C.) the dry weight decreases by about 2 per cent, of the original total weight, and the total weight increases by from 4–29 per cent., with a mean of 14 per cent.

4. The amount of water absorbed is independent of relative humidity within the range 50–90 per cent., and is approximately equal to the increase in total weight.

5. The critical relative humidity, below which the insects die and above which they absorb water, is shown to be substantially the same (from 45 to 50 per cent. R.H.) at 12°, 24° and 35°C.

6. After pupation the insects begin to lose water and continue to do so throughout the period. The rate of loss increases with decreasing humidity, though the effect of humidity is not very great.

7. Adults emerging from pupae kept at higher humidities weigh more, have higher percentage water contents, and live longer without food, than those emerging from pupae kept at lower humidities.

8. The results are discussed in the light of previous work, and suggestions as to the mechanism of the process of absorption of water are made.

The species described as new is placed in the genus Adelencyrtus, Ashmead, provisionally. The description is published at this time to provide a name, so that biological information concerning the species can be made a matter of record. The new species is most closely allied to Adelencyrtus. It differs from typical species of this genus with regard to the mandibles. In typical Adelencyrtus the mandibles are quadridentate, and the ventral margin is provided with a stout, cone-shaped seta. In the new species only the ventral tooth is distinct; the dorsal margin of the cutting edge appears as a wide truncation, which can scarcely be described as subdivided, and the ventral margin of the mandible lacks the stout conical seta. The most useful character for the identification of this species, and the one which reveals its relationship to Adelencyrtus most surely, is the distinctive male antennae. In this sex the antennal club is enormously cylindrically elongated, and the funicle is composed of two vestigial segments that are contained in a recess at the base of the club. Antennae of a similar kind have been described in the males of Habrolepis, Förster and Anabrolepis, Timberlake, two genera which are closely allied to Adelencyrtus. The males of Adelencyrtus have not been described.

The relationship of oviposition to weather, with a standard stimulus (4 per cent. ammonium carbonate), has been tested by a series of 134 exposures of a group of three sheep for one hour. 190 egg clusters were obtained, of which 169 were identified. With the exception of one cluster of L. caesar all were L. sericata.

There was a fairly close correlation (0·586) of oviposition with air-temperature. When the possible effect of other factors was eliminated, the correlation was little affected, showing that temperature was in itself responsible for the variations in oviposition. The lower critical limit of temperature was in the neighbourhood of 56°–58°F.

Solar radiation and oviposition had an apparent correlation, but this was found to be spurious, the effect being due to related air-moisture changes. At temperatures near the lower critical limit, insolation did not increase the oviposition rate, or lower its temperature threshold.

Humidity had an apparent inverse correlation with oviposition, but this also was an indirect effect, due to related temperature changes. Humidity showed a closer correlation when expressed as saturation deficiency than as relative humidity. Evaporation rate from a white atmometer sphere had only a low correlation with oviposition.

It is shown that the partial correlations of both saturation deficit and insolation with temperature effects eliminated, are insignificant, i.e. their apparent effects are due to related temperature changes. The multiple correlation coefficient for temperature humidity and insolation is practically identical with that for temperature.

Independent variations of insolation, i.e. variations not simultaneous with related temperature changes, had a significant effect on oviposition; for a given temperature, a high intensity of insolation was less favourable than a low, and this appeared to be a true insolation effect, and not due to associated humidity changes.

Independent variations of humidity had a suggestive but statistically insignificant effect, humidity tending to be inversely related to oviposition.

The regression of log oviposition on temperature, within the limits of this experiment, i.e. at temperatures up to 72°F., was linear. The slope was not significantly affected by the insolation and humidity factors, the total coefficient being 0·, and the partial coefficient 0·0428. These coefficients are the increase of the log number of egg clusters (plus one) for 1 degree F. increase, i.e. the oviposition rate increased in geometric progression for unit increase of temperature, the value (N+l) for egg clusters doubling itself for 7° increase.

(1) Up to 35 per cent, of adult Dysdercus nigrofasciatus from a heavily infested late cotton crop at Barberton were found to be parasitised by Tachinid larvae at the end of the season.

(2) The predominant Tachinid species was Alophora nasalis; Bogosilla fasciata was present in smaller numbers, and appears to be more common in regions of higher rainfall.

(3) The development of the Tachinid larva within the stainer was a protracted process under local winter conditions, the larval period of A. nasalis being of the order of 2–3 months, and parasitised stainers were correspondingly long-lived.

(4) The possible economic significance of the parasites is discussed.

Exposure of house-flies to residual films of DDT, deposited on wall-board from kerosene solutions, has shown that the initial toxicity increases (1) as the deposit of DDT per unit area increases, and (2) as the concentration of DDT in the solution increases, although the amount of DDT applied is kept constant. In practice, DDT in kerosene should be applied to absorbent materials at as high a concentration as possible, consistent with reasonable coverage, in order to avoid much of the DDT being carried by the solvent into the substrate, where it is no longer available for contact with the insects.

With wall-board, a critical value for the product of concentration and deposit of DDT has been shown to exist, above which any mechanical stimulus, including movement of flies on the treated surface, will cause the DDT present in supersaturated solution to crystallise, with consequent marked increase in toxicity of the film. Under some circumstances, removal of the crystal carpet is followed by its partial regeneration. If the product of the concentration and deposit falls below the critical value, the residual film is at no time very effective and soon loses its initial toxicity.

The persistence of toxic films of DDT on wall-board has been shown, over an exposure period of 18 months, to be closely bound up with the crystallisation of the deposits and their powers of regeneration during intermittent exposure to flies.

This work has been carried out as part of the programme of research of the Pest Infestation Laboratory, and this account is published by permission of the Department of Scientific and Industrial Research.

1. The method used is founded on those of Dunn (1927) and Harris (1942).

2. Results are given for 1943, 1944 and 1945 from areas in Kenya, Tanganyika and Madagascar.

3. An attempt is made to interpret these results in the light of the theoretical meanings of the Pot Index and the House Larval Index. This demonstrates that these two indices together can be used to assess the fluctuations in an Aëdes population and hence the efficiency of control measures.

4. Finally, the practical value of the Pot Index is discussed.

During the course of investigations into the use of the insecticides DDT and Gammexane, it has become increasingly clear that there is considerable loss through absorption into the treated surface. This loss of contact-available insecticide is most marked when simple oil solutions are used. Dosages of 100 to 200 mgms. per sq. ft., which on a non-absorbent surface (e.g. glass) are 100 per cent, toxic to flies exposed for very short periods, show little toxicity when applied to absorbent surfaces (e.g. mud).

(1) The experiment was carried out on a short term basis due mainly to the limited time available for stored food products work, but it does show the possibilities of giving to the carrier medium an “adhesive” quality for the purpose of retaining an external layer of DDT upon bagged commodities.

(2) The increased activity at night of insects attacking stored food is interesting and the movement of insect densities in bags containing foodstuffs needs further detailed investigation. It does seem that a very high percentage of adult beetles will migrate to the surface of bags from inside the contained foodstuffs, and this makes it possible to achieve a fair measure of control by coating bags with a deposit of DDT.

(3) When a concentrate mist of a DDT emulsion-gum arabic solution is allowed to settle upon a bag surface, there is no detectable penetration of DDT through the sacking texture and therefore no danger of contaminating the contained foodstuffs.

(4) A deposit of such a DDT film, at a concentration rate of 50 mgm. DDT/sq.ft. upon a jute bag surface, remains appreciably toxic to Tribolium castaneum, Calandra oryzae, Rhizopertha dominica and Laemophloeus spp. for a period of approximately 60 days.

During the past 30 years, at least seven species of injurious insects are known to have evolved strains that are more difficult to kill with recognised chemical insecticides than are the normal populations of these pests.

In 1939 it was reported from the East London area that farmers were experiencing difficulty in controlling the one host blue tick, B. decoloratus, by regular dipping in the recognised 7-day strength arsenical wash. Field observations confirmed this.

A technique for treating ticks in the laboratory is discussed in detail. This technique has been put to exhaustive test and some 15,000 adult female blue ticks have been subjected to in vitro treatments with remarkably consistent results.

Experiments are discussed that suggest that arsenic kills ticks by contact. It is further claimed that by using the technique described it has been possible to furnish proof that an arsenic-resistant strain of B. decoloratus does exist in South Africa. It would seem that when once the arsenic-resistant tick has established itself on any farm, the continued dipping of cattle in arsenical washes results in an unintentional artificial selection of those varieties within the tick population that are resistant to arsenic. Continued dippings in arsenic thus aggravate the position and some insecticide other than arsenic should be used to combat this arsenic-resistant strain of B. decoloratus.

Gammexane was experimented with and it is shown that 0·005 per cent. is sufficient to kill adult females of the arsenic-resistant tick and could be taken as a basis for further experiments. Oil base preparations and water suspensions of Gammexane are twenty times more toxic to the tick than are dust preparations.

Meteorus loxostegei, Vier., is another important endoparasite of Loxostege sticticalis, L. It is perhaps second to Bracon vulgaris, Cress., in general importance as a control agent; it appears to be somewhat more variable in numbers than the latter species, but neither in the present work has been seen to reach the degree of parasitism shown by Phytodietus in Alberta in 1942.