This review of investigations of Lygus simonyi, Reut., was originally written early in 1944 as a handing-over report, and was not intended primarily for publication. As I was then about to leave Uganda, it seemed desirable to place on record, for the information of my successors, the work which I and others had done, even though the investigations were still in an early stage. Since then, the opinion that publication of the report would be useful as a basis for future work has been expressed by the Empire Cotton Growing Corporation and others, and I have therefore agreed to publish it in spite of my consciousness of many shortcomings in it.

DDT (p,p'-dichlordiphenyl-trichlormethyl-methane) has been shown to be very toxic to the housefly, Musca domestica, L., when applied as a spray containing 0·1 per cent, w/v or more in kerosene. DDT at 1 per cent, gives an effective spray for practical use, but at lower concentrations the speed of knock-down is too slow. This disadvantage can be overcome by the admixture of a small amount of pyrethrum. A mixture of 0·03 per cent, w/v total pyrethrins and 0·1 per cent, w/v DDT in kerosene is recommended as a suitable fly spray for practical use. This mixture can be stored in glass bottles in the dark for at least 17 months at 27·5° C. without marked deterioration. Its toxicity may be increased by the incorporation of a suitable activator, e.g., sesame oil or isobutylundecylenamide.

The impurities in crude preparations of DDT appear to exert no toxic effect on houseflies.

DDT acts more slowly when dissolved in industrial methylated spirit than in kerosene.

Attention is drawn to the residual film effect of DDT on walls, etc., and an example is given to show how this effect was employed in the control of a fly population in a kitchen.

The symptoms of poisoning of flies by DDT are compared with those caused by pyrethrum. DDT is relatively slow in action; it is a severe irritant, causing the flies to buzz violently at one stage; it induces marked tremors during the coma preceding death; and, at death, it causes the legs to be tightly flexed at the femoro-tibial joint. When the pyrethrins and DDT are mixed in a spray, these constituents, so far as can be judged from the train of toxic symptoms, act independently, so that the rapid paralytic effect of the pyrethrins keeps the insects immobile until the slow lethal effect of the DDT supervenes.

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.

When I was revising the genera of the DIPRIONIDAE (Benson,1939), the British Museum had very scanty material of Neodiprion other than of the sole Palaearctic representative of the genus, N. sertifer (Geoffr.). The few North American specimens of the genus, only five females belonging to five species and a few unnamed males, were all ancient specimens in poor condition and pinned so as to obscure the shape of the scutellum. I had therefore to supplement my knowledge of Nearctic Neodiprion by information kindly sent to me by the late Miss Grace Sandhouse, gleaned from specimens in the collections at Washington. Atwood and Peck (1943), in dealing with long series of Canadian Neodiprion, have since found that the shape of the scutellum, as defined in my paper, is rather difficult to interpret and is liable to considerable individual variation.

(a) Small field experiments (not attempts at control) are described with DDT in emulsion and in solution in mineral oils, 5 per cent, pure DDT in each material. These were tested on mosquito larvae (mainly A. funestus) under conditions that provided good opportunities for repetition and measurement of dose per unit area. Considerable day to day fluctuations were observed in numbers of larvae obtained by dipping, before the insecticide was applied.

(b) Preliminary work showed that kerosene, or dieseline without DDT, were not larvicidal in doses up to 0·5 cc./sq. yard. The dose of oil that was harmful was not determined.

(c) It is clear that DDT, either in oil or as an emulsion, is a very effective larvicide, as is well known from work (mostly unpublished) in many parts of the world.

(d) One may compare the effectiveness of DDT as an emulsion (Mixture A) and in solution in dieseline, as follows:—

It is clear that, under these rather precise conditions of testing, the dieseline solution is more effective than the emulsion both in the minimum amount required to kill, and in lasting effect.

(e) Field tests seem to indicate that DDT dissolves from oil into water, so as to make a larvicidal solution, at least when the water is shallow.

(f) Even if one puts down a relatively high dose (say 0·10 cc. of 5 per cent. DDT per sq. yard, at least ten times the quantity that will kill all larvae) the effect passes off in a few days, even on stagnant waters. It is not known what happens to the DDT, and difficult to know why it disappears.

(g) A heavy dose of DDT (0·50 cc. as above) gives a period of complete kill, followed by a period of partial irregular control. This was more often observed with solutions of DDT than with emulsions and might last as much as four weeks. No explanation of this irregular effect is put forward. It seems most difficult to understand how an insecticide, applied over an area of only a few square yards, can continue to kill some but not all larvae for a period of weeks.

(h) Except in one experiment, in which emulsion destroyed small fish, there was no evidence that creatures which prey on mosquito larvae were destroyed. There was no reason for thinking that after the population of mosquito larvae got back to normal it rose to exceptionally high figures (as it might have, had the predators been decimated).

♂♀. Derm black, with uniform dense sandy-brown scaling above and opalescent scaling beneath.

Head short, not transversely impressed, the temples less than half as long as an eye; frons with the median stria partly obscured by scaling and with a few erect spatulate setae on each side; eyes strongly convex, highest behind the middle. Rostrum similar in the two sexes, a little longer than broad, about as wide at the genae as at the base, and with the sides slightly sinuate; dorsum with a high bare median carina that expands apically into a broad bare epistomal area, which is unevenly punctate and not marginate, the epistomal setae being rather sparse and narrow, the areas on each side of the carina densely squamose and obliquely impressed in the middle; mandibles less densely setose than usual and without scales; mentum with only a single row of setae along the apical margin. Antennae black, densely squamose throughout, scape straight, widening from base to apex; funicle with joints 1 and 2 equal, 3 as long as broad, 4–7 subequal and transverse; club with the basal joint pedunculate. Prothorax transverse (2:3), broadly rounded laterally in the basal half, widest at one-third from base, the basal angles rounded obtuse angles, not constricted apically, the base shallowly bisinuate with the median lobe short and broadly rounded; dorsum smooth, with dense overlapping striolate scales and short appressed spatulate setae, concealing the median stria, and with a large shallow impression in the basal angles.

Damage to citrus fruits by Noctuid moths is known to occur at Ibadan and Agege (about 14 miles north of Lagos). The majority of the observations recorded in this paper were made on Moor Plantation, Ibadan, during the 1938 and 1939 seasons. Box (1942) describes the crop ripening, in the Gold Coast, between April and August as the Main crop, and that ripening between September and December as the Mid crop; in Nigeria, the bulk of the citrus ripens during the latter period, which is known as the Main crop. In this paper the terms wet season and dry season crops are employed.

The eggs of A. gambiae var. melas are distinctly different from those of typical gambiae, and it is now regarded as a distinct species, A. melas. Other workers have found that the larvae also differ, physiologically and structurally. All adults with an extra dark band on the palps—4-banded forms— are known to be melas, but those adults with normal 3-banded palps can so far only be distinguished from typical gambiae by egg characters.

A. melas is now known to be an important vector of malaria in coastal districts in West Africa. In some estuarine and mangrove swamp areas it may be even more important than typical gambiae. In melas caught in Freetown estuary (mostly from Wellington village), 42 out of 1,000 glands dissected were positive, giving a sporozoite rate of 4·2 per cent. for all months of the year. The oocyst rate was 4·7 per cent., and the total infection rate was 7·8 per cent.

In Freetown estuary melas is rare in Freetown itself, and in the adjoining village of Kissy, but in all other parts of the estuary is at least as important as typical gambiae. In many places it is the dominant vector. In Wellington to the east of Kissy, and on the Bullom shore which forms the north shore of the estuary, melas forms about 90 per cent. of Anophelines caught in houses.