1. An attempt has been made to elucidate the confusion existing about the biology, morphology and nomenclature of the Oat-Apple Aphis, Rhopalosiphum prunifoliae, Fitch. A close study of the problem confirms the observations made by Börner that at least two distinct species have in the past been included under the name of R. prunifoliae. The names Rhopalosiphum padi, L., and Rhopalosiphum crataegllum, Theo., are adopted for these species.

2. Detailed descriptions and figures of the different generations are given and a comparison shows that the two species can readily be distinguished from one another.

3. R. padi appears to be of greater importance as a cereal pest than R. crataegllum. The latter species is a widespread pest of pip-fruit.

4. An account is given of the overwintering of R. padi on Prunus padus, and the results of experiments on estimating the size of the ova-populations is shown.

The author is indebted to Mr. R. A. Harper Gray for allowing him facilities to carry out the investigation; also to Mr. J. A. Dunn for assistance in collecting some of the material and much general help.

(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.

In April 1947, the laboratory stock of Glossina palpalis, R.-D., puparia collected from the Kaduna area suddenly became heavily infested with the pupal parasite, Syntomosphyrum glossinae, Wtstn. Presumably an infected pupa had been brought in from the bush and a few parasites had emerged undetected; it was not until the emergence of their offspring that the mass-infestation was revealed.

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.

1. A sketch is given of the Malaria Control Organisation in Service areas in Mauritius with a summarised history of malaria work in the Island since the first epidemic in 1865.

2. Keys to Mauritian Anophelines and their larvae with notes on their field recognition characters are followed by data on the distribution of adult Anophelines in the Colony and their relation to malaria intensity in different areas. A. melas appears to be absent from coastal swamps.

3. The influence of a number of environmental factors is discussed. It is concluded that temperature is an important limiting factor generally in winter and perennially in the highlands (above 1,000 ft.), but that the flushing action of heavy rains and probably the precipitation of food supply by colloidal iron moving under high rainfall conditions (over 100 ins.) from ferrugineous lavas both play their part in the natural control of A. funestus and A. gambiae.

The behaviour of A. gambiae with respect to temperature is expressed by an area enclosed by two symmetrical catenary curves, that illustrate well the adverse influence on development of low temperatures normally occurring in winter on the coast and all the year round in the residential uplands above 1,000 ft. The thermal death point of A. gambiae larvae is about 42°C. and that of A. funestus 40°C. and the lower limit of larval activity is 16·5°C. A. gambiae develops most rapidly at an estimated temperature of about 37°C.

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.