Infestations of the sugarcane pest Eldana saccharina Walker have been consistently serious in one part of the cane-growing belt of Natal, South Africa. Mortality in this region over seven years was estimated from moth catches in light traps, checked against population change measured from extensive larval counts, and plotted against climatic indices. The object was to construct a predictive model to illustrate mortality in other regions of the cane belt, to which infestations have spread in recent years. The spread southwards along the coast did not seem to have resulted from a decrease in natural mortality, but the spread to higher altitudes appeared to be due to lower mortality associated with warmer and drier years. The phenology of the insect and the effect of the annual harvesting cycle on phenology are discussed.

In insecticide trials in Southern Rhodesia against the woolly apple aphid, Eriosoma lanigerum (Hsm.), using methyl-demeton (0·078 and 0·052 per cent. active ingredient), dimethoate (0·0625 and 0·0417 per cent. active ingredient), diazinon (0·0625 per cent. active ingredient) and malathion (0·1041 per cent. active ingredient) as foliar sprays, all insecticides gave good control of infestations above ground, but methyl-demeton and diazinon gave the best control, and treatments were followed by slower rates of repopulation.Injecting the lower part of the trunks of trees 25 to 30 years old with ½ fluid ounce of a concentrate of a systemic insecticide, 50 per cent. methyl-demeton or 40 per cent. dimethoate, at a single point gave excellent control where that part of the sap stream supplying the aphid colonies was intercepted. By injecting with a spiral of small holes around the trunk using ½ fl. oz. 50 per cent. methyl-demeton, control of all aphids on the tree could generally be achieved.Good control of subterranean aphid colonies on 15-year-old trees was achieved by the application to the soil of 4 gal. per tree of a fluid containing 100 cc. of a concentrate containing 75 per cent. of V-C 13 (O,O-diethyl O-2,4-dichlorophenyl phosphorothioate) diluted with water.Biological control of E. lanigerum in Southern Rhodesia by the Hymenopterous parasite Aphelinus mali (Hald.), which was introduced in 1961, shows great promise.

The red locust, Nomadacris septemfasciata (Serv.), is known to exist perennially in large numbers in a few areas and it is considered that a plague can start only when swarms escape from these outbreak areas, of which the most important are the grassy plains surrounding Lake Rukwa, in south-west Tanganyika. Swarms are most likely to leave the outbreak areas when the locust population is large. Thus, in order to prevent the formation of swarms, the escape of which could start a plague, it is necessary to keep down locust numbers. Control of the numbers is being achieved successfully by spraying poison from aircraft, but this requires a permanent staff with expensive equipment capable of dealing with the heaviest outbreaks. A form of ecological control is desirable that would stabilise locust numbers at a low level and so reduce the need for chemical control. This might be achieved by altering the environmental conditions so that highly successful breeding would never occur. Alternatively, by ecological methods, the locusts might be induced to concentrate more effectively, so making chemical control easier and cheaper.In order to decide whether or not ecological control is possible, it is necessary to know what factors affect the breeding of the red locust, for it is in the breeding season that the fastest change in numbers occurs. The main factors, which are not entirely mutually exclusive, would seem to be climate and weather, soil MILES t t t Fig. 1 Map of North Rukwa, Tanganyika, showing position of experimental plot.

In insecticide trials in 1962–63 in Rhodesia against woolly apple aphid, Eriosoma lanigerum (Hsm.), no appreciable control was achieved by applying ½ fluid oz. of a 40 per cent, emulsifiable concentrate of dimethoate per tree at 2- to 3-week intervals for 16 weeks in any of the following ways: painted directly on the lower trunk; absorbed in a cotton-wool band applied to the trunk, after being diluted 1:3 in water; applied to a furrow around the stem after being diluted in four gallons of water; injected into the soil with a nematicide injector after being diluted 1:4 in water.A foliage spray of DDT (0·195% active ingredient) had a gradual controlling effect on the aphid and caused no upsurge such as might have occurred had the parasitic activities of Aphelinus mali (Hald.) been suppressed.Activity of the ant Pheidole megacephala (F.) was immediately halted on trees sprayed with DDT and was suppressed on trees the trunks of which were painted with dimethoate and on those banded with a dimethoate-soaked barrier.Over a fourteen-month period, the numbers of living aphid colonies fluctuated before decreasing at the same time as the activity of A. mali intensified.

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