The biology and control of termites damaging field crops in Tanganyika

Abstract

Many crops in southern Tanganyika are attacked by termites, especially those grown in the miombo woodland (Brachystegia-Pseudoberlinia), which covers much of the southern and western parts of the country. The termites chiefly concerned are Microtermes albopartitus (Sjöst.), M. redenianus (Sjöst.), Ancistrotermes latinotus (Hlmgr.) and Allodontermes tenax (Silv.). A pit dug to investigate their nest systems showed that M. albopartitus was the most numerous, 425 occupied cells being recovered from an area 50 × 24 ft. excavated to a depth of 6 ft. Cells of the other species included 166 of M. redenianus, 54 of Ancistrotermes latinotus and 49 of Allodontermes tenax. The cells of Ancistrotermes latinotus were aggregated into small clusters connected by long runways; those of the other species were more or less randomly scattered. The greatest concentration of cells of all species was within the top 2 ft. of the soil, but a number of cells were found at greater depths and it is certain that 6 ft. is not the maximum nesting depth. Descriptions of the nest systems and fungus combs are given.Observations at Nachingwea in 1959–63 showed that loss of maize stands from termite attack averaged 27 per cent, over the five years, and that of soya 33 per cent. The damage was often great on individual plots, as much as 90 per cent, being recorded from one plot of maize. Plant-population counts over three growing seasons showed that maize is lost mainly towards the end of the season, whereas soya may be attacked any time after planting, increased losses occurring during dry spells and at the end of the season.Control was achieved by the use of aldrin or dieldrin applied as dusts to the soil before planting or used in seed dressings. It was found in a series of field trials that good control of termites was afforded by aldrin worked into the soil along the planting ridges at a rate of 1 lb. active ingredient per acre, but that in practice ½ lb. per acre gave nearly as good results when measured by yields. In spite of the considerable losses, it was considered uneconomic to use aldrin to protect soya from termite attack, but the increased yields of 200–400 lb. maize per acre justified the expenditure on insecticide. The aldrin dust protected both crops for at least one further year after application, the effects on yield being of the same order as before.A seed dressing of 75 per cent, dieldrin gave excellent control and was considerably cheaper than soil application of aldrin. The cost was only a few shillings an acre when the dressing was used at the rate of 0·1 oz. per 1 lb. seed, and the effect was to raise yields of maize by 330–500 lb. and of soya by 110–180 lb. per acre.Trenches were dug to investigate the effects of soil treatment with aldrin on the nest systems of the termites. There was little effect on cell density eight months after application, but after 20 months there were signs of a reduction, especially in the top 9 in. of the soil.