Annual variations of dry-season populations of larvae of Busseola fusca (Fuller) in Northern Nigeria

Extract

The larval populations of Busscola fusca (Fuller), a major pest of the guineacorn (Sorghum vulgare) crop, which survive the dry season in and around villages near the Research Station, Samaru, Northern Nigeria, were assessed by sampling. The larvae of B. fusca survive the five to six rainless months in diapause in crop residues, most important of which are guineacorn stems, which are stacked in the fields after harvest. Between 1956 and 1962, 100-stem random samples were collected from as many stacks as possible within an area of about six square miles. Each of the 348 samples was dissected immediately after collection and the number of living larvae of B. fusca per sample was recorded. The mean number of larvae per sample varied annually and ranged from 7 in the 1960–61 dry season to 33 in the 1959–60 dry season. The mortality of larvae is comparatively low between January and March, when most samples were collected, and it is concluded that the date of sampling did not unduly influence the estimates of annual variations of the population. The location of sampling areas also had surprisingly little effect and, despite uneven growth of the crop, the estimates of larval populations were remarkably uniform throughout the ten sampling areas and between samples within the main sampling area of Bomo village.

It is concluded that there is considerable variation in dry-season populations from year to year. The factors causing this variation have not been determined, and it is suggested that other workers might profitably continue and expand these investigations.