Pink Bollworm, Platyedra gossypiella (Saund.), as a Pest of Cotton at Zeidab, Northern Sudan

Abstract

Losses from Pink Bollworm (Platyedra gossypiella) and from Spiny Bollworm (Earias insulana) were studied in the American Upland cotton crop grown on Zeidab pump irrigation scheme in the Northern Province of the Sudan. In 1948, a year of normal attack, 12·9 per cent. of the estimated potential yield was destroyed by bollworms. Pink Bollworm was responsible for 10·7 per cent. or a loss of 135 pounds of seed cotton per acre. Spiny Bollworm damaged 2·2 per cent. or 28 pounds per acre.Four-fifths of the total yield is derived from the bottom crop which is harvested before the end of September and consists of high grade seed cotton. The other fifth is produced as a top crop and consists of low grade seed cotton ripening in October and November. Only 3·5 per cent. of the bottom crop is lost on account of Pink Bollworm as against 33·3 per cent. of the top crop. The corresponding figures for Spiny Bollworm are 1·6 per cent. and 4·1 per cent.Some factors influencing the extent of pink bollworm attack are outlined. The Zeidab crop escapes serious damage through rapid maturity and even growth. Correct agricultural management is of great importance. Attack by Laphygma exigua in the seedling stage may result in increased damage by Pink Bollworm in the ripening crop.The origin of the initial pink bollworm infestation is discussed. Available evidence, which is not conclusive, suggests that local carry over of the dead season may not be sufficient to account for the initial infestations observed in the crop.Atmospheric water vapour saturation deficit appears to influence the duration of larval diapause in Pink Bollworm in the northern Sudan. Maximum emergence of moths from resting larvae in three areas occurs at or near the lowest saturation deficit of the year. The possibility is discussed that the degree of fixity of the diapause may be related to the gradient of the saturation deficit curve during the development of the resting larvae in the crop, a rising curve being associated with a well fixed diapause which lasts until the saturation deficit falls, and a falling curve being associated with a poorly fixed diapause which does not last but begins to break at once.