Microtermes najdensis is widely distributed throughout irrigated cropping areas of the Tihama region in Yemen Arab Republic. It is subterranean and damages young and mature plants by penetrating the root system and ultimately the stem, causing wilting and death. Surveys showed that plant-mortality without termite control ranged from 2-63% (average 20-30%) in cotton and maize. Pepper, okra and tomato were attacked less severely (average mortality of 10-20%). Tobacco, sorghum, millet and most vegetables suffered little damage (less than 2% stand loss) whereas experimental crops such as groundnuts, wheat and sesame suffered severe losses. Insecticides were evaluated as pre-sowing soil treatments in cotton in two trials, one near Hudaydah and one near Zabid. At Hudaydah, Microtermes foraging began late in the season and there was little damage; plant mortality in untreated plots was 8.1-9.3%. At Zabid, foraging began earlier and mortality in untreated plots was 39.7-48.5%. Aldrin and chlordane at 1.0-2.0 kg/ha gave significant control with mortality at 0.0-0.5%, in all trials. There were no significant differences in yields at Gumeisha, but at Zabid untreated plots yielded 3200-3500 kg/ha, significantly less than 3700-4500 kg/ha on aldrin and chlordane treated plots. Lindane, HCH, diazinon, phoxim, chlorfenvinphos, isofenphos (except at 7.5 kg/ha) and chlorpyrifos were significantly less effective than aldrin and chlordane in preventing mortality, even at high dose rates (e.g. 18.2-28.2% mortality at Zabid with chlorpyrifos at 14.4 kg/ha). Wood baits placed on the surface between cotton plants at Hudaydah were effectively protected at peak foraging times in the aldrin and chlordane treatments; 0-5% of baits were attacked compared with 25-26% in untreated controls and 19-25% in lindane and HCH. Diazinon (13-27%), phoxim (41%), chlorfenvinphos (55%), isofenphos (17-21%) and chlorpyrifos (21-22%) gave less effective protection than aldrin (0%). Attack on baits at Zabid in chlorpyrifos plots (31-35%) was similar to that on untreated plots (34%).
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