RELATIONSHIP BETWEEN THERMAL HEAT UNITS AND SIZE OF POPULATION OF THE COTTON LEAFWORM MOTHS, SPODOPTERA LITTORALIS (BOISD.) BY USING LIGHT TRAPS

The population dynamics of the cotton leafworm, S.littoralis dur‌ing three successive years of 1989, 1990 and 1991 were studied at Fa‌quoss and Diarb Nigrn Districts, Sharkia Governorate. The relationship between the thermal heat units and population fluctuation are summar‌ized as follows : There was a gradual increase in the population of S.littoralis moths associated with the increase of the thermal heat units expressed as daily degree to be a peak in June of each year with corresponding thermal units 880, 840 and 770 daily degrees in the years of 1989, 1990 and 1991, respectively. At Faquoss District, the highest peaks of S.littoralis moths were represented by 12123, 8019 and 10337 moths/ month at the corresponding heat units, 779, 840 and 770 daily degrees in the years of 1989, 1990 and 1991, respectively. At Diarb Nigm Dis‌trict, the same observation was obtained with the exception of the year 1989, where the highst peaks of caught moths were represented by 6656, 11887 and 31529 moths/month at the corresponding heat units 538, 840 and 770 daily degrees in the years of 1989, 1990 and 1991, respectively. The high reductions in S.littoralis moths occurred during December of the three years when the thermal heat units decreased from ca. 594 daily degree as an average in November as compared with that of ca. 355 in December. It is interesting to note that the average numbers of S.littoralis moths caught between May and October or November showed the high-