EFFECT OF CERTAIN WEATHER FACTORS AND SOME NATURAL ENEMIES ON THE POPULATION DENSITY OF THE BOLLWORMS AND COTTON LEAFWORM AT KAFR EL-SHEIKH GOVERNORATE, EGYPT

Abstract

Experiments were carried out at the Farm of Sakha Agricultural Research Station Kafr El-Sheikh Governorate, during two successive seasons, 2014 and 2015 to evaluate the effect of certain weather factors (temperature, relative humidity and wind speed), and some natural enemies (six insect predators were recorded, Coccinella undecimpunctata L., Scymnus interruptus Goez., Paederus alfierii Koch, Syrphus spp., Orius spp. and Chrysoperlla carnea (Steph.))on the population density of the bollworms larvae (pink bollworm, Pectinophora gossypiella (Saund.) and spiny bollworm, Earias insulana (Boisd.) and the egg-masses of the cotton leafworm, Spodoptera littoralis (Boisd.). The initial occurrence of the pink bollworm larvae on cotton bolls was recorded in the last week of July (26th) during the first season and week early (18th of July) during the second season and exhibited four peaks of population density in every season. Numbers of larvae were highly significant and negative correlated with changes of the temperature (-0.752** and -0.798**) of both seasons, respectively. While, the correlation between numbers of larvae and changes of the relative humidity was insignificantly and negatively (-0.103 and -0.140) in both seasons, respectively. But, the wind speed influenced on the larval occurrence were significant and negative (-0.472*) during the first season, and insignificant and positive (0.020) during the second season. So, the correlation were positive and significant (0.495* and 0.480*) between the density of larvae of pink bollworm and the insect predators during the two seasons, respectively. While, the initial occurrence of the spiny bollworm larvae on cotton bolls was recorded in the 9th and 15th of August during the two successive seasons, respectively, and exhibited three peaks of population density in every season, number of larvae of this insect was highly significant and negative correlated (-0.631** and -0.690**) with changes of the temperature during both seasons, respectively. While, the relationship between the relative humidity and number of the spiny bollworm larvae was negative and insignificant (-0.177) during the first season, but, it was positive and insignificant (0.083) during the second season, while, the wind speed influenced was significant and negative (-0.408*) during the first season, and it was insignificant and negative (-0.173) during the second season, on the larval occurrence of this insect. So, the correlation were positive and significant (0.542* and 0.585*) between density of the spiny bollworm and the insect predators during the two seasons, respectively. The cotton leaf worm egg-masses exhibited three peaks of population density in every season, the effect of temperature on the population density of the cotton leaf worm egg-masses was significant and positive (0.459*) during the first season, and insignificant and positive (0.212) during the second season, while, the effect of the relative humidity on egg-masses of this insect was insignificant and positive (0.347) during the first season, and negative (-0.134) during the second season. So, the effect of wind speed on egg-masses was insignificant and negative (-0.162) during the first season, and positive (0.263) during the second season. While, the correlation were highly significant and positive (0.631** and 0.620**) between the population density of cotton leaf worm egg-masses and the insect predators during the two successive seasons.