Vertical distribution of Bemisia tabaci Genn. and Empoasca spp. on cotton plants and its relation to some weather factors

The vertical distribution of insect pests on the plant is one of the most important factors in any sampling plan. An experiment was carried out at Sakha Agriculture Research Station Farm to determine the population density of whitefly, Bemisia tabaci Genn. and jassid, Empoasca spp. on the three levels of cotton plant (upper, middle and lower) as well as its relation to some weather factors during 2002 and 2003 seasons. The obtained results revealed that in both seasons the population of B. tabaci (immature stages) induced the highest number during September on the three levels of cotton plants. In both seasons, the highest number of immature stages of B. tabaci was recorded on the middle plant canopy (264.07 and 234.36 individuals), followed by the lower level (207.87 and 217.34 individuals), while the upper level harbored the least number recorded (58.67 and 60.53 individuals). The population of Empoasca spp. recorded the highest numbers during July in both seasons on all plant canopy. The upper level exhibited the highest number of jassids recorded (90.06 and 92.13 insects) followed by the lower level that harbored (40.36 and 47.66 insects) in both seasons, while the least number took place on the middle level (13.59 and 16.36 insects). Generally, the temperature was within the optimum range for the population activity of the two insects. Also, the population of whitefly was more affected by relative humidity than jassid, especially in the second season. The combined effect of the two weather factors on these insects was less pronounced. These obtained results are important in programs of insect management in cotton fields, as the pesticides should be applied to the place where the insects are present.