DEVELOPMENT OF ONION THRIPS, Thrips tabaci LINDEMAN, AS A FUNCTION OF CERTAIN AGRICULTURAL PRACTICES

The population fluctuation and development of onion thrips, Thrips tabaci Lindeman, on onion plants, under certain agricultural practices (locations, varieties and planting dates), was studied during two successive seasons (2004-2006). Under the traditional and newly reclaimed area, and during the two growing seasons, the obtained results revealed that the initial infestation occurred in December for Improved Giza 6 and Giza 20 varieties at the two planting dates. While, the maximum population exhibited in March for the two varieties and the tested two planting dates, except for Improved Giza 6 variety, that registed in February in the newly reclaimed area. Also, the results show that the infestation rate was lower in the newly reclaimed area than in the traditional cultivated land. The development of onion thrips population was divided into three phases (P₁ to P₃). The initial infestation P₁ occurred after 10 and 4 days after planting for the first and second planting dates on both varieties, respectively. The population increased to reach 10% of its maximum level (P₂), after 38.5, 45.5 and 56, 38.5days for Improved Giza 6, and Giza 20, during the first and second planting date, respectively. The maximum population density (P₃), achieved earlier on Improved Giza 6 than on Giza 20 in both planting dates. The coefficient of daily rate increase (α) seemed to be the same for both varieties during both planting dates. On the other hand, regarding the locations, (P₁) occurred earlier in newly reclaimed area than in traditional cultivated land, during the first planting date. While, vice versa were obtained during the second one. The 10% of maximum population (P₂) increase faster in newly reclaimed area than in traditional cultivated land for both planting dates. Concerning (P₃), found to be lower in the newly reclaimed area than in traditional cultivated land for both planting dates. The daily rate of population increase (α) was lower (0.012) in newly reclaimed area than in traditional cultivated land (0.017) in the first planting date. While, in the second planting date, it was higher (0.035)  in newly reclaimed area than in traditional cultivated land (0.022).