Factors affecting the population of Thrips tabaci Lind. (Thysanoptera:Thripidae) on onion crop in upper Egypt, with special reference to its chemical control

Abstract:
The population fluctuation of onion thrips, Thrips tabaci Lind. affected by natural predators, and weather factors was studied in onion fields in Upper Egypt during 1999-2000 and 2000-2001 seasons. Different chemical control strategies of T. tabaci were also studied. The population of onion thrips was divided into five phases (PI to P5) when December I S was used as starting date. The migration of T. tabaci into onion fields (PI) occurred within 6 days. The population increased to reach 10% of the maximum after about 51 days (PD. Maximum population density occurred after 95 days (P3) at maximum temperature 30.40C, minimum temperature 9.00C and R.H. 56.8%. After that, the population declined to10% of the maximum (P4) after 123 days and approximately vanished from onion fields (P5) after about 163 days. The coefficient ofdaily rate of increase (011) was relatively lower than that of population decrease @2). They were 0.021 and 0.038 individual/day, respectively. The population fluctuation of associated predators, the anthocorids, Orius spp. and the ladybird beetle, Coccinella undecimpunctata L. was also studied and was found to be coincided with the pest population. Generally, statistical analysis revealed that predators, maximum and minimum temperatures and relative humidity played the most important role in managing onion thrips population. To achieve an excellent chemical control against onion thrips, pirimiphosmethyl, furathiocarb, fluvalinate or pirimicarb were sprayed in Jan., 15 and Feb., 15.