Two field experiments were conducted during two successive seasons 2013-2014 and 2014-2015 at
the experimental farm, Faculty of Agriculture, Benha University, Egypt to study the effect of phytochemical
composition and anatomical characteristics of two onion cultivars (Giza 20 and Red onion) on their
susceptibility to infestation with Thrips tabaci. As well as, estimate the efficiency of different chemical and
biochemical compounds in reducing the population density of T. tabaci on onion plants. The thrips
population in two onion cultivars increased from the beginning of the experiment and reached the maximum
population during the period from 1st March to 5th April in 2014 and from 15th February to 5th April in the
second year of study 2015. Results also showed that Giza 20 cultivar was higher in its content of macroelements,
moisture and total protein than Red onion cultivar. On contrast, Red onion cultivar was higher in
total carbohydrates, reducing and non-reducing sugars than Giza 20 cultivar. Also, the anatomical parameters
(thickness of epidermis, thickness of Central tissue and number of vessels wood) of Red onion cultivar was
higher than the same parameters of Giza 20 cultivar. In addition, results showed that Pyrthrin reduced lower
of thrips infestation rate of two onion cultivars than other Radiant, Marshal and Confidor which gave higher
reduction rates in thrips infestation on the two onion cultivars.