Effect of Different Host Plants on the Onion Thrips, Thrips tabaci Lind. and the Land Snail, Monacha spp. Population Abundance According to Intercropping some Vegetable Crops and the Final Yield

Field experiments were carried out at El-Riad district, Kafr El-Sheikh governorate during  three successive seasons, 2014/15, 2015/16 and 2016/17. To study host preference and the effect of intercropping each of lettuce (Roman), onion (Buheirah red) and garlic (sids 40) cultivars, on the onion thrips, Thrips tabaci Lind.andthe land snail,Monacha spp.population abundance  and the resulting yield.  T. tabaci was the high attractive to onion followed by garlic,  while lettuce was least attractive during the three successive seasons. It can be noticed  the highest monthly average number of T. tabaci were recorded in March on onion plantations alone and  onion intercropping, with lettuce, followed by garlic plantations alone, garlic (intercropped with lettuce) in the three seasons, while lettuce plantations alone and lettuce intercropping,  with onion and with garlic were recorded in February in 2015 and 2016 but it was in March in 2017 season. Also, the highest monthly average number of Monacha spp. were recorded in March on lettuce plantations alone and  followed by lettuce intercropping, with onion and garlic, while garlic plantations alone, garlic (intercropped, with lettuce) and onion plantations alone and onion (intercropped,  with lettuce) were recorded in February or March. It can be noticed that,  Monacha spp. was the high attractive to lettuce,  while garlic and onion  were   the least attractive during the three successive seasons.  The population abundance of thrips and snails differed according to host plant, there were significant differences among host plants (p≤ 0.05).The rate of infestation was higher in the sole crops  than in those intercropped crops which caused reduction of T. tabaci and Monacha spp., and almost, significant differences were found (p≤0.05).The resultant yield, due to intercropping, was also affected. The lettuce, onion and garlic plants intercroppe reduced the resultant yield when compared with control.