Ecological Studies on Some Onion Pests and their Control in Assiut Governorate

Abstract

I. Field studies:

The present studies were undertaken for four onion growing seasons (1998-2002). The considered pests in this study were: the onion thrips, Thrips tabaci Lindeman, and the onion mites Rhizoglyphus robini Claparede and Hormosianoetus mahunkai Eraky and Shoker. The results of these studies can be summarized as follows:

1. Impact of onion varieties, planting dates and intervention of cotton cultivation in two locations on the population density of onion thrips, T. tabaci and bulb mite, R. robini and H. mahunkai inhabiting onion plants in relation to the onion bulbs yield

Two experimental sites were selected for the purpose of conducting this investigation [i.e., Fac. Agric. Exp. Farm "rather mosaic agroecosystem" and El-Ghorieb Exp. Farm "semi-arid ecosystem"], during the growing season of 1998/1999, in Assiut Governorate. Two onion varieties (Giza 6 Mohassan and Giza 20), transplanting in four planting dates (Nov., 1st. and 3rd. weeks; Dec., 2nd. and 4th. weeks) and the intervention of cotton cultivation, were investigated.

1.1. The onion thrips, T. tabaci

Generally, it can be concluded that the two tested omon varieties (Giza 6 Mohassan and Giza 20), cultivated in the two early planting dates (Nov., 1st. and 3rd. weeks), in either typical mosaic agroecosystem (Fac. Agric. Exp. Farm) or semi-arid ecosystem ("El­ Ghorieb" Exp. Farm), were achieved the lowest population density of onion thrips. Also, the tested intervention system can be adopted because of the infestation level by this insect pest did not significantly increased.

1.2. The bulb mite, R. robini and H. mahunkai

One with another, the proper planting date for transplanting any of the two onion varieties, under the circumstances of typical mosaic