The Effect of Tertiary Treated Sewage Effluent on Activity of major Piercing-Sucking Mouth-Parts Insects and their Natural Enemies on Alfalfa Crop

Abstract

This study was conducted during the period April 2009 to March 2010 in the Northern Governorate, Kingdom of Bahrain, to study the effect of treated sewage water on major alfalfa pests (aphids, leafhopper and plant bugs) and their natural enemies. The study was conducted on six farms, three irrigated by groundwater in the villages of Karranah, Jannusan and Jasra and three irrigated with treated sewage effluent in the villages of Dumistan, Elsahala and Abu Saiba. Insect samples were collected every ten days from five replicates using the standard sweeping net procedure to estimate the numbers of the above insects and their natural enemies. Pitfall traps were used to collect soft dwelling natural enemies. The results showed that irrigating alfalfa with treated sewage water led to a significant increase in population density of aphids and that the groundwater used for irrigation has led to a significant increase in the number of leafhoppers and plant bugs. As for natural enemies, Geocorissp, Dereaocorispallns were significantly increased in alfalfa plants irrigated by ground water, while Coccinella beetles significantly increased in numbers in alfalfa irrigated with treated sewage water Damselbug, aphids lions, ground beetle, tiger beetles, earwigs were not significantly affected by the type of water used. Regarding the seasonal activity of insects, leafhoppers, aphids,and plant bugs, results showed that the highest density of aphids was occurred during the second and third week of December and first week of January, leafhoppers in the second week of December and third week of February, and Plant bug in the second week of October. The activity of seasonal natural enemies had registered the highest density of Geocorissp during the first and third weeks of August. Coccinella beetles showed highest density during the second week of March, while Damselbugs highest density was noted in the fourth week of December and the first week of January. Aphid lions were most active during the fourth week of December and second week of February, whereas the predator Dereaocoris pallens was active during the third week of May and first week of July and ground beetles active during the first weekof May and the fourth week of July through first week of August. Cutting of alfalfa fields more frequent in activity period is a suggested tactic for the management of this pest, as IPM programs designed by the seasonal activity of the pest.