FIELD EVALUATION OF IMIDACLOPRID AND THIAMETHOXAM AGAINST SUCKING INSECTS AND THEIR SIDE EFFECTS ON SOIL FAUNA

Abstract

Abstract This work was carried out at Sakha Agriculture Research Station, Kafr El-Sheikh, Egypt during the 2010 and 2011 cotton growing seasons to evaluate the effectiveness of imidacloprid and thiamethoxam, used separately as seed treatments and foliar applications at the recommended rate against the sucking insects: thrips, thrips tabaci (lind), jassid, Empoasca spp., whitefly, Bemicia tabaci, and cotton aphid, Aphis gossypii (Glover.). The side effects of both insecticides on soil fauna was investigated as well. The experimental results showed the following trends: Seed treatment with imidacloprid and thiamethoxam protected cotton seedlings from thrips for at least 6 weeks from the onset of seed planting. Also, both insecticides induced a fast initial effect (after one week of treatment) on whitefly (immature stages). This fast initial effect then gradually decreased to reach a moderate effect according to the general mean of percent reduction. The two tested insecticides exhibited a moderate initial reduction in the population of whitefly (mature stages) and jassids during the two seasons and then this gradually decreased. Imidacloprid had a better efficiency against this sap sucking pest than thiamethoxam. Treatments with imidacloprid and thiamethoxam as foliar applications were highly effective against aphids, up to 14 days in the case of jassids, while the effect was moderate on the whitefly population (mature and immature stages). Imidacloprid had more initial and residual effect than thiamethoxam against jassids. For all soil arthropod groups implicated in this investigation, the used pesticide and depth, significantly affected their mean numbers. The least number of soil arthropods was sampled from the 10-20 cm layer treated with pesticides compared with the 0-10 cm layer. The control plot at both depths recorded the highest number of soil arthropods sampled. Collembola was most abundant while Psocoptera, Oribatida, Actinedida, and Gamasida were least abundant. Pesticide application increased the overall Collembola density compared to the control plots, while it decreased overall Psocoptera, Oribatida, Actinedida, and Gamasida density compared to the control plots. In case of the foliar treatment, there was a reduction in the mean number of examined micro-arthropods either under plants or between plants, in both depths. The reduction in the number of soil arthropods was significantly more in the 0-10 layer. The reduction was more significant between plants than under plants. The most influenced micro-arthropod was Oribatida. The results also revealed that imidacloprid had more adverse effects on soil fauna than thiamethoxam.