Resistance of Cotton Aphid, Aphis gossypii Glover (Homoptera: aphididae) to Selected Insecticides in Major Cotton Growing Areas of Ethiopia

Abstract

Resistance to insecticides in four populations of cotton aphids, A. gossypii Glover, collected from major cotton growing areas; (Arbaminch, Dubti, Goffa and Werer) were studied under laboratory conditions using a slide dip test. Mortality was recorded 24hrs after treatment and aphids were considered dead if do not respond to camel hair brush probing. Resistance ratios were determined by dividing LC50 values of the three field populations to LC50 of the susceptible Goffa population. Low to moderate level of resistance (12.14 to 22.2- fold) was detected for carbosulfan, fiirathiocarb and deltamethrin in all aphid populations. However, carbosulfan and furathiocarb gave 100% of aphid mortality at eight time's lower concentration than the recommended field rate. Dimethoate, endosulfan and pirimicarb have shown relatively low level of resistance (< 5.08-fold). But the mortality percentage of the cotton aphid
obtained from pirimicarb at the field rate was very low (16.7- 56.7%) for all populations tested. Deltamethrin and pirimicarb yielded 100% mortality only at two and 32-times higher concentrations than the field rate, respectively. Generally, this study confirmed that, in Ethiopia resistance to insecticides by cotton aphid is at its initial stage and therefore, frequent monitoring and designing o f resistance management strategy are at most urgent.