k. talebi jahromi

Water hardness can negatively affect the efficiency of pesticides. This study aimed to determine the effect of water hardness and adjuvants added to spray solution on the efficiency of insecticides. Three insecticides, namely, malathion, acetamiprid, and spiromesifen, were mixed in well water samples at 1,869, 645, and 265 mg L-1 hardness, standard, and deionized water, and applied against the second instar nymph of Bemisia tabaci using leaf dip method. In another experiment, Zero-7 at 150 ppm and Arkan at 180 ppm as additives were added to water with 1869 and 645 mg L-1 hardness, separately. LC50 values showed that the toxicity of malathion, acetamiprid, and spiromesifen was 40, 157, and 84 times less in hard water (1,869 mg L-1 hardness) than deionized water. The efficacy of malathion, acetamiprid, and spiromesifen was 13, 65, and 39 times less when they were diluted in water with 645 mg L-1 hardness than deionized water. Malathion provided 37.28 and 18.59% greater toxicity when applied in hard water containing Zero-7 and Arkan than water without the adjuvants. The efficacy of acetamiprid was, respectively, 16.93 and 18.68% greater when it was applied in hard water containing Zero-7 and Arkan compared to water without the additives. Zero-7 and Arkan in hard water enhanced the efficacy of spiromesifen by 10.26 and 13.68% compared to water without adjuvants. Generally, the toxicity of the insecticides on B. tabaci was considerably reduced at the highest levels of water hardness. In contrast, adjuvants overcame the antagonistic effects of cations in hard water.

The greenhouse whitefly, Trialeurodes vaporarium (Westwood), is an invasive insect pest of agriculture and horticulture worldwide. Imidacloprid as chemical pesticide has been used as a key pesticide for controlling sap-sucking pests and play a major role in controlling this pest. The main purpose of this study was investigation of resistance status of T. vaporarium to imidacloprid SC 35% (Confidor®) and cross resistance to Eforia® and Proteus® and effect of imidacloprid resistance on Encarsia formosa Gahan. Thirteen greenhouse whitefly populations were collected from greenhouses and fields and used for tests. Collected populations reared on cucumber plants under laboratory conditions at 25±2˚C, 70±10 % relative humidity and a photoperiod of 16:8 h (L: D). The LC50 values were estimated on the second instar nymphs for all populations using leaf dipping bioassay method. The VGR population showed highest LC50 that was 856.2 mg/L. The development of resistance to imidacloprid was confirmed for all tested populations with resistance factors ranging from 2.54 to 44.3. The most resistant strain showed cross resistance to Eforia® and Proteus®. There was no significant difference between LC50 values of E. formosa populations that collected form field, reared on the most resistant population and sensitive population of T. vaporarium. The LC50s were 388.7, 324.7 and 317.7, respectively. We discuss our results in regard to the evolve of imidacloprid resistance in T. vaporariorum populations and its implications for whitefly control.