Toxicity of Imidacloprid Administered Alone and in Combination with Heavy Metal Lead on Silkworm, Bombyx mori (Lepidoptera: Bombycidae)

In this study, we evaluated the single and joint toxicities of insecticide imidacloprid (commercial formulation and technical grade) and heavy metal lead (Pb) against 2nd, 3rd, 4th and 5th instars of silkworm. For treatment, leaf-dipping method was used and toxicity calculated after 48h exposure to the treatment. Both chemicals showed high toxicity against all instars of silkworm. However, results indicated that imidacloprid was more toxic for silkworm larvae compared to lead. The acute toxicity of imidacloprid formulation (IMF), imidacloprid technical grade (IMT) and Pb showed positive correlation with the concentration and negative with the age of larvae. From second to fifth instars, LC50 values of IMF ranges from 0.72 to 2.96, IMT from 0.86 to 2.75 and Pb from 1.93 to 6.88 mg/L. The toxicity of binary mixture of IMF + Pb showed synergism against all instars of silkworm. While, binary mixture of IMT + Pb displayed synergism, additive, and antagonism and antagonism activity in silkworm larvae in silkworm larvae. The results of our study provide useful data for the assessment of ecological risk of the tested compounds (single or mixture) against different silkworm instars.