Abstract
Heavy metal pollution has become a serious environmental concern to global biological diversity. The continuous accumulation of toxic metals in plants is affecting the growth, development and reproduction of herbivore insects. In the present study, heavy metal-induced toxicity through tomato, Solanum lycopersicum L., leaves in Hadda beetle, Epilachna vigintioctopunctata (Coccinellidae; Coleoptera), was assessed. Second instar grubs of E. vigintioctopunctata were exposed to two concentrations i.e. 300 mu g ml(-1) and 100 mu g ml(-1) of zinc (Zn) and lead (Pb) metals. Experiment was performed using CRD design under controlled conditions (28 degrees C, 65 % R.H. and 16L: 8D h). Feeding indices: relative growth rate (RGR), relative consumption rate (RCR), efficiency of conversion of ingested food (ECI), growth parameters: grub weight gain, grub length, leaf weight loss, and percent survival rate were recorded. Zn showed to have higher feeding indices (RGR, RCR, and ECI) at both concentrations. Pb, on the other hand, showed a significant reduction in RGR due to low consumption rate and poor efficiency of conversion of ingested food at both concentrations. Due to decreased feeding indices, grub growth also reduced in Pb treated insects compared to Zn. Survival rate was significantly decreased in Zn and Pb treated grubs compared to control. Observed effects were more detrimental in insects exposed to Pb. Future studies should focus other herbivore insects as bioindicators of heavy metal accumulation in agricultural ecosystems which will help improving environmental safety guidelines.