Effect of heavy metals (Cd, Cu, and Zn) on feeding indices and energy reserves of the cotton boll worm Helicoverpa armigera Hübner (Lepidoptera: Noctuidae)

Third-instar larvae of Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) were exposed to 12.5, 25, and 50 mg/kg concentrations of cadmium (Cd). The third-instar larvae were also exposed to 25, 50, and 100 mg/kg concentration of copper (Cu), and 25, 50, and 100 mg/kg concentrations of zinc (Zn). The heavy metal concentrations were each introduced separately into the artificial diet of the third-instar larvae. The third-instar larvae were 24 h old at the start of the treatment. The larvae were maintained in controlled conditions (26±1°C, 65±10% RH and 16L : 8D h) for 7 days. The feeding indices and the level of total protein, glycogen, cholesterol, and triglyceride were measured after the treatments. The results showed that high concentrations of Cd significantly increased approximate digestibility (AD). The relative growth rate (RGR) was significantly enhanced with a 25 mg/kg concentration of Cu. Efficiency of conversion of the ingested food (ECI%) increased significantly with lower concentrations of copper (25 and 50 mg/kg). The amount of cholesterol was also enhanced with 12.5 and 25 mg/kg concentrations of cadmium while the amount of triglyceride was significantly reduced in all Cd treatments. Glycogen, protein, and cholesterol were significantly enhanced in all Cu treatments. The amount of triglycerides at 25 and 50 mg/kg of Cu was significantly increased. Glycogen in all Zn treatments was significantly increased. Protein and cholesterol levels showed significant reduction with a 25 and 50 mg/kg concentration of zinc while triglyceride was enhanced with a 50 mg/kg concentration of Zn. It is clear from the present results that the presence of such heavy metals in the environment has an intense impact on H. armigera as far as food consumption and biochemical indices are concerned. Therefore, a need is shown for a more comprehensive study on the life table and immunology of this insect, under the presence of heavy metals.