Contamination of environment with heavy metals is increasingly becoming an issue of major concern across the globe. Heavy metals are highly toxic to humans as well as other organisms of the ecosystem. The translocation of heavy metals from soil to predatory insects via multi-tophic food chains can influence the growth, reproduction, metabolism and innate immune systems of the predators. This study was performed to observe the changes in energy metabolism and immune responses of Cryptolaemus montrouzieri feeding on heavy metal (Cd, Pb, Ni and Zn) contaminated pink hibiscus mealybug (Dysmicoccus neobrevipes). The average concentrations of Cd, Pb, Ni and Zn in mealybugs used for feeding assays were 30.57, 32.64, 31.47 and 33.19 mg/kg, respectively. The results showed a significant increase in total protein, glycogen, cholesterol and triglycerides content of C. montrouzieri feeding on heavy metals contaminated mealybugs compared with control groups. The activities of endogenous enzymes (acid phosphatase and alkaline phosphatase) as well as antioxidant enzymes (SOD, POD and CAT) were significantly higher in beetles feeding on heavy metals contaminated mealybugs. Our results provide basic insight into the influences of heavy metals (Cd, Pb and Ni) on energy metabolism and the innate immune system of the insect predator (C. montrouzieri) in a multi-trophic food chain. Further research on genetic processes involved in the regulation of metabolism and innate immune system of C. montrouzieri is still needed.
Keywords: Antioxidant enzymes; Endogenous enzymes; Heavy metals; Ladybird beetle; Metabolism.