Ecotoxicity of Cadmium along the Soil-Cotton Plant-Cotton Bollworm System: Biotransfer, Trophic Accumulation, Plant Growth, Induction of Insect Detoxification Enzymes, and Immunocompetence

Abstract

Cadmium (Cd) is a hazardous element that may jeopardize environmental safety and human health through biotransfer and trophic accumulation. Here, we tested Cd toxicity on cotton plants, cotton bollworms, and their responses. Results demonstrated that Cd accumulated in plant roots, aerial parts, insect larvae, pupae, and frass in a dose-dependent pattern. The ∼9.35 mg kg^-1 of Cd in plant aerial parts, ∼3.68 in larvae, ∼6.43 in pupae, and high transfer coefficient (∼5.59) indicate significant mobility. The ∼19.61 mg kg^-1 of Cd in larvae frass suggests an effective detoxification strategy, while BAF_cotton (∼1.14) and BAF_worm (∼0.54) indicated low bioaccumulation. Cadmium exposure resulted in compromised plant growth and yield as well as alterations in photosynthetic pigment contents, antioxidant enzyme activities, and certain life history traits of cotton bollworms. Furthermore, carboxylesterase activity and encapsulation rates of insect larvae decreased with increasing Cd concentrations, whereas acetylcholinesterase, phenol oxidase, glutathione S-transferase, and multifunctional oxidase exhibited hormesis responses.

Keywords: bioaccumulation; food chain; heavy metal; insect immunity; life history.

Figure 1

Effects of host plants grown in Cd-spiked soil on activities of CarE, GST, MFO, and AchE of cotton bollworm. Different lowercase letters above the error bars indicate under-treatment difference at P < 0.05. No among-enzyme comparison was conducted. Cd0, Cd10, Cd20, and Cd40 represent the control, 10, 20, and 40 mg kg^–1 Cd treatment groups, respectively. Note: Total Cd contents in the test soil after plant growth in the Cd0, Cd10, Cd20, and Cd40 treatment groups were 0.26 ± 0.037, 2.75 ± 0.52, 6.57 ± 0.32, and 16.32 ± 0.34 mg kg^–1, respectively.

Figure 2

Effects of host plants grown in Cd-spiked soil on hemolymph PO activities of cotton bollworm. Different lowercase letters above the error bars indicate significance at P < 0.05. Note: Total Cd contents in the test soil after plant growth in the Cd0, Cd10, Cd20, and Cd40 treatment groups were 0.26 ± 0.037, 2.75 ± 0.52, 6.57 ± 0.32, and 16.32 ± 0.34 mg kg^–1, respectively.

Figure 3

Effects of host plants grown in Cd-spiked soil on hemolymph encapsulation rate P cotton bollworm. Different lowercase letters above the error bars indicate significance at P < 0.05. Note: Total Cd contents in the test soil after plant growth in the Cd0, Cd10, Cd20, and Cd40 treatment groups were 0.26 ± 0.037, 2.75 ± 0.52, 6.57 ± 0.32, and 16.32 ± 0.34 mg kg^–1, respectively.