Variation of enzymes activities in haemocytes and serum of honeysuckle geometrid, Heterolocha jinyinhuaphaga Chu (Lepidoptera: Geometridae) larvae infected by Escherichia coli

Understanding the variations in activity of enzymes involved in the immune response of insects is important for developing effective microbial insecticides against pest species, the determination of bacteria dosage that caused variation of enzyme activities would assist us to prepare effective concentrations of microbial insecticides. In this study, we measured the activities of acid phosphatase (ACP), phenoloxidase (PO), peroxidase (POD), glutathione peroxidase (GSH-px), glutathione reductase (GR), and glutathione S-transferase (GST) in haemocytes and serum of larvae of the pest Heterolocha jinyinhuaphaga Chu (Lepidoptera: Geometridae) infected with Escherichia coli at different time points post-infection. Infection of fifth-instar larvae with different dosages of E. coli led to significant increases in the activities of these enzymes in haemocytes and serum at 3, 6, 12, and 24 h post-infection. Enzyme activities in haemocytes peaked at 6 h post-infection, but their activities began to decrease at 12 h post-infection. Enzyme activities in serum peaked at 12 h post-infection, and they began to decrease at 24 h post-infection. Additionally, enzyme activities increased with increasing dosages of E. coli. The activities of ACP, PO, POD, and GSH-px peaked at 1 × 10⁷ indiv/mL, and the activities of GR and GST peaked at 1 × 10⁶ indiv/mL, activities decreased thereafter. Two - way analysis of variance showed that the interaction of infection time and dosages of E. coli had no significant effect on the enzyme activities in haemocytes and serum of H. jinyinhuaphaga larvae (P > 0.05).