Changes in enzyme activities in Agrotis ipsilon (Lepidoptera, Noctuidae) as a response to entomopathogenic nematode infection

In present study changes in acetylcholinesterase (AChE), carboxylesterase (CarE), phenoloxidase (PO), protease, amylase, invertase and trehalase enzyme activities in 4th larval instar of Agrotis ipsilon under entomopathogenic nematode infection was investigated. The nematode infection reduces the digestive enzymes activity (amylase, trehalase and inveratse). The inveratse activity fluctuate in Heterorhabditis zealandica infected larvae while Steinernema abbasi infected larvae show an increase in inveratse activity until 24 hrs post- infection then the activity was decreased compared with the control. Significant increase in AChE activity during the first 8 hrs of nematode infection was observed. At 40 hrs post-infection, H. zealandica infected larvae exhibited higher AChE activity compared with S. abbasi infected and control larvae. Inhibition of AChE in S. abbasi infected larvae results in hyperactivities and consequently paralysis and larval death. PO activity decreased in the nematode infected larvae compared with the control and the reduction was remarkable in H. zealandica infected larvae. The CarE activity was increased by the time increase in S. abbasi infected larvae, reflecting the overactive stress response to the nematode infection. The protease activity was decreased after 16 hrs post-infection with H. zealandica and S. abbasi compared to the control. The observed decreases in protease enzyme activity is expected due to the insect body protein digestion caused by the symbiotic bacteria 16 hours post-infection while the increase in AChE and CarE activity after 16 hrs post-infection is due to the toxic substances released by the bacteria in the hemocoel. Changes in enzyme activities under nematode infection indicate the overreact response to the nematode infection.