Protease and phospholipase inhibition protect Veneza zonata (Hemiptera Coreidae) against septicemia caused by parasite trypanosomatid 563DT.

Veneza zonata (Hemiptera Coreidae) is an insect which causes losses in several crops, and it is also an important vector of lower trypanosomatids. V. zonata specimens were collected on rural properties in Londrina, state of Paraná, Southern Brazil. Inoculation of Leptomonas 563DT into V. zonata hemocoel caused insect death within approximately 24 h, with large bacterial proliferation into their hemocoels. Some bacteria which were found in the digestive tract of those insects, such as Escherichia coli, Providencia rettgeri, and Kluyveria ascorbata, were also found in their hemolymph, which suggests that trypanosomatid crossing into hemocoel caused mechanical lesions in the digestive tract that allowed intestinal bacteria to infect the hemolymph, thereby leading to lethal septicemia. In this study we analysed proteolytic activities from the 563DT Leptomonas strain, which is pathogenic for V. zonata, aiming at evaluating the potential use of this Leptomonas strain for the biocontrol of the insect. The proteolytic action was evaluated on cells and on culture supernatants of trypanosomatids. We also evaluated the gelatinolytic activities, the action over natural and synthetic substrates for aminopeptidases, and the action of protease inhibitors during all trypanosomatid growth stages. A significant reduction in the number of insect deaths was observed when Leptomonas 563DT were incubated with inhibitors of proteases and phospholipases before being inoculated into the insects, which suggests that those enzymes are involved in the pathogenic mechanism.