Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2008
Publication Date: 6/1/2008
Citation: Li, H., Tang, H., Swaminathan, S., Phillip, J., Harrison, R.L., Gatehouse, J.A., Bonning, B.C. 2008. Insecticidal Activity of a Basement Membrane-Degrading Protease against Heliothis virescens (Fabricius) and Acyrthosiphon pisum (Harris). Journal of Insect Physiology. 54:777-789. Interpretive Summary: Insect pests cause billions of dollars of damage to crops each year. The use of chemical insecticides to control insect pests can have negative ecological, environmental, and health consequences. Proteins that selectively kill insect pests without harming plants and other animals potentially can be used in place of chemical insecticides to protect crops. In this study, the activity of an insecticidal protein (a cysteine protease) was studied. It was found that two different kinds of insect pests could be killed with this protein. The information in this study will help researchers develop strategies for using this particular class of insect protein in crop protection.
Technical Abstract: ScathL is a cathepsin L-like cysteine protease derived from the flesh fly Sarcophaga peregrina that functions in basement membrane (BM) remodeling during insect development. A recombinant baculovirus expressing ScathL (AcMLF9.ScathL) kills larvae of the tobacco budworm, Heliothis virescens, significantly faster than the wild-type virus. Here we show that the occurrence of larval melanization prior to death was closely associated with the onset of high cysteine protease activity of ScathL in the hemolymph of fifth-instars infected with AcMLF9.ScathL, but not with AcMLF9.ScathL.C146A. Fragmented fat bodies, ruptured gut and malpighian tubules, and melanized tracheae were observed in AcMLF9.ScathL-infected larvae. The median lethal dose (LD50) for purified ScathL injected into fifth-instar H. virescens was 11.0 µg per larva. ScathL was also lethal to adult pea aphids, Acyrthosiphon pisum with a similar loss of integrity of the gut and fat body. Injection with purified ScathL.C146A or bovine trypsin did not produce any effect in either insect. These results illustrate the potent insecticidal effects of ScathL cysteine protease activity and the potential for use of ScathL in development of insect resistant transgenic plants when combined with an appropriate delivery system.