|Wright Osment, Maureen|
Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/27/2006
Publication Date: 6/5/2006
Citation: Wright Osment, M.M., Brandt, S.L., Coudron, T.A., Wagner, R.M., Habibi, J., Backus, E.A., Huesing, J.E. 2006. Characterization of digestive proteolytic activity in Lygus hesperus Knight (Hemiptera: Miridae). Journal of Insect Physiology. 52:717-728.
Interpretive Summary: Tarnished plant bugs are now considered to be primary pests of many crops, including canola, strawberries, vegetables, seed alfalfa and especially cotton. Environmental problems resulting from the field application of insecticides, a declining number of registered chemicals for insect-control use and the development of insect populations with resistance to a wide range of insecticides have increased greatly the need for new substances to control this insect and for new methods to deliver these substances to the insect. One of the new methods for delivering insect control substances is to express the substance(s) directly within the plant that serves as food for the insect. However, when a regulating substance enters the insect by way of the food it must be able to survive the potent digestive enzymes that are present in the insect digestive system. This paper describes a detailed analysis of one group of digestive enzymes found in this insect, the protein degrading enzymes known as proteases. The results show that the major proteases in the salivary gland differ from those found in the midgut and are active under differing conditions. However, together the salivary and midgut proteases complement one another and in doing so broaden the location and environmental conditions under which proteins in the food stream of this insect are degraded. This study presents critical findings that are important to researchers developing new substances to control the tarnished plant bug that are to be expressed directly within the plant.
Technical Abstract: The tarnished plant bug, Lygus hesperus Knight, is a pest that causes considerable economic losses to vegetables, cotton, canola, and alfalfa. Detailed knowledge of its digestive physiology will provide new opportunities for a sustainable pest management approach to control this insect. Little is known about how different classes of proteases interact to digest specific proteins. To this end, the proteolytic activities in female adult L. hesperus midgut and salivary gland homogenates were quantified over a range of pH’s, and the contribution of different classes of proteases to the degradation of the digestible protein, FITC-casein, was determined. In the salivary gland, serine proteases were the predominant class responsible for the digestion of FITC-casein, occurring within 9h with the rate of activity increasing with increasing pH. In contrast, both aspartic and serine proteases contributed to the digestion of FITC-casein in the midgut. Aspartic proteases predominated at a pH of 5.0 and were immediate, whereas serine proteases were largely responsible for FITC-casein digestion at a pH of 7.5 after a 9h incubation. The serine proteolytic activities in the salivary gland and midgut were distinctly different. Collectively, the proteolytic activities complement one another, broadening the location and pH range over which digestion can occur.