|Coudron, Thomas - Tom|
Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2000
Publication Date: N/A
Citation: Interpretive Summary: Insects produce saliva that helps break down their food before and during ingestion. Protein, in the form of enzymes, can often be a major component of insect saliva yet the protein composition of saliva from only a few insects is known today. Although many plants produce defensive compounds in response to injury by insect feeding, many pest insects appear able to overcome this response. This study was performed in order to determine if one mechanism for such resistance is the induction of proteins by these insects. We found that two plant-eating insects, in the group of true bugs, did increase the number and amount of protein in their saliva when switched from feeding on a sucrose diet to a plant diet. We also found that another plant-feeding true bug responded in an opposite manner; producing a greater number of proteins in their saliva when feeding on a sucrose diet versus a plant diet. Additionally, one insect-eating true bug did not show a change in the number of components or amount of protein in their saliva when switched between several natural food sources and an artificial diet. These results indicate that some plant-eating insects do increase the amount of protein in their saliva, and that plant food may induce the presence of different proteins in the saliva of these insects. However, not every insect responds in the same manner, nor to the same degree. In our studies, the plant-eating insects demonstrated a more advanced capability than insect-eating insects to distinguish and respond to dietary stimuli. Hence, knowledge of the ability of an insect to alter their digestive processes in response to changes in their diet, may prove valuable to researchers and practitioners in their efforts to manage resistance within insects.
Technical Abstract: A comparison of the salivary proteins from four hemipteran insect species was conducted, in order to better our understanding of salivary components that are involved in feeding, and to test the hypothesis that protein composition varies with diverse dietary composition. Saliva was analyzed for protein content using electrophoretic techniques under denaturing conditions. Two homopterans, Empoasca fabae and Empoasca abrupta, one primarily phytophagous heteropteran, Lygus hesperus, and one primarily entomophagous heteropteran, Podisus maculiventris, were used in this study. Saliva was collected in a protein-free solution before and after insects had been transferred from the rearing hosts to the treatment hosts. A greater number of proteins and an increase in the percentage composition of certain proteins were observed in saliva from E. fabae when the treatment was plant hosts (i.e. broad or pinto bean) versus artificial diet. The reverse result was found for E. abrupta; a greater number of proteins was observed when the treatment was artificial diet vs. plant host (pinto bean). Also, a greater number of proteins were observed for L. hesperus reared on artificial diet, when the treatment host was cotton or pinto bean. In contrast, there was minimal difference in the number and percentage composition of proteins secreted by the entomophagous hemipteran P. maculiventris when fed on any one of three natural hosts (i.e. cabbage looper, fall armyworm or Colorado potato beetle) or an artificial diet. This variability in salivary protein profiles of phytophagous hemipterans dependent on past dietary history may reflect both the excretory function of saliva in Hemiptera and the induction of proteins in response to diverse dietary constituents.