Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2007
Publication Date: 9/1/2007
Citation: Kwon, H.S., Stanley, D.W., Miller, J.S. 2007. Bacterial challenge and eicosanoids act in cell spreading. Entomologia Experimentalis et Applicata. 124:285-292. Interpretive Summary: Long-term agricultural sustainability is severely threatened by widespread use of classical insecticides. Threats include increasing resistance to insecticides and sharply decreasing environmental quality. Biological control is a proven method of pest management. Biological control is based on the idea that direct application of certain insect-specific predators, pathogens and parasites can reduce pest insect populations to a point that the pests exert only negligible economic damage. A major problem, however, is that use of biological control programs is limited by insect immune defense reactions. In previous work we discovered the key mediators in insect immunity and reported that inhibition of these mediators renders insects defenseless to infections. That work, however, did not reveal the exact roles of the mediators. Here we report that the mediators facilitate the cell spreading reaction to infection. This work identifies one specific defense action that depends on the mediators. Research such as this will impact scientists engaged in study of specific insect-killing mechanisms of biological control agents. A more important impact will be seen in later development of more effective agents which are able to exert multiple killing actions in pest insects. Deploying these agents may very well result in the long-term reductions in environmental insecticide loads.
Technical Abstract: We report on experiments designed to thoroughly document the roles of eicosanoids as crucial elements in cell spreading and on experiments designed to test the hypothesis that in vivo bacterial infections influence cell spreading on glass surfaces. We used hemocytes prepared from tobacco hornworms, Manduca sexta and four species of bacteria (Serratia marcescens, Echerichia coli, Bacillus subtilis, and Micrococcus luteus) in each experiment. Our protocols yielded several important results. One, hemocytes prepared from hornworms at 15 and 60 min following infection with, separately, each of the four bacterial species were fundamentally altered in size (all less than the 15 micron counting cutoff) and none of the hemocytes exhibited cell spreading behavior. Two, the influence of bacterial challenge on cell spreading declined with incubation time post challenge. Three, conditioned media (CM) prepared by exposing hemocytes to bacterial cells in vitro exerted a strong dose-dependent influence on cell spreading. Specifically, plasmatocytes increased in length from about 38 'm with 2.5% CM to a high of about 54 'm at 100% CM. Fourth, the retarding influence of dexamethasone (an eicosanoid-biosynthesis inhibitor) on cell spreading was reversed by AA, PGH2 and by CM. Taken together, these findings indicate that bacterial infection and eicosanoids are directly involved in hemocyte spreading processes.