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Host-pathogen interplay : a study of factors applicable to the infection efficacy of Metarhizium anisopliae to wireworms (Agriotes spp.) L. Ericsson, Jerry Daniel

Abstract

Wireworms have been a pest of agriculture crops in Canada for nearly 80 years. More recently the lack of pesticide control options have caused their threat to be serious. The insect pathogen Metarhizium anisopliae (Metch) Sorokin has been tested as a biocontrol for wireworm resulting in variable efficacy in both the field and laboratory. A series of tests were performed to determine the role of the wireworm immune system in this variability. All the major features of the invertebrate immune system were investigated before and after exposure to the fungus. Changes in hemocyte ratios and in the hemolymph protein concentration indicated that adverse health effects had occurred from the treatments, but otherwise no immune response was detected. Experiments were designed to test for interactions between combination treatments of M. anisopliae and three reduced risk pesticides; essential oil blend, halofenozide, and spinosad. A synergistic interaction was identified between spinosad and the fungus such that transmission of the disease was improved, and the total mortality was 2X greater than predicted when spinosad was at 3 ppm, and the fungus was at 10² conidia per gram sand. These results suggest that more sensitive tests are required to identify the immunological mechanisms that mediate the interplay between M. anisopliae and wireworms. This study has shown that combination treatments can be effective in improving transmission of a fungal disease, and that high mortality can be achieved without the use of traditional pesticides. Based on these results, it is suggested that field trials be tested to determine if a similar interaction would occur.

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