The immune response of the desert locust Schistocerca gregaria during mycosis of the entomopathogenic fungus, Metarhizium anisopliae var acridum

Topical application of Metarhizium anisopliae var acridum to the desert loc ust Schistocerca gregaria resulted in changes in the biochemistry and antim icrobial defenses of the haemolymph. M. anisopliae var acridum colonized th e host haemolymph from day two post application. The haemocytes did not att ach to, phagocytose or nodulate elements of the fungus. However, the presen ce of the fungus appeared to stimulate hemocyte aggregation over the first few days of mycosis though the number of aggregates declined subsequently. The total hemocyte count increased two days after application, indicating a n overall stimulation of the immune system, but declined to a value below t hat for uninoculated controls by day four. The differential haemocyte count showed that the initial increase in total haemocyte count was primarily du e to a larger number of coagulocytes. After day two consistent declines in cell number were observed for all haemocyte classes in mycosed insects. The activity of the enzyme, phenoloxidase, decreased during the course of infe ction. However, the converse was true for prophenoloxidase. Lysozyme levels were significantly smaller in infected than control locusts, There was a s ignificant correlation between lysozyme and PO activities when data from my cosed and control insects were combined. The total protein content of the h aemolymph decreased during the course of infection. (C) 1000 Elsevier Scien ce Ltd. All rights reserved.