Effect of Beauveria bassiana and Candida albicans on the cellular defense response of Spodoptera exigua.

A marked difference in the cellular response of Spodoptera exigua was observed when larvae were challenged with the insect mycopathogen Beauveria bassiana versus the yeast Candida albicans. Both fungi were rapidly phagocytized by circulating hemocytes. The relative growth rate of C. albicans as measured by daughter cell formation was partially suppressed, whereas B. bassiana blastospores produced germ tubes at rates equivalent to those under in vitro conditions. Limited growth by C. albicans within the phagocytic cells stimulated nodulation by hemocytes resulting in the protection of challenged larvae to C. albicans. Alternatively, B. bassiana suppressed the spreading ability of S. exigua hemocytes. These suppressed larvae, while capable of phagocytizing C. albicans, were unable to produce multicellular nodules. Circulating vegetative cells of both C. albicans and B. bassiana were observed to proliferate within these immunosuppressed host larvae.