External events related to the infection process of Cornitermes cumulans (Kollar) (Isoptera : Termitidae) by the entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae

The objectives of this study were to observe the external development of Metarhizium anisopliae and Beauveria bassiana on workers and soldiers of Cornitermes cumulans (Kollar) and to establish comparisons between the insect fixation techniques known as critical point and desiccator. Termite workers and soldiers inoculated with B. bassiana (447) and M. anisopliae (1037) were utilized. After inoculation, the insects were left at 25 +/- 0.5degreesC. In order to make observations, samples from both castes were removed at 0,6,12,24,48,72,96,120,144, and 168h after inoculation. The external development of M. anisopliae and B. bassiana conidia on the termite C. cumulans showed that M. anisopliae and B. bassiana conidial germination occurred on several regions of the termites body mainly between 6h and 12h and penetration mainly between 12h and 24h after fungal application. Several penetration points were observed originating from the same germ tube. Colonization of the host by M. anisopliae occurred between 24h and 72h, and most insects died between 72h and 96h. Conidiogenesis began between 96h and 120h with the peak between 144h and 166h for M. anisopliae and between 120h and 144h for B. bassiana. Thus, only conidiogenesis for B. bassiana started earlier, probably because this fungus/isolate shows a higher insect colonization speed. This factor, in addition to multiple penetration points for the same germination tube, could explain the higher virulence of the isolates. The critical point fixation technique provided the best preservation of structures in both the pathogen and the insect.