Housekeeping via defecation: not your average scrubbing bubbles

Conidia of the entompathogenic fungus Metarhizium anisopliae are common in soil environments. Thus, insects that move through and nest within soil have a high probability of becoming infected with this fungal pathogen. A case in point is the woordroach Cryptocercus punctulatus which nests as family units inside decayed and partially buried wood. Surprisingly, this species defecates within their nest. We tested the hypothesis that such fecal material has antifungal properties and prevents roaches and their offspring from becoming infected. Fungal conidia were incubated with five fresh crushed feces for 1, 3, 12 and 24 hours and subsequently plated on potato dextrose agar. Germination rates were recorded and compared with those of conidia in the absence of fecal material. Our results indicate that feces have a significant negative impact on conidia viability. Moreover, conidia germination was negatively correlated with incubation time. These results are of particular interest given that Cryptocercus is considered the ancestral stock that gave rise to the social termites. Termites also appear to have active fungistatic compounds in their feces. Therefore, the presence of antifungal chemicals in the feces of the roach-like ancestor may be considered an evolutionary preadaptation that allowed the primitive termites to cope with pathogenic selection pressures as they evolved social behavior.