Surveillance for Batrachochytrium dendrobatidis using Mixophyes (Anura : Myobatrachidae) larvae

Fourteen populations of anuran larvae (tadpoles), including three populations of the endangered Fleay's Barred Frog Mixophyes fleayi) and 11 populations of the comnnon Great Barred Frog (Mixophyo fasciolatus), in creek sites in the southeast region of Queensland were selected. Site selection was based on a history (within the district) of adult frog population declines and/or disappearances or records of infection of adult frogs or larvae by Batrachochytrium dendrobatidis. Larvae were collected once from each creek site between October 2002 and October 2004, and were between Gosner developmental stages 25 and 40. Total body length ranged from 18 nun to 100 mm. Mouthparts were examined under a dissecting microsope for grossly visible abnormalities, and then examined for histologic evidence of B. dendrobatidis. The most consistent mouthpart abnormalities found were multifocal depigmnentation of the jaw sheaths and loss or shortening of the tooth rows. At the individual larva level, presence of mouthpart abnormalities was strongly associated with histologic diagnosis of B. dendrobatidis (93%). At least one larva with abnormal mouthparts was detected at 12 of the 14 sites and histologic evidence of B. dendrobatidis was detected at 13 of the 14 sites. These findings suggest that larvae of Mixophyes species are suitable for surveillance for B. dendrobatidis. We conclude that surveillance of B. dendrobatidis where individual larva prevalences of mouthpart abnormalities and histologic evidence of B. dendrobatidis are as high as those observed in this study (66% and 78%, respectively), relatively small numbers of larvae are required to detect these infections. Medium to large larvae (body length > 30 mm) were much more likely to be affected than small larvae (body length <= 30 mm), suggesting that larger individuals should be targeted for surveillance.