2.6. Infection bioassays
Exposure bioassays with Aspergillus spp. can potentially be carried out, using in vitro reared larvae (Fig. 9), caged bees or colonies, due to its ability to infect larvae, pupae and adults. A bioassay with in vitro reared larvae has been conducted showing that stonebrood and chalkbrood had opposite temperature-dependent responses in virulence. Chilling of chalkbrood exposed larvae increased the pathogen virulence; whereas chilling of stonebrood exposed larvae increased larval survival (Vojvodic et al., 2011a). For infection of in vitro bee larvae with Aspergillus spp. the same precautions must be taken as described in paragraph 1.5.1. for A. apis.
Few experiments with caged bees have been conducted (Gilliam and Vandenberg, 1997). Infecting individual larvae while still in the brood frame is possible by placing the spore suspensions to be ingested in front of the larvae (Vojvodic unpublished).