Blowflies (Calliphora vomitoria) as an in Vivo Bioassay for Diarrhetic and Hemolytic Algae Toxins

Abstract

Using blowflies (Calliphora vomitoria) as test subjects, a bioassay method was developed for the detection of diarrhea-causing and hemolytic (i.e., ichthyotoxic) algae toxins in biological material. Flies were immobilized by refrigeration, and injected in series of 10 with the required doses of the toxins in question. Following injection, lethality of flies was monitored at 27°C over a 24-h period. Okadaic acid (OA), the most common diarrhea-causing toxin, gave a detectable lethality of flies after 2 h of monitoring. For this exposure time, a 50% lethal dose (LD50) of 666 μg OA/kg was detected, while an LD50 of 274 μg OA/kg was found after 4 h of surveillance. These figures are comparable to the lethal doses reported within a 24-h surveillance period for OA in mice, suggesting the fly bioassay as equivalent in sensitivity to the mouse bioassay for diarrhea-causing toxins, or even more sensitive by the use of a moderately longer time of surveillance than 4 h. Sensitivity of the fly bioassay appears limited by time, however, since high lethality of control flies was occasionally found after 16-24 h. Moderately toxic extracts of mussels exposed to the ichthyotoxic alga Prymnesium parvum gave detectable lethality in flies within 1 h of surveillance, suggesting an even faster toxic effect of hemolytic toxins in flies than that of diarrhea-causing toxins.