Effect of temperature on the infectivity of metacercariae of Zygocotyle lunata (Digenea : Paramphistomidae)

As a test of the energy limitation hypothesis (ELH), we predicted that temp erature would have a significant influence on the infectivity of metacercar iae of die digenetic trematode Zygocotyle lunata. Snails infected with Z. l unata were collected from ponds near Crawfordsville, Indiana, isolated at r oom temperature, and examined for the release of cercariae. Newly encysted metacercariae were collected and incubated 1-30 days at 1 of 5 temperatures (0, 3, 25, 31, 37 C). Twenty-five cysts were fed to each of 5 or 10 mice p er treatment group (temperature). At 17 days postinfection, mice were kille d and worms were recovered; data were collected on levels of infection in e ach group and the total body area of each worm. No worms were found in mice fed cysts that had been held at 0 C or 37 C (after 30 days). There were no differences in prevalence, infectivity, or mean intensity among the 3, 25, and 31 C treatments. Infectivity of metacercariae incubated at 37 C for 1 day was significantly greater than in all other treatments, while infectivi ty of metaercariae in the 37 C/15-day treatment was significantly lower tha n in all others. Mean body area of worms at 37 C/15 days was significantly greater than at other temperatures, suggesting density-dependent increases in growth. These results, particularly those from the 37 C treatments, are consistent with the ELH; infectivity was lower at high temperatures or when incubated for more time at 1 temperature (fewer energy reserves). It is su ggested that microhabitat conditions experienced by metacercariae of Z. lun ata could contribute to longer larval life, thus influencing this parasite' s temporal dispersal.