Parasites are expected to be associated with host developmental instability
because developmentally unstable hosts may be more susceptible to, or more
frequently exposed to, parasitic infections compared with developmentally
stable ones, or because parasites may directly disrupt host development. In
this study, we analysed the relationship between developmental stability i
n the weta Pleioplectron simplex (Orthoptera) and infections by hairworm an
d mermithid parasites. These parasites have a long development in their hos
t and the size of adult worms exceeds the length of the host by a considera
ble amount (15-20 cm). For one character (femora) we found that fluctuating
asymmetry was significantly higher in parasitized individuals compared wit
h unparasitized ones, in each of two samples collected in different years.
Because no relationship was observed between the level of fluctuating asymm
etry and the parasite size or number, however, infection by hairworm and me
rmithid parasites could be more a consequence of developmental instability
than a cause. For other characters (tibia, external and internal spines of
femora), the level of fluctuating asymmetry between parasitized and unparas
itized individuals was not significantly different. Our results are discuss
ed in relation to ecological constraints met by hairworm and mermithid para
sites to complete their life cycle.