Trait Characteristics Determine Pyrethroid Sensitivity in Nonstandard Test Species of Freshwater Macroinvertebrates: A Reality Check

We
exposed 34 species of stream macroinvertebrates, representing
29 families, to a 90 min pulse of the pyrethroid λ-cyhalothrin.
For 28 of these species, no pyrethroid ecotoxicity data exist. We
recorded mortality rates 6 days post-exposure, and the behavioral
response to pyrethroid exposure was recorded using automated video
tracking. Most arthropod species showed mortality responses to the
exposure concentrations (0.01–10 μg L–1), whereas nonarthropod species remained unaffected. LC50 varied by at least a
factor of 1000 among arthropod species, even within the same family.
This variation could not be predicted using ecotoxicity data from
closely related species, nor using species-specific indicator values
from traditional ecological quality indices. Moreover, LC50 was not significantly correlated to effect thresholds for behavioral
responses. Importantly, however, the measured surface area–weight
ratio and the preference for coarse substrates significantly influenced
the LC50 for arthropod species, with the combination of
small individuals and strong preference for coarse substrates indicating
higher pyrethroid sensitivity. Our study highlights that existing
pesticide ecotoxicity data should be extrapolated to untested species
with caution and that actual body size (not maximum potential body
size, as is usually available in traits databases) and habitat preference
are central parameters determining species sensitivities to pyrethroids.