Length-mass allometries of the larvae of aquatic dipterans: differences between taxa, morphological traits, and methods.

Body mass underpins many ecological processes at the level of individuals, populations, and communities. Often estimated in arthropods from linear morphological traits such as body length or head width, these relationships can vary even between closely related taxa. Length-mass relationships of mosquito (Diptera: Culicidae) larvae are poorly known despite the importance of this family to disease and aquatic ecology. To fill this gap, we measured ontogenetic changes in linear traits (body length, head width, and thorax width) and dry and wet masses and estimated length- and width-mass relationships in larvae of 3 culicid species inhabiting different niches: the tropical Aedes albopictus (Skuse, 1894), the temperate Culex pipiens (Linnaeus, 1758), and the snowmelt Ochlerotatus punctor (Kirby, 1837). We compared our results with published length-mass allometries of other aquatic dipteran larvae. We showed that thorax width and body length, but not head width, reliably predicted body mass for our 3 species. The length-mass allometry slopes in aquatic dipterans varied considerably between and within families but were independent of phylogeny, specimen handling, preservation techniques, and data fitting methods. Slope estimates became less precise with decreasing sample size and size range. To obtain reliable estimates of the allometric slopes, we have thus recommended using data on all larval stages for intraspecific allometries and a wide range of species for interspecific allometries. We also cautioned against the indiscriminate use of length-mass allometries obtained for other taxa or collected at lower taxonomic resolutions, e.g., when using length-mass relationships to estimate biomass production at a given site.