Body mass underpins many ecological processes at the level of individuals, populations and communities. Often estimated in arthropods from linear 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 taxon 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 three Culicidae 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 these data with published length-weight allometries of other larval aquatic dipterans. We show that thorax width and body length, but not head width, reliably predict body mass for the three mosquito species. The length-mass allometry slopes in aquatic dipterans vary considerably between and within families but are independent of phylogeny, specimen handling, preservation techniques, and data fitting method. However, slope estimates become less precise with decreasing sample size and size range. To obtain reliable estimates of the allometric slopes, we recommend using data on all larval stages for intraspecific allometries and a wide range of species for interspecific allometries. We also caution against indiscriminately using of length-mass allometries obtained for other taxa or collected at lower taxonomic resolution, e.g. when using length-mass relationships to estimate biomass production at a given site. 

Aedes albopictus and C. pipiens were raised in the laboratory. The eggs, from laboratory, were immediately placed in aged tap-water at 20°C upon delivery. After hatching, larvae of each species were kept together in 10 L containers in temperature-controlled rooms (18L:6D photoperiod) at ca. 25°C, and fed three times a week with Brewer's yeast Saccharomyces cerevisiae at ca 100 mg.L^-1. Ochlerotatus punctor larvae were collected in a swamp in the Czech Republic and maintained in 10 L plastic containers in thermal cabinets at 6°C (mean ± SD = 6.1 ± 0.2 °C) with 9L:15D photoperiod and fed with grounded Brewer's yeast.

We measured the total body length (TL; from the tip of the head to the base of the siphon), maximum thorax width (TW) and head width across eyes (HW) of each individual with QuickPhoto 3.1 software (Promicra, Czech Republic) from pictures taken with an Infinity1 camera (Lumenera, Canada) mounted on an Olympus SZX10 stereomicroscope. Each individual was then gently blotted on a slightly wetted paper towel to remove excess water and immediately weighted in a pre-dried and pre-weighted aluminium cup on the MSA6.6S-0CE-DM micro-balance (Sartorius, Germany) to determine the wet mass W to the nearest 0.001 mg. Afterwards, the individuals were oven-dried at 50°C for 24 h following (Benke and Huryn 2006) and weighed again using the same micro-balance to determine the dry mass (DW).