Mass-length and mass-volume relationships of larvae of Bradysia paupera (Diptera: Sciaridae) in laboratory cultures

Abstract

General relationships between body fresh and dry weights, and body length and volume are derived for a dipteran larva, Bradysia paupera. Adult midges were placed in containers with substrate consisting of a mixture of peat and ground beans. From these stock cultures, gravid females were released in containers with agar and a thin layer of ground grass powder, on which the larvae were cultured. A brief description of the life history of B. paupera is given. The body sizes of living larvae were measured on moist plaster of Paris immediately after which the larvae were weighed individually. The relationships of body mass versus size were based on logarithms of mass (M) and size (X, either length or volume) that allows the conversion of a power equation (M = a × X b ) to a linear regression. The derived regression equations that relate body size indices to body mass had a high predictive capacity ( r ranged from 0.934 to 0.991). Body volume, the integration of two size measurements (length and width), gave the most accurate estimation of body mass (length vs. fresh mass r = 0.977, volume vs. fresh mass r = 0.991; length vs. dry mass r = 0.934, volume vs. dry mass r = 0.958). Both size indices gave a more accurate estimation of the fresh mass than of the dry mass of the larvae. Differences between the predictive capacity of the size-mass regression equations are explained in the light of larval behaviour and compared with regression equations obtained from literature.