1. Growth rates of immature invertebrates can be of profound importance to
subsequent reproductive success in the adult stage. If diet selection in he
rbivores is a principal means of maximising growth and rate of development,
individuals should select food of the highest quality.
2. If disparities are found between performance and preference, these may b
e the result of individuals balancing nutritional gain against other demand
s on their behaviour, such as a need for shelter. The responses of the cran
e-fly herbivore Tipula montana Curtis (Diptera: Tipulidae) to a range of mo
ss genera from an upland environment were investigated to determine whether
diet selection was determined by food quality alone, as measured by its ef
fect on larval growth and survival.
3. Larvae were reared individually on single moss genus diets, and their gr
owth, development, and survival were measured. Each of the mosses supported
growth and development although the mean weights achieved differed by a fa
ctor of two between food genera. In two-choice preference experiments, indi
viduals broadly chose bryophyte foods as expected from their quality. One n
otable exception was the moss Pleurozium schreberi, which gave the best gro
wth performance but was among the least preferred.
4. The two methods of assessing preference gave different results: observat
ions of larvae showed relatively greater selection for dense mosses than fa
ecal pellet analysis. A strong dietary preference for an angiosperm, the se
dge Curer bigelowii, over all mosses supported the interpretation that cran
e-fly larvae benefit from bryophytes as a refuge, and that this factor may
override dietary quality.