Prey density and survival in damselfly larvae: field and laboratory studies

Faecal-pellet production by larvae of the damselfly Ischnura elegans was examined in the field throughout one year (1975). In only two months, May and November, did production deviate significantly from a mean figure. There was no evidence of diurnal periodicity in faecal-pellet production. In a controlled laboratory experiment in which prey density, temperature and larval instar were variables, prey density and larval instar contributed significantly to differences in faecal-pellet production. A comparison of field and laboratory faecal-pellet production and development rates and survival at known prey densities in the laboratory, suggests that larvae at the study site suffered little or no reduction in development rate and survival due to food shortage. The consequences of these findings for the control of larval damselfly populations are considered.