INFLUENCE OF TEMPERATURE ON LARVAL DEFECATION AND ITS USE IN ESTIMATING CANOPY POPULATION-SIZE OF PINE SAWFLIES (HYMENOPTERA, DIPRIONIDAE)

The frequency of defecation in relation to constant/simulated outdoor temperatures and larval age (instar) was examined under laboratory con ditions in four species of pine sawflies (Diprionidae): Gilpinia frute torum (Fabricius), Diprion pini (Linnaeus), D. similis (Hartig) and Ma crodiprion nemoralis (Enslin). Defecation interval and total faecal pr oduction was regular under higher constant temperatures (higher produc tion in younger instars, second and third) and production significantl y decreased under varying air temperatures during the same period (24 hours) when larvae of younger instars were influenced more by lower te mperatures. The influence of larval age (instar) on faecal production was insignificant if larvae were exposed to varying temperatures durin g 24 hours. Faecal production and temperature were positively correlat ed in each of the four species and instars tested, as well as in total (all the test species and instars combined). Implications of the resu lts for estimating canopy larval density by frass-drop measurements in the field are briefly discussed.