The allocation of fat resources to somatic and reproductive tissues was studied in females of five species of pine sawflies (Diprion pini (L.), Diprion similis (Htg.), Gilpinia frutetorum (F.), Gilpinia pallida (Klug), Neodiprion sertifer (Geoffroy); Hymenoptera, Diprionidae). The soma and eggs of newly emerged females were separated and then put in ether to extract and determine their fat content. The fat allocation patterns differed between species. The gregarious outbreak species D. pini and N. sertifer allocated most of the fat to their eggs, whereas the gregarious non-outbreak species, G. pallida, allocated most to its somatic tissues. No modification of these basic allocation patterns was observed with increasing total fat content. In contrast, the solitary non-outbreak species, D. similis and G. frutetorum, invested equal amounts of fat in soma and eggs, and the proportion allocated to the egg load decreased as total fat content increased. That is, they invested additional resources in somatic tissues. Apparently, outbreak species tend to allocate more fat to reproductive tissues than non-outbreak species.
Oviposition behaviour of Delia radicum is not only influenced by host plant duality but also by the duality of the substrate in which the plant grows. Direct behavioural observations showed that the females partition their visits to a host plant (cauliflower) into ovipositional bouts separated by exploration of the host plant surface. Ovipositional bouts were further partitioned into acts of egg deposition separated by exploration of the substrate. While the mean number of ovipositional bouts per visit (2.6), and eggs laid per egg deposition event (1.4) were stable, the mean number of egg deposition events per ovipositional bout significantly varied (from 2.1 to 7.3) with the duality of the substrate and the physiological state of the female (egg load). Ovipositing females adjusted the final number of eggs laid around the plant during the behavioural stage of substrate exploration. Additional experiments using plant surrogates treated with methanolic extract of Brassica leaves mounted in different substrates showed that: (a) the presence of living Brassica, Hordeum or Allium roots in a substrate enhances the number of eggs laid into this substrate, but females do not discriminate between the different plants; (b) females avoid both wet and dry substrates and prefer the substrates with a dry surface and moist particles directly accessible at a depth of about 5 mm; (c) substrates rich in organic matter are preferred to sand; (d) olfactory perception of volatile chemicals from the substrate must at least partially be responsible for the differences in oviposition in various substrates.