Maximum titers of vitellogenin and total hemolymph protein occur during the canalized phase of grasshopper egg production

Many organisms exhibit developmental plasticity only in sensitive phases an d cannot respond to environmental pertubations at other times. However, we know little about the physiological events that define plastic and canalize d phases. During egg production in insects, vitellogenin (Vg) accumulates f irst in the hemolymph and then in the eggs. In addition, storage proteins m ay be important resources for egg production. Therefore, we tested hypothes es on the relationships of Vg and TP (total hemolymph protein minus Vg) tit ers to the transition from flexible to inflexible development during egg pr oduction. In lubber grasshoppers, similar to 70% of TP is contained in thre e proteins that range from 68 to 83 kDa. We maintained females on food trea tments that produced defined plastic and canalized periods, collected hemol ymph every similar to4 d, and determined the ages at which oviposition and the maximum Vg and TP titers occurred. Both Vg(max) titer and especially TP max titer were predictors of the number of eggs produced. The time from ecl osion to Vg(max) was significantly affected by diet, but the time from Vg(m ax) to oviposition was not. Similarly, the time from eclosion to TPmax was significantly affected by diet, while the time from TPmax to oviposition wa s not. Hence, Vg(max) and TPmax are physiological landmarks that occur duri ng the canalized phase of egg production.