WIER, M.E.; RHOADS, K.M.; FEI, H.; BORST, D.W.; Illinois State University, Normal; Illinois State University, Normal; Illinois State University, Normal; Illinois State University, Normal: Nutritional effects on vitellogenesis in the lubber grasshopper

Vitellogenin (Vg) is produced by the fat body and deposited in oocytes during the oviposition cycle of the lubber grasshopper (Romalea microptera). Previously, we demonstrated that hemolymph levels of Vg and juvenile hormone (JH) rise during the early phases and fall during the later phases of the oviposition cycle. Furthermore, the duration of the cycle is lengthened in animals maintained at lower nutritional level and can be accelerated when animals are shifted from a lower to a higher nutritional level. In this study, we investigated the molecular and hormonal basis for these effects. In well-fed animals (4.5 g lettuce and 0.6 g oats per d), JH levels began to rise on ~ d10, reached a peak (~200 ng/ml) on d20-25, and declined thereafter. The levels of Vg-mRNA in these animals began to rise on ~d15, increasing about 19-fold by d25 and then declined on d30. Ovarian mass increased about 12-fold from d15 through d30. In low-fed animals (1.5 g lettuce and 0.2 g oats/d), JH levels remained relatively low through d30, and Vg-mRNA levels rose only 4-fold above initial levels by d20. Ovarian mass also increased modestly (4-fold) during this period. In animals switched from a low diet to a high diet on d20, JH levels rose quickly on d25 and reached a maximum on d30. Levels of Vg-mRNA also rose about 9 and 10-fold above initial levels on d25 and 30, respectively, and ovarian mass increased 11-fold above initial levels. These data suggest that nutritional level is an important environmental factor regulating Vg production and oocyte development, and the use of a nutritional switch may be a useful way to study the physiological changes associated with reproduction. (Supported by NSF grant DBI – 9978810 to DWB).