Effects of growth rates on development to metamorphosis in the lubber grasshopper, Romalea microptera.

We tested three developmental models postulating different effects of feeding and growth rates on nymphal development rate in female Romalea microptera (Beauvois). We also tested whether assimilation efficiency during the last stadium was affected by earlier feeding in ways that buffer effects of sub-optimal feeding. Hatchling R. microptera were raised in nine treatment groups consisting of high food, low food, and switches from low to high food, high to low food, and high to no food after molts to successive instars. High food during the middle three stadia (second through fourth) yielded significantly lower time to adulthood and larger adult size compared to low food during the middle three stadia. Feeding during the first and last stadia had no significant effect on mass at adulthood or total development time; however, some feeding and growth during the last stadium appeared to be required for successful metamorphosis. Feeding rate during one stadium usually had significant effects on durations of subsequent stadia. Assimilation efficiency in the fifth instar was significantly greater when food availability was low during early stadia, then high during the fifth stadium, compared to assimilation efficiency when food availability was high throughout development. Low food availability during the last stadium significantly lowered assimilation efficiency compared to high food availability during the last stadium, regardless of food availability during earlier stadia. Treatments did not significantly affect relative sizes of fore-, mid-, and hindguts. Our results suggest that development rate proceeds relatively independently of feeding during the last stadium. Our results support models that postulate loss of developmental plasticity late in nymphal life, and this constraint on plasticity may limit the ability of late-instar nymphs to respond to a variable environment.