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

We tested three developmental models postulating different effects of feedi ng and growth rates on nymphal development rate in female Romalea micropter a (Beauvois). We also tested whether assimilation efficiency during the las t stadium was affected by earlier feeding in ways that buffer effects of su b-optimal feeding. Hatchling R. microptera were raised in nine treatment gr oups 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. H igh food during the middle three stadia (second through fourth) yielded sig nificantly lower time to adulthood and larger adult size compared to low fo od 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 req uired for successful metamorphosis, Feedings rate during one stadium usuall y had significant effects on durations of subsequent stadia. Assimilation e fficiency in the fifth instar was significantly greater when food availabil ity was low during early stadia, then high during the fifth stadium, compar ed to assimilation efficiency when food availability was high throughout de velopment. Low food availability during the last stadium significantly lowe red assimilation efficiency compared to high food availability during the l ast stadium, regardless of food availability during earlier stadia. Treatme nts did not significantly affect relative sizes of fore-, mid-, and hindgut s. Our results suggest that development rate proceeds relatively independen tly of feeding during the last stadium. Our results support models that pos tulate loss of developmental plasticity late in nymphal life, and this cons traint on plasticity may limit the ability of late-instar nymphs to respond to a variable environment.