Exuviae eating: a nitrogen meal?

Many insects eat their cast cuticle (exuviae) after moulting. The functiona l significance of this behaviour has not been addressed experimentally. I t ested the hypothesis that exuviae eating constitutes a meal, so the animal recycles its nitrogen content. Nitrogenous compounds (protein and chitin) a n major components of the cuticle in Periplaneta americana, accounting for as much as 87% of the total weight. It was found that insects almost invari ably ate their exuviae during their larval life. The frequency of the behav iour decreased in newly emerged adults and varied between the sexes, males eating their exuviae less frequently than females. This may be due to the e xtra nitrogen endowment which females need for reproduction. Aposymbiotic a nimals, which lack the supply of essential amino acids from endosymbiotic b acteria, always ate their exuviae regardless of sex: When animals were rear ed on different diets throughout their larval life protein level in the die t correlated with exuviae eating. Animals reared on a low protein diet show ed the highest levels of exuviae eating; animals reared on a high protein d iet showed the highest levels of exuviae rejection. Analysis of the frass p roduced after exuviae meals showed that over 58% of the nitrogen present in the exuviae was recycled. This demonstrated that cockroaches digested nitr ogenous compounds contained in the cuticle. The possibility that the exuvia e meal has other functions is discussed, although the evidence supports a n utritional role. (C) 2000 Elsevier Science Ltd. All rights reserved.