Nutritional imbalance in an extreme generalist omnivore: tolerance and recovery through complementary food selection

As extreme generalists, cockroaches mix their diet from foods that vary greatly in their nutrient composition. It might thus be predicted that these insects have evolved robustness to enforced periods of nutritional imbalance and a well-developed ability to redress imbalances by compensatory food selection. We investigated these predictions for German cockroaches, Blatella germanica, using synthetic foods ranging in their balance of the macronutrients protein and carbohydrate. We first confined cockroaches for the duration of the final larval stadium either to a near-balanced food (% protein:% carbohydrate = 15:45), or one of four imbalanced foods (47:13 or 24:36 = excess protein; 13:47 or 4:56 = excess carbohydrate). All insects survived, but nutritional imbalance resulted in slowed development and skewed body composition. We then investigated the compensatory responses of nymphs confined during the first 48 h (approximately the first quarter) of the stadium to one of three nutritionally imbalanced foods, and thereafter allowed to select an intake from all three. Macronutrient intake was measured after 4, 10, 24, 48 and 120 h. Within 48 h all groups had entirely redressed the respective imbalances accrued during the 2-day pretreatment period, and thereafter consumed an indistinguishable balance of macronutrients. Our results show in B. germanica remarkable robustness to nutritional imbalance, and provide the first evidence of such effective compensation through complementary food selection for nutritional imbalance accrued over a timescale of days.