Gustatory adaptation affects sexual maturation in male German cockroaches,Blattella germanica

Adaptations to hazardous environmental factors are essential for survival, although they may be maladaptive in conditions where the hazard is absent. In German cockroach (Blattella germanica L.) populations, glucose aversion has evolved rapidly in response to glucose‐containing insecticidal baits, but little is known about the consequences of this behaviour in the absence of bait. In the present study, glucose‐averse (GA) and wild‐type (WT) male German cockroaches are restricted to a range of nutritionally defined diets containing either glucose or fructose as the sole carbohydrate source, and time to first expression of courtship is measured by stimulating the male antennae daily with isolated antennae from receptive, 6‐day‐old females. Glucose‐averse males that are restricted to glucose‐containing diets mature their courtship responses significantly later than GA males restricted to fructose‐containing diets, whereas there is no difference in maturation of courtship responses between GA males restricted to fructose‐containing diets and WT males restricted to diets containing either sugar type. Glucose‐averse males furthermore respond later to GA female antennae than to WT female antennae, all from 6‐day‐old females. This suggests that GA females are less sexually stimulating, and the results are also consistent with earlier findings showing that GA females contain less developed oocytes than WT females at this age. These findings demonstrate that an adaptive gustatory mutation conferring protection from a toxin may have comparatively detrimental effects under conditions where the toxin has vanished, both by delaying female sexual maturation and signalling and by delaying male sexual maturation and courtship under conditions where glucose is a major energy source.