An adaptive benefit of facultative coprophagy in the German cockroach Blattella germanica

1. A possible adaptive benefit of coprophagy was investigated in nymphs of the German cockroach Blattella germanica (L.). 2. Newly ecdysed first instars, given no source of food other than conspeci fic faeces, survived significantly longer than first instars deprived of fa eces. The faeces of adult males and females may be of different quality, ho wever, because nymphs given female faeces were more Likely to moult into th e second stadium than nymphs given male faeces. 3. In contrast to first instars, second inst ars provided adult faeces surv ived only slightly longer than starved counterparts. Faecal feeding is ther efore stage-specific, as is the benefit derived from it. 4. The relationship between the nutrient composition of faeces and the surv ival of nymphs was also examined. First instars fed the faeces of adults th at had been maintained on a high (50%) protein diet, died more slowly than first instars fed the faeces of adults that had been maintained on medium ( 22.5%) and low (5%) protein diets. Chemical analysis of faeces showed that the concentration of protein in adult faeces increased with the level of pr otein in the diet. Moreover, food choice assays showed that first instars, unlike adults, ingested more of the high-protein diets. 5. These data support the idea that coprophagy is a stage-specific adaptive behaviour that permits first instars to moult into the second stadium with minimal foraging.