Factors Affecting Coprophagy and Necrophagy by the German Cockroach (Dictyoptera: Blattellidae)

Abstract:
Modern bait formulations have been used successfully to control infestations of the German cockroach, Blattella germanica (L.) since the mid 1980s. Because of the slow-acting insecticides used in most bait formulations, unmetabolized insecticide may be excreted in the feces and oral secretions, and remain in the body of dead cockroaches. Coprophagy and necrophagy are reportedly important means of distributing insecticide into infested locations and inducing “secondary kill”. Our results question the significance of coprophagy and necrophagy as important means of insecticide transmission in typical German cockroach infestations. When either adult males or 1st-3rd instar nymphs were presented feces from adult male cockroaches killed by exposure to a variety of toxic baits or the dead cockroaches, there was <25% mortality after 14 d. Mortality declined even further when the cockroaches were provided a choice between food and either toxic feces or a dead cockroach. In many replicates, cockroaches would not feed at all on cadavers or feces even when starved for 24-72 h. In behavioral assays, cockroaches preferred virtually all alternative foods to cadavers or feces. Although there may be significant differences in food preferences and aversions among German cockroach strains, our data indicate that coprophagy and necrophagy are the last resort of starving cockroaches. These results also point out the importance of sanitation (removal of food sources) for successful management of German cockroach infestations.