Analysis of specific adaptation to a domicile habitat: A comparative studyof two closely related cockroach species

The German cockroach, Blattella germanica (L.), and the closely related spe cies B. bisignata (Brunner) belong to the germanica species group. They are similar in appearance, life history, reproductive cycle, and courtship beh avior. The most significant difference is habitat preferences: B. germanica is a household species and lives in crowded conditions, whereas the feral B, bisignata lives outdoors in a solitary manner. Nevertheless, B. bisignat a has recently been found in households. A comparison between the two speci es has shown that B. germanica displays gregarious behavior and produces an aggregation pheromone, whereas both characters are absent in B. bisignata. Mate preference experiments have revealed that B. germanica females accept ed only conspecific males, whereas B. bisignata females mated with males fr om both species, provided that long distance calling was bypassed. In addit ion, the high reproductive potential of B. germanica outcompeted the other species: when 10 pairs of B, germanica and of B. bisignata were kept togeth er in crowded conditions during 3 mo, B. bisignata was driven into extincti on. It is concluded that the chances of B, bisignata becoming a new househo ld species are remote.