Changes in population density, habitat preference and susceptibility to insecticides of cockroaches inhabiting in an underground shopping arcade in Osaka

Abstract

Cockroaches inhabiting in an underground shopping arcade in Osaka were investigated by using bait traps, and their susceptibility to insecticides were assessed by a topical application method. In the underground arcade, dominant species were Blattella germanica and Periplaneta brunnea accompanied by a small number of P. fuliginosa. The average number captured in the restaurant area of the arcade was almost equivalent between the dominant two species (1-2 roaches/(daytrap)). While B. germanica was dominant at cafe restaurants and Western style restaurants, P. brunnea was major at Japanese restaurants, Japanese pubs and sushi shops. The similar habitat preference was observed in the food store area, which had continuous floor and constant temperature and humidity among the shops. This habitat segregation has been basically unchanged during the 10 years of monitoring. It is supposed that one of the reasons of the habitat preference is originated from some difference of chemical factors in the food or food materials. In B. germanica, LD values for fenitrothion, pyrethrins and d-trans-permethrin had a tendency to increase gradually during the 10 years. All the final R/S ratio, however, still belonged to a low level. Against the P. brunnea, while LD value for fenitrothion was almost constant throughout the monitoring period, those for the two pyrethroids increased and, especially for d-trans-permethrin, the final resistance level was supposed to be of a moderate rank. According to these results, the current spray program in this field, multiple application of organophosphates (e.g. fenitrothion) and pyrethroids (e.g. permethrin), is considered an effective measure to suppress the population density of B. germanica as well as to prevent the development of their high resistance to insecticides. Against P. brunnea, however, it is suggested that successive monitoring studies should be necessary to watch the effectiveness of insecticides, particularly for synthetic pyrethroids.