Ineffectiveness of over-the-counter bait and aerosol insecticide products against field-collected German cockroaches (Blattodea: Ectobiidae)

Over-the-counter (OTC) insecticide products are popular, easily available, and inexpensive do-it-yourself options for home residents. In this study, we investigated the performance of OTC insecticides consisting of bait and spray products against susceptible and field-collected strains of the German cockroach, Blattella germanica (L.) (Blattodea: Ectobiidae) using several test methods. In open arena bioassays, all OTC baits tested were ineffective on field-collected German cockroaches. The least effective OTC bait was unable to kill all test cockroaches of any strains at 14 d post-treatment. Direct spray experiments demonstrated that cockroaches treated with pyrethroid spray registered significantly shorter mean knockdown times when compared to that of the natural product. On the other hand, the natural product spray caused significantly shorter mean survival time in test insects than the pyrethroid spray (<1 h vs. >1 d). The residual efficacy of spray deposits was evaluated in the Ebeling choice box and revealed that all sprays have poor residual performance against field-collected German cockroach strains. Insecticide resistance and potential avoidance behavior may have contributed to the low performance index (PI) values of pyrethroid-based sprays, as cockroaches may have survived initial contact and subsequently avoided treated surfaces. Conversely, natural product spray deposits exhibited negative PI values for most of the study period due to spatial repellency. In general, the performance of OTC insecticide products was lower on field-collected German cockroach strains than on the susceptible strain. These products are likely ineffective at controlling the German cockroach infestations in homes.