Common consumer residual insecticides lack efficacy against insecticide-susceptible and resistant populations of the German cockroach (Blattodea: Ectobiidae).

The German cockroach, Blattella germanica (L.) (Blattodea: Ectobiidae), is a ubiquitous pest in affordable housing. They represent a major threat to human health due to their contribution of asthma-exacerbating allergens and the potential to transfer pathogenic microorganisms indoors. Despite well-documented pyrethroid resistance, pyrethroid-based broadcast residual insecticide products are often used by residents to control cockroaches in their homes. Additionally, there is little empirical independent testing of these products. Thus, it remains unclear how effective these commonly used do-it-yourself products are at controlling German cockroaches. This study represents a comprehensive examination of the efficacy of these products with direct, limited, and continuous exposure assays on a variety of common household surfaces on field populations of cockroaches with varying levels of pyrethroid resistance. While most products performed well when applied directly to test insects, mortality was substantially lower across all surfaces with limited exposure (30 min). In continuous exposure assays on a nonporous surface, products took at least 24 hr to cause 100% mortality in a field population, with some products taking up to 5 d to achieve 100% mortality. The findings of this study demonstrate a lack of residual efficacy from common pyrethroid-based consumer-use pesticides products. Given that it is not feasible to find and treat every cockroach in a home directly, the residuality of spray-based formulations is critical for products designed to control German cockroaches. Without residual efficacy, as shown in the consumer aerosol and spray products tested, we expect these products to add little to no value to cockroach control.

Comparative toxicity and repellency of microencapsulated and other liquid insecticide formulations to the German cockroach (Dictyoptera: Blattellidae).

Responses of German cockroaches, Blattella germanica (L.) (Dictyoptera: Blattellidae), to microencapsulated (ME) formulations of six insecticides (bifenthrin, chlorpyrifos, cyfluthrin, deltamethrin, lambda-cyhalothrin, and permethrin) were compared with emulsifiable concentrates (EC) (chlorpyrifos, cyfluthrin, deltamethrin, and permethrin) or ready-to-use (RTU) formulations (bifenthin and lambda-cyhalothrin). Two rates were tested per comparison. Baseline toxicity (LT50 value) was determined by continuous exposure to residual deposits. Repellency, toxicity (LT50), and performance index (PI) values were determined using Ebeling choice boxes. Baseline toxicity of the permethrin formulations was similar, but all other active ingredients had significant toxicity differences at one or both formulation x dose comparisons. Baseline toxicity and repellency were negatively correlated. Choice box LT50 and the time to reach 50% of the maximum PI were positively correlated. The maximum PI was positively correlated (P < 0.06) with baseline LT50 and negatively correlated (P < 0.07) with repellency. Chlorpyrifos had the lowest repellency except for the EC at 0.25%. Bifenthrin ME and lambda-cyhalothrin ME had greater PI values than comparative RTU formulations. Cyfluthrin EC at 0.03% and deltamethrin ME at 0.01% had significantly lower PI values than comparison treatments. Permethrin PI value for the EC at 0.03% exceeded that for the ME, but at 0.05% the ME had a significantly greater PI. These data demonstrate the difficulty in making generalizations about the relative performance of ME compared with EC or RTU formulations. Variable results observed within, and between, formulations may be influenced by application rate, formulation type, other formulation components, and the toxicity-repellency of the active ingredient.