Effects of Two Temperature Storage Regimes on the Efficacy of 3 Commercial Gel Baits against the German Cockroach, Blattella germanica L. (Dictyoptera: Blattellidae)

Background: To compare the effectiveness of 3 commercial gel bait formulations containing fipronil (Goliath (c) Cockroach Gel 0.05% AI), chlorpyrifos-A (Clean Bait (c) Gel, 2% AI), and chloropyrifos-B (Serpa (c) Gel 2% AI) against German cockroaches (Blattella germanica) when stored at 23 degrees C and 30 degrees C after treatment. Methods: Laboratory bioassays consisted of placing groups of fifteen cockroaches (a random combination of adult, mixed sex and large nymphs-stage 6) into a 5 L cylindrical plastic container with one drop of product (avg 0.10 g +/- 0.01 g) applied to a 76 mm x 26 mm glass microscope slide affixed to the bottom of each container (one product tested per container). Cumulative mortality was assessed at 6 h, I, 2, 3, 4, and 5 d after application. To determine the further effects of storage temperature after treatment on residual activity of the gels, a drop of each product was applied to separate glass microscope slides and stored at either 23 degrees C (warm) or 30 degrees C (hot) under dark conditions for 0, I, 7, 14, 30, 45, 60 and 90 d after application. Results: Freshly applied baits (day 0) containing fipronil provided complete cockroach mortality (100%) within 5 d whereas chloryrifos-A and chlorpyrifos:B provided approximate to 72% and 88% mortality, respectively. Generally, cockroach mortality was greater when gels were stored at 30 degrees C compared with 23 degrees C. Conclusion: The fipronil gel formulation proved to be as efficacious as the chlorpyrifos gels and in some instances surpased the latter formulations depending on storage time and temperature by providing approximate to 90% mortality at 90 d post treatment.