Residual Effectiveness Evaluation Of Insecticides Against Cockroaches On Porous Surface

The residual effect of an insecticide is directly related to its formulation, active ingredient and application rates. The aim of this study was to evaluate the effectiveness of 2 distinct commercial insecticides products against Blattella germanica and Periplaneta americana during the following six months after their application on porous surface. The tested products were P1: 2.5% Lambda-cyhalothrin on a microencapsulated formulation (Demand 2.5 CS®) and P2: 3.5% Lambda-cyhalothrin combined with 11.6% Thiamethoxam on an EZ formulation – microencapsulated + suspension concentrate, respectively (Tandem®). The tested dosage followed manufacturers’ indications: P1: 10mL/1L of water and P2: 8mL/1L of water. Each insecticide solution was sprayed on a 20cm x 20cm cement surface, following 1L/20m² proportion. Two hours after the application, 10 Blattella germanica individuals (5 males and 5 females) were exposed on the treated surface for 15 minutes, and, after that, 10 individuals of Periplaneta americana (5 males and 5 females) were also exposed to the same surface, for the same time. Five repetitions were made for each treatment. Residual effectiveness was evaluated at 30, 60, 90, 120, 150 and 180 days after application. These evaluations followed the same proceedings: individuals exposed for 15 minutes, 5 repetitions for each treatment. All the surfaces were kept in a laboratory, under room temperature and humidity. After exposure, all the individuals were moved to an insecticide free arena, with food and water available. Mortality was evaluated until 96 hours after exposition. Results showed that P1 and P2 provided 100% of control even 6 months after applications. For both products, LT50 (time to reach 50% of mortality) for Blattella germanica and Periplaneta americana was inferior to 1 hour at 0, 30, 60, 90, 120, 150 and 180 days after application. LT90 (time to reach 90% of mortality) for both species was also inferior to 1 hour for both products, even after 180 days after application. Microencapsulated formulations provided long lasting residual effectiveness even on porous surface. The obtained information is valuable when designing an effective cockroach control program where residual effectiveness is required.