The Residual Efficacy of SumiShield™ 50WG and K-Othrine(®) WG250 IRS Formulations Applied to Different Building Materials against Anopheles and Aedes Mosquitoes

SIMPLE SUMMARY: The Anopheles mosquitoes that transmit malaria are targeted by the use of indoor residual sprays (IRSs), insecticides applied to the walls of homes to kill mosquitoes that rest there when coming into houses in search of a blood meal. K-Othrine(®) is an IRS based on the pyrethroid deltamethrin and is widely used against mosquitoes that transmit malaria. SumiShield™ 50WG is an IRS based on the insecticide clothianidin, developed to kill mosquitoes that have become resistant to other forms of insecticide. These products were applied to cement, wood, and mud tiles, representative of typical building materials in areas where malaria is endemic. For 18 months, the ability of these treated surfaces to kill adult female mosquitoes exposed to them was measured. The clothianidin IRS was highly effective against insecticide susceptible and resistant strains of Anopheles gambiae and An. funestus, key malaria vector species, with an improved performance compared to deltamethrin IRS, though was not so effective against Aedes aegypti or Culex quinquefasciatus. Both IRS formulations were shown to be more effective and long-lasting on cement and mud than on wood tiles. ABSTRACT: Insecticides with novel modes of action are required to complement the pyrethroids currently relied upon for controlling malaria vectors. One example of this is the neonicotinoid clothianidin, the active ingredient in the indoor residual spray (IRS) SumiShield™ 50WG. In a preliminary experiment, the mortality of insecticide-susceptible and resistant An. gambiae adults exposed to filter papers treated with this IRS product reached 80% by 3 days post-exposure and 100% by 6 days post-exposure. Next, cement, wood, and mud tiles were treated with the clothianidin or a deltamethrin-based IRS formulation (K-Othrine WG250). Insecticide resistant and susceptible Anopheles and Aedes were exposed to these surfaces periodically for up to 18 months. Pyrethroid resistant Cx. quinquefasciatus was also exposed at 9 months. Between exposures, tiles were stored in heat and relative humidity conditions reflecting those found in the field. On these surfaces, the clothianidin IRS was effective at killing both susceptible and resistant An. gambiae for 18 months post-treatment, while mortality amongst the resistant strains when exposed to the deltamethrin IRS was not above that of the negative control. Greater efficacy of clothianidin was also demonstrated against insecticide resistant strains of An. funestus compared to deltamethrin, though the potency was lower when compared with An. gambiae. In general, higher efficacy of the clothianidin IRS was observed on cement and mud compared to wood, though it demonstrated poorer residual activity against Ae.aegypti and Cx. quinquefasciatus.