Preliminary results show wall surface, not water pH affects insecticide efficacy

Control Cone Setup In Ethiopia

In Ethiopia, resistance to pyrethroid insecticides is rapidly spreading and is posing a major threat to preventing the transmission of malaria. Pyrethroid resistance is forcing IRS programs to move to carbamate-based insecticides. To learn more about the insecticides, AIRS Ethiopia is using cone bioassays to test the efficacy of two carbamates (propoxur and bendiocarb) in different pH levels of spray water and on different wall surfaces (dung and mud).

Many insecticides, particularly commonly-used carbamates, undergo a chemical reaction in the presence of alkaline water that reduces their effectiveness. The pesticide is rendered ineffective when it is mixed with water with a pH greater than 7. To prevent this, IRS implementers can use buffering agents to change the pH of water to a prescribed level.

For this study, the project constructed 12 experimental huts in two locations in the Adama district, about 90 kilometers southeast of Addis Ababa. The AIRS research team plastered six huts with mud and another six huts with dung.  Then huts were sprayed with different combinations of water, pH buffers, and insecticides. (See table below.) Vector mosquito mortality data were initially collected 24 hours after spraying, then data were collected monthly from May to October 2012.

Huts Tested by Wall Surface and Spray

Preliminary Results, April-July 2012

  • The pH of spray water had little effect on the decay of the insecticides.
  • Both carbamates showed signs of deterioration—one month after spray in mud coated walls and two months after spray in dung coated walls.
  • Propoxur performed better than bendiocarb.
  • Although there is nearly no difference in pH between dung and mud wall surfaces, both insecticides performed better on dung coated surfaces.

AIRS will use findings to inform spray campaigns in Ethiopia. Check back soon for the full report.




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