title: Short persistence of bendiocarb sprayed on pervious walls and its implication for the indoor residual spray program in Ethiopia.
abstract: BACKGROUND
  With the emergence and spread of vector resistance to pyrethroids and DDT in Africa, several countries have recently switched or are considering switching to carbamates and/or organophosphates for indoor residual spraying (IRS). However, data collected on the residual life of bendiocarb used for IRS in some areas indicate shorter than expected bio-efficacy. This study evaluated the effect of pH and wall type on the residual life of the carbamates bendiocarb and propoxur as measured by the standard World Health Organization (WHO) cone bioassay test.
  
  
  METHODS
  In phase I of this study, bendiocarb and propoxur were mixed with buffered low pH (pH 4.3) local water and non-buffered high pH (pH 8.0) local water and sprayed on two types of wall surface, mud and dung, in experimental huts. In the six month phase II study, the two insecticides were mixed with high pH local water and sprayed on four different surfaces: painted, dung, mud and mud pre-wetted with water. The residual bio-efficacy of the insecticides was assessed monthly using standard WHO cone bioassay tests.
  
  
  RESULTS
  In phase I, bendiocarb mixed with high pH water killed more than 80% of susceptible Anopheles arabiensis mosquitoes for two months on both dung and mud surfaces. On dung surfaces, the 80% mortality threshold was achieved for three months when the bendiocarb was mixed with low pH water and four months when it was mixed with high pH water. Propoxur lasted longer than bendiocarb on dung surfaces, staying above the 80% mortality threshold for four and five months when mixed with high and low pH water, respectively. Phase II results also showed that the type of surface sprayed has a significant impact on the bio-efficacy of bendiocarb. Keeping the spray water constant at the same high pH of 8.0, bendiocarb killed 100% of exposed mosquitoes on impervious painted surfaces for the six months of the study period compared with less than one month on mud surfaces.
  
  
  CONCLUSIONS
  Mixing the insecticides in alkaline water did not reduce the residual bio-efficacy of bendiocarb. However, bendiocarb performed much better on impervious (painted) surfaces than on porous dung or mud ones. Propoxur was less affected by wall type than was bendiocarb. Studies on the interaction between wall materials, soil, humidity, temperature and pH and the residual bio-efficacy of new and existing insecticides are recommended prior to their wide use in IRS.
authors.affiliation: The President's Malaria Initiative Africa Indoor Residual Spraying Project, Abt Associates, Gerji Road, Sami Building, 1st Floor, Addis Ababa, Ethiopia.
authors.forename: Yemane
authors.initials: Y
authors.lastname: Yeebiyo
authors.affiliation: The President's Malaria Initiative Africa Indoor Residual Spraying Project, Abt Associates, 4550 Montgomery Ave., Suite 800 North, Bethesda, MD, 20814, USA. Dereje_Dengela@abtassoc.com.
authors.forename: Dereje
authors.initials: D
authors.lastname: Dengela
authors.affiliation: The President's Malaria Initiative Africa Indoor Residual Spraying Project, Abt Associates, Gerji Road, Sami Building, 1st Floor, Addis Ababa, Ethiopia.
authors.forename: Alemayehu Getachew
authors.initials: AG
authors.lastname: Tesfaye
authors.affiliation: The President's Malaria Initiative Africa Indoor Residual Spraying Project, Abt Associates, Gerji Road, Sami Building, 1st Floor, Addis Ababa, Ethiopia.
authors.forename: Gedeon Yohannes
authors.initials: GY
authors.lastname: Anshebo
authors.affiliation: The President's Malaria Initiative Africa Indoor Residual Spraying Project, Abt Associates, 4550 Montgomery Ave., Suite 800 North, Bethesda, MD, 20814, USA.
authors.forename: Lena
authors.initials: L
authors.lastname: Kolyada
authors.affiliation: Entomology Branch, Centers for Disease Control and Prevention, 1600 Clifton Road, Atlanta, GA, 30329-4027, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Wirtz
authors.affiliation: U.S. Agency for International Development (USAID), Entoto Street, Addis Ababa, Ethiopia.
authors.forename: Sheleme
authors.initials: S
authors.lastname: Chibsa
authors.affiliation: President's Malaria Initiative, United States Agency for International Development, Bureau for Global Health, Office of Health, Infectious Disease & Nutrition, 10082A, 2100 Crystal Drive, Arlington, VA, 22202, USA.
authors.forename: Christen
authors.initials: C
authors.lastname: Fornadel
authors.affiliation: President's Malaria Initiative, United States Agency for International Development, Bureau for Global Health, Office of Health, Infectious Disease & Nutrition, 10082A, 2100 Crystal Drive, Arlington, VA, 22202, USA.
authors.forename: Kristen
authors.initials: K
authors.lastname: George
authors.affiliation: President's Malaria Initiative, United States Agency for International Development, Bureau for Global Health, Office of Health, Infectious Disease & Nutrition, 10082A, 2100 Crystal Drive, Arlington, VA, 22202, USA.
authors.forename: Allison
authors.initials: A
authors.lastname: Belemvire
authors.affiliation: National Malaria Control Program, Federal Ministry of Health, Addis Ababa, Ethiopia.
authors.forename: Hiwot Solomon
authors.initials: HS
authors.lastname: Taffese
authors.affiliation: The President's Malaria Initiative Africa Indoor Residual Spraying Project, Abt Associates, 4550 Montgomery Ave., Suite 800 North, Bethesda, MD, 20814, USA.
authors.forename: Bradford
authors.initials: B
authors.lastname: Lucas
mesh_terms: D000818:Animals; D000852:Anopheles / Q000187:drug effects; D005002:Ethiopia; D005243:Feces; D006798:Housing; D007306:Insecticides / Q000737:chemistry*; D010573:Pesticide Residues / Q000737:chemistry; D048448:Phenylcarbamates / Q000737:chemistry*; D001074:Propoxur / Q000737:chemistry; D012987:Soil / Q000737:chemistry; D013499:Surface Properties; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D007306:Insecticides; D010573:Pesticide Residues; D048448:Phenylcarbamates; D012987:Soil; D014867:Water; D001074:Propoxur; C007725:bendiocarb
keywords: Anopheles arabiensis; Bendiocarb; Ethiopia; Experimental hut; IRS; Propoxur; Vector control