Insecticide resistance monitoring of field‐collected <i>Anopheles gambiae s.l</i>. populations from Jinja, eastern Uganda, identifies high levels of pyrethroid resistance

Abstract

<jats:p>Insecticide resistance in the malaria vector <jats:italic>Anopheles gambiae s.l</jats:italic>. (Diptera: Culicidae) threatens insecticide‐based control efforts, necessitating regular monitoring. We assessed resistance in field‐collected <jats:italic>An. gambiae s.l</jats:italic>. from Jinja, Uganda using World Health Organization (WHO) biosassays. Only <jats:italic>An. gambiae s.s</jats:italic>. and <jats:italic>An. arabiensis</jats:italic> (≅70%) were present. Female <jats:italic>An. gambiae</jats:italic> exhibited extremely high pyrethroid resistance (permethrin LT<jats:sub>50</jats:sub> &gt; 2 h; deltamethrin LT<jats:sub>50</jats:sub> &gt; 5 h). Female <jats:italic>An. arabiensis</jats:italic> were resistant to permethrin and exhibited reduced susceptibility to deltamethrin. However, while <jats:italic>An. gambiae</jats:italic> were DDT resistant, <jats:italic>An. arabiensis</jats:italic> were fully susceptible. Both species were fully susceptible to bendiocarb and fenitrothion. <jats:italic>Kdr 1014S</jats:italic> has increased rapidly in the Jinja population of <jats:italic>An. gambiae s.s</jats:italic>. and now approaches fixation (≅95%), consistent with insecticide‐mediated selection, but is currently at a low frequency in <jats:italic>An. arabiensis</jats:italic> (0.07%). <jats:italic>Kdr 1014F</jats:italic> was also at a low frequency in <jats:italic>An. gambiae</jats:italic>. These frequencies preclude adequately‐powered tests for an association with phenotypic resistance. PBO synergist bioassays resulted in near complete recovery of pyrethroid susceptibility suggesting involvement of CYP450s in resistance. A small number (0.22%) of <jats:italic>An. gambiae s.s</jats:italic>. ×<jats:italic>An. arabiensis</jats:italic> hybrids were found, suggesting the possibility of introgression of resistance alleles between species. The high levels of pyrethroid resistance encountered in Jinja threaten to reduce the efficacy of vector control programmes which rely on pyrethroid‐impregnated bednets or indoor spraying of pyrethroids.</jats:p>