High Level of DDT Resistance and Reduced Susceptibility to Deltamethrin in <i>Anopheles gambiae</i>, <i>Anopheles coluzzi</i>, and <i>Anopheles arabiensis</i> from Urban Communities in Oyo State, South-West Nigeria

Abstract

Selection of vector populations capable of withstanding doses of insecticides is a major threat facing insecticide based vector control interventions. In view of the rapidly evolving insecticide resistance in the primary vector, Anopheles, there is need to provide information on the status of insecticide resistance in Oyo State where Long Lasting Insecticide Treated Nets (LLIN) is the only intervention that has been deployed over the years. Morphologically identified Anopheles mosquito larva were collected from six localities (Ojoo, Iwo road, Bodija, Oluyole, Oyo town and Eruwa) in Oyo State. The larval samples were reared to adults and exposed to DDT (4%) and Deltamethrin (0.05%), according to WHO criteria. Knockdown was recorded every ten minutes and mortality scored at 24 hrs post exposure. The KDT 50 and KDT 95 were determined using probit regression analysis and species identification was by adult morphology and Polymerase Chain Reaction techniques. A total of 1,800 female anopheline mosquitoes were exposed to DDT and Deltamethrin insecticides. All the Anopheles mosquito populations from the six localities were resistant to DDT with 13-84% mortality. The anopheline mosquito populations from Iwo road and Oyo town were susceptible to Deltamethrin, while those from Ojoo and Eruwa showed reduced susceptibility to the insecticide. However,mosquito populations from Oluyole and Bodija were resistant to Deltamethrin. The knock down values for DDT and Deltamethrin across all sites was comparatively high indicative of some degree of selection within the populations. Of the 1,764 positively identified anophelines, 639 (36.2%), 1,034 (58.6%) and 91 (5.2%) were Anopheles coluzzi, Anopheles arabiensis and Anopheles gambiae s.s. respectively. This data indicates the widespread resistance of Anopheles coluzzi, Anopheles arabiensis and Anopheles gambiae s.s. to Dichlotrichloroethane (DDT) in Oyo State. It also showed an ongoing selection against pyrethroid which poses a major threat to the ongoing LLIN intervention in the State.

High Pyrethroid Resistance to Deltamethrin and DDT in Major Malaria Vector Anopheles gambiae s.l. from South-Western Nigeria is Probably Driven by Metabolic Resistance Mechanisms

“…Mosquito populations in the present study were highly resistant to Deltamethrin and DDT which indicate cross-resistance within the populations [13]. This resistance data is consistent with previous reports from South-West Nigeria [9,10,28]. In many populations, cross-resistance has been largely attributed to the presence of kdr resistance gene [29][30][31].…”

“…There is widespread use of LLINs and IRS in sub-Saharan Africa and these have led to reduction in the incidence of the disease over the years [7]. However, mosquito populations have developed resistance to all insecticides recommended by WHO for malaria vector control and this has negatively impacted the progress recorded in previous years [8,9].…”

Low frequency of knockdown resistance mutation (L1014F) and the efficacy of PBO synergist in multiple insecticide-resistant populations of Anopheles gambiae in Ikorodu, Lagos State, Nigeria

“…gambiae s.l. from the study locations were resistant to DDT, similar to previous studies in south-western Nigeria and other parts of the country 25 – 29 . Similarly, resistance was also reported in pyrethroid; deltamethrin and lambda cyhalothrin in the study areas.…”

Widespread Report of Multiple Insecticide Resistance in Anopheles gambiae s.l. Mos-quitoes in Eight Communities in Southern Gombe, North-Eastern Nigeria

“…gambiae and An. coluzzii in Nigeria (4, 6, 8 and 24). Evidence of resistance to pirimiphos-methyl (mortality rate between 65–95%) was observed in the An.…”