Abstract
Introduction Behavioural resistance to insecticides restrains the efficacy of vector control tools against mosquito-transmitted diseases. The current study is aimed at determining the impact of insecticide resistance on major malaria vectors' biting, feeding, and resting behaviour in areas with and areas without insecticide resistance in Teso North and Teso South, Busia County, Western Kenya. Methods Mosquito larvae were sampled using a dipper, reared into 3-5-day-old female mosquitoes [4944] which were exposed to 0.75% permethrin and 0.05% deltamethrin using World Health Organization tube assay method. Blood meal, species identification, and kdr Eastgene PCRs were also performed on adult mosquitoes sampled using mosquito collection methods [3448]. Biting, feeding, resting, and exiting behaviours of field-collected mosquitoes from five selected clusters were analysed. Results The lowest Kdr genotypic frequency (SS) proportion was found in female Anophelines collected in Kengatunyi at 58% while Rwatama had the highest genotypic frequency at 93%, thus susceptible and resistant clusters, respectively. The peak hour for mosquito seeking a human bite was between 0300 and 0400 hrs in the resistant cluster and 0400-0500 hrs in the susceptible cluster. The heterozygous mosquitoes maintained the known 2100-2200 hrs peak hour. There was a higher proportion of homozygous susceptible vectors (86.4%) seeking humans indoor than outdoor bitters (78.3%). Mosquito blood meals of human origin were 60% and 87% in susceptible Kengatunyi and resistant Rwatama cluster, respectively. There was significant difference between homozygous-resistant vectors feeding on human blood compared to homozygous susceptible mosquitoes (p ≤ 0.05). The proportion of bovine blood was highest in the susceptible cluster. A higher proportion of homozygous-resistant anophelines were feeding and resting indoors. No heterozygous mosquito was found resting indoor while 4.2% of the mosquitoes were caught while exiting the house through the window. Discussion. A shift in resistant Anopheles gambiae sl highest peak hour of aggressiveness from 2100-2200 hrs to 0300-0400 hrs is a key change in its biting pattern. Due to the development of resistance, mosquitoes no longer have to compete against the time the human host enters into the formerly lethal chemical and or physical barrier in the form of long-lasting insecticide-treated net. No heterozygous LS mosquito rested indoors possibly due to disadvantages of heterozygosity which could have increased their fitness costs as well as energy costs in the presence of the insecticidal agents in the treated nets. Conclusions and recommendations. Out of bed biting by female mosquitoes and partial susceptibility may contribute to residual malaria transmission. Insecticide-resistant vectors have become more endophagic and anthropophillic. Hence, insecticidal nets, zooprophylaxis, and novel repellents are still useful chemical, biological, and physical barriers against human blood questing female mosquitoes. Further studies should be done on genetic changes in mosquitoes and their effects on changing mosquito behaviour.
Highlights
Behavioural resistance to insecticides restrains the efficacy of vector control tools against mosquito-transmitted diseases
World Health Organization (WHO) criteria for susceptibility are as follows: mortality rates between 98% and 100% indicate full susceptibility; mortality rates between 90% and 97% require further investigation while in mortality rates
WHO criteria for phenotypic susceptibility are as follows: mortality rates between 98% and 100% indicate full susceptibility; mortality rates between 90% and 97% require further investigation while in mortality rates < 90%, the population is considered resistant to the tested insecticides
Summary
Behavioural resistance to insecticides restrains the efficacy of vector control tools against mosquito-transmitted diseases. Biting, feeding, resting, and exiting behaviours of field-collected mosquitoes from five selected clusters were analysed. The lowest Kdr genotypic frequency (SS) proportion was found in female Anophelines collected in Kengatunyi at 58% while Rwatama had the highest genotypic frequency at 93%, susceptible and resistant clusters, respectively. The peak hour for mosquito seeking a human bite was between 0300 and 0400 hrs in the resistant cluster and 04000500 hrs in the susceptible cluster. There was a higher proportion of homozygous susceptible vectors (86.4%) seeking humans indoor than outdoor bitters (78.3%). Mosquito blood meals of human origin were 60% and 87% in susceptible Kengatunyi and resistant Rwatama cluster, respectively. There was significant difference between homozygous-resistant vectors feeding on human blood compared to homozygous susceptible mosquitoes (p ≤ 0:05). A higher proportion of homozygous-resistant anophelines were feeding and resting indoors. Malaria is decreasing through intensified interventions since mid-2000s onwards, these environmental changes might expose population in the highlands of east Africa to an increase risk of malaria and its epidemic if the current interventions are not sustained [7, 8]
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