A study of bittng patterns in anopheles gambiae sensu lato (S.l.)

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The recent evidence indicating a modification in the biting pattern of vector populations could pose a challenge to the increased use of Insecticide treated bed nets as a malaria vector control strategy. This modification includes adaptation to biting humans when they are out of bed that is early evening and dawn together with increased outdoor biting. This modification might not necessarily be as a result of an adaptive change in vector behaviour but due to selective pressure against mosquitoes biting when bed nets are in use. This study therefore seeks to determine if discrete vector populations with specific biting times exist within Anopheles gambiae populations. An. gambiae sampled from 6pm to 6am in the field were pooled into four categories based on their time of biting; 6pm-9pm, 9pm-12am, 12am-3am and 3am-6am. Generations were raised on which feeding experiment and selection were performed. Non anophelines were separated from anophelines and PCR run on An. gambiae for species identification and molecular forms. An. gambiae formed the dominant species comprising 90.7% (739/815), 7.6% (62/815) for Culex species, 0.6% (5/815) for Mansonia, 0.5% (4/815) for Aedes, 0.5% (4/815) for An. funestus species and the least being An. pharoensis with 0.1% (1/815). Anopheles sampled comprised of An. gambiae (99.3%), An. funestus (0.5%) and An. pharoensis (0.1%) [n=744]. Different numbers of F1 and F2 progeny were obtained and used for feeding experiments for the different time groups. The percentages for the F1 groups that fed at same time periods as parents in the field (compared with feeding at other time points pooled together) were 90.5% (P=0.013) for 9pm-12am, 66.3% (P=0.029) for 12-3am and 62.3% (P=<0.0001) for 3-6am, whilst F2 had100% (P=0.228) for 9-12am and 91.2% (P=0.037) for 12-3am. The comparison of the feeding frequencies of F1 and F2 progeny for the time groups were [9pm-12am, F1 = 90.5% (38/42) and F2 = 100% (12/12)] and [12am-3pm, F1 = 66.3% (252/380) and F2 = 91.2% (52/57)]. However, irrespective of the period F1 and F2 from different collection times were exposed to feed, a high proportion was found to take a blood meal. PCR run on 138 Anopheles gambiae showed 97.1% An. gambiae s.s. with no amplification for 2.9%. Furthermore, 134 Anopheles gambiae s.s. which were identified by PCR and subjected to restriction fragment length polymorphism (RFLP) analysis for the various molecular forms gave 94.8% S forms and 5.2% M forms. Vector behaviours such as host preference, biting pattern and resting have been linked to genetic influence but results obtained for F1 and F2 generations showed otherwise probably due to extrinsic factors.
A thesis submitted to the Department of Theoretical and Applied Biology, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirements for the degree of Master of Philosophy, 2013