This study has demonstrated that MR08had nearly the same results compared to the gold standard repellent DEET in both laboratory and field situations. In the laboratory, DEET 30% (v/v) had protection efficiencies of 100% for the two mosquito species while MR08 had a protection efficiency of 100% and 91.2% for Cx. quinquefasciatus and An. gambiae s.s respectively, against mosquito bites 1 hour post exposure. Under field conditions, 30% MR08 had the highest protection efficiency (92.39%) while DEET 30% had a protection efficiency of 88.17% for seven hours (from 18:00 hrs to 01:00 hrs). These hourly intervals coincided with the first effective host seeking cycles of malaria vectors, An. gambiae s.l. In both laboratory and field evaluation of various repellent dosages, protection was found to be dosage dependent as found elsewhere [30, 31] while with blends, the synergistic effect was dosage mixture dependent [11, 32]. The strategy of using repellents in combination (Blends) conferred a better protection with little amount of repellent used (Blend 2 and Blend 3) compared to DEET and MR08 30% alone. Both blend 2 and 3 protected volunteers by 82 and 85%, and 98.4 and 92.8% in the field and laboratory respectively up to a period of 7 hours. Mosquito densities and efficacy of compound evaluated in the field had the same environmental variability, such as wind and house locations, thus these findings are likely to be as a result of the chemical compounds in the repellents. The application of repellents reduced the density of mosquito landing on the treatment group compared to the control volunteers (Figure 4).
In northern Tanzania, high distribution and usage of ITNs have shown increased protection to communities against malaria vectors when more than 80% of the population own and use bed nets properly [33, 34]. In other studies, bed net utilization has proved to reduce malaria infections when used properly as personal protection tools [35, 36]. There is increased exposure risk to those who are out of bed net either in the evening or morning during the peak biting cycles of the malaria vectors . Due to high coverage of ITN and IRS programmes, malaria vector feeding and resting behaviours’ are likely to have changed to maximize available feeding opportunities. Reports suggest that An. gambiae s.s has changed from being endophagic and endophilic to exophagic and exophilic respectively [2, 24, 38, 39]. This behavioural adaptation may present a problem in the personal protection in individuals when outdoors .
Application of MR08 as topical repellent could reduce the biting risk to those outdoors, hence adding protective value for individuals who are outside the bed nets during earlier and late biting cycles. These findings suggest that the protective efficacy which is maintained for a period of 7 hours is believed to be realistic for users who retire late to bed under the protection of the bed net. Field evaluations of repellents (18:00 to 01:00 hrs) were conducted during the first host seeking cycles of mosquitoes . Therefore, one can extrapolate the efficacy of these products in protecting individuals against random opportunistic host seeking mosquitoes. Thus, MR08 can complement the effects of ITNS and IRS for the unprotected individuals when used as the topical repellent . Currently in western Kenya, the decrease of relative abundance of vector species have been observed due to high implementation of intervention tools against malaria vectors  while in other places the displacement of the vector species composition have been reported . In Dar-es-salaam Tanzania, outdoor feeding among malaria vectors has been reported to be increasing due to wide ITNs coverage, hence increasing biting pressure on unprotected individuals outdoors .
In the current study, the observed reduction in biting rates both in laboratory and field evaluations may have great impact on infective bite reduction when incorporated with wide use of IRS and ITNs in the community. Malaria decline in different parts of Africa is associated with high ITN and IRS coverage [45, 46] and reliable diagnostic and treatment services . On the other hand, it has been observed that, when vector density declines, communities have a tendency to useless personal protection tools, such as bed nets, against disease vectors . It is necessary for the community to become more aware of using topical repellents.
In controlling African malaria vectors, ITN and IRS have been deployed with the assumption that vector behaviour remains endophilic and endophagic. This assumption is derived from classical behavioural studies by Gillies and Coetzee . These vectors have changed behaviour and tend to feed outdoors (exophagic) due to massive IRS, house modifications and ITN coverage [7, 39, 48]. In most malaria endemic areas, covering all households with IRS and ITNs is practically impossible [40, 49]. Another important limitation of ITN and IRS is that many people do not retire indoors or to bed earlier and miss the benefit of the protection offered by these methods during the earlier biting cycles of malaria vectors . Additional tools, such as repellents, should be considered to supplement existing vector protection tools.
Protection against infective bites from arthropods can be achieved by either avoiding infested areas, protective gear usage (cloth with repellents and ITNs), house modifications or applying topical insect repellents and use of IRS [7, 11, 50]. Most commercially available repellents and formulations have up to 40% DEET, which is preferred for use in areas with high biting pressure or environmental conditions that promote the loss of repellent on skin surface [51–53]. This amount of DEET (40%) seemed to be higher than MR08 blends (of 10% and 20%), which could reduce the production costs and be affordable to the large populations.
Thousands of plant resources have been tested as sources of insect repellents [4, 11, 20, 54, 55]. ITN, treated curtains and IRS coverage have critically reduced entomological inoculation rates [36, 47] and integrating the evaluated MR08 repellents in reducing human-vector contact might further reduce EIR to even lower rates than currently reported at0.54 ib/trap/year in the study area . But this reduction of EIR can only be estimated for the indoor biting mosquitoes and not for the outdoor biting ones, where other tools, such as ITN and IRS cannot be implemented . Therefore, during outdoor movements and late retirement to bed, application of topical repellents should be emphasized , together with house design modification for indoor vector reduction . MR08 and other repellents could be taken into consideration to fill the gap to reduce transmission rate during this unprotected time.
Currently, slow release and vaporization methods are being tested to enhance the effectiveness of MR08 in preventing mosquito bites inside the household.
The appropriate method of delivering MR08 repellent to be protective and effective for all house occupants for longer duration of time is still on-going.