Tsetse-transmitted trypanosomiases are among the most neglected tropical diseases in sub-Sahara Africa. Although all tsetse species are susceptible to trypanosome infections, their differential attraction/feeding preferences for different wildlife, domestic animals, and/or humans constitute critical determinants of trypanosomes species they predominantly transmit. Artificial bait technologies, based on long-range tsetse olfactory responses to natural cues emitted by preferred hosts and blends of synthetic versions that mimic these cues, have successfully been applied in attractant-odor-based (“pull” tactic) reduction of field populations of some tsetse species. Olfactory attribute associated with active avoidance of tsetse-refractory non-hosts has similarly been exploited in design of repellent-odor-based (“push” tactic) protection of livestock. These tactics have opened possibility of spatially strategic deployment of the two sets of odor baits in “push-pull” tactics. Possibility of developing blends with enhanced attraction and repellence compared with those associated with savannah tsetse fly hosts and non-hosts, respectively, have been explored, where structure activity and blends of different components generated two novel blends. The studies evaluated structure activity and blends of different components. One based on attractive constituents associated with buffalo (Syncerus caffer) comprised of ε-nonalactone, nonanoic acid, 2-nonanone (in 1:3:2 proportion) delivered together with acetone, which showed significantly better attractancy on savannah tsetse fly than the standard blend comprised of 3-propylphenol, octenol, p-cresol, and acetone (POCA). The other blend comprised of δ-nonalactone, heptanoic acid, 4-methylguaiacol and geranylacetone (in 6:4:2:1 proportion) was significantly more repellent than previously characterized blend based on tsetse fly refractory waterbuck (Kobus defassa) constituents (δ-octalactone, pentanoic acid, guaiacol and geranylacetone). So far, no effective attractants or repellents of riverine tsetse fly species have been characterized. Optimized attractant and repellent blends for savannah tsetse flies lay down useful groundwork for future development of the “push-pull” deployment tactic for area-wide control of tsetse flies. Better understanding of the physiological, cellular, and molecular basis of response in the tsetse fly to odors can potentially augment the current tsetse fly-control interventions.

Odor from preferred/non-preferred tsetse fly vertebrate hosts have been exploited in R&D of attractants/repellents of the fly for human and livestock protection. Odors from vertebrate hosts of Glossina austeni and Glossina pallidipes tsetse flies can facilitate formulation of novel attractants effective against G. austeni or improvement of existing attractant blends for G. pallidipes. We compared vertebrate blood meal sources of both fly species at Shimba Hills National Reserve, Kenya, to establish putative preferred host of either species, hence potential source of G. austeni or G. pallidipes specific odors. We trapped sympatric adult flies in 2021 and 2022 using NGU traps/sticky panels baited with 3-propylphenol, octenol, p-cresol, and acetone (POCA), collected their blood meals and characterized the meals using High Resolution Melting (HRM) vertebrate 16S rRNA- PCR (for host identification), and compared host profiles using GLM and Fisher’s exact tests. We collected 168 and 62 sympatric G. pallidipes and G. austeni with bloodmeal, respectively in 2021 and, 230 and 142 respectively in 2022. In 2021, we identified putative hosts of 65.48 and 69.35% of the G. pallidipes and G. austeni respectively and 82.61 and 80.28%, respectively in 2022. In 2021, we detected harnessed bushbuck, buffalo, common warthog and cattle putative host bloodmeals, and additionally bushpig and suni antelope bloodmeals in 2022. Putative vertebrate bloodmeal sources were significantly different by tsetse fly species (χ²(1, N=457) = 43.215, p < 0.001) and sampling year (χ²(1, N=457) = 8.044, p = 0.005). Frequency of common warthog bloodmeals was higher in G. pallidipes (65.79%) than in G. austeni (38.60%), and that of suni antelope and harnessed bushbuck putative bloodmeals higher in G. austeni (21.05-28.07%) than in G. pallidipes (6.84 - 17.37%) in 2022. There was an apparent change in putative feeding preference/host choices in both fly species between 2021 and 2022. Host bloodmeals in G. pallidipes or G. austeni predominantly from putative harnessed bushbuck, suni antelope or common warthog reveal that these vertebrates have potential odors that can be harnessed and formulated into appropriate attractants for respective species and integrated into routine control regiment for G. pallidipes and/or G. austeni.

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