Previous studies have shown that δ-octalactone is an important component of the tsetse-refractory waterbuck (Kobus defassa) repellent odour blend. In the present study, structure-activity comparison was undertaken to determine the effects of the length of the side chain and ring size of the lactone on adult Glossina pallidipes and Glossina morsitans morsitans. The responses of the flies to each compound were studied in a two-choice wind tunnel. Increasing the chain length from C3 (δ-octalactone) to C4 (δ-nonalactone) enhanced repellency to both species (G. pallidipes from 60.0 to 72.0 %, and G. m. morsitans from 61.3 to 72.6 %), while increasing the ring size from six (δ-octalactone) to seven members (ε-nonalactone) changed the activity from repellency to attraction that was comparable to that of the phenolic blend associated with fermented cow urine (p > 0.05). Blending δ-nonalactone with 4-methylguaiacol (known tsetse repellent) significantly (p < 0.05) raised repellency to 86.7 and 91.7 % against G. pallidipes and G. m. morsitans respectively. Follow-up Latin Square Designed field studies (Shimba hills in coastal areas in Kenya) with G. pallidipes populations confirmed the higher repellence of δ-nonalactone (with/without 4-methylguaiacol) compared to δ-octalactone (also, with/without 4-methylguaiacol). The results show that subtle structural changes of olfactory signals can significantly change their interactions with olfactory receptor neurons, and either shift their potency, or change their activity from repellence to attraction. Our results also lay down useful groundwork in the development of more effective control of tsetse by ‘push’, ‘pull’ and ‘push-pull’ tsetse control tactics.
Tsetse fly exhibit species-specific olfactory uniqueness potentially underpinned by differences in their chemosensory protein repertoire. We assessed 1) expansions of chemosensory protein orthologs in Glossina morsitans morsitans, Glossina pallidipes, Glossina austeni, Glossina palpalis gambiensis, Glossina fuscipes fuscipes and Glossina brevipalpis tsetse fly species using Café analysis (to identify species-specific expansions) and 2) differential expressions of the orthologs and associated proteins in male G. m. morsitans antennae and head tissues using RNA-Seq approaches (to establish associated functional molecular pathways). We established accelerated and significant (P<0.05, λ = 2.60452e-7) expansions of gene families in G. m. morsitans Odorant receptor (Or)71a, Or46a, Ir75a,d, Ionotropic receptor (Ir) 31a, Ir84a, Ir64a and Odorant binding protein (Obp) 83a-b), G. pallidipes Or67a,c, Or49a, Or92a, Or85b-c,f and Obp73a, G. f. fuscipes Ir21a, Gustatory receptor (Gr) 21a and Gr63a), G. p. gambiensis clumsy, Ir25a and Ir8a, and G. brevipalpis Ir68a and missing orthologs in each tsetse fly species. Most abundantly expressed transcripts in male G. m. morsitans included specific Or
The essential oils of Ocimum gratissimum Linn, Hyptis suaveolens (L) Poit and Vitex keniensis, which are used traditionally in Western Kenya for personal and space protection against mosquito bites, were screened for repellence against Anopheles gambiae Sensu Stricto. Essential oils were extracted from their leaves by hydrodistillation, characterised by gas chromatography linked with mass spectrophotometer and electroantennogram detectors. The repellency of the oils and their selected blends was studied by the reduction in probing and feeding on the human arm. The oils showed promising repellency for Anopheles gambiae, O. gratissimum (RD 50 = 2.77 × 10-5 mg cm-2, 95 % CI), Vitex keniensis (RD 50 = 5.68 × 10-5 mg cm-2) and Hyptis suaveolens (6.27× 10-5 mg cm-2) as compared to that of DEET (control) RD 50 = 1.25×10-5 mg cm-2). The bioactive constituents of each oil were identified by Gas chromatography-linked with Mass spectrometry and Electroantennography. Some compounds were confirmed by co-injections of the oil with available authentic standards. The results provide a scientific rationale for the traditional use of these plants in repelling disease vectors and other biting insects, and lay down some useful groundwork for downstream development of more effective products for personal and space protection.
Savannah tsetse flies avoid flying toward tsetse fly-refractory waterbuck (Kobus defassa) mediated by a repellent blend of volatile compounds in their body odor comprised of δ-octalactone, geranyl acetone, phenols (guaiacol and carvacrol), and homologues of carboxylic acids (C5-C10) and 2-alkanones (C8-C13). However, although the blends of carboxylic acids and that of 2-alkanones contributed incrementally to the repellency of the waterbuck odor to savannah tsetse flies, some waterbuck constituents (particularly, nonanoic acid and 2-nonanone) showed significant attractive properties. In another study, increasing the ring size of δ-octalactone from six to seven membered ring changed the activity of the resulting molecule (ε-nonalactone) on the savannah tsetse flies from repellency to attraction. In the present study, we first compared the effect of blending ε-nonalactone, nonanoic acid and 2-nonanone in 1:1 binary and 1:1:1 ternary combination on responses of Glossina pallidipes and Glossina morsitans morsitans tsetse flies in a two-choice wind tunnel. The compounds showed clear synergistic effects in the blends, with the ternary blend demonstrating higher attraction than the binary blends and individual compounds. Our follow up laboratory comparisons of tsetse fly responses to ternary combinations with different relative proportions of the three components showed that the blend in 1:3:2 proportion was most attractive relative to fermented cow urine (FCU) to both tsetse species. In our field experiments at Shimba Hills game reserve in Kenya, where G. pallidipes are dominant, the pattern of tsetse catches we obtained with different proportions of the three compounds were similar to those we observed in the laboratory. Interestingly, the three-component blend in 1:3:2 proportion when released at optimized rate of 13.71mg/h was 235% more attractive to G. pallidipes than a combination of POCA (3-n-Propylphenol, 1-Octen-3-ol, 4-Cresol, and Acetone) and fermented cattle urine (FCU). This constitutes a novel finding with potential for downstream deployment in bait technologies for more effective control of G. pallidipes, G. m. morsitans, and perhaps other savannah tsetse fly species, in ‘pull’ and ‘pull-push’ tactics.
Bedbugs are blood-feeding arthropods that cause anemia in humans upon heavy feeding. Control measures are unsuccessful due to resistance to development, environmental pollution, and cost. There is a need to explore natural herbal-based phytochemicals to combat bedbugs. In this study, compounds from Comiphora africana resin were sequentially extracted, fractionated, identified, and evaluated against bedbugs as individual compounds and in combinations. The chemical constituents of the most active fraction were identified using Gas Chromatography-Mass Spectrometry. Results showed that the dichloromethane crude extract had the highest mean repellency (98.5% with an LC50 of 4.96 mg/L after 24 and 72 h of exposure time, respectively), similar to the positive control (neocidol). Column chromatographic separation of the dichloromethane extract yielded 9 fractions where “FR7” (eluted with 60% n-hexane in ethyl acetate) demonstrated the highest mean repellency of 79.0% with an LC50 of 10.12 mg/L after 2 and 24 h exposure times, respectively. From the identified compounds of FR7, cedrol had significantly ( P < .05) higher mean repellency (80.5%) after 6 h of exposure and toxicity (27.43 mg/L) after 24 h exposure. A six-constituent blend of compounds from FR7 [9-octadecenoic acid-ethyl-ester, octadecadien-1-ol, citronellyl formate, cedrol, n-hexadecanoic acid, (1,2)-dihydro-6-methoxy-naphthalene] had the highest mean repellency (93.4% after 12 h exposure) and toxicity (8.83 mg/L after 72 h exposure) than the other blends and individual compounds. This study reports fractions/compounds that can be used in bedbug control measures.
Tsetse flies use antennal expressed genes to navigate their environment. While most canonical genes associated with chemoreception are annotated, potential gaps with important antennal genes are uncharacterized in Glossina morsitans morsitans. We generated antennae-specific transcriptomes from adult male G. m. morsitans flies fed/unfed on bloodmeal and/or exposed to an attractant (ε-nonalactone), a repellant (δ-nonalactone) or paraffin diluent. Using bioinformatics approach, we mapped raw reads onto G. m. morsitans gene-set from VectorBase and collected un-mapped reads (constituting the gaps in annotation). We de novo assembled these reads (un-mapped) into transcript and identified corresponding genes of the transcripts in G. m. morsitans gene-set and protein homologs in UniProt protein database to further annotate the gaps. We predicted potential protein-coding gene regions associated with these transcripts in G. m. morsitans genome, annotated/curated these genes and identified their putative annotated orthologs/homologs in Drosophila melanogaster, Musca domestica or Anopheles gambiae genomes. We finally evaluated differential expression of the novel genes in relation to odor exposures relative to no-odor control (unfed flies). About 45.21% of the sequenced reads had no corresponding transcripts within G. m. morsitans gene-set, corresponding to the gap in existing annotation of the tsetse fly genome. The total reads assembled into 72,428 unique transcripts, most (74.43%) of which had no corresponding genes in the UniProt database. We annotated/curated 592 genes from these transcripts, among which 202 were novel while 390 were improvements of existing genes in the G. m. morsitans genome. Among the novel genes, 94 had orthologs in D. melanogaster, M. domestica or An. gambiae while 88 had homologs in UniProt. These orthologs were putatively associated with oxidative regulation, protein synthesis, transcriptional and/or translational regulation, detoxification and metal ion binding, thus providing insight into their specific roles in antennal physiological processes in male G. m. morsitans. A novel gene (GMOY014237.R1396) was differentially expressed in response to the attractant. We thus established significant gaps in G. m. morsitans genome annotation and identified novel male antennae-expressed genes in the genome, among which > 53% (108) are potentially G. m. morsitans specific.
Bedbugs (Cimex lecturalius Linnaeus) are ecto-parasite pests that wholly feed on human and domestic animals’ blood causing anemia to the host on excessive feeding. Bedbug control has proved futile due to various challenges including; development of insecticide resistance, high associated cost and environmental pollution. Natural herbal-based phytochemicals remain unexploited and we focused on Comiphora africana (A. Rich.) Engl. resin traditsionally used bedbug control. We previously showed that dichloromethane extract of C. africana resin is highly repellent and toxic against bedbugs. In this study, we isolated compounds from the dichloromethane extract using column chromatographic techniques. The isolated compounds were evaluated for repellency and toxicity against bedbugs; and characterized using conventional spectroscopic techniques. Five compounds (taraxasterol, pseudo-taraxasterol, beta-sitosterol, fungisterol and guggusterol) were isolated and characterized for the first time in this plant. Fungisterol had the highest repellency (75%) against bedbugs which was not significantly different (P > .05) to the positive control (neocidol) (74%) after > one-hour exposure. Fungisterol also elicited highest toxicity against bedbugs with LC50 of 25.73 mg/L after 24 h exposure. Blending fungisterol with other identified active terpenes did not synergize the overall repellent/toxic responses. This study identifies active compounds in C. africana resin and therefore lays a solid background in bedbug control using isolated compounds.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.