Comparative analysis of the repellency activity of single compounds and the synthetic blends of semiochemicals from Aframomum melegueta (R.schum) and Dennittia tripetala (Bak.F) against Rhizopertha dominica in Calabar, Nigeria

Bioassay experiments were carried out in Calabar to compare the repellency activity of single compounds and the synthetic blends of Semiochemicals extracted from Afromomum melegueta and Dennittia tripetala. The aim of the experiment was to determine the efficacy of single compounds and the synthetic blends in suppressing the reproductive potential and adult emergence of Rhizopertha dominica, (Fabricius), a primary pest of stored cassava pellets and cereal grains in Sub-Saharan Africa. Insect culture of the adult R. dominica was set up in the laboratory at Federal College of Education Obudu to obtain fresh insects for the bioassay experiments. Dried seeds of A. melegueta (R. Schum) and D. tripetala (Baker f.) Schatz were procured from the main market in Obudu for the purpose of the research work. 100g each of the dried fruits of the spice plants were pounded separately with the laboratory pestle and mortar for the extraction of the essential oils (EOs). The oils extracted were tested for toxicity and reproductive potential deterrence against R. dominica. The chemical constituents of the essential oils were isolated, identified and tested against R. dominica. Synthetic blends of individual compounds were prepared based on their natural ratios and were also tested for toxicity and reproductive potential deterrence against the insect pests in the laboratory. The result showed that both the single compounds and the synthetic blends were toxic and repellent to the insect pest, and could significantly suppress the reproductive potential thereby inhibiting the emergence of adult insect. However, synthetic blends exhibited a stronger efficacy in their toxicity against the pest thereby providing a broad spectrum of insecticidal bioactivity against R. dominica than the single compounds. This action of the synthetic blends of extracts from the spice plants demonstrated their potential for development in stored products protection especially at the small scale resource poor farmer’s level in Nigeria.

Mosquito repellent finishes on textile fabrics (woven & knit) by using different medicinal natural plants

In textile, Finishing is one of the significant processes which augment the performance of the fabric and functional properties as well. Health is always thought to be an indispensable requirement for human beings to live without any stress and it aids to give the best output of any work. Hygiene is also one of the important elements to live comfortably. A mosquito repellent textile protects the human beings from the bite of mosquitoes and ensures safety from the diseases like malaria and dengue fever. Medicinal plants like neem (Azadirachta indica), tulashi (Ocimum tenuiflorum) & mint-leaf (Mentha) etc. are used for induction of organic mosquito repellent activity and all of them are ecofriendly. This project is an exiguous endeavor in developing an eco-friendly mosquito repellent finished fabric using the herbal extract from neem, tulshi and mint-leaf .The extracted chemicals are finished on to the fabric by pad-dry-cure process & exhaust process and are evaluated using a mosquito repellency activity test .Then the repellency behavior of fabrics were checked after washing at three intervals – 5th,7th & 9th washes .Finally, the finished fabrics showed a great amount of mosquito repellent activity for both knit and woven fabric which was calculated in percentage.

Chemical Variation and Implications on Repellency Activity of Tephrosia vogelii (Hook f.) Essential Oils Against Sitophilus zeamais Motschulsky

The aim of this research is to characterize the variation in the chemical composition of Tephrosia vogelii essential oils from different locations and to investigate the repellency of essential oils against Sitophilus zeamais. Chemical variability in the components of T. vogelii essential oils from eastern Uganda was identified using principal component analysis (PCA) and agglomerative hierarchical clustering (AHC). Based on the profiles of the compounds of the farnesene family, three chemotypes were found: farnesol (chemotype 1), springene (β-springene and α-springene) and β-farnesene were all distinctive in chemotype 2 and a mixed variety of farnesol and springene. In the three cases, alkyl benzenes (o-xylene, m-xylene and ethylbenzene) were significant components in the oil. The compounds 1,4-dihydroxy-p-menth-2-ene, 6,10-dimethyl-5,9-undecadien-2-one, and 3,4-dimethyl-3-cyclohexen-1-carboxaldehyde were other prominent constituents. The yields of the essential oils did not vary significantly, however the chemical composition varied with harvesting time during the rainy and dry seasons. In choice repellency tests, chemotype 1 and chemotype 2 were more active against Sitophilus zeamais than the mixed chemotype. Farnesol was found to be effective only at a higher concentration as a repellent against S. zeamais. We therefore hypothesize that farnesol is a key player in this and we demonstrated the weak repellency of this compound. However, further study that aims to optimize and standardize the varieties and harvesting period is needed for recommendation to smallhold farmers.

USE OF VEGETABLE OILS TO CONTROL BEAN WEEVIL DEVELOPMENT ON COWPEA GRAINS

ABSTRACT Callosobruchus maculatus, commonly known as cowpea weevil, is the main pest affecting stored cowpea Vigna unguiculata. The damage resulting from the penetration and feeding of cowpea weevil larvae within the grains or seeds of V. unguiculata leads to weight loss, reduction of germination power and nutritional value and commercial depreciation of this plant. The objective of this work was to evaluate the insecticidal activity and repellency of vegetable oils extracted from fennel, citronella, neem and 'moringa' against C. maculatus adults. To evaluate the insecticidal activity, we placed 20 adult insects in plastic containers lined with filter paper impregnated with different doses (0.0 x 106, 5.0 x 106, 1.0 x 105, 1.5 x 105, 2.0 x 105, 3.05, 4.0 x 105 and 5.0 x 105 L) of each vegetable oil. The number of insects was analyzed 24 hours later. To evaluate the repellency activity, we used an arena formed by five circular plastic containers with the central container interconnected symmetrically to the others by plastic tubes arranged diagonally. Samples of 30 g of cowpea were impregnated with different doses (5.0 x 106, 1.0 x 105, 1.5 x 105 and 2.0 x 105 L) of each vegetable oil. We released 50 adults of C. maculatus in the central container and counted the number of insects per container 24 hours later. Citronella and fennel oils at a dose of 3.0 x 105 L demonstrated a higher insecticidal effect on C. maculatus. However, citronella oil presented the best repellent action.

Excito-repellency Activity of Andrographis paniculata (Lamiales: Acanthaceae) Against Colonized Mosquitoes

Excito-repellency activity of plant extracts have been increasingly studied as mosquito repellents. In this study, the crude extract of Andrographis paniculata was evaluated for its noncontact repellency, contact excitation (irritancy + repellency), and knockdown/toxicity response against five colonized mosquitoes; Aedes aegypti (L.), Aedes albopictus (Skuse), Anopheles dirus Peyton & Harrison, Anopheles epiroticus Linton & Harbach, and Culex quinquefasciatus Say (Diptera: Culicidae) using an excito-repellency assay system under laboratory-controlled conditions. The escape responses were observed at four different concentrations (0.5–5.0% w/v) with A. paniculata showing strong spatial repellency against Ae. albopictus (96.7% escape) and Ae. aegypti (71.7% escape) at the 2.5% and 0.5% concentrations, respectively. At 0.5% and 5.0% concentrations, the greatest repellency was seen for An. dirus (48.2% escape) and Cx. quinquefasciatus (59.7% escape), respectively. Comparatively, low repellency action was observed against An. epiroticus (1.6–15.0% escape). Escape in contact assays (before adjustment) was generally less pronounced compared to noncontact spatial repellency, with Ae. albopictus showing highest percent escape (71.4% escape) in the contact assay at 1.0% concentration. After adjusting for spatial repellency, escape due to contact irritancy alone was either not present or an insignificant contribution to the overall avoidance response for all species. No knockdown or mortality at 24-h postexposure was observed in any trials. These findings indicate that the A. paniculata crude extract is more active against day-biting mosquitoes; however, this may be a reflection of the time of testing. This study demonstrates compelling evidence that A. paniculata extract performs primarily as a spatial repellent. Further investigations exploring the use A. paniculata as a potential active ingredient in repellent products are needed.

Odorant receptors from Culex quinquefasciatus and Aedes aegypti sensitive to floral compounds

Mosquitoes rely heavily on the olfactory system to find a host for a bloodmeal, plants for a source of energy and suitable sites for oviposition. Here, we examined a cluster of 8 odorant receptors (ORs), which includes one OR, CquiOR1, previously identified to be sensitive to plant-derived compounds. We cloned 5 ORs from Culex quinquefasciatus and 2 ORs from Aedes aegypti, ie, CquiOR2, CquiOR4, CquiOR5, CquiOR84, CquiOR85, AaegOR14, and AaegOR15 and then deorphanized these receptors using the Xenopus oocyte recording system and a large panel of odorants. 2-Phenylethanol, phenethyl formate, and phenethyl propionate were the best ligands for CquiOR4 somewhat resembling the profile of AaegOR15, which gave the strongest responses to phenethyl propionate, phenethyl formate, and acetophenone. In contrast, the best ligands for CquiOR5 were linalool, PMD, and linalool oxide. CquiOR4 was predominantly expressed in antennae of nonblood fed female mosquitoes, with transcript levels significantly reduced after a blood meal. 2-Phenylethanol showed repellency activity comparable to that of DEET at 1%. RNAi experiments suggest that at least in part 2-phenylethanol-elicited repellency is mediated by CquiOR4 activation.

DEET and other repellents are inhibitors of mosquito odorant receptors for oviposition attractants

In addition to its primary function as an insect repellent, DEET has many “off-label” properties, including a deterrent effect on attraction of gravid female mosquitoes. DEET negatively affects oviposition sites. While deorphanizing odorant receptors (ORs) using the Xenopus oocyte recording system, we have previously observed that DEET generated outward (inhibitory) currents on ORs sensitive to oviposition attractants. Here, we systematically investigated these inhibitory currents. We recorded dose-dependent outward currents elicited by DEET and other repellents on ORs from Culex quinquefasciatus, Aedes aegypti, and Anopheles gambiae. Similar responses were observed with other plant-derived and plant-inspired compounds, including methyl jasmonate and methyl dihydrojasmolate. Inward (regular) currents elicited by skatole upon activation of CquiOR21 were modulated when this oviposition attractant was coapplied with a repellent. Compounds that generate outward currents in ORs sensitive to oviposition attractants elicited inward currents in a DEET-sensitive receptor, CquiOR136. The best ligand for this receptor, methyl dihydrojasmolate, showed repellency activity, but was not as strong as DEET in our test protocol.