Bioassay-guided isolation of iridoid glucosides from stenaria nigricans, their biting deterrence against aedes aegypti (diptera: culicidae), and repellency assessment against imported fire ants (hymenoptera: formicidae).

Authors: ZULFIQAR, FAZILA - University Of Mississippi; ALI, ABBAS - University Of Mississippi; ALI, ZULFIQAR - University Of Mississippi; KHAN, IKHALAS - University Of Mississippi

Submitted to: Molecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2022
Publication Date: 10/19/2022
Citation: Zulfiqar, F., Ali, A., Ali, Z., Khan, I.A. 2022. Bioassay-guided isolation of iridoid glucosides from stenaria nigricans, their biting deterrence against aedes aegypti (diptera: culicidae), and repellency assessment against imported fire ants (hymenoptera: formicidae).. Molecules. 27,20, 7053.
DOI: https://doi.org/10.3390/molecules27207053

Interpretive Summary: The cause of many human diseases is mosquito transmitted pathogens. For example, Aedes aegypti (L) and Ae. albopictus (Skuse) are known vectors of Zika virus. The use of insect repellents such as DEET significantly reduces mosquito bites. The mosquito species have developed resistance against commonly used insecticides. Imported fire ants are important pests throughout most of the southeastern United States and parts of several western states Most products currently available on the market for fire ants’ control are synthetic insecticides. Plants are a potential source of bioactive natural compounds with low mammalian toxicity. Stenaria is a small genus in Rubiaceae with six species native to Mexico and the United States. Stenaria species has not been investigated for phytochemistry or evaluated for biological potential. In our natural product screening program, hundreds of in-house plant extracts were screened for biting deterrent activity against Aedes aegypti L and fire ants. Stenaria nigricans extract showed significant biting deterrence against mosquitoes. Seven iridoid glucosides, including four undescribed ones, were isolated through bio-guided fractionation of the methanol extract of S. nigricans. This study reports the systematic bio-guided isolation and characterization of seven iridoid glucosides from the methanol extract of S. nigricans and their biting deterrent activity against Ae. Aegypti and repellency against hybrid imported fire ants. Methanolic extract of aerial parts of Stenaria nigricans and pure compounds (iridoid glucosides) present a potential to be used as Aedes aegypti repellents. However, none of these compounds showed any activity against fire ants.

Technical Abstract: Mosquitoes transmitted pathogens cause human diseases such as dengue fever, yellow fever, Rift Valley fever, malaria, Zika, chikungunya, and West Nile are pathogens that affect a large population of the world. The methanolic extract of Stenaria nigricans aerial parts showed significant biting deterrence, similar to DEET, against Aedes aegypti. Four undescribed iridoid glucosides together with three previously reported ones were isolated through mosquito-biting deterrent bioassay-guided chemical investigation of the methanolic extract of Stenaria nigricans aerial parts. Structure elucidation was achieved by sophisticated NMR (1D and 2D) and mass spectral data analysis. Undescribed metabolites were characterized as stenigrosides A-D while known compounds were identified as asperuloside, deacetylasperuloside, and daphylloside. Based on biting deterrence index (BDI) values, the isolated compounds showed biting deterrence similar to DEET. The pure compounds did not show repellency at the concentration of 125 µg/g against hybrid imported fire ants.