Tiririca demonstrates action against fall armyworm

Researchers have identified insecticidal and antifeedant activity of cadalene, a compound isolated from rhizomes of purple nutsedge (Cyperus rotundus), against fall armyworm larvae, Spodoptera frugiperda. The study evaluated plant extracts and the purified compound in tests of contact toxicity, feeding inhibition, larval development, and detoxification enzyme activity.

The dichloromethane fraction showed the highest insecticidal activity among the extracts tested. The median lethal dose reached 4,58 micrograms per larva after 24 hours. Cadalen alone showed a median lethal dose of 4,12 micrograms per larva in the same period. Cypermethrin, used as a positive control, showed a median lethal dose of 0,01 micrograms per larva.

Leading molecule

The results indicate the potential of cadalene as a lead molecule for botanical insecticide research. However, the study was conducted under laboratory conditions. The researchers themselves point to the need for evaluations regarding field persistence, photostability, phytotoxicity in corn, and effects on pollinators and other beneficial organisms.

In the work, the dried rhizomes of Cypress round The samples underwent sequential extraction with hexane, dichloromethane, ethyl acetate, and ethanol. Methanol yielded the highest crude extract yield, at 4,37% by dry weight. Even with lower yields, the dichloromethane and hexane extracts concentrated the most relevant biological activities against... Spodoptera frugiperda.

Contact toxicity

In contact toxicity tests, researchers applied the extracts to second-instar larvae. All extracts showed activity. The dichloromethane extract reached a median lethal dose of 4,58 micrograms per larva in 24 hours and 4,04 micrograms per larva in 48 hours. The hexane extract showed 5,83 micrograms per larva in 24 hours. The ethanol extract registered 6,49 micrograms per larva. Ethyl acetate showed the lowest toxicity, with 13,95 micrograms per larva.

The team selected the dichloromethane extract for compound isolation. Chromatographic separation yielded ten fractions. Fraction F2 underwent preparative thin-layer chromatography. The process resulted in the isolation of cadalene, obtained as a colorless oil. Identification was performed using hydrogen and carbon nuclear magnetic resonance spectroscopic analyses. The estimated purity exceeded 95%.

Cadalene maintained activity close to that of the original extract. In a contact bioassay, the compound showed a median lethal dose of 4,12 micrograms per larva at 24 hours and 3,76 micrograms per larva at 48 hours. In an artificial diet, the compound also reduced larval feeding. The median feeding inhibition value was 11,07 milligrams per gram of diet after 24 hours.

Action in nutrition

The extracts also affected feeding on artificial diets. After 12 hours, the dichloromethane extract showed a median feeding inhibition of 12,07 milligrams per gram of diet. The ethanol extract registered 14,91 milligrams per gram. The hexane extract showed 15,65 milligrams per gram. After 24 hours, the ethyl acetate extract showed the lowest value, with 8,51 milligrams per gram.

In a test using corn leaf discs, the hexane extract showed a greater antifeeding effect at the beginning of exposure. The median feeding inhibition value reached 17,13 micrograms per square centimeter after 2 hours. The dichloromethane extract registered 24,48 micrograms per square centimeter during the same period. After 4 and 6 hours, the dichloromethane extract maintained a more consistent effect, with 27,68 and 28,46 micrograms per square centimeter, respectively.

Insect development

The treatments also altered insect development. Larvae fed treated diets did not show immediate mortality in the feeding assay, but exhibited lower pupation and higher cumulative mortality until adult emergence. The dichloromethane extract reduced pupation to 53,33% and increased cumulative mortality to 60%. Cadalene resulted in pupation of 50,33% and cumulative mortality of 53,33%. In the control, pupation was 90% and cumulative mortality was 10%.

Enzymatic analysis showed interference in detoxification pathways. At median lethal doses, the dichloromethane extract reduced carboxylesterase activity from 886,60 to 639,63 nanomoles of p-nitrophenol per minute per milligram of protein. Cadalene reduced this activity to 557,85 nanomoles of p-nitrophenol per minute per milligram of protein.

Glutathione S-transferase also showed a reduction with cadalene at a median lethal dose. The activity dropped from 7,06 to 4,98 times 10⁻³ CDNB conjugate product per milligram of protein per minute. The dichloromethane extract reduced the value to 6,06 times 10⁻³ CDNB conjugate product per milligram of protein per minute.

Evidence of interference

Researchers interpret these results as evidence of interference in detoxification mechanisms. However, they caution that the data do not allow them to distinguish between direct biochemical inhibition and secondary effects resulting from toxic stress. The study only evaluated median lethal dose concentrations and median food inhibition. Assays with higher concentrations and in vitro enzymatic tests are still needed to confirm the mechanism of action.

The study also highlights limitations for agricultural application. The evaluations were conducted in a laboratory. There was no phytotoxicity testing on corn plants. There was also no evaluation in semi-fields or in a greenhouse.

Further information can be found at doi.org/10.1016/j.napere.2026.100201