Epazote oil outperforms neem against the fall armyworm

The essential oil of Dysphania ambrosioides — a plant known as epazote or mastruz — demonstrated insecticidal activity against Spodoptera frugiperda larvae in a laboratory trial in the United States. Treatment at a XNUMX% concentration reduced caterpillar weight gain and caused XNUMX% mortality over a ten-day evaluation period (DOI XNUMX/agrochemicalsXNUMX).

The research evaluated the essential oil incorporated into an artificial diet. The caterpillars received the treated food seven days after hatching. The researchers compared seven groups: control with water, 1% wormwood oil, 5% wormwood oil, 1% neem oil, 5% neem oil, control with 1% Tween 80, and control with 5% Tween 80. Each group had 50 larvae.

Expressive result

The most significant result occurred in the group treated with 5% wormwood oil. At the end of the period, 31 out of 50 caterpillars had died. This group also showed the lowest final average weight, at 7,8 milligrams. The difference compared to the other treatments was statistically significant, according to the analysis presented by the researchers.

Treatment with 1% wormseed oil did not cause mortality. Even so, it reduced caterpillar growth. The average final weight of this group reached 52,1 milligrams. The controls with water and Tween 80 showed greater development. The control with water reached an average final weight of 289,0 milligrams. The control with 1% Tween 80 reached 269,3 milligrams. The control with 5% Tween 80 reached 203,0 milligrams.

Neem oil served as a natural reference in the assay. The 1% neem treatment resulted in three deaths. The 5% neem treatment showed no mortality. The final average weight reached 209,8 milligrams in the 1% neem group and 45,7 milligrams in the 5% neem group. According to the researchers, 5% neem oil outperformed the neem treatments in reducing larval growth and mortality.

Chemical analysis

Chemical analysis of the essential oil of wormseed identified major compounds. The volatile profile showed 29,2% alpha-terpinene, 25,2% ascaridole, 18,0% isoascaridole, and 7,4% limonene. Researchers highlight ascaridole isomers as compounds frequently associated with the insecticidal activity of wormseed essential oil.

The study used dried leaves of Dysphania ambrosioides grown in a greenhouse. The material underwent hydrodistillation for two hours. Afterwards, the essential oil was analyzed by gas chromatography coupled with mass spectrometry.

Spodoptera frugiperda larvae were kept under controlled laboratory conditions. The temperature was maintained at 22 degrees Celsius, with a relative humidity of 40% and a 12-hour light cycle. Researchers recorded daily mortality and weight variation. Each caterpillar received a new Petri dish and a new portion of artificial diet each day.

The results indicate the potential of wormwood essential oil as a natural insecticidal ingredient. However, the researchers state that the study was preliminary and conducted in a controlled environment. They recommend further research to clarify the mechanism of action of the essential oil. They also indicate the need for trials under field or greenhouse conditions (on plants), due to the inherent limitations of tests conducted on artificial diets.