Insecticidal and Ovicidal Activity of Cymbopogon citratus Essential Oil and Its Nanoemulsion Against Hemipteran Crop Pests with Mortality, Antennal Malformations, and Volatile Alterations.

Hemipteran insects such as Euschistus heros and Dysdercus peruvianus are important pests of soybean and cotton, respectively, making them relevant targets in pest management programs. This work aims to evaluate the insecticidal and chemical activity of Cymbopogon citratus essential oil (CC-EO) and its nanoemulsion against E. heros and D. peruvianus. A mixture of citral stereoisomers (59.5%) was identified as the major constituent of CC-EO The topical application of nanoemulsion resulted in 53.33% and 33.33% mortality in E. heros and D. peruvianus, respectively. Contact treatment caused 83.33% mortality in E. heros and 86.70% mortality in D. peruvianus, also inducing antennal deformities observed by scanning electron microscopy and reflected in altered behavioral responses in a Y-tube olfactometer assay. Ovicidal effects were observed in contact treatment for both species, affecting nymph emergence from eggs treated with nanoemulsion. Treatments with pure EO resulted in 100% nymph mortality and complete inhibition of egg hatching in both insects. Headspace solid-phase microextraction (HS-SPME) analysis revealed changes in the volatile profile of treated insects, showing the presence of semiochemicals related to defense and alarm, such as terpenes and alcohols. The multiple lethal and sublethal effects demonstrated by CC-EO highlight its potential as a candidate for integrated pest management programs, offering an eco-friendly alternative to conventional chemical control methods.