Plant essential oil (EO) is a natural alternative to synthetic chemical insecticides for mosquito control. EOs from Citrus aurantium L., Cymbopogon citratus (Stapf.), and Cinnamomum verum (J. Presl.) were selected for topical assay of their ovicidal activity against Aedes aegypti (Linnaeus) and Aedes albopictus (Skuse). Their efficacy was compared to that of 1% (w/w) temephos. In addition, their non-toxicity against aquatic mosquito predators, Poecilia latipinna and Poecilia reticulata, was tested. Found by GC–MS analysis, the major constituent of C. verum EO was trans-cinnamaldehyde, of C. aurantium EO was d-limonene, and of C. citratus EO was geranial. Both C. verum EO and trans-cinnamaldehyde at a high concentration (30,000 ppm) exhibited high ovicidal activity against Ae. aegypti and Ae. albopictus eggs after 48 h of incubation with an inhibition rate of 91.0–93.0% for C. verum EO and 96.7–95.2% for trans-cinnamaldehyde. The combination of C. verum EO + geranial exhibited the strongest synergistic inhibition activity (100%) against the two mosquito vectors and was five times more effective than temephos. Moreover, they were not toxic to the non-target fishes. As a safe ovicidal agent for mosquito egg control, the combination of C. verum EO + geranial has excellent potential.

Natural ovicidal and repellent agents against Periplaneta americana L. are urgently needed, and plant essential oils (EOs) can assume this role quite readily. In this study, ovicidal and repellent activities against Periplaneta americana of EOs from Cymbopogon citratus (Stapf.), Cinnamomum verum (J. Presl.), Eucalyptus globulus (Labill.), Illicium verum (Hook.f.), and Zanthoxylum limonella (Alston) in soybean oil and in ethyl alcohol were determined by topical and dual-choice assays, as well as 10% cypermethrin and a combined formulation of 5% C. verum EO + 5% I. verum EO. Cypermethrin at 10% provided the highest toxicity (100% inhibition rate) against the eggs, but only slightly higher than that (99.3%) provided by the combined EO formulation, while the highest repellent activity against the adults was provided by the combined formulation (89.5% repelled cockroaches at 48 h after treatment). In addition, all EO formulations in soybean oil provided higher ovicidal and repellent activities than those in ethyl alcohol. To conclude, the combined EO formulation in soybean oil can replace cypermethrin because their efficacy was nearly equivalent, but the combination should be much safer to use.

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Plant essential oils (EOs) can fulfill the role of safe and effective fly repellent and adulticide. Individual and binary mixture formulations of Cymbopogon citratus (Stapf.) and Illicium verum (J. Presl.) EOs and their major constituents were assayed for their repellent and adulticidal activities against Musca domestica L. and non-target pollinator, Apis florea F. Their efficacy was compared to that of 1.0% (w/v) α-cypermethrin. A GC-MS analysis found that geranial and trans-anethole were the major constituents of C. citratus EO (45.23%) and I. verum (93.23%), respectively. All binary mixture formulations exhibited high and synergistic repellent and adulticidal effects: an increased repellent value between 18.7 to 57.6%, and a mortality rate value between 41.9 to 92.7%. The highest synergistic repellent effect was from 2.5% C. citratus EO + 2.5% I. verum EO, while the highest synergistic adulticidal effect was from 1.0% C. citratus EO + 1.0% trans-anethole. Both were more effective than 1.0% (w/v) α-cypermethrin. On the other hand, they were not toxic to the non-target pollinator. To conclude, C. citratus EO + I. verum EO and C. citratus EO + trans-anethole have a high potential as repellent and adulticidal agents against M. domestica which are safe for a pollinator, Apis florea.