Adulticidal synergy of two plant essential oils and their major constituents against the housefly Musca domestica and bioassay on non-target species
Mayura Soonwera, Tanapoom Moungthipmalai, Cheepchanok Puwanard, Sirawut Sittichok, Jirisuda Sinthusiri, Hataichanok Passara
Abstract
Single and mixture formulations of lemongrass ( Cymbopogon citratus (DC.) Stapf.) and star anise ( Illicium verum (J. Presl.)) essential oils (EOs) and their major constituents were assayed for their adulticidal activities against housefly, Musca domestica L., and two non-target species, stingless bee ( Tetragonula pegdeni Schwarz) and guppy ( Poecilia reticulata Peters). The efficacies of the mixture formulations were compared against those of the single formulations and 1.0% α-cypermethrin, a common synthetic insecticide. GC-MS analysis found that the major constituent of lemongrass EO was geranial (45.23%), and that of star anise EO was trans- anethole (93.23%). Almost all mixture formulations were more effective in adulticidal activity against housefly adults than single formulations and 1.0% α-cypermethrin. A mixture of 1.0% lemongrass EO + 1.0% trans- anethole exhibited the strongest synergistic insecticidal activity with a 100% mortality rate (KT 50 of 3.2 min and LT 50 of 0.07 h). The relative percentage increase in mortality rate over single formulations was between 1.6 and 91.9%. In addition, it was three times more effective than 1.0% α-cypermethrin. To find the mechanism of adulticidal action, scanning electron microscopy (SEM) was done to find morphological aberrations, such as antennal and mouthpart aberrations, after the houseflies were treated with 1.0% lemongrass EO + 1.0% trans- anethole. The aberrations included deformed and abnormal shape of arista and flagellum, change in labellum pigmentation, and damage to pseudotracheae. Regarding toxicity against non-target species, all single and mixture formulations were not toxic to the two non-target species, while 1.0% α-cypermethrin was highly toxic. To conclude, a mixture of 1.0% lemongrass EO + 1.0% trans- anethole can be an excellent, natural, sustainable housefly adulticidal agent.