Botanical insecticides containing a mixture of plant essential oils (EOs) are considered suitable for the management of houseflies (M. domestica). The adulticidal efficacies of single EOs and mixtures of EOs, including lemongrass (C. citratus), star anise (I. verum), nutmeg (M. fragrans), and their components (geranial, trans-anethole, and α-pinene), against houseflies were determined in comparison to 2% (w/v) α-cypermethrin as the positive control and distilled water as the negative control. The mixture of star anise EO (1%) + geranial (1%) was the most effective adulticide, superseding single EOs, other combinations of EOs, and its active component, α-cypermethrin, and distilled water. This mixture was highly synergistic and was found to be over 74% more toxic than all single EOs and almost 2.6 times more toxic than α-cypermethrin. Furthermore, the tested EOs did not cause mortality in guppies (P. reticulata) or earthworms (E. fetida), and caused a maximum of 48% mortality in honeybees (A. mellifera) at 24 h; by contrast, α-cypermethrin led to 100% mortality in honeybees within 0.5 h and in guppies and earthworms within 24 h, although it had low toxicity toward houseflies. Thus, a mixture of star anise EO + geranial is a promising source of EO-derived insecticides for housefly control that is also safe for important non-target species.
Passara et al. (Fri,) studied this question.