Evaluation of essential oils and diluents against Chrysomya megacephala, an important mechanical vector

Chrysomya megacephala represents a major threat to public health. It is a mechanical vector of various pathogens, such as viruses, bacteria, and protozoan cysts, while their larvae may cause myiasis. The alternative to synthetic insecticides, which are harmful to the environment and man`s health, is to use natural insecticides that are safe for both. Plant derivatives have gained prominence in this field, but little is known about how the diluents used in the formulations can influence the insecticidal activity, and the physiology of insects. In this work, among the diluents tested, ethanol, DMSO and miglyol did not affect the viability and the development of C. megacephala, while propylene glycol and mixtures containing Tween® 20 or Tween® 80 caused mortality and increased the total development time from newly hatched larvae to adult. Furthermore, essential oils and their compounds were solubilized in selected diluents to evaluate their insecticidal activities against C. megacephala. Lippia sidoides essential oil, which contained 96.14% thymol, caused mortality of 90%, while Laurus nobilis essential oil caused mortality of 63.7%. The monoterpenoids 1,8-cineole at 125 μg/μL and linalool at 30 μg/μL, that are the main constituents of L. nobilis essential oil, caused mortality of 67.6% and 100% respectively. These effects were confirmed by scanning electronic microscopy. The present study also showed that linalool and the thymol-enriched fraction of L. sidoides essential oil were as active as the synthetic insecticide used as positive control.