Nanoemulsions containing some plant essential oils as promising formulations against Culex pipiens (L.) larvae and their biochemical studies.

The chemical composition of cypress, lavender, lemon eucalyptus, and tea tree oils has been investigated using gas chromatography/mass spectrometry (GC/MS). These oils were tested for larvicidal activity against Culex pipiens alongside their nanoemulsions (NEs) and conventional emulsifiable concentrates (ECs). Oil-in-water (O/W) NEs preparation was based on a high-energy ultra-sonication technique. The effect of independent variables of preparation on the different outputs was studied using the response surface method to obtain the optimum preparation technique. The droplet sizes of prepared NEs were significantly different (71.67, 104.55, 211.07, and 70.67 for cypress, lavender, lemon eucalyptus, and Tea tree NEs, respectively). The zeta potentials of NEs were recorded to have a high negatively charge (-28.4, -22.2, -23.6, and - 22.3 mV for cypress, lavender, lemon eucalyptus, and tea tree NEs, respectively). The results showed that the tea tree oil has the most significant effect with LC50 = 60.02 and 57.10 mg/L after 24 and 48 h of exposure, respectively. In comparison, cypress oil proved the lowest toxicity with LC50 values of 202.24 and 180.70 mg/L after 24 and 48 h, respectively. However, lavender oil does not show any effect against larvae at tested concentrations. In addition, pure oil exhibited the lowest larvicidal activity. However, the EC of all tested insecticides slightly improved the toxic action against the larvae. While the NEs showed significantly high toxicity compared to the EO and EC. An in vivo assessment of acetylcholine esterase (AChE), adenosine triphosphatase (ATPase), and gamma-aminobutyric acid transaminase (GABA-T) revealed that the NEs exhibited higher activity than the pure oils and ECs. This work describes these oils with potential use against C. pipiens larvae as eco-friendly products.

Pediculicidal activity of certain plant essential oils against head lice Pediculus humanus capitis.

This paper reports the pediculicidal activity of certain monoterpenoids of plant essential oils compared to several anti-head lice formulations. It also reports the molecular features required for a chemical to kill head lice. Live adult Pediculus humanus capitus were collected from children living in the Qabary area, Alexandria, Egypt and used in in vitro bioassays. The data demonstrated that the commercial formulation, Quick (0.5% malathion) was the most potent formulation against head lice, while Para plus was the least potent. It was clear that the potency of the tested monoterpenoids was at least similar to Quick. The data also revealed that, monoterpenoid phenols and alcohols were more potent against head lice than monoterpenoid aldehydes, esters and acyclic monoterpenoids. One of the molecular features that is evidently important for monoterpenoid toxicity against head lice is the presence of electronegative group such as a hydroxyl group. In conclusion, this study reports an alternative chemical control that is safer, and more effective against head lice.