“Citronella oil has an adulticidal effect on adult mosquitoes, other flying insects, and cockroaches.”

Because citronella products protected humans from mosquito, tick and flea bites for at least one hour, and they provided a relatively non-toxic alternative, the EPA determined that citronella oil and its derivatives met the criteria for reregistration.

By contrast, menthol had a more significant effect on adults than citronella, lethal concentration at 50 scale (LC50) values of 1.03, 0.89, and 0.9 mg, and LC95 values of 5.09, 2.01, and 1.59 mg, after 24, 48 and 72 h, respectively. For citronella oil, the LC50 values were 2.09, 1.76, and 1.70 mg after 24, 48, and 72 h, and the LC95 values were 5.5, 3.7, and 1.5 mg after 24, 48 and 72h. The percent mortality of different concentrations of citronella against adults RPW [red palm weevil, a flying insect] 24, 48, and 72 h after treatment: After 24 h the percent mortality was 100% at the high concentration 7mg, while it reached 6.7% at the lower concentration of 1mg.

Citronellal derivatives were tested for repellency against two mosquito species, the major malaria vector Anopheles gambiae and the arbovirus vector Aedes albopictus, and found to be endowed with longer protection time with respect to DEET. The mixture of citronellal derivatives showed protection of 100% for 5 h and the repellency was >98% for the following 3 h. When tested on the major malaria vector A. gambiae at a lower dosage (83 μg cm−2), a 90% efficacy of citronellal derivatives lasted 7 h (PE = 100% for 6 h).

The repellency of citronella oil decreased over time, from 97.9% at 0 h to 71.4% at 1 h and 57.7% at 2 h. In contrast, the repellency of DEET remained over 90% for 6 h. The CPT (Complete Protection Time) of DEET (360 min) was much longer than the CPTs of citronella (10.5 min) and fennel oil (8.4 min).

Oil of citronella is unlikely to affect birds, fish or other wildlife in a harmful way because of its low toxicity and use patterns.

Piperonyl butoxide (PBO), Amyris, Canadian balsam fir, citronella, and guaiacwood all produced statistically significant mortality compared to the ethanol control at 24 h when applied at 10 µg/insect; however, only PBO, Canadian balsam fir, and guaiacwood produced mortality that was greater than 50%. Citronella: 29 ± 3% knockdown at 1 h, 29.3 ± 2.8% mortality at 24 h.

These were cinnamon, citronella, savory and thyme. As expected, permethrin showed a toxic effect at 1%. Conversely, whatever the concentration, none of the plant extracts showed a toxic effect on adults of the mosquito Culex quinquefasciatus.

A meta-analysis found that citronella oil consistently repelled Aedes, Anopheles and Culex mosquito adults in replicated studies. Citronella oil at 10% also killed 100% of Culex quinquefasciatus and Anopheles dirus and 97.6% of Aedes aegypti adults in 24 hours post exposure. Topical application of citronella oil is more effective in repelling mosquitoes than when it is applied as… By contrast, citronella was only marginally effective as a mosquito larvicide.

Allyl isothiocyanate caused 100% mortality to the adult cockroaches 24 h after treatment at the concentration of 5 μl l−1 of air and A. sativum oil caused over 95% mortality to the adult cockroaches 48 h after treatment at the concentration of 5 μl l−1. Among the 9 tested commercial essential oils and monoterpenoid components, allyl isothiocyanate at the concentration of 5 μl l−1 of air caused 100% mortality in adult cockroaches 24 h after treatment.

The tested essential oils showed contact toxicity, fumigant toxicity and repellent activity against the brown-banded cockroach compared to control group during the experiments. Rosemary oil was determined as the most toxic oil because of 100 % mortality rate at the concentration range of 2.5% to 30%. Concentrations of 30% and 15% of the five essential oils caused 100% mortality against the cockroach nymphs using continuous exposure method.

The combination of four plant essential oils (EOs) from star anise, citronella grass, lemon grass, and cinnamon was evaluated for repelling American cockroaches by the dual-choice method. A combination of star anise + citronella grass had a repellency rate of 95%. The combination of 1% star anise + 1% citronella grass was most effective at 150 minutes, repelling 95% of adults.

Citronella insect repellant products do not kill the adult insects they target. The components of citronella leaf extract could cause larval death, however, because they inhibit the respiratory function of the larvae.

The mortality rate of the phases was 8.20, that the effect of black seed oil increases with increasing concentration and this is in agreement. It is clear from Table No. (1) that the highest mortality rate of nymphs resulting from clove oil for a concentration of 1% was 12.45%, after that concentration was 0.5, as it reached 4.16%, higher than concentration of 0.25.

Citronella oil is primarily recognized as a repellent rather than a potent adulticide for mosquitoes; EPA-registered products focus on repellency. Studies show variable contact toxicity to adult mosquitoes at high concentrations (e.g., >10%), but no established adulticidal efficacy against cockroaches or broad flying insects in standard applications. Larvicidal effects are more consistent in lab settings.