<i>Baccharis</i> Species Essential Oils: Repellency and Toxicity against Yellow Fever Mosquitoes and Imported Fire Ants

Essential oils from five <i>Baccharis</i> species were screened for their toxicity and biting deterrence/repellency against yellow fever mosquito, <i>Aedes aegypti</i> (L.), and imported fire ants, including <i>Solenopsis invicta</i> Buren (RIFA), <i>Solenopsis richteri</i> Forel (BIFA) and their hybrids (HIFA). <i>Baccharis microdonta</i> DC. and <i>B. punctulata</i> DC. at 10 µg/cm² showed biting deterrence similar to DEET, <i>N</i>, <i>N</i>-diethyl-<i>meta</i>-toluamide at 25 nmol/cm², whereas the repellency of <i>B. pauciflosculosa</i> DC., <i>B. sphenophylla</i> Dusén ex Malme and <i>B. reticularioides</i> Deble & A.S. Oliveira essential oils was significantly lower than DEET against mosquitoes. Two major compounds from the active essential oils, kongol and spathulenol, also exhibited biting deterrence similar to DEET against mosquitoes. The highest toxicity exhibited against mosquitoes was by <i>Baccharis punctulata</i> essential oil (LC₅₀ = 20.4 ppm), followed by <i>B. pauciflosculosa</i> (LC₅₀ = 31.9 ppm), <i>B. sphenophylla</i> (LC₅₀ = 30.8 ppm), <i>B. microdonta</i> (LC₅₀ = 28.6 ppm), kongol (LC₅₀ = 32.3 ppm), spathulenol (LC₅₀ = 48.7 ppm) and <i>B. reticularioides</i> essential oil (LC₅₀ = 84.4 ppm). <i>Baccharis microdonta</i> essential oil showed repellency against RIFA, BIFA and HIFA at 4.9, 4.9 and 39 µg/g, respectively. <i>Baccharis microdonta</i> essential oil also showed toxicity with LC₅₀ of 78.9, 97.5 and 136.5 µg/g against RIFA, BIFA and HIFA, respectively, at 24 h post treatment.