Toxicity and repellency of the essential oil from Lippia gracilis to the coconut mite Aceria guerreronis (Acari: Eriophyidae)

Abstract

The essential oil (EO) from different genotypes of Lippia gracilis Schauer (Verbenaceae) present two distinctive chemotypes containing either thymol or its isomer carvacrol as major compounds, both of which have proven bioactivity against several agricultural pests. Recently, we have shown that L. gracilis accession LGRA 106 and its major compound thymol are toxic and repellent against the coconut mite, Aceria guerreronis Keifer (Acari: Eriophyidae), a key pest of coconut plantations in Asia, Africa and America. Since intraspecific variation affects the chemical composition of EO and hence, its bioactivity, here we assessed the acaricidal and repellent effects of L. gracilis accession LGRA109 to A. guerreronis. Leaves of this accession contain carvacrol (49.35%) as major compound. The LC 50 of the EO and of carvacrol estimated for A. guerreronis were 28.01 and 6.84 mg/mL, respectively. Carvacrol, at its LC 50, as well as the EO and carvacrol at their LC 99, repelled the mite. Our results indicated that carvacrol and the EO of L. gracilis accession LGRA109 were bioactive against A. guerreronis; however, the EO was less effective than its major compound.

Incorporation of essential oil from Vitex gardneriana (Lamiaceae) in microemulsions systems based on mineral and cottonseed oils increased its bioactivity against a coconut pest mite

“…Another study determined the LC 50 of the OE of the accession LGRA106 of Lippia gracilis Schauer (Verbenaceae) and its major constituent thymol as 4.28 and 5.34 mg/mL, equivalent to 4280 and 5340 ppm, respectively (Dos Santos et al, 2019). On the other hand, the LC 50 of the OE of the accession LGRA109 of L. gracilis and its major constituent carvacrol was determined as 28.01 and 6.84 mg/mL, equivalent to 28010 and 6840 ppm, respectively (Teodoro et al, 2021). Also, the LC 50(80) of EO of Citrus sinensis L. (Osbeck) (Rutaceae) grafted on Citrus limonia Osbeck was estimated at 4.28(10.39)mg/mL, equivalent to 4280(10390)ppm, respectively (Brito et al, 2021).…”