Acute toxicity , sublethal effect and changes in the behavior of Lasioderma serricorne Fabricius ( Coleoptera : Anobiidae ) exposed to major components of essential oils

The objective of this work was to evaluate the acute toxicity, sublethal effect and behavioral alteration of L. serricorne exposed to the major components of essential oils, thymol, camphor, terpineol, camphene, eucalyptol, limonene, βpinene and eugenol. The adults of L. serricorne , aged 5 days, not sexed, were submitted to acute toxicity by fumigation, used fumigation chambers, 200 ml glass containers with 20 insects, subsequently the sublethal effect, longevity and behavioral response. The results show that the major components and mixtures caused acute toxicity, reduced the survival time and production of offspring and altered the behavioral activity of L. serricorne. The major components eucalyptol and terpineol presented 65% mortality, in which the mixtures terpineol + eucalyptol and camphor + thymol presented 47 and 52% over adults of L. serricorne. The mixture between terpineol + limonene allowed only 4% ofadults to L. serricorneemerge. Behavioral activity was altered by the eucalyptol + eugenol mixture. The results showed that the major components and mixtures are promising for the preparation and production of new insecticides.

environmental pollution and rising storage costs (Rajendran and Narasimhan, 1994;Jovanovic et al., 2007;Phillip and Throne, 2010). The search for substances for insect control, which are environmentally friendly, becomes a necessity nowadays. Thus, essential oils and their major components have played a significant role in the development of insecticides (Bachrouch et al., 2010).
In recent years, research on essential oils extracted from plants, as well as studies such as the isolated or associated use of the major components present in essential oils, have been considered promising for insect pest control (Erdemir and Erler, 2017;Martins et al., 2017).   Development, v. 9, n. 8, e170985581, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5581 The experiment was carried out at a temperature of 34 ± 1 ºC, 70± 10% (RH) and a photophase of 12 h. In assessing the fumigant effect, the adapted methodology of Aslan et al., (2004) was adopted. Glass containers (volume 200 ml) were used as fumigation chambers, where 20 adult L. serricorne not sexed at 5 days old were confined. The major components and their mixtures (Table 1), without any solubilization vehicle, were applied with an automatic pipette, 10 µl in 18 cm filter papers, fixed on the bottom surface of the container lid. To avoid direct contact of the mixtures of the major components with the insects, fabric "filó" was used.

Acute toxicity by fumigation
For each major component, their mixtures and control were performed five repetitions.
After 72 hours of exposure to treatments, the number of adult L. serricorne dead was counted.
To confirm the mortality of adults L. serricorne, they were touched with a fine bristle brush, the L. serricorne immobile were considered dead.

Discussion
The major components of essential oil can cause insect mortality, as demonstrated in the present study, where in the evaluated economically viable dosage it promoted up to 60% of mortality in adult L. serricorne, among which, eucalyptol and terpineol and the mixtures terpineol+eucalyptol and camphor+thymol were the most promising. These components are monoterpenes that play a lipophilic role, which can bind to the trachiolar fluid, inhibiting enzymes or deactivating proteins in cells (Pavela, 2015). Chopa and Descamps (2012) and Kiran and Prakash (2015) suggest that the acute toxicity of grain pests stored by essential oils