Fumigant toxicity of Melissa officinalis L. essential oil against Tribolium castaneum Herbst: Modeling and optimization by Response Surface Methodology abstract
The red flour beetle, Tribolium castaneum Herbst (Coleoptera: Tenebrionidae), is one of the cosmopolitan pests of flour, cereal grains, and oilseeds. It can destroy the quantity and quality of foods and transfer some pathogenic and nonpathogenic microbes. Although the use of chemical fumigants is the main method in the management of such stored-product insect pests, the overuse of these harmful agents resulted in several side effects, including a threat to human health, environmental contaminations, the outbreak of secondary pests, and the development of pest resistance. Plant-derived essential oils were considered as eco-friendly alternatives to chemical fumigants based on their promising insecticidal effects, biodegradability, and low toxicity to mammals than the chemicals. This study was conducted to evaluate the fumigant toxicity of the medicinal plant lemon balm, Melissa officinalis L. (Lamiaceae), against the adults of red flour beetle. In this regard, the essential oil was isolated from aerial parts of lemon balm (4 cm of the top) was extracted by Clevenger apparatus and its fumigant toxicity was evaluated at five concentrations after 24, 48, and 72-h exposure times against 1-7 day-old adults of red flour beetle. The modeling and optimization of insect pest mortality beforehand essential oil were performed by RSM (Response Surface Methodology). The mathematical model between independent variables time and essential oil concentration and dependent insect mortality was measured using multiple linear regression analysis: Y=βo+∑_(i=1)^k▒〖β_i X_i+〗 ∑_(i=1)^k▒〖β_j X_j+〗 ∑_(i=1)^k▒ ∑_(j=1)^k▒〖β_ij X_i X_j 〗+∑_(i=1)^k▒〖β_jj X_j^2 〗, in which Y is the dependent variable (mortality), Xi and Xj are independent variables (time and concentrations), k is the number of independent variables, βo is the model intercept, βi and βj are the coefficients of the linear parameters, and βij is the coefficient of a quadratic parameter. The lemon balm essential oil revealed concentration-time-dependent effective fumigant toxicity against adult insects. According to correlation coefficients of determination (R2), adjusted R2, and predicted R2 (0.981, 0.980, and 0.978, respectively) the insect pest mortality was positively dependent on essential oil concentrations and exposure times. A quadratic equation was obtained for the mortality of insect pest: Mortality = 23.57 + 0.29(A) - 2.41(B) + 0.11(B2), in which A and B are the exposure time and essential oil concentration, respectively.
Optimization results discovered that 35.00 µL/L of essential oil and 72.00 h-exposure time would be adequate to achieve 96.95% mortality of insect pest. According to the results of this study, the RSM can be considered as an appropriate method in the modeling and optimization of the insecticidal activity of lemon balm essential oil. Additionally, based on the promising fumigant toxicity against red flour beetle, the lemon balm essential oil can be a candidate for further investigations regarding the safe and effective management of this insect pest. .
