Lethal and Sublethal Effects of Commercial Essential Oils on the Life Cycle of Spodoptera exigua (Hubner)

Essential oils are plant compounds produced as secondary metabolites with toxic activity against some insect pests. Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae) is widely distributed and recently caused phytosanitary contingency in maize (Zea mays L.) and sorghum (Sorghum bicolor (L.) Moench) in Mexico. For alternative control, 16 commercial essential oils were tested using three exposure routes to determine their toxic lethal and sublethal effects in the insect developmental cycle. Essential oils in vapor phase bioassay were significantly toxic against S. exigua larvae, with LC50 values ranging from 2.23 to 32.16 mg/ml. Essential oils that killed fewer than 50% by feeding bioassay were chosen to assess sublethal effects in each developmental stage. Exposure to mint, cinnamon, clove, geranium, and citronella oils decreased the average weight of larvae 11 to 43%. Lime, peppermint, and tangerine oils caused an increase of 20 to 37% in the average weight of larvae. Average weight of pupae was not affected. According to the population size, the number of eggs laid with mint or tangerine oil exceeded that expected, although oviposition with other treatments was less than the check, and least oviposition was with clove oil. In most cases about 90% of the eggs hatched, except for clove with 40%, and 76 and 72% hatching with geranium and citronella oils, respectively. Essential oils caused different sublethal to lethal effects promising effectiveness against S. exigua.