Bioefficacy of Marigold (Tagetes spp.) Oil as Biopesticide Against Eggplant Fruit and Shoot Borer (Lepidoptera: Leucinodes orbonalis)

Eggplant (Solanum melongena) is one of the most important vegetable crops in the Philippines, commonly grown in backyard and commercial farms. It is widely consumed by most Filipinos due to its nutritive value. However, its production is often affected by the eggplant fruit and shoot borer or EFSB (Leucinodes orbonalis), a pest known to cause serious damage and yield loss. Local farmers commonly address this pest problem with synthetic insecticides, however, excessive reliance on those synthetic chemicals poses environmental and health risks. Hence, this study assessed marigold (Tagetes spp.), a promising repellant plant with insecticidal potential, as a botanical-based biopesticide alternative for managing L. orbonalis larvae. This study investigates the efficacy of non-phytotoxic marigold plant in oil-emulsion concentration to EFSB mortality. The experiment was done in Completely Randomized Design (CRD), involving two experiments: a phytotoxicity experiment to test if the marigold oil-emulsion would harm the young eggplant leaves; and a laboratory bioassay to observe the larval mortality of EFSB treated with different marigold oil-emulsion concentrations (0.1%, 0.3%, and 0.5%) at 1, 2, and 3 hour/s after treatment (HAT). The study showed that the concentrations used were non-phytotoxic as observed on the marigold oil-emulsion solution-treated young leaves. Furthermore, the insect mortality experiment showed that the higher the concentration, the higher the larval mortality, with 0.5% treatment reaching 88.89% mortality in 3 HAT, which was statistically comparable to the chemical control with 100% mortality. Based on these results, non-phytotoxic marigold oil-emulsion at 0.5% is a potential option for managing L. orbonalis in eggplant, however, further study under field condition is needed before recommendation as regular use.