Evaluation of tea tree oil formulations contact and stomach toxicity against the Egyptian cotton leafworm, Spodoptera littoralis (Boisduval, 1883) (Lepidoptera: Noctuidae)

The insecticidal potential of tea tree oil formulations was tested for contact and stomach poison toxicities against various stages of the Spodoptera littoralis ((Boisduval, 1883) (Lepidoptera: Noctuidae) larvae under laboratory conditions. The study was carried out at Yozgat Bozok University Faculty of Agriculture between 2020 and 2021. In the contact toxicity test, the formulations were tested at different stages of larvae by topical application. Among the tested formulations, TTO (100%), F14 (91.72%), and F15 (89.20%) formulations caused the highest mortality in the S. littoralis 3rd stage larvae after 72 h. Dose-response bioassay with the most promising formulations (TTO, F14 and F15) revealed that LD50 values were 0.016, 0.046, and 0.076 mu g/larvae for TTO, F14, and F15, respectively. The stomach poison effects of the formulations were tested by applying a 0.16 mu g/cm2 dose to lettuce leaf discs. The F17 and F18 formulations produced the highest mortality with mortality rates of 75% and 65% after 10 days of incubation, respectively. The calculated LC50 values for these formulations were 0.027 and 0.042 mu g/cm2 for F17 and F18 formulations after 10 days of incubation, respectively. These results revealed that tea tree oil and its main components containing formulations have the potential in controlling this destructive lepidopteran pest species.