Evaluation of tea tree oil formulations toxic and behavioral effects against the egyptian cotton leafworm, spodoptera littoralis (Boisduval, 1833) (Lepidoptera: Noctuidae)

The insecticidal potential of tea tree oil (Melaleuca alternifolia) formulations was tested for contact and stomach poison toxicities against various stages of the Spodoptera littoralis ((Boisduval, 1883) (Lepidoptera: Noctuidae) larvae under laboratory conditions. In the contact toxicity test, the formulations were tested at different stage larvae by topical application. Stomach poison test was carried out with disk feeding method. Dose response bioassays were carried out with the most promising formulations for contact and stomach poison test on 3 rd instar larvae. In contact toxicity test, TTO (100%), F14 (91.72%), and F15 (89.20%) formulations caused the highest mortality in the S. littoralis 3. stage larvae. Dose-response bioassay revealed that LD50 values were 0.016, 0.046, and 0.076 μg/larvae for TTO, F14, and F15 respectively. In the stomach poison tests, the F17 and F18 formulations produced the highest mortality with 75% and 65% mortality rates after 10 days of incubation respectively. The calculated LC50 values for these formulations were 0.027 and 0.042 µg/cm2 for F17 and F18 formulations after 10 days of incubation respectively. Biological and behavioral effects of tea tree oil formulations were carried out with the calculated dose based on dose-response bioassays. TTO formulations produced the greatest antifeedant effects with 46.57% reduction in feeding ration. The greatest reduction in egg laying rate was seen in F14 formulation with 36.39%. In the larval weight gain tests, F15 and F17 formulations were the most effective in the contact toxicity as TTO was in the stomach poison test. These results revealed that tea tree oil and its main components containing formulations have the potential in controlling this destructive lepidopteran pest species.