Evaluation of the insecticidal effect of some plant extracts and nanoparticles on spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) larvae

This study investigated the insecticidal effects of methanol extracts and nanoparticles of Achillea wilhelmsii L. (Yarrow), Tagetes erecta L. (Marigold), Matricaria chamomilla var. recutita L. (May Daisy), and Chenopodium album subsp. album var. album L. (Lambsquarters) on Spodoptera littoralis (Boisd.) (Cotton Leafworm). Methanol extracts of Tagetes erecta (flowers and leaves), Achillea wilhelmsii (flowers), Chenopodium album subsp. album var. album (leaves and flowers), and Matricaria chamomilla var. recutita (flowers) were prepared. These extracts were diluted with 10% acetone-water solution to a concentration of 100 g/L. These extracts were applied topically at a dosage of 2 µl per insect using a micro-aplicator to the thorax dorsum of 3rd instar S. littoralis larvae. The treated larvae were then transferred to 90 mm diameter glass Petri dishes containing lettuce leaves. To determine the effects of a single dose of stomach poison, the extracts were adjusted to 100g/L with 10% acetone-water solution. This mixture was applied to both sides of 10 mm diameter lettuce leaves at a rate of 10 µl. The treated lettuce leaves were transferred to 60 mm diameter Petri dishes, and 3rd instar S. littoralis larvae were added. In dose-mortality studies, the methanol extracts that showed successful results in topical application were applied at doses of 10g/L, 15g/L, 25g/L, and 50g/L. The experiments were conducted at a temperature of 25±2°C and 60±10% relative humidity. Live and dead larvae were recorded on the 1st, 3rd, 5th, 7th, 9th, and 11th days. Five 3rd instar S. littoralis larvae were used in each treatment and control group. The experiments were replicated 5 times with 2 repetitions each. The methanol extract of T. erecta flowers had the highest effect with 83.3±3.33% mortality on the 5th day, while the nanoparticle extract of T. erecta flowers caused 46.6±4.21% mortality. M. chamomilla var. recutita as a stomach poison caused 100.0±0.0% mortality on the 5th day. The methanol and nanoparticle extracts of T. erecta leaves caused 93.3±3.33% mortality as a stomach poison on the 7th day. In dose-mortality studies, the LC50 values for M. chamomilla var. recutita (flower), T. erecta (flower), and T. erecta (leaf) were 5.5 g/L, 5.8 g/L, and 6.6 g/L, respectively. In light of the results obtained, there is potential for the control of cotton leafworm. Further detailed studies are needed on insecticidal effects of plant contents.