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Article

Activity of Ajuga iva Extracts Against the African Cotton Leafworm Spodoptera littoralis

1
Department of Evolutionary and Environmental Biology, The Faculty of Natural Science, University of Haifa, Haifa 3498838, Israel
2
Department of Plant Pathology and Weeds Research, Newe Ya’ar Research Center, Agricultural Research Organization, Ramat Yishay 30095, Israel
3
Department of Entomology, Agricultural Research Organization, The Volcani Center, Rishon LeTsiyon 7528809, Israel
*
Author to whom correspondence should be addressed.
Insects 2020, 11(11), 726; https://doi.org/10.3390/insects11110726
Received: 25 September 2020 / Revised: 21 October 2020 / Accepted: 21 October 2020 / Published: 23 October 2020
(This article belongs to the Special Issue Natural Substances against Insect Pests: Assets and Liabilities)
Pest insects cause tremendous damage and losses to global agriculture, and their control relies mainly on chemical insecticides, which are greatly harmful for human health and the environment. Many Ajuga plant species have secondary metabolites such as phytoecdysteroids (analogues of insect steroid hormones—ecdysteroid) that control insect development and reproduction. In this study, the effect of ingestion of Ajuga iva phytoecdysteroid plant extract on the growth and development of the African cotton leafworm Spodoptera littoralis was carried out. Our results clearly showed the susceptibility of S. littoralis to phytoecdysteroid ingestion. Crude leaf extracts and fractionated phytoecdysteroids significantly increased mortality of first-instar S. littoralis by up to 87%. Third-instar larval weight gain decreased significantly by 52%, and crude leaf extract (250 ppm) reduced gut size, with relocation of nuclei and abnormal actin-filament organization compared to the controls. In conclusion, the use of phytoecdysteroids against pest insects is not an alternative for chemical insecticides, but they could have an important role in integrated pest management strategies for controlling S. littoralis and possibly other lepidopterans.
Control of the crop pest African cotton leafworm, Spodoptera littoralis (Boisduval), by chemical insecticides has led to serious resistance problems. Ajuga plants contain phytoecdysteroids (arthropod steroid hormone analogs regulating metamorphosis) and clerodanes (diterpenoids exhibiting antifeedant activity). We analyzed these compounds in leaf extracts of the Israeli Ajuga iva L. by liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) and thin-layer chromatography (TLC), and their efficiency at reducing S.littoralis fitness. First and third instars of S. littoralis were fed castor bean leaves (Ricinus communis) smeared with an aqueous suspension of dried methanolic crude extract of A. iva phytoecdysteroids and clerodanes. Mortality, larval weight gain, relative growth rate and survival were compared to feeding on control leaves. We used ‘4’,6-diamidino-2-phenylindole (DAPI, a fluorescent stain) and phalloidin staining to localize A. iva crude leaf extract activity in the insect gut. Ajuga iva crude leaf extract (50, 100 and 250 µg/µL) significantly increased mortality of first-instar S. littoralis (36%, 70%, and 87%, respectively) compared to controls (6%). Third-instar larval weight gain decreased significantly (by 52%, 44% and 30%, respectively), as did relative growth rate (−0.05 g/g per day compared to the relevant controls), ultimately resulting in few survivors. Crude leaf extract (250 µg/µL) reduced gut size, with relocation of nuclei and abnormal actin-filament organization. Ajug iva extract has potential for alternative, environmentally safe insect-pest control. View Full-Text
Keywords: Ajuga iva; clerodane; pest control; phytoecdysteroid; Spodoptera littoralis Ajuga iva; clerodane; pest control; phytoecdysteroid; Spodoptera littoralis
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MDPI and ACS Style

Taha-Salaime, L.; Lebedev, G.; Abo-Nassar, J.; Marzouk, S.; Inbar, M.; Ghanim, M.; Aly, R. Activity of Ajuga iva Extracts Against the African Cotton Leafworm Spodoptera littoralis. Insects 2020, 11, 726. https://doi.org/10.3390/insects11110726

AMA Style

Taha-Salaime L, Lebedev G, Abo-Nassar J, Marzouk S, Inbar M, Ghanim M, Aly R. Activity of Ajuga iva Extracts Against the African Cotton Leafworm Spodoptera littoralis. Insects. 2020; 11(11):726. https://doi.org/10.3390/insects11110726

Chicago/Turabian Style

Taha-Salaime, Leena, Galina Lebedev, Jackline Abo-Nassar, Sally Marzouk, Moshe Inbar, Murad Ghanim, and Radi Aly. 2020. "Activity of Ajuga iva Extracts Against the African Cotton Leafworm Spodoptera littoralis" Insects 11, no. 11: 726. https://doi.org/10.3390/insects11110726

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