Biological activity of Ajuga iva extracts against the African cotton leafworm Spodoptera littoralis

The African cotton leafworm , a major crop pest worldwide, is controlled by chemical insecticides, leading to serious resistance problems. plants contain phytoecdysteroids (analogs of arthropod steroid hormones that regulate metamorphoses) and clerodanes (diterpenoids exhibiting antifeedant activity). We analyzed phytoecdysteroids and clerodanes in leaf extracts of the Israeli by LC-TOF-MS and TLC, and their efficiency at reducing fitness. Castor bean leaves were smeared with an aqueous suspension of dried methanolic crude extract of phytoecdysteroid and clerodanes from leaves (50, 100 and 250 µg/µl). First and third instars of larvae were fed with 1 treated leaf for 3 and 4 days, respectively. Mortality, larval weight gain, relative growth rate and survival were compared to feeding on control leaves. To evaluate and localize crude leaf extract activity in the insect gut, we used DAPI and phalloidin staining. Crude extract of leaves (50, 100 and 250 µg/µl) significantly increased mortality of first instar larvae (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 day, compared to the relevant controls). larvae were further affected at later stages, with few survivors. Insect-gut staining showed that 250 µg/µl crude leaf extract reduces gut size, with relocation of nuclei and abnormal actin-filament organization. Our results demonstrate the potential of extract for alternative, environmentally safe insect-pest control.