GENOTOXICITY OF SOME PLANT ESSENTIAL OILS IN COTTON LEAFWORM, SPODOPTERA LITTORALIS (LEPIDOPTERA: NOCTUIDAE): THE POTENTIAL ROLE OF DETOXIFICATION ENZYMES

Increasing incentives for discovering effective and eco-friendly bio-insecticides seem to be a very important challenge nowadays. Plant essential oils play a promising role in integrated pest-management programs. In the present study, the insecticidal activities of six essential oils from clove (Syzygium aromaticum), crane’s-bills (Geranium sp.), citronella (Cymbopogon sp.), dill (Anethum graveolens), cinnamon (Cinnamomum camphora) and basil (Ocimum basilicum) were investigated against the cotton leafworm, Spodoptera littoralis “Boisduval” (Lepidoptera: Noctuidae). The toxicity test revealed that all the tested essential oils have noticeable insecticidal activity. The basil oil was the most efficient against the 3rd instar larvae, with the lethal concentration (LC)50=0.42%; while the dill oil showed higher toxicity than the other oils against the 5th instar larvae (LC50=0.49%) after 48 hours of treatment. The impact of the tested essential oils on the acetylcholinesterase (AChE), carboxylesterase (CE), and glutathione S-transferase (GST) activities was also assessed. The basil oil induced the activity of AChE in both the 3rd and the 5th instar larvae. All tested oils elevated GST activity in the 5th instar larvae, except citronella oil. The dill oil decreased CE activity in both instars. Genotoxicity analysis using comet assay revealed that all assay parameters differed significantly, compared to the control. The maximum percentage of damaged DNA was detected in larvae treated with basil followed by dill, cinnamon, clove, citronella and crane's-bills, respectively. It was concluded that these essential oils could play a promising role in controlling S. littoralis and providing a biological alternative to synthetic insecticides in the control programs.