Elicit effects of potassium phosphite versus to emamectin benzoate on the defensive response of cotton seedlings against Spodoptera littoralis (Lepidoptera : Noctuidae)‎

Abstract EN

This study was investigated on a novel rule of potassium phosphite as promising elicitors comparing to emamectin benzoate against Spodoptera littoralis (Boisduval) ( Lepidoptera: : Noctuidae) .

The toxicity on the 2nd instar larvae showed that LC25, LC50 and LC90 values of emamectin benzoate (0.005, 0.012 and 0.248 mg L-1, respectively) had more toxic than potassium phosphite (1326.2, 5302.4 and 73757.2 mg L-1, respectively) after 96 hrs post-treatment.

Gas chromatography–mass spectrometry (GC-MS) analysis identified the induced VOCs from untreated cotton seedling compared to those induced by potassium phosphite and emamectin benzoate.

Induce Volatile organic compounds (VOCs) by potassium phosphite were featured by dibutyl phthalate, ßcaryophyllene, ethyl palmitate, ethyl linoleate and methyl linolenate, docosane and benzaldehyde, 3-phenoxy-.

Major VOCs induced by emamectin benzoate were dibutyl phthalate, bis (2-ethylhexyl) phthalate, squalene and methylprednisolone.

Biological tests at LC25 and LC50 values of emamectin benzoate showed pupal weights (150.4 and 95.2 mg, respectively) ˂ potassium phosphite (262.3 and 224.3 mg, respectively) compared to 309.2 mg in the control.

Adult emergence percentages of emamectin benzoate at LC25 and LC50s were 31.7 and 18.3%, respectively ˂ potassium phosphite were 72.3 and 53.8%, respectively compared to 86.8% in the control.

Emamectin benzoate significantly prolonged the larval durations (16.4 and 17.2 days, respectively) ˃ potassium phosphite (14.3 and 15.9 days, respectively) compared to the control (13.8 days).

While no significant changes in pupal durations in both treatments.

Significant decreases in pupation percentage revealed at LC50s of emamectin benzoate (21.5%) and potassium phosphite (57.3%) compared to 90.3% in the control.

Olfactometer dual choice tests on 2nd instar larvae showed preferable response to untreated cotton seedling versus to each of the two treatments at LC90 and LC50s.

Choice tests between the two treatments showed surpasses of potassium phosphite in orienting responses of larvae.

Finally, these olfactory and biological assessments could enroll potassium phosphite as a novel elicitor against S.

littoralis.