Toxicity and Bioefficacy of Cyromazine on Growth and Development of the Cotton Leafworm Spodoptera littoralis (Lepidoptera: Noctuidae)

TLDR: The present work was conducted to evaluate the effects of Cyromazine on survival, growth, development and metamorphosis of Spodoptera littoralis and found that the developmental duration had been slightly prolonged indicating regressed developmental rate, regardless the time of treatment.

Abstract: The present work was conducted to evaluate the effects of Cyromazine on survival, growth, development and metamorphosis of Spodoptera littoralis. A series of concentrations (200.0, 100.0, 50.0, 10.0, 1.0, 0.1, 0.01 & 0.001 ppm) was applied on the newly moulted larvae of 5 (penultimate) and 6 (last) instars through the fresh food plant. After treatment of penultimate instar larvae, Cyromazine caused larval and pupal mortalities only at the higher concentration levels. No adult mortality was observed. LC50 was 74.44 ppm. After treatment of last instar larvae, Cyromazine failed to exhibit a pupicidal activity, regardless the concentration level and caused adult mortality only at 1.0 and 0.1 ppm. LC50 was 82.91 ppm. The larval growth was drastically suppressed, regardless the time of treatment and the concentration level. The developmental duration had been slightly prolonged indicating regressed developmental rate, regardless the time of treatment. Treatment of penultimate instar larvae with Cyromazine concentration levels, other than the lower two ones, caused prohibition of pupation in a dose-dependent course. Also, the pupation program was impaired since some larvalpupal intermediates had been produced. Cyromazine failed to affect the adult emergence, at the majority of the concentration levels except 100 ppm. Except the lower three concentration levels, treatment of last instar larvae with other concentration levels resulted in prohibited pupation rate and impaired pupation program. At only 100 and 50 ppm of Cyromazine, the adult emergence was partially blocked.