Efficiency of gibberellic acid on feeding, biological and biochemical parameters of <i>Spodoptera littoralis</i> (Lepidoptera: Noctuidae) on tomato <i>Solanum lycopersicum</i>

The plant growth regulators (PGRs), such as gibberellic acid (GA3), are used to improve the quality and quantity of the tomato crop, Solanum lycopersicum. The effect of different concentrations of GA3 on feeding, biological, and biochemical parameters of Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) larvae was studied. After foliar spray of GA3 concentrations on S. lycopersicum plants, the treated leaves were brought to the laboratory for this study. The larvae fed on treated leaves with GA3 exhibited feeding inhibition, where feeding inhibition indices (FII) increased as the concentration increased and days post-treatment. The calculated sublethal concentration (LC50) of GA3 caused disturbance in the biological parameters of S. littoralis; it prolonged larval and pupal periods. The pupation (68.75%) and emergence (80%) percentages were decreased for treated larvae. The reduction in larvae weights can only result from insufficient feeding caused by the anti-feeding activity, which appears from the results of FII indices. Some malformations were observed when larvae reached the pupation stage, these malformations may be responsible for mortality and decreasing in pupation percentage. The LC50 of GA3 decreased the phenoloxidase and protease enzyme activities relative to control larvae by (-20.79%) and (- 60.16%), respectively. It slightly increased the activity of α-and β-esterase enzymes by 3.74 and 20.18%, respectively. It also decreased the amount of total carbohydrates in treated larvae by (-25.26%) compared with control ones. This study supported the idea that plant growth regulator GA3 can be used as a potential insecticide against S. littoralis larvae. GA3 treatment caused feeding inhibition and disturbance in both biological and biochemical parameters of S. littoralis larvae.