The effects of luteolin on phenoloxidase and the growth of Spodoptera exigua (Hübner) larvae (Lepidoptera: Noctuidae)

The effects of luteolin on phenoloxidase (PO) from Spodoptera exigua larvae were investigated with the use of a microtitration assay in the present paper. The results showed that luteolin could inhibit the activity of PO and the concentration of this inhibitor that led to a 50% (IC50) activity reduction was estimated to be 0.47 mmol/l. The inhibitory kinetics were analyzed by Lineweaver–Burk plots and the compound was found to be a reversible competitive inhibitor with a Ki of 13.11 mmol/l. The compound was obviously toxic against the larvae (≤3rd instar) of Spodoptera exigua. The highest inhibitory percentage in the older larvae (≥3rd instar) was greater than 60% with luteolin treatment. The pupation rate and percentage of eclosion was also evidently reduced with luteolin treatment by the ingestion method in this investigation.