Insecticidal activities and effects on three enzymic activities caused by 5-aminolevulinic acid (ALA) on Oxya chinensiswere studied. Fourth-instar nymphs of O. chinensis were treated with different doses of ALA (A1, 250 mM; A2, 450 mM;A3, 750 mM; A4, 1 000 mM). Mortality and the activities of acetylcholinesterase (AChE), glutathione S-transferase (GSTs),and glutathione peroxidase (GPx) were determinated. The mortality of O. chinensis rose with an increasing dose of ALA.The mortality of high-dose treatments A3 and A4 reached 66.19 and 80.21%, respectively. The value of LD50 was3.61 (3.29-3.93) mg g-1 body weight (95% confidence interval). Biochemical studies showed that the activities of AChE andGPx in the A4 treatment declined by 51.53 and 42.82% in the female, and 42.65 and 43.85% in the male compared to thecontrol, respectively, and the degree of decline reached a significant level at P < 0.05. Meanwhile, the GSTs activitiesof O. chinensis enhanced with increasing dose of ALA. The GSTs activities of female and male O. chinensis in the A4treatment remarkably increased by 171.05 and 97.42% compared to the control (P < 0.05). ALA had an obviously toxiceffect on O. chinensis. Moreover, ALA caused the photoinactivation of AChE and GPx, which induced nerve transmissionblocking and the capability to defend oxidation damage declining. Meanwhile, a high dose of ALA could activate GSTs,which caused a feedback inhibition of the insect to the phototoxic substance.
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