| Oxya chinensis(Thunberg)(Orthoptera:Acridoidea) is a common species of Oxya Serville,Mainly distributes in Africa,Australia,Asia widely and abundantly distributes in most regions of China.The grasshopper have specific diet and have serious damage to gramineous plants.They are an important agriculture pest to crops.In recent years,due to the increasing resistance to traditional organophosphorus insecticides and the break of the ecological environment and agricultural conditions,the occurrence of O. chinensis is more frequent.At present,for the control of O.chinensis,we mainly use chemical control,but long-lasting use of chemical insecticides have caused serious pollution to people's and animals' health and ecological environment.Meanwhile,the grasshopper have a certain degree of resistance to these pesticides.Therefore,research and development of new environment-friendly pesticides to control agricultural pests have an important theoretical and practical significance.The acute toxicity of photosensitive pesticides 5-aminolevulinic acid(ALA) to O.chinensis and its biochemical mechanism were discussed in this paper.Various instars nymphs of O.chinensis from Jinyuan district of Taiyuan, Shanxi province were treated with different methods,then measured acute toxicity of 5-aminolevulinic acid and its effect to enzyme activities on O. chinensis,for discussing the toxicity and the biochemical mechanism of the drug.The nymphs of O.chinensis were treated with different doses of ALA (250 mM;450 raM;750 mM;1000 mM).After treated for 48 h(the first 14 h was dark-keeping,then given 3h light and kept indoors for 48h),the test insects appeared significant death and the activities of acetylcholinesterase (ACHE),glutathione S-transferase(GSTs) and glutathione peroxidase(GPx) were determinated.Biochemical studies showed that with increasing dose of ALA,the activities of ACHE and GPx in treatments significantly declined in female and male compared to control(P＜0.05).Meanwhile,the GSTs activities of female and male O.chinensis in treatments remarkably increased compared to control(P＜0.05).The results obtained from the above analysis indicated that ALA had obviously toxic effect on O.chinensis and the sensitivity of female and male to ALA was similar.Moreover,ALA caused the photoinactivation of AChE and GPx,and activated GSTs.Based on the above findings,the fact was determined that ALA indeedly played a significant role on poisoning the insects and affect the activities of some enzymes of O.chinensis.The paper carried out a further study to find not only a more reasonable application method on the concentration of ALA and the treatment approach,but also the relationship between toxicity and the instar.The glutathione S-transferase(GSTs) and esterase activities of the head,chest and abdomen of the insects were measured.Various instar nymphs of O.chinensis were treated with different doses of ALA(0.00597 mM;0.0597 mM;0.597 mM;5.97 mM) using film analysis. After treated with ALA,the insects first kept in dark for 17-20 h,then given 2 h light.During irradiation,the insects showed some obvious toxical reaction to drug,as left from the grass,climbed onto the wall of glass bottle and restlessness,then lay on the ground and died in succession.Toxicity results showed that the concentration of ALA was 100-1000 times lower using application of film bioassays than injection method when reached the same mortality.Biochemical studies showed that with increasing dose of ALA,the activities of GSTs in treatments of every instars nymphs significantly enhanced compared to control(P＜0.05).Moreover the increasing trend of GSTs activities indicated that the older the nymphs were the more significant changes the GSTs activities had.The GSTs activities of fourth-instar nymphs in head,chest and abdomen all appeared signicicant increase;its of first-instar nymphs showed significant rising only in abdomen(P＜0.05). Esterase activities(three substrates:α-NA,α-NB,β-NA) did not showed signicicant changes in trends in every instar nymphs.Based on the above resultes,we analyzed that concerded to GSTs and Esterase these two kinds of metabolism and detoxification enzymes,GSTs could be ALA-induced activitated and played a role on speeding up the metabolism of ALA and reduced toxic effects of oxidative damage caused by ALA.Esterase almost no involved in the ALA-related biochemical metabolism.The studies on the toxicity and biological effects of ALA on O.chinensis indicated that porphyrin insecticides indeedly showed obvious toxicity at very low concemtrate to various instar nymphs,furthermore its toxic effects correlated with application concerntrate,application method and illumination. ALA was confirmed as a highly efficient and development-potential new insecticide on control of O.chinensis.This paper made an elementary studies on the effects of ALA to some conrrelative enzymes of O.chinensis. However,because of the complexity of the toxicological mechanisms of ALA,it is expected that further systemic researches will be made on the application of ALA and the metabolic enzymes mainly impacted,as well as the distribution of oxidative,damaging tissues. |
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