氟虫腈对意大利蜜蜂工蜂幼虫及幼龄工蜂的亚致死效应

Sublethal Effects of Fipronil on Larvae and Young Worker Honey Bees(Apis mellifera ligustica)

蜜蜂是重要的授粉昆虫,亦是重要的环境污染指示生物。氟虫腈对蜜蜂剧毒,Pesticide Properties Data Base(PPDB)数据库中登记的其对蜜蜂的急性经口及接触半数致死剂量(LD_(50))分别为0.00417μg·蜂^(-1)和0.00597μg·蜂^(-1),正因为对非靶标生物的毒性较高,其使用也受到了限制,目前仅用于卫生害虫防治和一些旱田作物的土壤处理等。尽管有关氟虫腈对蜜蜂的危害已有一些报道,但有关其对蜜蜂幼虫和幼龄工蜂的亚致死作用研究仍较为缺乏,鉴于此,本文以意大利蜜蜂(Apis melliferaL.)的工蜂幼虫和新出房工蜂(<24 h)为研究对象,采用人工饲喂重复染毒法,分别测定了10^(-3)、10^(-2)、0.1、1和10μg·L^(-1)的氟虫腈对工蜂幼虫的21 d慢性毒性和1、5和10μg·L^(-1)的氟虫腈对新出房工蜂7 d和14 d的慢性毒性。结果表明,与对照相比,10^(-3)~10μg·L^(-1)范围内的氟虫腈可以使幼虫化蛹率显著降低20.83%~47.91%(P<0.05),羽化率显著降低25.00%~43.72%(P<0.05);对于幼龄工蜂,1μg·L^(-1)和5μg·L^(-1)氟虫腈暴露7 d和14 d时蜜蜂死亡率均<10%;10μg·L^(-1)氟虫腈暴露7 d时,死亡率<20%,当暴露时间延长至14 d时,成蜂死亡率高达(65.0±17.7)%(P<0.0001),显著高于对照组,这说明氟虫腈对蜜蜂具有一定的时间累积毒性(time reinforced toxicity,TRT)。此外,通过对蜜蜂幼虫和工蜂体内抗氧化酶(超氧化物歧化酶(SOD)、过氧化氢酶(CAT))、解毒酶谷胱甘肽转移酶(GST)酶活力及谷胱甘肽(GSH)、脂质过氧化产物丙二醛(MDA)含量的测定结果表明,氟虫腈暴露可显著提高幼虫体内CAT的酶活力和MDA含量(P<0.05),但GST的酶活力显著降低(P<0.01);而成蜂在经过处理后,体内CAT和GST的酶活力、GSH的含量均会显著降低(P<0.05),这说明亚致死剂量的氟虫腈可干扰蜜蜂机体稳态,引发蜜蜂幼虫和成蜂显著的氧化损伤,从而危害蜜蜂健康。氟虫腈具有较强的内吸特性和环境稳定性,作物种子处理或卫生施用依然可能导致其在花粉、土壤和水体中的痕量级残留,本研究中发现氟虫腈对蜜蜂幼虫和成蜂生存及各生理指标的最低可观察效应浓度(LOEC)可低至10^(-5)μg·L^(-1)和10μg·L^(-1),相关结果可以补充低残留浓度下氟虫腈蜜蜂风险评价数据的不足,为未来氟虫腈的安全用药指导提供参考。

Bees are important pollinators which are also known as sensitive bioindicators for environmental pollutants.Fipronil is highly toxic to honey bees,and the acute oral and contact median lethal dose(LD_(50))of fipronil to honey bees registered in Pesticide Properties Data Base(PPDB)are 0.00417μg·bee^(-1) and 0.00597μg·bee^(-1),respectively.As it is highly toxic to not-target organisms,the application of fipronil has been limited to sanitary pest control and soil treatment in the dryland fields.In spite of the studies relating to the high risk of fipronil to honeybees,its sublethal effects to the honeybee larvae and young adults remain insufficient.To fill the gap in this field,we investigated the sublethal effects of fipronil to the larvae(10^(-3),10^(-2),0.1,1 and 10μg·L^(-1))and newly emerged worker(1,5 and 10μg·L^(-1))honeybees(Apis mellifera ligustica),by repeated artificial feeding in the laboratory.The experiments lasted 21 d for larvae and 7 d or 14 d for adult bees,respectively.The major findings of this study are:Compared with the control group,10^(-3)~10μg·L^(-1) of fipronil significantly reduced the rate of larvae pupation and eclosion by 20.83%~47.91%(P<0.05)and 25.00%~43.72%(P<0.05),respectively.For young adult bees,the mortality was<10%in 1μg·L^(-1) and 5μg·L^(-1) exposure during 7 d and 14 d experiment;for 10μg·L^(-1) group,the mortality was<20%after 7 d exposure,which significantly increased to(65.0±17.7)%(P<0.0001)at the 14^(th) d.These data indicated that the risk of fipronil to young adults could be time-reinforced.In addition,the activity of antioxidant enzymes superoxide dismutase(SOD),catalase(CAT),detoxifying enzyme glutathione S-transferase(GST),and content of glutathione(GSH)and lipid peroxidation product malondialdehyde(MDA)were also measured in both larvae and adult bees.Results showed that fipronil increased CAT activity and MDA content in larvae(P<0.05),but inhibited GST activity(P<0.01).Regarding young adult bees,all of the CAT,GST,and GSH were decreased during exposure period.These findings indicated that fipronil could disturb the homeostasis in bees and induced oxidative damage,which brought negative impacts to the bees.As Fipronil is highly systemic and stable in environment,the crop seeds treatments and application in home or public areas may also result a trace residue in pollen,soil and aquatic system.In this study,the lowest observed effect concentration(LOEC)of fipronil on survival and calculated parameters of larval and adult bees were low to 10^(-5)μg·L^(-1) and 10μg·L^(-1),respectively.Overall,these findings highlight the deficiency in the risk assessment of fipronil to bees at trace level,which also provide necessary guidance for safety usage of fipronil in the future.