空心莲子草叶甲对越冬保护的响应与控害效能

Response of the alligator weed flea beetle,Agasicles hygrophila( Coleoptera:Chrysomelidae) to overwintering protection and its controlling effect on alligator weed Alternanthera philoxeroides( Amaranthacese: Alternanthera)

空心莲子草叶甲Agasicles hygrophila是入侵杂草空心莲子草Alternan thera philoxeroide的重要天敌,冬春季低温冰冻是影响其安全越冬的关键胁迫因子。为了探明采取保护措施是否能提高越冬后的种群基数问题,在低温冰冻天气来临前,用塑料膜覆盖网室构建空心莲子草与空心莲子草叶甲保护生境(PH),分低温期(2009年1月21日至4月9日)、升温期(4月15日至5月1日)与自然生境(NH)中叶甲成虫初现期(从6月1日至29日)3个阶段,调查比较PH与NH两类生境中空心莲子草叶甲种群数量、结构、空间生态位分布特征及控害效能。结果表明:在保护生境中,低温期空心莲子草叶甲不休眠,且能安全越冬,当晴天温度较高时,成虫主要在直立茎或嫩枝上活动取食、补充营养,而在阴雨低温天气则停留在匍匐草层或土壤表层、缝隙中,少活动。随着气温回升,成虫转移到直立茎生态位上活动取食,并于4月上旬开始产卵繁殖,种群数量迅速增加,对空心莲子草的地上部分有较好的控制效果。在自然生境中,直到6月初才见少量成虫活动,此时草生长茂密,较低的空心莲子草叶甲种群难以发挥生防因子的作用。比较两种生境中6月1日与6月15日的控草效果显示,空心莲子草株高增长率分别为:PH-13.91%,NH-2.94%,NH中空心莲子草株高极显著高于PH,且单株生物量的控制率为PH(47.56%)极显著高于NH(4.89%)。在6月15日与29日的调查表明,单株叶片控制效果PH极显著优于NH,PH中的空心莲子草茎上均无叶,叶片或被取食殆尽、或被害后干枯脱落。茎被害率、茎蛀孔数与蛀茎率均为PH极显著高于NH。结果说明覆膜保护能显著提高叶甲越冬种群基数,使其提前进入繁殖期,从而能更有效地控制生境中的空心莲子草。

The alligator weed flea beetle, Agasicles hygrophila （ Coleoptera ： Chrysomelidae） is a biological control agent of the alligator weed Alternanthera philoxeroides （ Amaranthacese ：Alternanthera）, a worldwide invading weed. Low temperature and frost stress in winter-spring seasons are the key factors that affect A. hygrophila. To explore whether the protections used in habitat could increase the population of overwintered A. hygrophila, we investigated and compared the populationnumber, structure, distributing characteristic in spatial niches of A. hygrophila and the controlling efficiency of A. hygrophila on A. philoxeroides in protected habitat （PH） with those in natural habitat （NH）. The investigation was phased with the variation of air temperature and the elapse of time. Low temperature stage was from 21th, January to 9th, April, 2009, followed by temperature rise period from 15t＂, April to lS＇, May, and the third investigated period which was the first emergence time of beetle adults in NH from 1st to 29＇h, June. The protected habitat was constructed by covering plastic film on net room before low temperature and freezing came. The results showed that A. hygrophila could overwinter smoothly and no dormancy was observed in protected habitat at low temperature in winter-spring time. Adults gadded and fed on up-right stems of A. philoxeroides both in sunny and air temperature rising day in winter-spring time, but were inactive and stayed creep layer of weed or surface or crevice of soil at overcast, rainy or low temperature time. Beetle adults in protected habitat laid eggs in early April. There was a rapid increasing of the populationwhich played an important role in controlling the above ground parts of A. philoxeroides. Only a few beetle adults can be found in natural habitat even at the beginning of June. Consequently, the weed grew very well due to the low density of the beetle population which was difficult to play the role of a biocontrol factor. Comparing the results obtained in the first day with that in 15th, June, the increasing rate of stem height of A. philoxeroides in this interval of time were -13.91% in the protected habitat and -2.94% in the natural habitat, respectively. The stem height of A. philoxeroides in the natural habitat was significantly higher than that in the protected habitat. The control rate of a plant biomass of A. philoxeroides by A. hygrophila in the protected habitat was 47.56% which was significantly stronger comparing with the control rate of 4.89% in the natural habitat. The control effect to leaves of A. philoxeroides in the protected habitat was extremely better as compared with that in the natural habitat in the interval of time from 15＇h to 29＇h, June. There were no leaves left on stems of A. philoxeroides plants as leaves being either eaten up by A. hygrophila or withered after attacked by A. hygrophila in the protected habitat. The rate of damage stem, rate of stem bore hole and the number of stem bore hole per plant in the protected habitat were significantly higher than that in the natural habitat. These results suggested that the overwintered A. hygrophila population could be significantly increased by covering plastic film to protect the habitat. The beetle adults in protected habitat could lay eggs ahead of time compared to that in the natural one, thus could effectively control the growing of weed.