| The ragweed beetle, Ophraella communa LeSage (Coleoptera: Chrysomelidae), originates fromNorth America, and feeds on the leaves of the invasive common ragweed, Ambrosia artemisiifolia L.(Asterales: Asteraceae) on the stages of larva and adult. It has been identified as a potential biologicalcontrol agent against the invasive common ragweed by America, Canada, Australia, South Korea, Japan,China and so on because of its intensive feeding, high host specificity and strong ecological adaptation.In China, O. communa was discovered for the first time in the suburbs of Nanjing City, JiangsuProvince, where after it spread rapidly to the areas invaded by common ragweed in Southern provinces.O. communa as a kind natural enemy is suitable for the subtropical regions, and the plasticity to coldhardiness plays a key role in the further range expansion of this biological control agent into moretemperate regions of mainland China. However, the ability of cold resistance of O. communa has theplasticity in the geography and seasons. In the natural fluctuating low temperature of early spring, wewonder if the cold hardiness of O. communa has also the plasticity. In order to analyze the trade-off ofsurvival and reproduction of O. communa under the sub-optimal low temperature, we constructed theage-stage, two-sex life table of O. communa in early spring and mimicry-diurnal alternating temperature,and compared the diurnal variation of cold hardiness physiological indexes in order to analyze thefitness for the sub-optimal low temperature and physiological metabolism mechanisms to lowtemperature. Our studies also give answer to the reason of effect of sub-optimal low temperature onpopulation fitness of O. communa in early spring. Our main results are as follows:1. The construction of the age-stage, two-sex life table of O. communa under sub-optimal lowtemperature.The results suggested that the developmental periods for egg, larva, pupa, and entire immaturestages of O. communa increase under sub-optimal low temperature（15℃~23℃，18℃~26℃）. Thesurvival rates of larva and entire immature stages decreased in response to the stress of sub-optimallow temperature, with the exception of egg and pupa. The stress of sub-optimal low temperatureprolonged the total preovipositional period and longevity of females, decreasing the fecundity offemales. Life table of O. communa was constructed based on the data at three fluctuatingtemperatures. The stress of sub-optimal low temperature decreased significantly the life tableparameters of O. communa.2. The construction of the age-stage, two-sex life table of O. communa in early spring.Development durations for egg, larva, pupa and entire immature stage of O.communa were13.6,21.1,7.9and42.8days, respectively, in early spring of Langfang city. Adults could survive to37.41d, no differences in the longevities between female and male were found, and fecundity was713.1eggs per female. The intrinsic rate of increase (r), finite rate of increase (λ), net reproductiverate (R0), and mean generation time (T) were0.0660d-1,1.0683d-1,73.9offspring/individual and63.0d, respectively. 3. The variation of cold hardiness of O. communa adults under sub-optimal low temperature.Compared with the control21℃~29℃,the SCPs of O. communa have no significance undersub-optimal low temperature（15℃~23℃，18℃~26℃）. However, the water contents and totalsugar contents decreased and glycerol contents increased under sub-optimal low temperature15℃~23℃.Under sub-optimal low temperature18℃~26℃,the glycerol contents and lipid contentsincreased and the total sugar contents decreased. During the diurnal fluctuating temperatures, theSCPs of O. communa adults decreased gradually with the development of time. The SCPs was thelowest at23:00-2:00. However, the lipid contents get to the higher level at5:00-8:00and23:00-2:00. The water contents and lipid contents of females of O. communa were lower than thatof males under the18℃~26℃.The SCPs and lipid contents of females of O. communa were lowerthan that of males under the15℃~23℃. Under sub-optimal low temperatures, the water contentsand glycerol contents of adults decreased, and the total sugar contents increased after mating.4. The variation of cold hardiness of O. communa adults in early spring.There is no significance of SCPs between Langfang and Changsha. The water and lipidcontents of Langfang were higher than that of Changsha in early spring. During the diurnalfluctuating temperatures, the cold hardiness indexes of O. communa had significant fluctuatingtrends. The glycerol and lipid contents were lowest and the total sugar contents were highest at5:00-8:00. Moreover, the lipid contents were highest and the total sugar contents were lowest at23:00-2:00. The glycerol and lipid contents of females of O. communa were lower than that ofmales. However, the SCPs of females were higher than that of males in Langfang. After mating, theSCPs, water contents and glycerol contents decreased, and the total sugar contents increased inLangfang.Conclusion suggested that the stress of sub-optimal low temperature of early spring couldreduce the population fitness of O. communa, resulting in decreased fecundity. However, the coldhardiness increased responding to the adaptation to sub-optimal low temperature by thephysiological metabolism regulation. In addition, the cold hardiness of O. communa has theplasticity during the diurnal fluctuating temperatures. The gender and copulation behavior couldexert significant impact on the cold hardiness. The study has important theoretical and practicalsignificance for the biological control of common ragweed in early spring, and lays foundation forthe expansion into the north of China. |
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