Evolution Of Voltine Biotypes Of The Asian Corn Borer And Impact Of Their Response To Climate Warming

Previous researches suggested the Asian corn borer（ACB）,Ostrinia furnacalis（Guenée）,is a facultative diapause insect and can occur 1-7 generation（s）from far northeast to south China.The population of ACB in northeast spring maize area includes uni-voltine and bi-voltine ecotype populations and the division of vlotine is based on the difference of critical photoperiod that induced larvae enter into diapause.The dominance of uni-voltine ecotype individuals,as the resource insects of the first generation,in the overwintering population is the potential resource insects of the 1^st generation ACB that would be going to play a key role in resulting an outbreak.The proper rainfall from May to August is the suitable environmental factor stimulating ACB outbreak,while the temperature had no significant effect on the outbreak.However,diapause individuals occur in every generation of the natural population,the elevated temperature will accelerate the growth and development,which will lead to shorter lifecycle and enhance more occurrence generations.It is impossible to distinguish either individuals of the first or second generation are the resource insects that result in outbreak based on the number of larvae per hundred plants at the time of harvest.On the bases of reviewing and analysis of the previous researches,we proposed a concept model and hypothesis from internal,and external factors as well as their interaction,i.e.,（1）there are three types of voltine biotypes in the ACB population including uni-voltine biotype（characterizing obligatory diapause,only 1 generation per year）,multi-voltine biotype（characterizing facultative diapause,1 or more generations per year）,and non-diapause biotype;（2）outbreak is possibly due to the dominance of multivoltine biotype individuals in the population;（3）as one of the environmental factors,elevated temperature plays the important role for stimulating the ACB outbreak.To clarify these problems is of great theoretical and practical significance for analyzing the differentiation of diapause habit and voltine biotypes of ACB,clarifying the response mechanism of insects to climate change,predicting population dynamics and guiding integrated control.In present study,efforts have been conducted to establish different biotype strains using recurrent selections under various simulated temperature and photoperiod environments,to character the inheritance of the diapause traits by marking genetical crosses,and to assess the phylogenetic performances of natural population in the OTCs,laboratory and field conditions.Uni-voltine and multi-voltine population were selected respectively under long daylength stress and 28℃,non-diapause population was under short daylength stress and 24℃.We cross the selected uni-voltine and multi-voltine population to study the genetic heritage of ACB.We investigated the voltinism in two natural populations from Harbin（H）and Gongzhuling（G）as well as a laboratory（Lm）population of the ACB at ambient and elevated atmospheric CO₂（a CO₂ 390μL/L and e CO₂750μL/L）and temperature（a T and e T=a T+2°C）.The genome of ACB was re-sequenced and the transcriptome of two different voltine populations was compared to select the genes that may be related to diapause.Uni-voltine population（not sensitive to the photoperiod,selected from HH population）was obtained under long daylength 16 h stress and 26-28℃.Diapause incidence of the selected uni-voltine population is about 80%under photoperiod（L:D=16:8）and 28℃.Multi-voltine population（sensitive to the photoperiod,selected from H population）was obtained under long daylength 16 h stress and 28℃,which will develop under long daylength 16 h and enter diapause under short daylength 13 h.Non-diapause population（not sensitive to the photoperiod,selected from the multi-voltine population）was selected under short daylength 13 h stress which still tends to develop in short daylength.The results showed that the diapause incidence of F₁ hybrids decreased significantly,and there was no significant difference between reciprocal crosses,which indicated the control of ACB not enter diapause was a dominant genetic trait.There was no high diapause incidence in F₂generation,which indicated that the inheritance of uni-voltine biotype（obligate diapause）fits polygenic recessive or quantitative traits.The H population fitted sympatric uni-and multi-voltine biotypes with multi-voltine dominant.Climate warming could significantly inhibit the diapause incidence of multi-voltine biotypes induced by short daylength,and then increase the proportion that the 2^nd generation occur and the reproduction and finally increase damage degree of the population（the total number of insects in autumn harvest）.Warmer temperature and declined latitudinal（shorting daylength）and their interaction would drive the ACB evolving to more homogeneity for multi-voltinism.The genome of ACB was re-sequenced.The size of the assembled genome was 436.7 MB with 528scaffolds,sequencing depth exceeds 150×.The haploid genome predicted 16,699 genes,and 16,303 genes were annotated.In conclusion,there are three biotypes in ACB,uni-voltine biotype,multivoltine biotype and non-diapause biotype.The uni-voltine biotype is not response to long daylength and higher temperature for development and performs obligatory diapause,which lead to have only one generation per year.The multivoltine biotype is response to short daylength and lower temperature for diapause induction and performs facultative diapause,which lead to have 1 or more generations per year depending on the photoperiod and temperature.The non-diapause biotype is not response to short daylength and lower temperature for diapause induction and performs continuous development.The uni-voltinism trait is controlled by polygenetic recessive genes or quantitative genetic locus.The H and G populations are consisted of sympatric uni-,multi-voltine and non-diapause biotypes,of with multi-voltine biotype is dominant.Based on these,we assume and validate that the proportion of multivoltine biotype in the overwintered population of ACB in northeastern China is the internal factor related to potential outbreak.In addition,climate warming（elevated temperature）is one of the key environmental factors（external factors）driving the population outbreak.