Study On Reproductive Pattern And Cold Hardiness Of The Grain Aphid,Sitobion Avenae (Fabricius)(Hemiptera:Aphididae)

Sitobion avenae?Fabricius?is an important and common insect pest on cereal crops.Except directly sucking juice,it not only causes the drop of 1000-grain weight and quality of wheat,but transmits barley yellow dwarf virus,causing greater indirect damage.The high economic status of aphids was not only related to the rapid development rate and high fecundity,but also closely related to its complex life history.In this paper,the reproductive pattern of aphid and the difference of cold hardiness of different aphid types were studied,and the reproductive pattern and cold hardiness of aphid were studied.The main conclusion as follows:?1?Under the condition of low temperature and short light,the alate and apterous parthenogenetic aphids were produced from G₁ to G₄ generation of Stiobion avenae in Gansu,and the andropara and gynopetera,as well as the sexupara and male aphids,were continuously induced under the condition of low temperature and short light,in which the gynopetera and the andropara gave birth to the G₁ generation.The percentage of gynopetera and the andropara in G₂ generation decreased sharply to 1.00%and 2.00%,respectively,and a large number of gynopetera?86.00%?,and a small number of andropara?6.00%?.Winged parthenogenetic aphids?4.00%?and wingless parthenogenetic aphids?1.00%?.The male aphids of G₃ generation appeared in large numbers,reaching 50.00%.The ratio of winged parthenogenetic aphids in this generation was higher than that in G₂generation.The ratio of winged parthenogenetic aphids in G₄ generation continued to increase.It reached 91.00%,and a small number of wingless parthenogenetic aphids?8.00%?and sexupara?1.00%?appeared at the same time.During induction,the sex ratio of G₂ generation?female:male?was 73:5,and that of G₃ generation was 2:13;G₄generation was 1:0.In this study,the fertilized eggs were successfully obtained after mating.?2?At 15?,the hatching time of fertilized eggs of Stiobion avenae fluctuated in the range of 38-45 d,the average developmental duration was 41.36±1.73 d,and the hatching rate was 46.67±20.55%.There was no significant difference in development time and survival rate among different ages of fundatrix,and all of them were wingless individuals after development and maturation.The progenies of the fundatrix were fundtrigenia,including winged and wingless individuals,accounting for 54.00%and46.00%,respectively.The survival rates of fundatrix and fundtrigenia were 86.67±8.82%and 93.57±0.71%,respectively.There was no significant difference between the two groups.The development time of nymph in fundatrix?15.13±0.39 d?was significantly higher than that in wingless fundtrigenia?12.5±1.32 d?,but there was no significant difference between alate fundtrigenia and apterous fundtrigenia?14.92±1.83d?.There were significant differences in total fecundity and the mean daily reproduction between fundatrix and fundtrigenia?alate and apterous?,among which fundatrix had the highest mean daily reproduction and winged fundtrigenia was the lowest.?3?The supercooling point and freezing point of fertilized eggs of Stiobion avenae were-31.6±-5.1?and-31.3±-2.5?,respectively,which were significantly lower than those of alate viginopara,apterous viriginopra,andropara,gynopetera,male and sexupara,fundatrix.The results of low temperature acclimation showed that the supercooling point of male aphid domesticated at 5?for 5 days was significantly higher than that of the control,while the first instar nymph,alate viginopara,apterous viriginopra,andropara,gynopetera,male and sexupara,fundatrix were significantly higher than those of the control.There was no significant difference in supercooling point between male aphid and fundatrix and the control of the same aphid type,which indicated that there was no cold acclimation reaction at supercooling point of aphid.?4?The survival rate analysis of subzero low temperature showed that the lethal temperature LT₈₀?80%mortality?of fertilized eggs was the lowest,fluctuating at about from-20?to-25?.The lethal temperature LT₈₀?80%mortality?of the first instar alate viginopara,apterous viriginopra,andropara,gynopetera,male and sexupara,fundatrix fluctuated in the range of from-8?to-10?,and the lethal temperature of eggs was significantly lower than that of other aphid morphs.At the same time,rapid cold acclimation improved the survival rate of the first instar nymph,alate viginopara,apterous viriginopra,andropara,gynopetera,male and sexupara,and fundatrix.The fertilized eggs hatch successfully and continue to raise to support the possibility of overwintering successfully in autumn.The results of supercooling point and low temperature survival rate analysis showed that Stiobion avenae belonged to chill susceptible insects.Low temperature can cause highly mortality of parthenogenetic aphids,even all dead,and the cold tolerance of fertilized eggs is more hardiness.In order to survive in the harsh low temperature environment,the cold resistance eggs is closely related to the existence of overwintering phenomenon by changing the reproductive mode to enhance their cold tolerance.So overwintering with eggs in winter in severe cold region is one of the important adaptive strategies to resist low temperature.