Study On Occurrence And Diapause Of Harbin Population Of Ostrinia Furnacalis (Guenée)

Ostrinia furnacalis(Guenée)is widely distributed in the world.It is seriously harmful to corn plants and other crops in our country.And it is one of the most important pests in maize,which seriously threatens the healthy production of corn in our country.In this experiment,the development progress of Asian corn borer was investigated outdoors,the occurrence pattern of Asian corn borer and the distribution characteristics of the egg mass on corn plants in the suburbs of Harbin were studied through the corn cage observation method in field.Dissecting straw in the fall to investigate the damage law of the corn straws and female ears.Calculate the development threshold temperature and effective accumulated temperature of the period that diapause larvae developed into pupae.The larvae were treated by combining different temperature and photoperiods to determine their diapause types and the critical photoperiods at different temperatures were obtained.The dynamic changes of body water and energy substances in larvae at different time periods were determined.The results are as follows:(1)Harbin is a mixed area of the first and second Asian corn borer generations,and about 10% of individuals occur in the second generation.The initial immigration periodof overwintering pupae was late May after terminating the diapause of overwintering larvae.The mid-June period was the beginning stage of pupation and the active stage that overwintering generations pupated was late in June.Pupation lasted 54-58 days.The initial immigration period of overwintering adults was early June,the beginning stage of emergence was mid-to-late June,the peak stage of adult emergence was early July,and the emergence lasted 45-52 days.The first generation egg emerged at the end of June,peaked in early July,and the spawning time was about 40 days.The peak period of the second generation eggs was at the end of August and the spawning time was about 20 days.The egg hatching rate of the first generation was significantly higher than the second generation,parasitism rate and predatory rate were lower than those of the second generation eggs.(2)Adults tended to concentrate their eggs on the top of corn plants.The oviposition height of the overwintering adults that emerged earlier was mainly 1.2 to 1.6 m,which was mainly distributed on the top 3 to 6 leaves of the corn.The adult oviposition height of late emergence was mainly above 1.8 m,mainly distributed on the first to fourth leaves of the upper corn.The first generation eggs were not distributed below 0.8 m in corn plants.The distribution of the second-generation egg masses was more dispersed than that of the first-generation egg masses,and the height of oviposition was lower than that of the first generation eggs.Asian corn borer egg masses were mainly distributed within 2 cm of the midrib near the back of the corn leaf and 20 to 50 cm away from the leaf axils.(3)The borer holes were mainly distributed in the 4th to 7th culms,the damage was more serious in the corn ears' head position and upper and lower nodes.The damage rate of ear tips and pedicel of corn ears was significantly higher than that of middle ears and lower ears.(4)At 19?,22?,25?,28? and 31?,the critical photoperiods of Harbin population of Asian corn borer were 17.24 h,16.69 h,15.65 h,15.34 h and 14.81 h,respectively.When the photoperiod was greater than 13 h,some larvae could continue to develop without diapause under high temperature conditions,and emerged as adults.At each temperature,the diapause rate of Asian corn borer larvae gradually decreased with the increase light duration from the time of light that could emerge.Under the same light conditions,the diapause rate of larvae decreased with increasing temperature.It indicates that the key factor causing the diapause of Asian corn borer is the photoperiod.Temperature can help the photoperiod to affect their diapause,and high temperature can inhibit their diapause.The diapause type of Asian corn borer population in Harbin is long-illumination development or short-illumination diapause.(5)The water content of Asian corn borer larvae showed a downward trend from October to February,especially with the lowest moisture content in January and February when the temperature was the lowest.However,from March to May in the period of diapause termination,the body's water content increased significantly.The larvae had the highest body fat content in November and the lowest in May.There was a significant difference between November and April and May.In August,the total sugar content in larvae was the highest,and it decreased in February of the following year,and the content increased slowly from March to May.The glycogen content in the body was higher from September to December,and then gradually decreased,and the content was lowest after the overwintering larvae were released from diapause in May of the following year.The trehalose content of the corn borers maintained a high level from August to November,decreased in December and January,then began to increase,reached the highest level in March of the whole year,and then began to decrease.After the overwintering larvae were released from diapause in May,the trehalose content reduced significantly.However,except for March,the trehalose content was not obviously different.Judging from this,the Asian corn borer larvae in Harbin are glycogen accumulation diapause.