Study On The Feeding Habit, Economic Threshold And The Relationship Between Environmental Factors And The Oviposition Of Locusta Migratoria Tibetensis

Locusta migratoria tibetensis Chen is the new subspecies named by Chen Yonglin in 1963.In recent years,Locusta migratoria tibetensis outbreak seriously in Tibet,Qinghai,and west Sichuan plateau.The research of Locusta migratoria tibetensis,by now,is only subject to the Morphology and Characteristic,biological characteristics,cold resistance and the distribution,but the diet habit of different instar,food consumption,economic threshold,and the spawning habits of the Locusta migratoria tibetensis haven't been researched and reported.Through the inner and outside enfold experiments,the diet habit,food consumption,economic threshold of the Locusta migratoria tibetensis has been studyed in detail.The study has acquired the important research as follows:1.The feeding area and the feeding preferences of Locusta migratoria tibetensis have greater changes coming along with the increase of the instar.The 1^st and 3^rd instar locust nymph like to eat the pasture grass;The 4^th instar locust nymph prefer to eat the highland barley and winter wheat,but the feeding frequency of pasture grass is relatively decreasing.The field research showed that,the feeding habit of Locusta migratoria tibetensis will be changed coming along with the local plants seasonal change.The new hatched locust nymph mainly feed on the pasture grass;from June to July,the older instar of the locust nymph will spread to the strong growth highland barley and the wheat field for feeding;in August,the locusta will have a cluster harm to the highland barley,wheat and pasture grass; when the August passed,Locusta migratoria tibetensis will mainly feed on the pasture grass land,and complete the egg-laying.2.There is certain relation between the feeding frequence of Locusta migratoria tibetensis and the time.Before 8 a.m.,the feeding frequence for all the instar of the locust nymph is relatively low;at 11 a.m.,there is a feeding peak;from 12 a.m.to 14 p.m.,the feeding frequency is relatively low;there also has a feeding peak between 15 p.m.to 17 p.m.There is certain distinguish of the relativety relationship of the feeding frequency and the time for all the instar of the locust nymph.The feeding frequency of the 1st to the 2nd instar of the locust nymph is low for all the time;it is mainly concentrated in the time of 11 a.m.,15 p.m.to 17 p.m.But the 4th to the 5th instar of the locust nymph have a wide time range for feeding activities:there also has a wide distribution for the feeding peak.3.The growth of Locusta migratoria tibetensis is effected by different plants.In nature condition, Locusta migratoria tibetensis will feed on the Gramineae and the Cyperaceae plants,and could complete the process of growth,development and reproduct,but under the man-made duress condition, it also can teed on the Seabuckthorn and the Cruciferae plants,but it could not competed the process of growth and development.If it was fed on the cabbage,even through it could compete the growth and molting,but it couldn't adult moult.4.The food consumption of the Locusta migratoria tibetensis has a close relationshiop whit the older of the locust The Food consumption of the 1^st to 3^rd instar of the locust nymph is small;but the food consumption of the 4^th instar o to the adult is increasing;the period of 5^th instar of the locust nymph to the adult is the overeating period.5.Through eating the leaves and stems,Locusta migratoria tibetensis will cause the damage to the highland barley and the reduction of the production.Within the factors which constituted to the production,the thousand kernel weight is most likely to be affected;the followed factor is the number of the grains.The highland barley production((?)₁) and the loss ratio((?)₂),population density(x) have a close correlation.The regression equation showed as:(?)₁=-7.3306x + 373.9(R²=0.9871);(?)₂= 0.0188x(R²=0.9834).The economic threshold of Locusta migratoria tibetensis to the highland barley is ET=3.01 adults/m².The major harm to the pasture grass of Locusta migratoria tibetensis is eating on and breaking down it,the most harmly period is the 5^thto the adult.The conomic threshold of Locusta migratoria tibetensis to the pasture grass is ET=4.44 adults/m².6.Different plants affect the egg laying amount of Locusta migratoria tibetensis.There has certain difference of the number of the spawning block and the average fecundity per female of Locusta migratoria tibetensis on different plants.The number of the spawning block on grassland environment is the most,the river meadow environment,the highland barley environment,the mountains environment followed.7.Different plants affect the selection of Locusta migratoria tibetensis egg-laying on.Under the circumstance of the temperature,humidity,food same as the field environment,the Locusta migratoria tibetensis egg-laying have a different selection on different soil.The grassland is the optimum soil type for Locusta migratoria tibetensis laying egg on;the followed is the river meadow and the highland barley land;the third optimum soil is the mountain and vegetable land;but Locusta migratoria tibetensis has not choose to lay egg on the river shoal rubble land.Whih the pH value from 7.29 to 7.55, the egg-laying selection have no specific regularity with the pH value;Whit the water content from 4.134%to 18.218%,Locusta migratoria tibetensis laying egg has certain selection to the water content of the soil;There has a optimum water content condition;The organic content of the soil do not have a significant effect to the Locusta migratoria tibetensis egg laying;The size of the soil particle have a certain effect to the Locusta migratoria tibetensis egg-laying selection.8.Making the model of laying egg selection of the Locusta migratoria tibetensis to the different soil of physical and chemical properties.Through the ternary quadrati degree of contributionc regression general rotation design,the Locusta migratoria tibetensis egg-laying proportion(p),salt content(z₁), water content((z₂),and the pH value have showed the regression equation as: (?)=-101.5638k-0.0060z₁²k-13.6110z₂²k-0.3965z₃²k-2.7036z₁k-58.3328z₂k-8.4956z₃k The k means a constant needed to be determined.The comprehensive physical and chemical indicators of the optimum soil was as followed:salt content is 0.081%～0.120%,water content is 2.908%～3.752%, pH value is 7.353～7.647.The single-factor analysis showed as:the Locusta migratoria tibetensis laying egg selection is very sensitive to salt content of the soil;if the salt content of the soil is increasing,the Locusta migratoria tibetensis laying egg selection will be sharply decreasing;the water content for the Locusta migratoria tibetensis to laying egg is 7.5%;the optimum pH value of the soil is 7.5.Through the analysis of the relation between the two factors and the experimental indicator,and the analysis of contribution degree,we found that during the three factors of the salt content,water content,pH value which will have a greater significant effect to the Locusta migratoria tibetensis egg-laying proportion,it showed as the salt content water＞content＞pH value.