Study On The Adaptability Of Temperature And Host And Fumigation Control Of Acanthoscelides Obtectus(Say)

Acanthoscelides obtectus(Say)belongs to Coleoptera Bruchidae.Native to South America and Central America,it is now found worldwide and is a worldwide pest of many common beans.With beans seeds,it is carried through trade and introduction.It is a quarantine pest of important agriculture and entry plants.In recent years,A.obtectus has been in some parts of Guizhou Province,a large number of hazards,and Guizhou beans constitute a serious threat.Therefore,on the one hand,by studying the effect of host and temperature on the adaptability of A.obtectus,the developmental threshold temperature and the effective accumulated temperature of each insect state were determined,and the effects of different hosts on the growth and reproduction of A.obtectus were compared.This will provide a reasonable reference for the sustainable management of A.obtectus.On the other hand,the research on effect of ethyl formate fumigation and enzymes activity in A.obtectus,aims to provide a theoretical basis for the control of pests.At the same time,more in-depth exploration of its toxicological mechanism to lay the foundation.1.Effects of temperature on the development and reproduction of Acanthoscelides obtectus(Coleoptera: Bruchidae)The duration of different developmental stages of Acanthoscelides obtectus were measured at different temperatures(20,23,26,29 and 32?),the relationship between temperature and developmental stage was fitted using line regression,Logistic and “Wang-Lan-Ding” model,the developmental threshold temperature and effective accumulated temperature were calculated by using least square method,and the life tables of the experimental populations were established.Results show the duration of various developmental stages of A.obtectus shortened with the rise of temperature,whereas the development rate was positively correlated with temperature.For the relationship between development rate and temperature,the Logistic model and “Wang-Lan-Ding” model fitted better than the line regression model.The developmental threshold temperature and the effective accumulated temperature for generation were 6.44? and 858.22 degree days,respectively.Fecundity,hatchability and survival rate were the highest at 26?(52.71 eggs,82.67% and 75.67%,respectively),and the lowest at 32?(33.20 eggs,69.33% and 41.67%,respectively).The rm values were 0.05,0.07,0.08,0.09 and 0.08,and the R0 values were 25.54,33.80,39.87,34.52 and 13.86 at 20,23,26,29 and 32?,respectively.Temperature has a significant effect on the population growth and reproduction of A.obtectus,and the optimum temperature range for its growth and development and reproduction is between 23-29?.2.Effects of the development and reproduction of Acanthoscelides obtectus(Say)fed on different hostsIn order to find out the development and reproduction of Acanthoscelides obtectus(Say)fed on different beans,seven kinds of beans were selected to feed A.obtectus to observe its developmental stages,survival rates and fecundities.Results show that A.obtectus could lay eggs on all seven kinds of beans,but there were differences in egg hatchability.The hatchability reached the highest on Phaseolus vulgaris(65.65%)and was the lowest on Abrus precatorius(59.59%).Larvae could survive in P.vulgaris,Phaseolus lunatus,Vigna umbellata,Vigna radiate,A.precatorius and the generation survival rate reached the highest on P.vulgaris(61.22%)and was the lowest on V.radiata(46.15%).The shortest developmental period of the whole generation of A.obtectus on P.vulgaris was 45.83 d and the higher single female fecundity was 52.90 eggs.The reproductive and intrinsic rates were 45.84 and 0.08 respectively.The results show that the fecundity table of P.vulgaris is higher than those of V.radiata and A.precatorius and the same as P.lunatus and V.umbellata,which indicates that A.obtectus develops faster,fecundity and survive rates better on P.vulgaris,P.lunatus and V.umbellata.A.obtectus failed to have a complete life cycle on Glycine max and G.soja,which indicates that A.obtectus is unable to have a normal development on these two beans.3.Fumigation activity of ethyl formate against Acanthoscelides obtectus(Say).In this paper,we sealed jar to fumigate Acanthoscelides obtectus(Say).The effects of ethyl formate fumigation activity to each life stage of A.obtectus were measured under different concentrations,time and temperature conditions.Results showed ethyl formate has a very fast-acting fumigation on A.obtectus.After treated A.obtectus with a concentration of 45 ?L/L for 12 hours or 45 ?L/L for 12 hours,ethyl formate can make its mortality reached more than 90%.Increasing the concentration,temperature and time of ethyl formate,the mortality of adults of A.obtectus(Say)will increase gradually.Comparing the resistance of each state: The level of concentration of ethyl formate significantly affect the resistance of different stages of A.obtectus(Say).The resistance of eggs is the worst at low concentration,while eggs and adult are the worst under high concentration.4.Effect of ethyl formate fumigation and enzyme activity of Acanthoscelides obtectus in simulation chamberIn this study,Acanthoscelides obtectus were fumigated by ethyl formate and tested for enzymatic activity.Results showed ethyl formate has a very fast-acting fumigation on A.obtectus in simulation chamber.After treated A.obtectus with a concentration of 50 ?L/L for 24 hours,ethyl formate can make its mortality reached more than 94%.The same concentration at different levels showed effect was significantly different.Treating 35 ?L/L of ethyl formate,the lower mortality rate was only 78.82%,while the upper mortality rate was 87.86%.The determination results of enzyme activity showed fumigating ethyl formate,protective enzyme of A.obtectus significantly activated,activation rate of SOD was highly 152.17%.With the prolongation of fumigation time,the activity of CAT gradually increased.In the short term,the activity of POD was inhibited,but the late activation rate is still as high as 55.23%.AchE of A.obtectus had no obvious inhibitory effect,the enzyme activity obvious increased after fumigating.The results showed that the protective enzymes and detoxification enzymes of A.obtectus were involved in the reaction of ethyl formate,enhancing the ability of detoxification and ability of free radical scavenging.