Studies On Main Factors Of Outbreak Damage Of Grapholitha Molesta (Busck) And Host Selection

The oriental fruit moth,Grapholitha molesta(busck)is a boring pest and is responsible for substantial economic loss in recent years in China.Compared with other pests,the loss caused by G.molesta larva was related to its population number and boring rate directly.However,the present study focused the effect of population number of G.molesta on damage and these results could not solve effectively some key problems in orchards,such as generation overlap,frequent outbreaks and unstable control effects.In order to investigate the reasons for the generation overlap and frequent outbreaks of G.molesta,the relationship between climate warming,rainfall,planting pattern and the population number and boring rate was studied in this paper.The host selection of G.molesta larva and adult was also studied in this paper,which provided a basis for compounds and new control technologies.Based on the above results,the existing parameters of field prediction and chemical control of G.molesta were improved.The main results are as follows:1.The effects of temperature and humidity on the population and boring rate of G.molesta(1)Within the experimental setting range,the single temperature affected significantly populations and boring rate of G.molesta.However,the variable temperature eliminated this effect: oviposition amount of per female,egg hatching and boring rate were the highest at 25 ?;and the differences between at 27.5 ? and at 25 ? were no significant.At above 27.5 ? or below 25?,the individual weight,oviposition amount and hatching rate were reduced significantly.The boring rate decreased from 73.37% at 25 ? to 41.69% at 20? and 36.52% at 35 ?,respectively.The individual weight,oviposition amount and boring rate of G.molesta were significantly higher in variable temperature than the single temperature,the boring rate were 68.13% at 20 ? and 52.17% at 35 ?.(2)Within the scope of the experiment,humidity was a key factor that affected the population and boring rate of G.molesta larva,the number of eggs laid of per female increased significantly with increased RH,and the oviposition amount(117.13 eggs/female)was the highest in RH 70% which was 1.89 times in RH 25%(62.07 eggs/female).The influence of humidity on different stages of G.molesta was below from high to low: boring stage> adult stage> egg stage> pupa stage> final instar larva.Hatching rate,boring rate,emergence rate and generation survival rate increased significantly with increasing humidity,from 48.08%,42.67%,82.48% and 12.76% in RH 25% to 96.33%,74.67%,95.85% and 68.78% in RH 85%,respectively.Among them,the relative humidity was positively correlated with generational survival rate and boring rate of G.molesta,respectively.The results showed that humidity should be added into the forecasting and prevention in the field.(3)Higher temperature and higher humidity were more significant influence on the population and boring rate of G.molesta: The boring rate and survival rate was significantly lower at 20 ?+RH 25 % treatment than that at 20 ?+RH 55% treatment?20 ?+RH 70% treatment and 20 ?+RH 85% treatment.The generation survival rate was 1.68 times at 20 ?+RH 85% treatment than that at 20 ?+RH 25% treatment.The generation survival rate was 7.68 times at 30 ?+RH 85% treatment than that at 30 ?+RH 25% treatment.The results showed that the population and boring rate of G.molesta had large increase in higher temperature and higher relative humility.These rules explained the reason of serious damage and outbreak of G.molesta.Therefore,humidity should be paid attention to in the higher temperature stage.2.The effects of host on the population and boring rate of G.molesta(1)Host species and development state all had significant effect on the boring rate of G.molesta: the boring rate of G.molesta larva in different fruits followed from high to low: nectarine,apple,pear and peach.Except nectarine,the fruit development stage had significant effect on boring rate of G.molesta.The boring rate was the highest(73.69%)in fruitlet and the lowest(32.51%)at coloring stage in apple.With the development of fruit,the boring rate of G.molesta increased from 1.49% and 1.98% in fruitlet to 45.37% and 46.28% in mature stage of peach and pear,respectively.The late development of peach and pear were benefited for boring of G.molesta.(2)Host species and development stage also affected significantly the weight of G.molesta: the weight of G.molesta which fed by different fruits was difference significantly,and mature fruit was conducive to the increase of weight of G.molesta.However,only the weight of G.molesta female was positively correlated with oviposition amount of per female,and the effective ovisipotion time was prolonged from 6-7 d to 12-13 d that made overlap generations possible.Combined effect of temperature,humidity and host fruit,if it rains frequent or lasting rainfall in mature stage of fruits,the population number and damage rate of G.molesta increased significantly and may caused outbreak damage.(3)The shift of a large number adults had nothing to do with the species and development stage of fruits,but was related to the presence or absence of fruit.The trapping amount of adults of G.molesta were 116-2426 males/trapper ·15 d and more eggs per fruit in different varieties orchards with fruits and tender shoot.The trapping amount was 6-32 males/trapper · 15 d and no eggs when there was no fruit or tender shoot in different varieties orchards.Under indoor conditions,the ovipsition amount of G.molesta was 93.05-112.33 eggs/female in the different fruit speices or stage,and oviposition amount of G.molesta decreased from 95.73 to 64.08 eggs/female in no fruit,and the ovipsition time was delayed 3 d.The shift of mass G.molesta was also a main factor affecting population change and outbreak damage.3.The host selection of G.molesta larva and adult(1)The larva had the ability to select host: the larva had different selection to 7 kinds of fruits,and the selection level was related to their instars.The host selective ability of 1st instar was the highest.On the contrary,it was the lowest of the final instar larva.Antennae were main sensory organ.These results provided a theoretical basis for the selection of attractants and repellents.(2)The type and quantity of diets eaten in larval stage affected significantly the EAG response level and Y-tube selection of G.molesta adults.The EAG response and Y tube choice of G.molesta adults fed with apple was significantly higher than those fed with artificial diets.The EAG response and Y-tube selection of G.molesta larger adult fed with apple to the mixture of 4 volatiles was higher than that of individuals fed with artificial diets at a lower concentration.However,the individual fed with artificial diets was higher to the mixtures of 5 volatiles than individuals fed with artificial diets.The rule of host selection of G.molesta adult provided a theoretical basis for choices of volatiles.4.Improved technical parameters of prediction and chemical controlFrom the expanding stage of pear to maturity stage,the logarithm of accumulated relative humidity in the field had a positive linear relationship with the logarithm of accumulated trapping number,and an exponential relationship with boring rate.According to the relationship among humidity,host state,the population number,and damage rate,humidity should be an important forecasting parameter for the chemical control of this pest.In summary,fruit late stage,high temperature and frequent rainfall were the main factors that caused the outbreak damage of G.molesta.The shift of large number adults after harvesting was also one of the main reasons for the damage of G.molesta.Based on these,humidity should be used an important parameter for forecasting.The main sensor of larva of host selection and the host selection rules of larva and adults were clarified which provided a basis for new efficient prevention and control technology.