Fitness Of Cacopsylla Chinensis (Hemiptera: Psyllidae) On Different Pear Cultivars

Cacopsylla chinensis(Hemiptera: Psyllidae)is an important pest of pear ecosystems in China,which affects the quality and yield of pears seriously.The host fitness and related factors of C.chinensis to different pear cultivars of Pyrus bretschneideri R.(i.e.,BSL and BHXS)and Pyrus communis L.(i.e.,CB and CRB)was studied,based on differently susceptible degree of C.chinensis on several pears.Firstly,the resistance level of different pear cultivars was classified,and tested cultivars were screened and determined according to the population density,hazarded index,selection and oviposition preference,antibiosis index,etc.Secondly,to evaluate the different fitness of C.chinensis on these hosts,the population life table of C.chinensis on tested cultivars was established and analyzed by using age-stage two-sex life table theory.Thirdly,The leaves volatiles of different pears were collected by dynamic headspace adsorption technology and their components were identified by gas chromatography-mass spectrometry,and the biological activity of related substances against C.chinensis was assayed with fumigation and Y-olfactometer.Repellent effect of active substances was also carried out in field.Besides,the metabolites of different pear cultivars leaves were identified by high performance liquid chromatography-mass spectrometry,and significantly different metabolites and metabolic pathways were screened.Finally,it was confirmed that C.chinensis has the less fitness on P.communis(i.e.,CB and CRB),and the important factors were determined preliminarily as the terpenoids from leaf volatiles.The main results are as follows:(1)Performance of suitability on four different cultivars of pear: Two susceptible cultivars(i.e.,BSL and BHXS)and two resistant cultivars(i.e.,CB and CRB)were selected as further experimental materials by the investigation of the susceptible index of C.chinensis on 50 pear cultivars.The result shows that the population size,settling and oviposition of adults,feeding index of nymphs on two P.bretschneideri cultivars(i.e.,BSL and BHXS)were significantly more or higher than that on two P.communis cultivars(i.e.,CB and CRB).Under selection conditions,the amount of eggs laying per branch of four hosts(i.e.,BSL,BHXS,CB and CRB)was 187.25,170.75,38.25,and 15.25,respectively.Feeding index of nymphs on four hosts(i.e.,BSL,BHXS,CB and CRB)was 1.78,1.75,0.95,and 0.89,respectively.The results indicate that C.chinensis has preference for eggs laying and feeding on BSL and BHXS,while CB and CRB have repellent effect.(2)The analysis of age-stage,two-sex life table established upon four cultivars of pear: Compared with P.bretschneideri cultivars(i.e.,BSL and BHXS),longer preadult duration(female and male)and pre-oviposition period(TPOP),shorter oviposition days,lower preadult survival rate and fecundity occurred on two P.communis cultivars(i.e.,CB and CRB),and these differences were significant.For example,TPOP of C.chinensis on BSL,BHXS,CB and CRB was 35.06 d,36.22 d,45.20 d,and 42.25 d,respectively.Fecundity(eggs per female)on BSL,BHXS,CB and CRB was 64.50,70.78,30.90,and 25.75,respectively.The population growth of C.chinensis on CB and CRB was limited,for intrinsic rate of increase(r),finite rate of increase(λ),net reproductive rate(R0)of C.chinensis on CB and CRB were significantly lower than those on BSL and BHXS.Intrinsic rate of increase(r)on BSL,BHXS,CB and CRB was 0.0367 d-1,0.0393 d-1,0.0086 d-1,0.0034 d-1,respectively.The above results indicate that slower development and lower growth rate of C.chinensis occurred on hosts of P.communis cultivars(i.e.,CB and CRB),which implies that C.chinensis has less fitness on CB and CRB.(3)Collection,identification of leaves volatiles from different pear cultivars and bioassays and field trials of variant volatiles: A total of 58 compounds were detected from the leaves of four tested pear cultivars of P.bretschneideri(i.e.,BSL and BHXS)and P.communis(i.e.,CB,and CRB).The unique volatiles in P.communis(i.e.,CB,and CRB)were 1,2-Benzenedicarboxylic acid,butyl 2-methylpropyl ester,camphor,and α-pinene.The result shows that the mortality of C.chinensis adults was 18.75%,50.00%,and 100% when they was fumigated for 12 h,24 h,and 36 h with 2 m L/L α-pinene,respectively,while the mortality reached 100% under the concentration of 10 m L/L α-pinene after 12 h.The mortality of adults was 28.41%,68.86%,and 100% using 768 mg/L camphor for 12 h,24 h,and 36 h,respectively.In addition,the adults had a significantly negative trend reaction to 12 mg/L-192 mg/L camphor,and had no obvious selection reaction to α-pinene.After 3 d and 7 d continuous spraying 19.2 mg/kg camphor,the number of adults on per plant(i.e.,6.25 and 3.75)was lower than that on the control plants(i.e.,13.25 and9.50).These bioassays of the insecticidal activity,behavior tests and field trials indicate that two compounds-α-pinene and camphor have toxic effect against C.chinensis adults,and mortality is correlated with fumigation time and concentration,and it is camphor that has repellent effect to them also.(4)Identification,analysis of the metabolites from leaves of different pear cultivars,and screening of significant metabolic pathways among different pear cultivars: A total of 111 significantly different metabolites from leaves were screened in pairs among four tested pear cultivars(i.e.,BSL,BHXS,CB,and CRB).There were 68 significantly different metabolites between two P.bretschneideri(i.e.,BSL and BHXS)and two P.communis(i.e.,CB and CRB).In which,the relative content of 8 flavonoids were more(Quercitrin and Biorobin both more than 100 times),and 4 flavonoids were less(Kaempferol-7-neohesperidoside and Genistin both less than 1/100 times)in both two P.communis(i.e.,CB and CRB)than two P.bretschneideri(i.e.,BSL and BHXS).18 biosynthetic pathways were annotated using 111 significantly different metabolites.A total of 9 metabolic pathways were significantly different between two P.bretschneideri(i.e.,BSL and BHXS)and two P.communis(i.e.,CB and CRB)by enriched analysis.Among which,flavone and flavonol biosynthesis,flavonoid biosynthesis were two most prominent metabolic pathways.(5)The factors of different cultivars of pear influence the fitness of C.chinensis: It was found that the specific volatile terpenoids from the less favorable hosts of P.communis had not only repellent effect to adults,but also insecticidal activity.Therefore,terpenoids of volatile maybe the primary factors influencing selection preference of C.chinensis to hosts.These substances can provide a new way for integrated management of C.chinensis.