| Grapholita molesta Busck(Lepidoptera: Tortricidae),oligophagy,is one of the bore-fruit pests which can feed tender shoots and fruits of members of the family Rosaceae in the world.The effective identification of Grapholita molesta for host plants is the key to their population prosperity,and secondary metabolites of host plants play an important role in the identification.How do pregnant females effectively select oviposition sites which are benefit to the growth,development and reproduction of their offspring?How do secondary metabolites play the role on oviposition of adults and feeding of larvae? The effects of key secondary metabolites on ovipositing of pregnant females,larval feeding and offspring performance,and the effects of feeding experience on ovipositing and feeding selection were investigated in this study.The correlation between adult preference and offspring performance of Grapholitha molesta was explored.The main results as follow:1.Adult oviposition preference and the effect of benzaldehyde on oviposititon behavior(1)Oviposition preference of pregnant females to different damaged host plants According to the distribution and cultivation characteristics of the host plants on Grapholita molesta in China,three host plants were selected for the oviposition preference test of pregnant females,and the treatment host plants were: intact,pest damage and mechanical damage respectively.The results showed that the pregnant females had higher oviposition selection rates on pest damaged-peach shoots in April,apple fruits in May,peach,pear and apple fruits in June,pear and apple fruits in July and pear fruits in August.Meanwhile,the pregnant females had higher oviposition selection rates on mechanical damagedpear shoots in April,peach,pear and apple fruits in May,peach fruits in July and apple fruits in August.During the whole annual occurrence period of Grapholita molesta,the pregnant females have the higher oviposition preference on pest and mechanical damaged host plants than on intact host plants.(2)Volatiles extraction of different damaged host plants Headspace adsorption and GC-MS were used to collect and analyze the volatiles of three host plants.Special volatiles of host plants from April to August were analyzed,among which,7 main kinds of componds on pest damaged-host plants were 2-Hexenal,Benzyl nitrile,Butanoic acid,ethyl ester,1,4-Benzenedicarboxaldehyde,1,3,6-Octatriene,3,7-dimethyl-,Piperidine,Bicyclo[3.1.1]heptane,6,6-dimethyl-2-methylene-,(1S)-.7 main kinds of componds on mechanical damaged-host plants were Butanoic acid,butyl ester,2-Hexenal,(E)-,Hexanal,2-Hexen-1-ol,acetate,(Z)-,3-Hexen-1-ol,(Z)-,3-Hexen-1-ol,acetate,(Z)-,Azulene.And 9 main kinds of componds on pest and mechanical damagedhost plants were Benzaldehyde,4-ethyl-,D-Limonene,.alpha.-Farnesene,Benzaldehyde,Nonanal,Ethane,1,1-diethoxy-,Acetic acid,butyl ester,Acetic acid,hexyl ester,Hexanoic acid,ethyl ester.(3)Response of pregnant females to benzaldehyde The effects of benzaldehyde on oviposition of pregnant females were studied by EAG,wind tunnel and oviposition selection determination.The results showed that 10 μg/μL benzaldehyde could cause the strongest EAG response of pregnant females,and the EAG response increased first and then decreased as the concentration increased.In the wind tunnel behavior test,the response rate of pregnant females to benzaldehyde was higher when the concentration was 1-10 μg/μL.In the oviposition selection test,the pregnant females had oviposition tendency to low concentration benzaldehyde(0.01μg/μL and 0.1μg/μL),and the highest oviposition selection rate was 66.67% when the concentration was 0.01μg/μL.In non-selective oviposition test,low concentration(0.1 μg/μL)benzaldehyde could promote the oviposition of pregnant females.When the concentration of benzaldehyde was high,it would not only inhibit the oviposition of pregnant females,but also start to avoid the pregnant females.2.Effects of amygdalin on feeding and performance of offspring(1)Weight analysis of different performance indexes The life indexes of Grapholita molesta different stages were measured and weighted.The results showed that the effects of food on different life indexes were not completely consistent.In the evaluation of fitness,the weight coefficients of survival rate of pupation(0.076),larval duration(0.075),pupal weight(0.075),total no.eggs laid per female(0.071),total tunnel length(0.070)and survival rate of exiting(0.070)were relatively high,which resulted in the consistent fitness ranking of host plants.However,the index with lower weight coefficients,such as pupal duration(0.059),total preoviposition time(0.057),life table parameters(0.050-0.059),oviposition period(0.041),resulted in the inconsistent fitness ranking of host plants which compared with the former.The indexes with higher weight coefficient is more important to the performance fitness.(2)Content of amygdalin in different host plants Amygdalin is widely distributed in rosaceae fruit trees.The contents of amygdalin in different host plants were detected by HPLC.Standard curve of amygdalin was drawn,and the linear equation between concentration and peak area was y = 14.689x-22.186(R2 = 0.9995).The highest content was found in peach shoots,followed by apple shoots,and amygdalin was not detected in pear shoots in April.Amygdalin were detected only in peach fruits in May.The amygdalin content of peach fruit in June was the highest,followed by pear fruit.Amygdalin were detected only in pear fruits in July,and only in apple fruits in August.The amygdalin content in peach was higher than pear and apple.Meanwhile,the content of amygdalin in peach shoots was much higher than peach fruits,with a relative content of 3.14mg/g,followed by peach fruits in June,with a relative content of 0.86mg/g.(3)Effect of amygdalin on larval feeding choice and offspring performance Artificial diet without amygdalin was used as the control,and the artificial diet with amygdalin(concentration of 5,10,20,30,40,50 mg/g)was used as the experimental group.The results showed that larvae preferred to feed artificial diet with 5 mg/g amygdalin,and the feeding choice rate on 5,10 and20mg/g was higher than control.After feeding the artificial diet with 5-20 mg/g amygdalin,the duration of each stages were shorter than control,but the survival rate was higher than control.After feeding the artificial diet with >30 mg/g amygdalin,the duration of each stages were longer than control and the survival rate was lower than control.The No.eggs laid per female was higher than control at low concentration(5-30 mg/g),but lower than control at high concentration(>30 mg/g).The λ,r,and R0 values were higher than control at concentrations of 5 mg/g,and the T value was shorter than control.R0 value was higher than control at low concentration(5-10 mg/g).At low concentration(5-20 mg/g),I value was higher than control,and reached the highest at 5 mg/g.Amygdalin had a promoting effect at the low concentration(5-20 mg/g)and an inhibiting effect at the high concentration(>30 mg/g)for Grapholita molesta.(4)Scanning electron microscope of larva head sensilla The larval antennae and mouthparts were observed,described and illustrated with the help of scanning electron microscopy,with particular focus on the sensilla.The antennae had three types of sensilla: two sensilla chaetica,six sensilla basiconica,and a sensillun styloconicum.The labrum had six pairs of sensilla chaetica.The apex of each mandible is dentate,with five teeth.On the maxilla,both cardo and stipes had a sensillum chaeticum.Each galea had three short-sharp sensilla basiconica,two big sensilla styloconica and three sensilla chaetica.The maxillary palp had seven sensilla basiconica,a sensillun styloconicum,distally a sensillum digitiformium and two sensillum placodeum.Each labial palp had laterally a cone-shaped sensillum chaeticum and a long sensillum styloconicum.The antennae and maxilla have the most important sensory receptors for the larvae.3.Effect of larval amygdalin feeding experience on the selection of pregnant females for benzaldehyde The behavior response of pregnant female which from amygdalin feeding population(breeding with artificial diet with amygdalin)to benzaldehyde were measured,and compared with non-amygdalin feeding population(breeding with artificial diet whithout amygdalin).The results showed that change trend of antennal EAG response to different concentrations of benzaldehyde in amygdalin feeding population was consistent with non-amygdalin feeding population,reached the max-value when the concentration was 10μg/μl,but the overall EAG response was higher than non-amygdalin feeding population.In the wind tunnel test,the concentration range of benzaldehyde also was 1-10 μg/μL which could cause higher behavior response rate of pregnant females,but the amygdalin feeding population adapted to a wider range of benzaldehyde(extending to low and high concentration),the overall reaction intensity was greater,and the preference to benzaldehyde was stronger than non-amygdalin feeding population.The highest oviposition selection rate of amygdalin feeding population was 83.33% on the concentration of 0.1 μg/μl and 1 μg/μl,and 0.01-1 μg/μl could promote pregnant females oviposite.The oviposition preference to benzaldehyde of pregnant females in amygdalin feeding population was stronger,the adaptive range of concentration was wider,and they were more sensitive to the change of concentration than non-amygdalin feeding population.In this paper,the correlation between adult oviposition and larval feeding of Grapholitha molesta which under the action of secondary metabolites was studied.The key volatile compond affected oviposition of pregnant females and nonvolatile compond affected larval feeding and offspring performance,as well as their roles in maintaining the correlation between adults and larvae were determined.The defensive and counter-defensive strategies between Grapholitha molesta and its host plants was explored. |
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