The Attractive Effect Of Body Volatiles Of Scale Insects To The Natural Enemy Ladybeetles

Drosicha corpulenta(Kuwana),Ceroplastes japonicus Green and Didesmococcus koreanus Borchsenius(Insecta:Hemiptera:Coccoidea)are three important pests of fruit orchards in north China,especially damaging persimmon,jujube and peach trees.Rodolia limbata Motschulsky,Harmonia axyridis(Pallas)and Chilocorus rubidus Hope which belong to Coleoptera:Coccinellidae are the primary predators of the three scale insects.In order to explore attractive effect of body volatiles of the scale insects to the natural enemy ladybeetles,volatile components of the three scale insects and chemotactic responses of the ladybugs in the laboratory were studied.Attracting effect of the natural enemy attractant to R.limbata was carried out in the field,which provided theoretical basis for the future use of scale insects pheromone in biological control.The content and conclusion are summarized as follows:1.The components of D.corpulenta(female adult,egg)by eluted with ethyl acetate,dichloromethane and the volatile components of the insect in different instars were studied.The results showed that a total of 10 compounds in female adult eluent were analyzed and identified,including esters,alcohols,alkanes and so on,in which 6,9-octadecadiynoic acid,methyl ester was the most component.While 21 compounds in egg eluent were found,in which buty14,7,10,13,16,19-docosahexaenoate was the largest one.Altogether 43 compounds were studied in the volatile components of D.corpulenta,including alkanes,alkenes,esters,Benzene compounds,etc.In which 7 single compounds were selected,the Y-tube tendency assays of R.limbata toward the 7 kinds of components at four concentrations of 10-3 g/mL,10-4 g/mL,10-5 g/mL and 10-6 g/mL were tested.Five significant attractive compounds were found,including eucalyptol in 10-5 g/mL,1R-.alpha.-Pinene in 10-6 g/mL,phthalic acid,diisobutyl ester in 10-6 g/mL,1-chlorooctadecane in 10-6 g/mL and phenylethyl alcohol in 10-4 g/mL.12 mixture ratios which had the best attractive effect to R.limbata were singled out after two-component attractive experiments.Furthermore,binary artificial attractant was tested in the persimmon forest land,and attractive effect of 4 ternary attractants reached significantly different level(P<0.01),of which 1R-.alpha.-pinene in 10-3 g/mL:1-chlorooctadecane in 10-3 g/mL:eucalyptol in 10-2 g/mL(2:1:16)was the best one.2.Selection response of H.axyridis to C.japonicus was investigated by using the Y-olfactory instrument,the results showed that the ladybirds showed obvious selection to C.japonicus in different instars,and the selective effect to adult reached significantly different level(P<0.01).The volatile components of C.japonicus(egg,nymph,adult)were studied by headspace solid phase micro-extraction and gas chromatography-mass spectrometry(HS-SPME-GC/MS).A total of 47 compounds were analyzed and identified,including alcohols,alkenes,alkanes and so on.Furthermore,the two compounds(1-Octen-3-ol and 1R-.alpha.-Pinene)were selected from the volatiles to examine their attraction to the ladybugs,H.axyridis.The result indicated that 1-Octen-3-ol displayed an obvious attractiveness to the ladybirds at the concentration of 10-4 g/mL and 10-5 g/mL,while 1R-.alpha.-Pinene did the same role in 10-5 g/mL and 10-6g/mL.And the tendency percentages to 1-Octen-3-ol at concentration of 10-4g/mL and 1R-.alpha.-Pinene at concentration of 10-5g/mL were 73.65%and 76.41%respectively,which reached significantly different level(P<0.01).3.Selection response of C.rubidus to D.koreanus was investigated by using the Y-olfactory instrument,the results showed that the ladybirds showed obvious taxis to D.koreanus in different instars,and the selective effect to nymph and adult reached significantly different level(P<0.01).The volatile components of D.koreanus in different instars were studied by HS-SPME-GC/MS,and a total of 29 compounds were analyzed and identified,including alkanes,Benzene compounds,alcohols,ketones and so on.Furthermore,1-Octen-3-ol was selected from the volatiles to examine their attraction to the ladybugs,C.rubidus.The result indicated that 1-Octen-3-ol displayed an obvious attractiveness to the ladybirds at the concentration of 10-4 g/mL,10-5 g/mL and 10-6 g/mL,and the tendency percentages to 1-Octen-3-ol at concentration of 10-5g/mL was 75.13%,which reached significantly different level(P<0.01).4.Based on the transcriptome sequencing information and analysis result of D.corpulenta adult female,we identified 16 putative transcripts encoding of fatty acyl-CoA reductase(FAR)and predicted their amino acid sequences by ORF finder.The 7 amino acid sequences contained the NADH binding motif T-G-X-T-G-F-L-(G/A)were in line with the characteristics of the FAR gene.Meanwhile,these seven genes shared high amino acid identities with Acyrthosiphon pisum,Apis mellifera,Camponotus floridanus and Acromyrmex echinatior.The FAR-12 gene was got by RT-PCR,which probably be involved in other aspects of the wax secretion process of D.corpulenta,although it did not have the typical characteristics of FAR.