Study On The Responses Of Asian Citrus Psyllid,Diaphorina Citri Kuwayama To Murraya Exotica L. Volatiles

The Asiatic citrus psyllid,Diaphorina citri Kuwayama,develops on immature leaves of citrus and other hosts.It is the most important and widespread vector of ‘Candidatus Liberibacter asiaticus’ the pathogen that causes huanglongbing,the most devastating disease of citrus.During long-term co-evolution with insects,the secondary metabolites produced by host plants have important effects on the biological learning of insect,such as host plants orientation,feeding,mating,spawning,escaping,and pollinating behavior.In order to determine plant volatiles influencing responses of D.citri to it most favoured host plant,Murraya exotica L.,this study sought to clarify reported increased attraction of immature shoots of M.exotica to adult D.citri after prior feeding by the psyllid.The volatile components of the immature shoots of M.exotica before and after feeding by adult psyllids was analyzed,and the responses of the monomeric standard sample with large differences and their mixtures to D.citri were further determined under laboratory conditions.The main results of the study are as follows:1.Colonization of immature M.exotica flush by adult D.citri on which other adults were allowed to feed before being removed or allowed to feed and remain were compared with colonization of immature growth of the same age on which adults had not previously fed(control)were studied using "H" type selector.Prior feeding(damage to flush growth)significantly increased the attractiveness of flush.In the first instance,35% of the adults colonized control flush and 65% colonized flush on which feeding had previously occurred.In the second instance,25% of adults colonized control flush,and 75% colonized flush on which feeding had occurred and on which the psyllids that had fed on the flush were still present.2.Headspace solid-phase micro-extraction and gas chromatography-mass spectrometry were used to analyze the volatile components of M.exotica before and after psyllid damage.The results showed that the volatile components of the young shoots before and after the psyllid damage contained alkenes,alcohols,esters and other substances.Sixteen chemicals were the most common volatile compounds before damage in contrast to fifteen after damage.Differences in the content of the same chemicals before and after damage were obvious.Differences in the type of volatiles before and after damage were also significant.Six volatile compounds were detected before damage,and eight after damage.3.Electroantennogram responses of D.citri to four compounds with large differences before and after damage were measured by an electroantennogram instrument.The four compounds were α-curcumene,α-zingiberene,ledene and methyl salicylate.The results showed that the relative values of EAG responses of female or male to the four chemicals were significantly higher than for the control,and the relative value of the EAG response of males to α-zingiberene at a concentration of 1 μL/m L was the highest,up to 1.15 ± 0.07 mv.4.The responses of D.citri to the above the monomeric standard chemicals and mixtures of them was measured with a four-arm olfactometer.Ledene was a significant attractant to females at 0.01 μL/m L,and a significant repellent to females at 1 μL/m L.It was also a significant attractant to both females and males at 0.1 μL/m L.Methyl salicylate was a significant attractant to both females and males at 0.01 μL/m L.Mixtures of α-curcumene andα-zingiberene were significant repellents to females at 0.001 μL/m L and 0.1 μL/m L,and significant attractants to males at 0.01 μL/m L and 1 μL/m L.Mixtures of α-curcumene and ledene were significant attractants to females at 0.1μL/m L and 1μL/m L.A mixture of α-zingiberene and ledene was a significant attractant to males at 0.1μL/m L.Mixtures of α-curcumene,α-zingiberene and ledene had a significant attraction to male at 0.001 μL/m L and0.1 μL/m L,and significant attraction to female and a significant repellency to male at 0.01μL/m L.A mixture of α-curcumene,α-zingiberene,ledene and methyl salicylate exhibited significant repellency to females at 0.01 μL/m L.5.The above-mentioned specific concentrations of monomers and mixtures affecting the behavior of psyllid were observed visually using the half-leaf method.These observations confirmed responses of the psyllid in the colonisation and EAG components of the study.The results showed that 0.1 μL/m L of ledene attracted significantly more females and males than the control.A mixture of 0.01 μL/m L α-curcumene and α-zingiberene attracted significantly more males than the control,and at 0.001 μL/m L repelled significantly higher numbers of females than the control.A mixture of 0.01 μL/m L α-curcumene,α-zingiberene and ledene attracted significantly more females than the control.The results show that feeding by adult D.citri on immature flush of M.exotica significa nt l y enhanced the attractiveness of the plant to the psyllid.Ledene and the two mixtures of volatile chemicals(α-curcumene and α-zingiberene,and α-curcumene,α-cingiberene and ledene)attracted adults.The attractive monomers or mixtures may play important roles in psyllid recognition of M.exotica,and the repellent monomers or mixtures may have roles in optimising defense responses of M.exotica to the psyllid.