| Volatile semiochemicals play an important role in the daily life of insects,and can regulate most insects behaviors like searching for food resources,mating partners,and oviposition sites.In the open environment,many abiotic and biotic factors,such as the constituent of semiochemicals and their concentration,the physiological state of the target insects,can influence the intensity of behavioral responses of insects to semiochemicals.The diamondback moth Plutella xylostella(L.)is one of the most notorious insect pest of cruciferous crops all over the world,and is a model insect pest to be used to study insect behavior and insect physiology.The Exploitation of the influence of abiotic and biotic factors on the behavioral responses of P.xylostella to semiochemicals can provide guidance to the study of insect behavior and efficient control of P.xylostella.So,in this study,we examined the effects of nine volatile semiochemicals,semiochemicals dosages,P.xylostella sex,age,and body size on the electroantennogram(EAG)and choice responses of P.xylostella.We further evaluated the trapping efficiency and egg laying stimulation of some semiochemicals on P.xylostella in green house.The main results and conclusions are listed below:1.the EAG responses of P.xylostella to semiochemicals(1)In our tested four general semiochemicals,to which P.xylostella age did not influence the EAG responses of P.xylostella.In trans-2-Hexenal,trans-2-Hexenol,and Heptanal treatment,the EAG response level of female P.xylostella was stronger than that in male.cis-3-Hexen-1-ol treatment showed the similar EAG responses of both female and male P.xylostella.The two factors,semiochemicals concentration and sex,had interaction effects on EAG responses of P.xylostella in trans-2-Hexenal,trans-2-Hexenol,and cis-3-Hexen-1-ol treatments.The EAG responses of P.xylostella were enhanced with the increase of the semiochemicals concentration,while the degree of enhancement of EAG responses in females was larger than in males.In Heptanal treatment,the Heptanal concentration and P.xylostella sex did not showed the interaction effect,and both female and male P.xylostella had the similar EAG response intensity and trend.(2)In our tested three specific isothiocyanate semiochemicals,factors that contain the concentration of Allyl isothiocyanate,2-Phenylethyl isothiocyanate,and Methyl isothiocyanate,the P.xylostella sex and age,were all influence the EAG responses of P.xylostella,and some of these factors had interaction effects on the EAG responses of P.xylostella.In Allyl isothiocyanate treatment,EAG responses of female P.xylostella firstly enhanced with the increasing concentration of Allyl isothiocyanate,and then reached the highest value in 10μg/μL Allyl isothiocyanate,and after that weakened with the increasing concentration of Allyl isothiocyanate.The EAG responses of male P.xylostella to Allyl isothiocyanate were enhanced with the increasing concentration of Allyl isothiocyanate.In 2-Phenethyl isothiocyanate,and Methyl isothiocyanate treatments,the EAG responses of both female and male P.xylostella were enhanced with the increase of the semiochemicals concentration,and the degree of enhancement of EAG responses in females P.xylostella was larger than in males.(3)In our tested two main female P.xylostella sex pheromone components semiochemicals,age did not influence the EAG responses of P.xylostella to(Z)-11-hexadecenal,but significantly influence that to(Z)-11-hexadecenyl acetate.The concentration of the two sex pheromone components and sex had interaction effect on EAG responses of P.xylostella.The EAG response values of male P.xylostella to(Z)-11-hexadecenal and(Z)-11-hexadecenyl acetate were significantly higher than that in female,and were enhanced with the increase of the(Z)-11-hexadecenal and(Z)-11-hexadecenyl acetate concentration.While the EAG response of female P.xylostella to(Z)-11-hexadecenal and(Z)-11-hexadecenyl acetate maintained in a low value,and did not change with the increase of the two semiochemicals concentration.(4)Body size of P.xylostella did not influence the EAG responses of both female and male P.xylostella to all tested volatile semiochemicals.2.The choice behavior of P.xylostella to semiochemicals(1)The concentrations of the four tested general semiochemicals could significantly influence the choice behavior of P.xylostella,and in Heptanal treatment,P.xylostella sex and age had interaction effect on the choice behavior of P.xylostella.The details were list:(1)the choice behavior of both female and male P.xylostella to cis-3-Hexen-1-ol was decreased with the increase of the concentration of cis-3-Hexen-1-ol.(2)Three day old female and six day old male P.xylostella showed the positive and negative choice behavior to 0.1 μg/μL Heptanal,respectively.Three day old male P.xylostella showed negative choice behavior to 1 μg/μL Heptanal.Four day old and seven day old male P.xylostella showed negative and positive choice behavior to 10 μg/μL Heptanal,respectively.One to seven day old female and one to five day old male P.xylostella showed little choice behavior to 100 μg/μL Heptanal.(3)The choice behavior of female P.xylostella to trans-2-Hexenal was decreased with the increase of the concentration of trans-2-Hexenal.The male P.xylostella showed negative choice behavior to 100 μg/μL trans-2-Hexenal.(4)Female P.xylostella did not show choice behavior to all tested concentrations of trans-2-Hexenol.The choice behavior of male P.xylostella to trans-2-Hexenol was decreased with the increase of the concentration of trans-2-Hexenol.(2)The concentrations of the three tested specific semiochemicals could significantly influence the choice behavior of P.xylostella.In Allyl isothiocyanate and 2-Phenethyl isothiocyanate treatments,P.xylostella sex and age had interaction effect with the two semiochemicals concentratons.The details were list:(1)one day and five day old female P.xylostella showed positive choice behavior to Allyl isothiocyanate.Four day old male P.xylostella showed positive choice behavior to Allyl isothiocyanate.Female P.xylostella showed positive choice behavior to 1 μg/μL and 10 μg/μL Allyl isothiocyanate.Male P.xylostella showed positive and negative choice behavior to 1 μg/μL and 100 μg/μL Allyl isothiocyanate,respectively.(2)female and male P.xylostella showed positive and negative choice behavior to2-Phenethyl isothiocyanate,respectively.Female P.xylostella showed significantly positive choice behavior to 1 μg/μL and 10 μg/μL 2-Phenethyl isothiocyanate.Male P.xylostella showed significantly negative choice behavior to 100 μg/μL 2-Phenethyl isothiocyanate.(3)The choice behavior of female P.xylostella to Methyl isothiocyanate was firstly increased with the increase of Methyl isothiocyanate concentration,and was decreased with the increase of Methyl isothiocyanate concentration,which was bigger than 1 μg/μL.The choice behavior of male P.xylostella to Methyl isothiocyanate was decreased with the increase of Methyl isothiocyanate concentration.(3)The two main sex pheromone components(Z)-11-hexadecenal and(Z)-11-hexadecenyl acetate had different effect on choice behavior of P.xylostella.The details were list:(1)Female P.xylostella had negative choice behavior to 100 μg/μL(Z)-11-hexadecenal.Male P.xylostella just had positive choice behavior to 1 μg/μL(Z)-11-hexadecenal.(2)Female P.xylostella had no choice behavior to all tested concentration of(Z)-11-hexadecenyl acetate.(3)Male P.xylostella had significantly positive choice behavior to 0.1 μg/μL,1 μg/μL,and 10 μg/μL(Z)-11-hexadecenyl acetate.The results suggest that(Z)-11-hexadecenyl acetate had wider efficient concentration range to induce posititive choice behavior of male P.xylostella,and might be play the dominant role main in P.xylostella sex pheromone trapping male P.xylostella in fields.3.the trapping and egg laying stimulation effects of semiochemicals on P.xylostellaTo evaluate the effects of specific concentration of cis-3-Hexen-1-ol and Allyl isothiocyanate on the trapping efficiency and egg laying stimulation of P.xylostella,we recorded the adult P.xylostella catch number on cis-3-Hexen-1-ol and Allyl isothiocyanate loaded traps,and daily egg laying number on specific pakchoi Brassica chinensis plants.The results showed that during the consecutive 11 day survey,the total catch number of P.xylostella in traps loaded with 0.1μg/μL cis-3-Hexen-1-ol or 1μg/μL Allyl isothiocyanate was less than three.In 1μg/μL Allyl isothiocyanate treatment,the daily egg number laying on pakchoi plant next to the Allyl isothiocyanate at the 1st,2nd,3rd,6th,7th,8th,9th,10 th,11th day,was larger than that laying on a random pakchoi plant in the green house.This difference reached significance level on the 10 th and 11 th day.In 0.1μg/μL cis-3-Hexen-1-ol treatment,the daily egg number laying on pakchoi plant next to the cis-3-Hexen-1-ol at the 1st,2nd,3rd,4th,5th,6th,7th,9th,10 th,11th day,was larger than that laying on a random pakchoi plant in the green house.This difference reached significance level on the 2nd,3rd,4th,day.Our results suggest that cis-3-Hexen-1-ol and Allyl isothiocyanate had the potential to stimulate P.xylostella laying eggs at one place,even though these semiochemicals had no trapping capability on adult P.xylostella.Based on our results,we made two hypotheses.One is that cis-3-Hexen-1-ol and Allyl isothiocyanate have the ability to lure P.xylostella at long distance,and play no role in P.xylostella host plant location and landing at close range.The other hypothesis is that cis-3-Hexen-1-ol and Allyl isothiocyanate play no role in P.xylostella host plant searching and location,but have the ability to stimulate the P.xylostella around them to lay more eggs. |
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