Effect Of Odor Source And Walking Substrate Angel On Helicoverpa Armigera Larval Walking Behavior And Odor Exposure Experience Effects At Generational Level

Helicoverpa armigera(Hübner)is a worldwide polyphagous pest.It mainly damages as larvae.Although the feeding positions of newly emerged larvae were dominantly depended on female oviposition,the larvae still need to approach to the most suitable feeding sites through intra-plant crawling.Additionally,effect of odor exposure on larval movement has been demonstrated,but the effect of long-term odor exposure at one stage on the movement behavior of subsequent stages has not been elucidated.Therefore,I tested the approaching response of H.armigera 3rd instar larvae to plenty of plant-derived volatiles on a LC-300 Track Sphere,and then I tested the effects of different combinations of odor sources and angles between walking substrate and horizontal direction on the walking direction and walking distance of newly born larvae.Finally,I explored the effect of odor exposure on subsequent stage at a generational level.The main results are summarized as follows:(1)The approaching response of third instar larvae to 17 terpenes,nine green leaf volatiles,eight aromatic compounds,four long-chain fatty acids,three repellent or deterrent compounds,as well as eight other compounds was tested on a LC-300 Track Sphere.The result shows that six original parameters(track length,vector length,mean walking speed,straightness,upward length,upward straightness)could by simplified as two principal components as activity factor and attractivity factor via principal component analysis.The most active compounds eliciting activity factor of the larvae were linalool,salicylaldehyde,and E-2-hexenal,and the strongest compounds eliciting attractivity factor were nonyl acetate and geranyl acetate.Integrated the two factors,the most active compounds for attracting H.armigera larvae were geranyl acetate,nonyl acetate,E-2-hexenal,carvacrol,salicylaldehyde,myrcene,and β-caryophyllene.(2)Effect of odor source and angles between walking substrate and horizontal direction on movement of newly born larvae.The result shows that the larvae exhibited strong positive geotaxis.Ever-increasing the angle,downward walking distance was farther,which shows a linear relationship.Odor sources placing above did not affect this positive geotaxis.When these odor sources were placed downward,two synthetic blends(see in the text)could enhance positive geotaxis,while cis-3-hexenyl acetate could weaken positive geotaxis.(3)Effects of odor exposure of seven plant-derived volatiles(geranyl acetate,nonyl acetate,E-2-hexenal,carvacrol,β-caryophyllene,cis-3-hexenyl acetate,and phenylacetaldehyde)on movement of subsequent stages.The results show that behavioral plasticity of the newly born larvae was stronger than that of the other stages(odor exposure was conducted at the egg stage),all but nonyl acetate could produce significant induced preference.Among them,all but geranyl acetate and nonyl acetate could elicit significant olfactory preference of non-experienced larvae.After odor exposure,the innate olfactory preference of cis-3-hexenyl acetate,phenylacetaldehyde,β-caryophyllene,E-2-hexenal was masked,the innate preference of carvacrol was further strengthened,and the behavioral neutral compound,geranyl acetate,induced significant positive olfactory preference of the larvae.When odor exposure was conducted at the third instar during rearing and odor preference was tested at the fifth instar,non-experienced larvae only showed significant olfactory preference to cis-3-hexenyl acetate,the other six compounds were behavioral neutral.Between-group comparison shows that only β-caryophyllene(attraction was strengthened)and nonyl acetate(induced avoidance)could produce significant induced preference.cis-3-Hexenyl acetate could also elicit significant preference of the experienced larvae,but it has not significant induced effect.When odor exposure was conducted at pupal stage and odor preference was tested at adult stage,the induced effects of both sexes were summarized as follows.For females,only geranyl acetate and phenylacetaldehyde produced significant induced preference.Within the non-experienced female group,only geranyl acetate could elicit significant avoidance,carvacrol and β-caryophyllene exhibited significant attractive activity,while the other compounds were behavioral neutral.After odor exposure at pupal stage,the olfactory preference of phenylacetaldehyde was significantly weakened(although the within-group difference of the experienced group was still not significant).The innate preference of carvacrol as well as the innate avoidance of geranyl acetate was masked.The significant olfactory preference of β-caryophyllene was remained in the experienced group(no significant induced effect).For males,only cis-3-hexenyl acetate exhibited significant induced effect.However,this induced effect was so strong that the significant attractive activity was reversed to significant repellent activity.Phenylacetaldehyde exhibited significant repellent effect on non-experienced group,but after exposure at pupal stage,this compound changed to behavioral neutral to experienced males(no significant between-group difference).Altogether,I screened seven strong attractive plant-derived odors for larvae: geranyl acetate,nonyl acetate,E-2-hexenal,carvacrol,salicylaldehyde,myrcene,and β-caryophyllene via service sphere bioassay.Generally,the third instar larvae exhibited positive geotaxis in cotton-line simulated bioassay,and the downward walking distance was positively related to the cross-angle between walking substrate and horizontal direction.The olfactory plasticity of neonates was strongest.The strength and direction of induced effect of odor exposure experience was depended on exposed odor and has no generic rule.