Study On The Floral Cues Used By Helicoverpa Armigera Moths

Helicoverpa armigera(Hübner)is one of the most serious insect pest species in North China.Previously,we have screened out an effective blend of floral attractant for trapping noctuid moths.Therefore,if a suitable visual cue(color or pattern)is added to this blend,we expect that the attractiveness will be improved further.However,references about the floral cues used by H.armigera moths during flower-visitation are relatively lack.In this paper,the author simulated the pattern of natural flowers by using novel combined technologies: n-petaled rose curve and radial gradient.The experimental items include:(1)preference of both sexes to eight plain-colored flower models(red,green,blue,magenta,black,white,cyan,and yellow);(2)the effect of radial gradient on moth preference;(3)the effect of corolla petals on flower-visitation;(4)optimal combination of visual cues and olfactory cues;(5)learning performance of color appetive conditioning in this moth;(6)cue-selective learing of dual conditioned stimuli(visual cues and olfactory cues).The main results are summarized as follows:1.Blue and cyan are two preferred colors shared by both males and females among the eight tested flower models.The males mostly preferred magenta and cyan colors,followed by blue color;while the females showed strong preference to blue and green,followed by cyan.2.Helicoverpa armigera moths showed a stronger preference to cyan-blue radial gradient pattern than its two component colors,especially in males.When data from males and females are pooled,the most preferable pattern will be the cyan-blue radial gradient pattern.3.When the cyan-blue radial gradient patterns with different corolla petals(4,8,and 12)were compared within each sex,there was no significant effect of corolla petal number on approaching response of the moths,although the four-petaled pattern was chosen slightly more often than the other two patterns.4.A floral attractant blend for trapping noctuid moths(total dose: 2 ?L;the ratio of phenylacetaldehyde,benzyl acetate,and salicylaldehyde was 26 : 15 : 2)was chosen as test olfactory cue and tested the effect of the addition of olfactory cue to visual cue on the response of both sexes of H.armigera moths.The following four treatments are placed together in a bioassay setup:(1)white-blue radial gradient pattern;(2)cyan-blue radial gradient pattern;(3)white-blue radial gradient pattern plus floral attractant;(4)cyan-blue radial gradient pattern plus floral attractant.The result shows that at least in our test environment,the males and the females showed differential responses about their primary sensory modality for using in flower-visitation: the males visited an artificial flower mainly depended on olfactory modality,while the females mainly depended on visual modality.However,in this test,the white-blue radial gradient pattern was mostly preferred by both sexes.5.Color appetitive conditioning.Two colors,yellow and blue,were used as conditioned stimuli,respectively.Within each sex,a na?ve group,a color-exposure group,and an associative learning group were established,respectively.After 24 h training,the choice responses of the three groups within each sex to yellow vs.blue were tested.When blue was used as conditioned stimulus,the preference of trained females to blue was significantly increased,but it was not the true when yellow was used as conditioned stimulus,suggesting that the females learned faster to their innate preferred color.The differential conditioning procedure could not improve the learning performance of the females,but it could improve that of males.Non-reward learing could be occurred in the color exposure groups of both sexes.6.cue-selective learning of dual conditioned stimuli.Yellow and blue were chosen as visual conditioned stimuli,respectively,and salicylaldehyde and benzyl acetate were chosen as olfactory conditioned stimuli,respectively.One of the two visual cues and one of the two olfactory cues were combined to provide dual conditioned stimuli.The full combinations of these cues were tested in each sex.After training,the choice responses of test insects between yellow and blue as well as between salicylaldehyde and benzyl acetate were tested.The results show that when yellow and salicylaldehyde were combined,the females mainly visited the reward depending on visual cue(yellow).When yellow and benzyl acetate were combined,the females could use both cues as the indicators of artificial flower.When blue and salicylaldehyde were combined,females showed a stronger preference to blue when compared with the na?ve group.When blue and benzyl acetate were combined,both sexes could not learn the associative relationship between these cues and the sucrose solution.When yellow and salicylaldehyde were combined,the trained males mainly search for the nectar depending on the olfactory cue(salicylaldehyde),similar result was obtained when blue and salicylaldehyde were combined,suggesting that the olfactory cue could be learned easier than visual cue.In summary,both sexes of H.armigera moths prefer to radial gradient patterns.They showed fairly strong preference to the white-blue-and the cyan-blue-radial gradient patterns.The two sexes showed a differentiation as for their primary sensory modality during flower-visitation.Finally,the differentiation was corresponding to their cue-selective learning performance,i.e.,the moths exhibited a better learning performance to the conditioned stimulus used as their primary sensory modality.