Effects Of Sucrose And Sinigrin On Feeding Preferences And Gustatory Perceptions Of Caterpillars In Two Helicoverpa Species

The cotton bollworm Helicoverpa armigera(Hübner)(Lepidoptera: Noctuidae)and the oriental tobacco budworm Helicoverpa assulta(Guenée)are closely related species and can be hybridized and backcrossed in the condations of laboratory to produce viable offspring.H.armigera is a true agricultural pest with a general breadth whicn could feeds on at least 161 plant species in 49 plant families,including cotton,sweet corn,tobacco,sunflower,hot pepper and so on.On the contrary,H.assulta is a specialist with a narrow host plant range,and mainly feeds on plant species in the Solanaceae such as tobacco,hot pepper,and several Physalis species.Then,it is valuable to investigate the host factors contributing to the difference of host ranges between the two Helicoverpa species.It is also evolutionary importance to investigate the functions of phagostimulants and deterrents on the feeding preference of herbivorous insects.In this present paper,the functions of the a phagostimulant sucrose and a deterrent sinigrin in the process of feeding preference behaviors of the two Helicoverpa caterpillars were investigated by two choices assay and the mechanisms of gustatory perception for the two compounds were investigated by using single sensillum recording.Effects of sucrose and sinigrin on the feeding preference of two Helicoverpa speciesThe feeding preferences for sucrose-treated leaf discs and sinigrin-treated discs or mixtures of two compound-treated leaf discs were investigated by using two-choice leaf assay.The results show:(1)Sucrose could significantly induce the feeding preference of caterpillars of both Helicoverpa species.Compared to the specialist species H.assulta,the lowest threshold of inducing the feeding preference for sucrose in the generalist H.armigera is a bit high.(2)Sinigrin could significantly inhibit the feeding preference of caterpillars in both Helicoverpa species.The lowest threshold of sinigrin to inhibit the feeding preference between the two species is similar.(3)The effects of mixtures of sucrose and sinigrin on the feeding preference of two species exhibit a dynamic pattern.Firstly,the relatively high concentration of sucrose in mixtures could counteract the influence of inhibiting activity of sinigrin in the feeding preferences of caterpillars.When the concentration of sinigrin in mixtures is fixable,the feeding preference for mixture-treated leaf discs changes from negative to preferring with the concentration of sucrose increasing in mixtures.(4)In contrast,relatively high concentration of sinigrin in mixtures also could counteract the influence of stimulating feeding of sucrose in the feeding preferences of caterpillars.When the concentration of sucrose in mixtures is fixable,the feeding preferences for mixture-treated leaf discs change from positive to inhibiting with the concentration of sinigrin increasing in mixtures.(5)The effects of sucrose on the feeding preference of H.assulta is a little slight higher than on that of H.armigera,and the effects of sinigrin on the feeding preference of H.armigera is a little slight higher than on H.assulta.Effects of sucrose and sinigrin on the gustatory perception of two Helicoverpa speciesThe gustatory receptor neurons of caterpillars of the two Helicoverpa species were investigated in the electrophysiological responses to sucrose,sinigrin and mixtures of the two compounds by using single sensillum recording.The results show as followed.(1)The lateral sensillum of both the two Helicoverpa species contains a sucrose sensitive receptor neuron and a sinigrin receptor neuron.Either the two neurons exhibit a dose-dependent response pattern in the response to sucrose or to sinigrin.(2)The responses of receptor neuron in lateral sensillum to sucrose or sinigrin lonely were compared between the two Helicoverpa species.Results show the specialist H.assulta exhibit a slight higher response than the generalist H.armigera in the response to sucrose,whereas the generalist H.armigera exhibits a slight higher response than the specialist H.assulta in the response to sinigrin.(3)The synergistic interactions of sucrose-sensitive neuron and the sinigrin-sensitive neuron were investigated by testing the responses of sensillum to mixtures of the two compounds with different concentrations.The results show that the presence of sinigrin in mixtures could reduce the impulse frequency of the sucrose-best neuron in caterpillars of both Helicoverpa species.Similarly,the presence of sucrose in mixtures could reduce the impulse frequency of the sinigrin-best neuron in caterpillars of the two Helicoverpa species.(4)The influence of sinigrin on the sensitivity of sucrose-best neuron is higher in the generalist H.armigera than in the specialist H.assulta.(5)Whereas the influence of sucrose on the sensitivity of sinigrin-best neuron is higher in the specialist H.assulta than in the generalist H.armigera.Integrated comparison of feeding behaviors and gustatory perception in the two speciesThe present results show sucrose and sinigrin or mixtures of the two compounds exhibit a similar effect pattern on caterpillars of the two species in both feeding hebaviors and gustatory perception.The effects of the two compounds mainly lie in the difference of context degree of each compound on the Helicoverpa species.The effects of sinigrin on th generalist H.armigera is higher than that on the specialist H.assulta,whereas the effects of sucrose on the specialist H.assulta is higher than on the generalist H.armigera.In addition,our results show the trade-off of feeding behaviors and the gustatory perceptions of the two closed Helicoverpa species to the phagostimulant and the deterrent,which may contribute to the understanding of the evolutionary theories of taste,behaviors,feeding habits of inects and to the pest management using insect taste.