| The flying spider-monkey tree fern,Alsophila spinulosa is an ancient relict plant.In recent years,a large number of herbivorous insects(Phthonoloba viridifasciata and Rhoptroceros cyatheae)have been found in A.spinulosa and its congeners Gymnosphaera metteniana var.subglabra,causing the leaf tissue to be nibbled to varying degrees,posing a certain threat to the growth and development of these two plants.In order to clarify the relationship between two kinds of herbivorous insects and different host plants,the host selectivity of two kinds of herbivorous insects to different plants and the growth and development of R.cyatheae larvae feeding on different tender leaves were measured by using the method of laying egg in insect cage and leaf dish method.Comparing the physical and chemical components of leaves(volatile components,water,wax,soluble sugar,soluble protein,total flavonoids,tannin)is of great significance for mastering the population dynamics of insects in the forest and effective pest control.The research results are as follows:1.Host selection in female adults of P.viridifasciata and trend selection in larvae.P.viridifasciata showed a significant oviposition preference to A.spinulosa(P < 0.01),and the adults selected host plants in the following order: A.spinulosa back > A.spinulosa front > G.metteniana var.subglabra back > G.metteniana var.subglabra front,there will also be some eggs on the cage.In contrast to green leaf discs,whether in light or darkness,the every age of larvae of P.viridivasciata can accurately locate the host plant.Within 30 min,there was no significant difference in the preference trend number of the 2nd to 4th instar larvae to the two host plants,but the preference trend number of the 1st instar larvae to A.spinulosa was significantly higher than that of G.metteniana var.subglabra(P < 0.05).The search time of A.spinulosa by the 1st and 4th instars was significantly lower than that of G.metteniana var.subglabra(P <0.05).There was a difference between the preference selection within 30 min and the successful selection after 12 h.After 12 h,the number of successful selection of A.spinulosa was significantly higher than that of G.metteniana var.subglabra(P <0.05).2.Feeding selection and behavior of P.viridifasciata larvae.The 1st to 4th instar larvae of P.viridifasciata showed a significant preference to A.spinulosa feeding(P <0.01),and the feeding amount of A.spinulosa was 2.54,2.80,1.73,2.72 times than that of G.metteniana var.subglabra.The percentage of larvae on A.spinulosa was higher than G.metteniana var.subglabra at 1 to 12 h after inoculation,and larvae would transfer between host ranges with the extension of observation time;The feeding behaviors of larvae are divided into six behaviors: searching,identification,leaving,feeding,cleaning and resting.3.Host selection and adaptation of R.cyatheae.R.cyatheae showed a significant oviposition preference to G.metteniana var.subglabra on laying eggs(P < 0.05);Eggs developed on A.spinulosa and G.metteniana var.subglabra had no significant difference in hatching rate,but the egg stage developed on G.metteniana var.subglabra was significantly lower than that of A.spinulosa(P < 0.01).The larvae also preferred to feeding G.metteniana var.subglabra(P < 0.01),and the feed intake of the 2nd to 5th instars of G.metteniana var.subglabra was 2.42,1.43,1.54 and 1.44 times than that of A.spinulosa after 4 h.There was no significant difference in the larval development stage,emergence rate,and adult lifespan between the larval feeding on two plants,while the mature larval stage and pupal stage of the larval feeding on A.spinulosa were significantly prolonged(P < 0.01),and the larval survival rate and pupation rate were significantly reduced(P < 0.05).Regardless of which host plant was fed,the sex ratio was close to 1:1,indicating that the host plant had no effect on the male to female ratio.4.Relationship between spawning selection in adults and feeding selection of larvae of P.viridifasciata and R.cyatheae.The amount of eggs laid by P.viridifasciata on different plants were significantly positively correlated with the amount of food consumed by the 1st and 2nd instar larvae under selected conditions(P < 0.05);There was a significant positive correlation with the feeding amount of the 4th instar larvae(P < 0.01).The amount of eggs laid by R.cyatheae on different host plants were significantly positively correlated with the feeding amount of the 4th instar larvae(P< 0.05).5.Chemical composition analysis of A.spinulosa and G.metteniana var.subglabra.The volatile components of A.spinulosa and G.metteniana var.subglabra were analyzed by SPME-GC-MS,and 29 and 26 volatile components were identified from young and old leaves of A.spinulosa,respectively.Eighteen volatile components were identified in young leaves and 26 volatile components in old leaves of G.metteniana var.subglabra.There were 13 volatile components in young leaves of G.metteniana var.subglabra;The chemical constituents of A.spinulosa and G.metteniana var.subglabra leaves were analyzed by organic solvent extraction and temperament combination(SE-GC-MS),and it was found that both of them contained a large number of alkane compounds.Eleven and five different compounds of A.spinulosa and G.metteniana var.subglabra were identified.A.spinulosa had significantly lower water content,waxy content and soluble sugar content than G.metteniana var.subglabra(P < 0.01),but significantly higher content of soluble protein,Total flavonoids and tannin than G.metteniana var.subglabra(P < 0.05).6.Relationship between feeding selection of P.viridifasciata larvae and physicochemical content of A.spinulosa and G.metteniana var.subglabra.The feeding amount of the first,1st,2nd and 4th instars of P.viridifasciata larvae was negatively correlated with water content,wax content and soluble sugar content of leaves(P < 0.05).It was positively correlated with soluble protein content in leaves(P< 0.05).7.Relationship between Feeding selection,growth and development of R.cyatheae larvae and physicochemical content of A.spinulosa and G.metteniana var.subglabra.There was a significant positive correlation between the feeding amount of R.cyatheae’s 2nd to 3rd instar larvae and the water content of their leaves(P < 0.05);The feeding amount of 5th instar larvae is positively correlated with leaf wax(P <0.05)and negatively correlated with soluble protein content(P < 0.05);The feeding amount of 2nd instar larvae was significantly positively correlated with the soluble sugar content in leaves(P < 0.05),while negatively correlated with the tannin content in leaves(P < 0.05).The survival rate of larvae was positively correlated with water content and wax content(P < 0.05),and the pupation rate was positively correlated with wax content(P < 0.05);The survival rate of larvae was significantly negatively correlated with tannin content(P < 0.01);The pupation rate was significantly negatively correlated with tannin content(P < 0.05),while the rest of the growth and development performance was not correlated with the measured physical and chemical substance content. |
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