| Eucryptorrhynchus scrobiculatus Motschulsk and E.brandti(Harold)are two closely related species of the same genus.They can coexist on their single host Ailanthus altissima(Mill.).The larvae of E.scrobiculatus feed on the root of A.altissima,while the larvae of E.brandti feed on the trunk of A.altissima.The feeding sites of most insect larvae are usually closely related to the oviposition sites of female adults.In this study,based on the differences in the feeding sites of the two weevil larvae,the oviposition behavior and oviposition sites of the two weevils were carried out.The internal and external rostrum morphology of the two species were compared using the process of oviposition behavior as a clue.We seek to show the relationships between specific oviposition sites and morphological traits of the investigated weevils from the perspective of "structure-biological role",discuss the ecological morphological adaptation mechanism between them,and try to explore the causes of these structural changes by looking for genes related to the development of the rostrum of two species.The main results are as follows:1.The oviposition behavior of E.brandti was recorded and described.It was found that the gravid females of E.brandti mainly lay their eggs in the daytime,and the excavation stage was the longest component of the oviposition process.Females showed no obvious preferences in the direction of the body turning during oviposition,with random leftward or rightward rotation having no effect on the process.Oviposition success was positively correlated with excavation time,during the peak period of oviposition,the excavation time can be used as a predictor of the success or failure of gravid E.brandti.2.The oviposition behavior of E.scrobiculatus was recorded,described and compared with that of E.brandti.There was obvious differentiation in oviposition sites between E.scrobiculatus and E.brandti in the field.E.scrobiculatus females laid eggs in the soil near A.altissima and compound leaf petioles,while E.brandti females laid eggs in the trunk of A.altissima,and the eggs in compound leaf petioles did not hatch in the field.3.The allometric relationship between adult rostrum length and body size of the two species was tested.The results showed that there were no interspecific differences in adult female body size to rostrum length allometric relationships,and rostrum length was equally correlated with body size in either species.The increased rostrum length was probably a by-product of the larger body sizes of individuals.4.The internal and external structures of the rostrum of the two species were described in detail.The comparison of morphological results revealed that there were significant differences in the internal and external morphologies of the two rostra,which mainly showed: There were differences in the morphology of mandibles between E.scrobiculatus and E.brandti.The E.scrobiculatus female had one large tooth and one small tooth in each mandible,but the size of the two teeth of each mandible of E.brandti female had little difference;There was no difference in the size of the abductor muscles that control the extension of the mandibles between the two weevils,but there were significant differences in the size of the adductor muscles that control the contraction of the mandibles between the two weevils;The whole rostrum of E.scrobiculatus female had convex edges,concave grooves,bristles and pores.While the whole rostrum of E.brandti female was smooth,with few bristles and pores;The rostral cuticle thickness of the two weevils was uneven in the entire rostrum.All these reflected the response of the rostrum structure to oviposition sites in E.scrobiculatus and E.brandti.5.Nine Hox genes of E.scrobiculatus and E.brandti were identified,respectively.Expression patterns of Hox genes in egg stage,larva stage,pupa stage and adult stage of E.brandti were examined by RT-q PCR.The results showed that all Hox genes were highly expressed in the egg stage,which proved that Hox genes play an important role in the embryonic development of E.brandti.It lays a foundation for the further study of the role of Hox genes in the rostrum development of the two species.In summary,this study showed that structural differences that reflect the functional potential ovipositional tactics of rostra in the outer and inner morphology to adapt to ecological demands of oviposition by studying the oviposition behavior,oviposition sites and ecological morphology adaptation mechanism of the E.scrobiculatus and E.brandti,which allow E.scrobiculatus females laid eggs in the soil near A.altissima and compound leaf petioles,E.brandti females laid eggs in the trunk of A.altissima.The different oviposition sites of the two species females allow the larvae to feed on different areas,reducing the competition for the same host resource A.altissima and promoting the coexistence of the two species.These results provided new insights for the coexistence of the two weevils in the single host A.altissima. |
