| Spodoptera frugiperda is a phytophagous pest with a wide host range,high migratory ability and high fecundity,which has posed a serious threat to crop production in China after invading China.Although chemical control is currently the most important emergency control measure to control the occurrence of S.frugiperda in China,the management experience of S.frugiperda in the world has shown that biological control is one of the most effective control means.Therefore,it will certainly become a necessary support of the integrated management strategy of S.frugiperda in China.Based on the investigation of the natural enemy species of S.frugiperda in corn fields in Yangling District,Shaanxi Province,we found S.frugiperda larvae parasited by Cotesia ruficrus and investigated the ontogeny of C.ruficrus,the selectivity to different host instar larvae,the effects of different instar larvae and different parasitic times on the growth,development and longevity of C.ruficrus,and the effects of exogenous nutrients on the longevity of the parasitoid adults.Finally,we evaluated the parasitic potential of C.ruficrus on the larvae of S.frugiperda using functional response.The main results were as follows:1.There are four predatory natural enemies and three parasitoids natural enemy species of S.frugiperda found in corn fields in Yangling District and surrounding area in Shaanxi Province,namely,Propylaea japonica,Harmonia axyridis,Coccinella septempunctata,Arma chinensis,Campoletis chlorideae,C.ruficrus,and a parasitoid belonging to the subfamily Microgastrinae.2.The ontogeny of C.ruficrus included egg,larva,pupa and adult.The egg was gourd-shaped and had a pedicle.The larvae were divided into three instars:the first instar had a pair of keratinized mendibles,the second instar had developed caudal sac,and the third instar had a shrunken caudal sac.The pupa was wrapped into a cocoon with white silk,and the pupa cuticle gradually blackened and eventually eclosion.The adult of C.ruficrus had a black body,and the middle part of its abdomen was yellowish-brown and the antennae were dark brown.The feet were yellowish-brown,and the part of the hind feet close to the body,the ends of femur and tibia,and the tarsal and pretarsus were black.The female had needle-like ovipositor at the end of the abdomen.3.The supplement nutrition of honey water and sucrose water increased the longevity of C.ruficrus adults.In the 10%to 40%concentration range,the longevity was significantly prolonged with the increase of honey water concentration,but the concentration of sucrose water had no significant effect on adult longevity.4.The parasitoid parasitized 1st-3rd instar larvae of S.frugiperda,and hardly parasitized 4th and above instars.The parasitoid had higher parasitic rate on the 1st and 2nd instar larvae and lower parasitic rate for 3rd instar larvae,but there was no significant difference among them.There was no significant difference in the developmental period,emergence rate of cocoons,sex ratio,adult longevity,and body size of the parasitoid after parasitizing the 1st,2nd,or 3rd instar larvae of S.frugiperda.The parasitic times of C.ruficrus had no significant effect on the egg-adult development duration and eclosion rate of the parasitoid,but the increase of parasitic times reduced the sex ratio,adult longevity,and body size of the parasitoid.5.The functional response of C.ruficrus to the 2nd instar larvae of S.frugiperda accorded with Holling II model.When the host density was from 0 to 15,the parasitic rate increased with the increase of host density;after the host density reached 15,the parasitic rate tended to be stable.The fitting Holling II functional response disc equation was Na=1.043N0/（1+0.059N0）,with an attacking coefficiency of 0.043,a handling time of 1.368h,and a maximum daily parasitized hosts of 17.5.In conclusion,the natural enemy species of S.frugiperda in cornfields in Yangling District and surrounding areas in Shaanxi Province are relatively abundant.C.ruficrus is a natural enemy of S.frugiperda,which can parasite the 1st to 3rd instar larvae of S.frugiperda,and has a high parasitism rate and good control ability to the 2nd instar larvae.The parasitic times on host larvae can affect the developmental period of the parasitoid and characteristics of eclosion adults.Supplementary nutrient has a significant effect on the longevity of the parasitoid.These results suggested that the parasitoid has a certain control effect on the occurrence of S.frugiperda,and should be protected and utilized.This study not only provides a theoretical basis for the conservation and utilization of natural enemy resources of S.frugiperda,but also lays a foundation for the large-scale propagation and application technology development of C. ruficrus. |
