Reproductive Characteristics And Parasitism Potency Of Campoletis Chlorideae

Campoletis chlorideae Uchida is the dominant parasitic wasp controlling Helicoverpa armigera(Hubner),a major crop pest in the world.It plays an important role in controlling many agricultural insect pests of Noctuidae and is an important biological control factor.It is widely distributed in China and is of great value for protection and utilization because of its excellent characteristics of parasitic wasps:In order to improve the biological control effect and parasitism potency of C.chlorideae,the reproductive characteristics of this wasp were studied firstly.The morphological changes of testicular development,spermatogenesis,ovary development and oogenesis were observed in detail.The oviposition rhythm of this wasp was revealed on the basis of its oviposition characteristics,reproductive organ development and gametogenesis.Furthermore,the factors affecting the fertility of C.chlorideae were systematically investigated,and the internal relationship between host age,parasitoid body size,number of ovary tubes,number of fertile eggs and fertility was identified.In addition,the control efficiency of C.chlorideae against the major invasive pest of Spodoptera frugiperda in China was studied.The following results were obtained:l.The testicular development and spermatogenesis in Campoletis chlorideaeSex determination is based on the haploid-diploid in parasitic wasps.The females only deposit male progenies in the absence of males.Therefore,the males play key roles in determining the offspring sex ratio.However,there is a lack of research on the reproductive characteristics of male parasitoid,no related work was done on the biological control agent Campoletis chlorideae Uchida.In this study,the morphological changes of testicular development and spermatogenesis in each developmental stage were observed.The results showed that the internal reproductive organs of C.chlorideae mainly consisted of a pair of testes,paired of elongated narrow vas deferens,a pair of accessary glands,a pair of seminal vesicles,and a ejaculatory duct.A pair of testes is separate in larval stage.The development of a pair of testes begins at the larval stage.A pair of yellow testes develops rapidly and the testicular volume increases significantly in the pupal stage being accompanied by the deposition of pigments.The testicular index increased from 30678.47±6085.36μm2 in larval stage to 58138.63±9553.63μm2 in pharate adult.At the same time,the internal spermatogenic vesicles undergo spermatogenesis.The two mature testes are secondarily fused into a single structure during the later pupal stages.At the time of eclosion,a large number of spermatozoa have accumulated in the fused testes to ensure insemination as soon as emergency,indicating that the sperm development is precocious.The above results could provide a theoretical basis for improving the mating success and breeding efficiency of C.chlorideae.2.Ovarian Development and oogenesis in Campoletis chlorideaeTo investigate the ovarian development and oogenesis in Campoletis Chlorideae Uchida can provide basis for its use in improving biological control effects.In this paper,the structure and development dynamics of the female reproductive system of C.chlorideae were studied under microscope.The anatomy results showed that the internal reproductive system of female C.chlorideae was mainly composed of a pair of ovaries,a pair of laternal oviduct,common oviduct,spermatheca,alkaline gland,and the acid gland with reservoir.The length of ovary increased from 264.30±45.60μm in mature 4th instar larva to 1124.92±129.38μm in adult larva.The width of ovary increased from 186.61 ±35.96μm in mature larva to 334.588±54.39μm in adult larva.The ovarian index(the length x width of the ovary)varies with the age of the parasitic wasp,The 50440.39±18197.01μm2 of the end of larvae increased to the adult stage 381781.40±38442.83μm 2.The same trend occurred in other reproductive organs.No egg chamber was found in the early stage of the pupa e of this parasitoid.Until the end of the pupae,the egg chamber was formed.During the period of pharate adult,trophoblast and oocytes can be seen in the ovarian tube,and in adult stage,mature eggs are already available.The ovaries of parasitic wasps have many pairs of ovarian tubes,in which the oocytes are close to the trophoblast,and they both are connected to form an egg chamber,which can be divided into three periods:1.trophoblasts are larger than oocytes(before 4d of pupa stage)2.Trophoblast equals oocytes(Pupa stage 5d)3.Trophoblast is smaller than oocytes(after hidden adult period).3.Oviposition rhythm in parasitization of Helicoverpa armigera larvae by the larval parasitoid Campoletis chlorideaeTo make clear of the oviposition rhythm of Campoletis chlorideae is very important in breeding and making use of this biological control agent efficiently.In the laboratory at 25±2℃,60%-80%%RH,and 12:12 h light:dark,Oviposition activities of parasitizing females occurred mainly during photophase.However,under constant dark or light,these circadian rhythms were changed a little.This suggests that the observed rhythms can be modified by the direct environmental influence.Under natural conditions,such a flexible oviposition rhythm may be of advantage for these parasitoids enabling them to use any opportunity for reproduction.In biocontrol practice,the lability of parasitization rhythms may enable C.chlorideae females to adapt immediately to any new light-dark regimes.While parasitizing at emergence days three,females could lay 55.2±16.7 eggs after 6-7 days emergence.The female emergency age at parasitizing had significant effect on their egg laid.The number of egg laid by younger female was higher than that of older ones.This suggests that younger females had more opportunity to realize their max fecundity.4.Biological factors affecting fecundity of Campoletis chlorideaeCampoletis chlorideae is the dominant natural enemy for field control of Helicoverpa armigera in China and India.In order to better develop and utilize the biological control factor,the research on reproductive characteristics is the key.The ability to control pests is determined by the fecundity of the wasp,and egg production comes from the ovariole.Therefore,this paper systematically studied the biological factors affecting fecundity,such as the influence of host instar on wasp body size,ovariole number,egg loads and fecundity,as well as the relationship among these factors,under the indoor culture conditions of 25±2℃,RH60%-80%,1500-2000LX.Firstly,the characteristics of the ovariole number of the wasp were determined,the average number of ovariole number was 31.4±1.1.Then,according to the different host instar,i.e.the host size represented different nutritional quality and immunocompetence.According to the wasp to the host egg selection,the most suitable host instar was selected,and It was found that the adult wasp size was related to the host age.The wasp preferred parasitic larvae of 2-3 instar.Compared with the 1st and 3rd instar hosts,the wasps born from the 3rd instar were not only large in size,but also had a large number of ovary tubes.A large ovariole number represented a high egg loads,which was reflected in fecundity,namely high parasitic ability to host.The results showed that the reproductive ability of C.chlorideae reared from the 3rd instar was significantly better than that from the 1st instar.Therefore,wasp body size can be used as an important index and indicator to evaluate wasp fecundity.5.Parasitism potential of Campoletis chlorideae on the invasive Spodoptera frugiperdaTo make clear of the parasitism potency,the parasitic ability and preference indexes of Campoletis chlorideae to different larval instars of Spodoptera frugiperda were firstly explored in the present study.Furthermore,the preference of C.chlorideae to two host insects between Helicoverpa armigera and S.frugiperda,the quality of the offsprings from these two parasitzed hosts,and cage experiment outdoor were investigated.The results showed that C.chlorideae could parasitize the 1st,2nd and 3rd instars of S.frugiperda larvae,and preferred to the 2nd and 3rd larval instars.Compared with the optimum host H.armigera,the parasitism rate and preference index of this ichneumonid to S.frugiperda was 65.7%and 0.43,lower than 87.1%and 0.57,respectively.However,the total fecundity had no significant difference.The body size and the number of ovarioles of the offsprings from parasitized S.frugiperda were lower than those from H.armigera.The cage experiment outdoor showed that the parasitism rate of this wasp to S.frugiperda feeding on maize leaves was up to 72.5%,and the offspring could complete development normally and parasitize successfully.This study firstly provides sufficient basis for the control of invasive insect pest S.frugiperda by native natural enemy C.chlorideae,and the protection,breeding and release of this wasp will be strengthened in the future.