| Gephyraulus lycantha Jiao&Kolesik is a serious gall-forming pest of Lycium barbarum L.(Solanaceae),a perennial deciduous shrub,whose fruits,known as wolfberry or Goji,are used in traditional Chinese medicine.G.lycantha is a typical gall-forming insect that feeds on the ovary and causes the deformity of the L.barbarum flower bud and the formation of gall.Pseudotorymus jaapiellae Yang et Chen,a main parasitic natural enemy of G.lycantha larva,is an important biological factor controlling the population of G.lycantha.G.lycantha is a typical gall insect,while the female adult of P.jaapiellae could accurately deposite the eggs in the age-appropriate galls induced by G.lycantha.So,how does the female of P.jaapiellae accurately seek,locate,identify and parasitise the larva of G.lycantha in the complex plant habitat?Is there any chemical signal between the parasitoid and G.lycantha that can guide the parasitoid to locate its host?Here,based on the systematic study of the biological characteristics of P.jaapiellae,we analyzed selection preference of the parasitoid for galls at different developmental stages,discussed the main factors affecting host selection of the parasitoid,and preliminarily defined the material basis and the structural characteristics of the receptors for host recognition of the parasitoid.Main results were shown as follows:1.Pseudotorymus jaapiellae,a new natural enemy species of G.lycantha was discovered for the first timeBy investigating the natural enemy communities of G.lycantha in different producing areas of Lycium barbarum in China,a main parasitic natural enemy of G.lycantha larvae was found for the first time,which provided a new natural enemy resource for biological control of G.lycantha.The parasitoid was named Pseudotorymus jaapiellae Yang et Chen by Prof.Yang Zhongqi from the Chinese Academy of Forestry Sciences and Prof.Chen Jun from the Institute of Medicinal Plant Development,Chinese Academy of Medical Sciences.Pseudotorymus jaapiellae belongs to the Toiymidae,Hymenoptera,which has important conservation and utilization value.2.It was confirmed that P.jaapiellae was the dominant parasitoid of G.lycantha,whose parasitism rate was different in different goji plantations.Four types of insects were found in the dissected galls,they were the gall-forming insect G.lycantha,the parasitic and predatory natural enemy of G.lycantha,and hyperparasitoids,respectively.Twelve species of parasitoids were observed in the galls,including P.jaapiellae,Pteromalus janssoni,Aproslocetus calvus,and 9 unidentified species,of which P.jaapiellae was a new species,also was the dominant parasitic wasp of G.lycantha,which accounted for more than 99%of all the parasitoid.The parasitism rate of P.jaapiellae varied greatly in different goji orchards,with the highest parasitism rate reaching 64%-77%in abandoned goji orchards.The parasitism rate of organic goji plantations was followed with value of 14%-70%,and the parasitism rate of conventional goji plantations was the lowest with value of 10%-39%.The use of chemical pesticides seriously affected the parasitism rate of P.jaapiellae.3.The biological characteristics of P.jaapiellae were systematically studied.P.jaapiellae larvae were divided in 5 instars,they overwintered in the galls with mature larvae(76%)or pupae(24%)in the galls.It took 18.2 days to complete the development of one generation for P.jaapiellae.Adults supplied with 10%sucrose water survived longer than that without any food supplementation with average lifespan of 25.2 d in female and 15.4 d in male,respectively.The lifespan of female parasitoids after oviposition was significantly reduced,and the maximum lifespan was only 1/2 of that of non-oviposition females.P.jaapiellae could reproduce either sexually or parthenogenetically,and there was no significant difference in hatching rate and incubation progress between the two reproductive modes.There was a pre-oviposition period with an average of 1.9 days for females.The females in 3-day age laid more eggs than the others with an average of 3.2 eggs in one day.A female parasitoid can lay 17.2 eggs in her lifetime,with 1 to 2 eggs in each gall.In the natural state,the female-male ratio was close to 2:1.The parasitism of G.lycantha larvae by P.jaapiellae was sustainable.After the larvae of P.jaapiellae hatching in the galls,they first paralyze part of G.lycantha larvae in the galls with their mouthparts,and then absorb the host body fluids one by one.Unparalysed larvae of G.lycantha could grow and develop smoothly and leave the gall,thus ensuring their population continuity.4.The age of G.lycantha and the age,nutritional status,mating and learning experience of P.jaapiellae had significant effects on host selection of P.jaapiellae.According to the developmental stages of G.lycantha larvae inside the galls,the galls were divided into flower bud with eggs(1 d after oviposition of G.lycantha adults),young galls(5-8 d after oviposition of G.lycantha adults)and mature galls(9 d or above after oviposition of G.lycantha adults).The host preference of P.jaapiellae to galls at different developmental stages was studied by free selection or restricted selection methods.The results showed that both the number of probing and the number of laying eggs on young gall were significantly higher than those of other treatments(P<0.01),and the selection preference coefficient(CN)was 0.56±0.38,which was significantly different from that of Cn=0(P<0.01).The preference of P.jaapiellae to the young galls indicated that the growth and development of the eggs and larvae of P.jaapiellae were highly consistent with the growth and development of the larvae of G.lycantha their galls in space and time.In the young gall stage,the larvae of G.lycantha began to feed on the ovary,causing constriction at the base of the ovary and fonning a cavity between the ovary and the corolla,providing a living space for the parasitoid.According to the developmental period(2-4 d)of P.jaapiellae eggs and the developmental stage(3-6 d)of G.lycantha young larvae developing to mature and leaving the galls,P.jaapiellae females laying eggs in the young galls could guarantee that the larvae of parasitoids could hatch and paralyze the larvae of G.lycantha before they leaving the galls,can hatch and complete the wasp larvae.Consequently,the parasitoids could get enough food for their growth and development.The age of the P.jaapiellae and other developmental conditions significantly affected their selection and parasitism to the galls.Among them,the probing and laying number of parasitic wasps at different days of age were significantly different.The probing number of 5-day-old females was significantly higher than that of other day-old females,but the laying number of 9-day-old females reached the highest value.The effective oviposition rate of female wasps fed 10%honey water and 10%sucrose water was almost the same,which was significantly higher than that fed with water and starvation control group(P<0.01).However,the number of eggs laid by mating females was significantly lower than that of non-mating females(P<0.01).Learning experience significantly increased the effective oviposition rate of female bees(P<0.01)while decreased the number of female hosts probing.5.It was found that the volatiles emitted from young galls had a significant indicator effect on host recognition of P.jaapiellae.The indirect selection results showed that the volatiles emitted from young galls had a stronger stimulating effect on the probing behavior of P.jaapiellae than that emitted from mature galls when the healthy buds of L.barbarum were used as the probing substrate(P<0.01).Behavior bioassay of P.jaapiellae was conducted with Y-olfactometer,the results showed that female parasitiods showed a significant tendency to the galls induced by G.lycantha(P<0.05),and the attraction tendency of young galls to female wasps was more significant(P<0.001).Ninety-five percent of parasitoids chose young galls,while only five percent chose healthy buds.The volatiles were collected by solid-phase headspace adsorption method and solid-phase microextraction method.The results of GC-MS analysis showed that there were significant differences in the types and release amounts of volatiles between galls at different development stages and healthy buds of L.barbarum.The volatiles collected from galls at different stages and healthy buds of L.barbarum were divided into three groups by principal component analysis.The main components of young galls were cyclohexanone,2,3,5,8-tetramethyldecane,benzaldehyde and 6-ethyl-2-methyl-octane,which had little or no content in mature galls and healthy buds.A total of 20 compounds inducing sustained antennae potential response of female parasitic wasps were detected from young galls,mature galls and healthy flower buds by GC-EAD,of which benzyl alcohol only existed in the galls,and caused the potential response of the parasitoids only in the young galls,while 2-butyl-1-octanol and p-xylene,which could cause the potential response of the parasitoids in the healthy flower bud,were absent or had a low content in the gall.6.The types,morphological structure and number distribution of sensilla on antennae and ovipositors of P.jaapiellae were studied.Scanning electron microscopy(SEM)was used to identify,describe,and predict the morphology,distribution and number of sensilla on antennae and ovipositors of P.jaapiellae for the first time.The geniculate antennae of both male and female P.jaapiellae were each composed of a scape with a basal radiculum,a pedicel,an anellum and a flagellum.Nine sensilla types were present on the antennae of both sexes,including three sensilla trichodea(ST),one sensillum basiconicum(SB),two sensilla chaetica(SCh),one sensillum placodeum(SP),one sensillum coeloconicum(SCo),and one sensillum campaniformia(SCa).There was no difference in the type of sensilla on the antennae of males and females,but there was a difference in the number of sensilla.Six types of sensilla(three ST,one SB.and two SCa)were present on the females' ovipositors.On the oviposition needle,one type of ST and two types of SCa were observed,and on the oviposition sheath,two types of ST and one type of SB were observed. |
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