Biological Characteristics Of Tamarixia Radiata Parasitoid Of The Citrus Psyllid

The Asian citrus psyllid,Diaphorina citri Kuwayam(Hemiptera: Psyllidae)is the main known vector pest that transmits huanglongbing(HLB)in nature,which is the most destructive citrus pathogen in the world.The control of citrus psyllid is an effective measure for the management of the citrus HLB.Tamarixia radiata Waterston(Hymenoptera: Eulophidae)is the dominent parasitoid of D.citri,and exhibited a narrow host range and high host specificity,so the establishment of T.radiata for the classical biological control of citrus psyllid poses negligible environmental risk.In current study,we investigated the field population dynamics of citrus psyllid and T.radiata in citrus groves,and successfully established the host plant-citrus psyllid-T.radiata research system in the laboratory.Then,the parasitoid behavior and ontogeny of T.radiata,the influence of temperature and host stages on the life histoty of T.radiata have been studied.The results are expected to provide important theoretical and technical support for the sustainable management of citrus psyllids.The main findings are as follows: 1.The field population dynamics of citrus psyllid and T.radiata in citrus groveIn citrus orchards without pesticides and other man-made interference,a small amount of citrus psyllid overwintering adults start to lay eggs in March,and then the population of nymph increased,T.radiata firstly appeared in early May.The number of T.radiata population began to rise as temperature rise,and its population reached to the peak in September.During the field investiage,averaged 48 wasps every hundred branches were found,which can control the citrus psyllid population effectively.2.The life table of T.radiataUnder laboratory conditions(25±1? and 70±10%RH),T.radiata completed its life history within 13.41 d,including the egg,larva,pupa and adult stages.The female adults usually deposit one and very rarely two eggs on the ventral side of the D.citri 3-5 instar nymphs,mostly in the groove between thorax and abdomen and close to the point of attachment of hind coxae,which eggs are creamy white,appeared like a grain of rice.Larvae of T.radiata can divided into four stages,which sucks fluid from the site of attachment for their own growth and development.Pupation of T.radiata take place underneath the mummified nymph and the pupa is yellow in the early,then becoming darker brown as it growing.The adults emerge by chewing a circular exit hole in the integument of the thoracic region.The female and male of T.radiata adults were significantly different in their appearance,which can be identified clearly under the microscope.The main difference is: firstly,females are significantly larger than males in total length and width;secondly,male antennas contain long and slightly curved setae compared to female antennas with short setae;finally,the yellow part of the anterior dorsal gaster of females is significantly bigger than males.3.Reproduction and offspring development of the T.radiata at different temperaturesThe current study investigated the biology and determined the fertility life table of T.radiata in different temperatures,we found that 26?was the optimum temperature for T.radiate survival,where the rate of oviposition was 15.6 eggs/female/day in average,of which up to 18 eggs/female/day.The highest parasitism rate(78%)was also obtained at a temperature of 26?,as the highest survival rate(87.58%)of its progeny.Both extremely higher and lower temperatures can influence the parasitism and survival rates of offspring.Lower emergence percentages of the parasitoid occurred at 18? to 22?(78.98,70.62%,respectively),and the lowest survival rate of egg was observed at a higher temperature of 34?.Temperature also had a significant impact on the duration of various developmental stages of parasitoid.As the temperature gradually increased,the developmental duration of T.radiata turned into shorter and shorter.4.Effectc of host stage on the parasitism and developmental time of T.radiataResults showed that T.radiata dose not parasite the 1st and 2nd instars nymphs of citrus psyllid.The highest parasitic rate of T.radiata to citrus psyllid was found on 5th instars nymph(84.25%)under the laboratory conditions,and when the parasitoid deposited eggs on 5th instar nymph of the host,the survival rate of its progeny was 80.96%,higher than those survival rates of offspring on 3rd and 4th instar nymph.Host stage also influenced the developmental time of T.radiata offspring.The smaller the host stage was,the shorter the developmental duration became.Also,76.56% of offspring were female when eggs were laid on 5th instar nymphs as against 60.06 and 42.78% females when eggs were laid on 4th and 3rd instars respectively,which indicated that more female offspring were produced form larger hosts.5.The detection of endosymbionts in citrus psyllid and T.radiataThe endosymbiont diversity differed from the different sex of citrus psyllid and T.radiate,and the infection rate of one endosymbiont varied between different hosts.Results showed that the population of citrus psyllid,and the female and male of T.radiata were all infected with Wolbachia,while the Wolbachia in T.radiata China population belongs to the Wolbachia Pip group of supergroup B,and the Wolbachia in citrus psyllidof China,America,Iran and Pakistan populations all belong to the Stri group of supergroup B.