Effects Of Sugar Diets On The Parasitism Of Encarsia Formosa On Bemisia Tabaci And Analysis Of Induced Expression Of Sugar Transporter Gene

The sweetpotato whitefly,Bemisia tabaci?Gennadius?belongs Hemiptera,Aleyrodidae,being a major pest of cotton,vegetable and horticultural plants.At least 34 morphologically indistinguished biotypes?cryptic species?of B.tabaci were found until now and the B and Q B.tabaci are two most invasive and damaged in China.The adult and nymph of whitelfies can utilize the mouthpart feeding phloem sap of the host plant for nutrition.The B.tabaci not only directly secretes honeydew causing plant physiological abnormality,but also indirectly transmits hundreds of viruses causing serious plant virus diseases,which caused huge economic losses on the agriculture production.Currently,whitefly controlling mainly depends on various chemicals resulting in the resistance to kinds of overused insecticides,which bring the challenges and difficulties to the chemican control of whiteflies.Biological control plays an important part in the integrated management of B.tabaci field populations.The important parasitoid,Encarsia formosa Gahan?Hymenoptera,Aphelinidae?,can parasitize and feed on B.tabaci nymph,and the effective control on the whiteflies has been obtained in the protected cultivation worldwide.During the mass rearing of E.formosa,sugars as supplemental diets could not only improve the egg laying,but also prolong the longvity of E.formosa.However,the effects of different sugars on the parasitism of E.formosa on B.tabaci and induced expression of sugar transporter gene is still unkown.In order to reveal the above questions,three aspects have been carried out in this present study.Firstly,based on the construction of the age-stage life tables of E.formosa parasitizing on B.tabaci Q and B in the laboratory,the population parameters of E.formosa after parasitizing on the B and Q B.tabaci and the subsequent parasitism of parasitoid on the whiteflies were evaluated.Secondly,effects of six sugar diets on the fecundity and parasitism of E.formosa on B.tabaci was analyzed.Finally,sugar transporter gene of E.formosa was cloned and its induced expression after sugar treatment was studied.The main results are as followed.1.Population parameters analysis of E.formosa parasitizing on the B.tabci B and QIn order to understand the development and reproduction of E.formosa parasitizing on the B.tabaci Q and B,age-stage life tables of the experimental population of E.formosa were constructed in the laboratory.The results showed that the survival rate(S_xj)from egg to pupa of E.formosa parasitizing on the B.tabaci B reduced slowly from the 17^th day and all the parasitoids died after 27d.The intrinsic rate of increase?r?,the finite rate of increase???,the net reproductive rate?R₀?and the mean generation time?T?of E.formosa parasitizinge on the B.tabaci Q were 0.198,1.218,37.806 and18.341,respectively;while those parameters on the B.tabaci B were 0.207?1.230?42.697 and 18.148,respectively.The population dynamic parameters suggest that the population growth of E.formosa parasitizing on the B.tabaci B is faster than those parasited the B.tabaci Q.It is speculated that E.formosa parasitoids would have higher control effacy on the B.tabaci B than Q,when they were released for whitefly biocontrol in the field.and the results would provide a theoretical basis for the strategy decision on the integrated control of the whiteflies in the field.2.Effects of six sugar diets on the biological characteristics of E.formosa on B.tabaci QThe current research assessed the effects of six sugar diets on the fecundity and subsequent parasitic characteristics of E.formosa on the 3^th instar nymph of B.tabaci Q biotype,the most prominent species in China;the diets consisted of 10%?w/v?solutions of glucose,fructose,sucrose,trehalose,melezitose,and honey.The E.formosa adults carried more mature eggs after feeding on any of the six sugar diets for 2 h than after feeding on water for 2 h;no mature eggs have been found in water treatment.The length and width of the mature eggs were both greatest with fructose,sucrose,and honey.The parasitism rate and emergence rate of E.formosa on B.tabaci Q biotype were highest when the parasitoid had fed on glucose,fructose,sucrose,or honey for 2h.All six sugars decreased the developmental rate of E.formosa,and fructose and glucose significantly increased E.formosa longevity.The results suggest that diets of fructose,glucose,or honey can increase E.formosa fecundity and E.formosa parasitism of B.tabaci.The use of these sugars as supplemental diets could improve the mass-rearing of E.formosa and could increase the control of B.tabaci by E.formosa in the field.3.Cloning and induced expression of sugar transporter gene in E.formosaThe sugar transporter gene of E.formosa named EfST1 was cloned;sequence alignment and the phylogenetic analysis revealed that EfST1 shared more than 65%homology with other parasitoids.Real-time PCR showed that EfST1 was significantly expressed by feeding different concentrations of glucose.After feeding sugar for different periods?2—48 h?on 10%glucose,Ef ST1 gene expression was found to be increased compared to the water control.Besides,there were no significant differences between the 2h and 48h feeding treatments.In conclusion,the EfST1 gene was probably related to sugar supplement and transportation;and the gene expression induced by different sugar concentrations was not greatly fluctuated.The results will provide a basis for studying the nutrition supplement and transportation mechanism during the biological control of parasitoids.