| Agromyzid leafminers are the most economically small pests of vegetables and floricultural crops throughout the world,whose adullts and larvae both damage.Agromyzid leafminers parasitoids are species richness in nature,and they have played an important role in control leafminers.They are common to occur the interspecific competition when multiple parasitoids coexist in sympathy in the field.Interspecific competition effect can not only influence the community structure and steady of parasitoids,but also regulate the occurrence and damage of leafminers.Diglyphus isaea Walker and Neochrysocharis formosa(Westwood)are dominant idiobiont larvae parasitoids of vegetable leafminers,and both parasitoids can usually coexist in sympathy in the field and share a common host resource.They are typical host-killing parasitoids,which have three host-killing behaviors(parasitism 、 host feeding and host stinging).Now,there are many studies in competitive interactions of parasitoids,but it is few researches in interspecific competition of host-killing parasitoids,which can make competitive interactions become more complex.We have emphasized interspecific competition interactions of the two host-killing parasitoids as the subject and carried out the experiments in the following three aspects.Firstly,taking the occurrence of agromyzidae leafminers in Beijing as examples,we studied the species and composition of leafminers parasitoids in detail and simultaneously expound the seasonal dynamics and coexistence of dominant parasitoids.Then,we surveyed the distribution areas of D.isaea and N.formosa aiming at the major occurrence areas of agromyzid leafminers in China.Lastly,we further studied the interspecific competition interactions between two parasitoids in the greenhouse.Main results are as follows:1.Leafminer parasitoids’ species and composition in BeijingIn order to explicate the species and composition of leafminer parasitoids,we carried out the field survey on leafminer parasitoids in Beijing from May to August in 2015,and analyzed important parasitoids dynamics following seasonal variation.The results showed: we have collected three leafminers species in total,respectively Chromatomyia horticola(Goureau)、 Liriomyza chinensis(Kato)、 L.sativae(Blanchard)and 3411 parasitoids,which consisted of three family(Eulophidae 、pteromalidae and Braconidae)13 genus 28 species.Eulophidae parasitoids were 9 genus 23 species,occupying 90.9%;pteromalidae parasitoids were 3 genus 4 species,occupying 6.5%;species of Braconidae parasitoids were only one,occupying 6.5%.It occured in the early spring for Chro.horticola and serviously damaged vegetable crops and weeds.Its predominant parasitoids were D.isaea,occupying 40.9%;suboptimum parasitoids were Cirrospilus vittatus Walker,occupying 19.4%.L.chinensis mainly damaged Allium fistulosum L.at the late spring and early summer;D.isaea and N.formosa were predominant parasitoids,occupying 44.1% and 20.6% respectively.L.sativae importantly damaged the vegetable crops in summer,and Closterocerus lyonetiae(Ferriere)and N.formosa were predominant parasitoids,occupying 57.9% and 22.9% respectively.Above all,D.isaea werepredominant parasitoids in the early spring;Clos.lyonetiae and N.formosa were predominant parasitoids in summer.D.isaea and N.formosa had more females than males adults.This could cause thelytokous cryptic species or strains in the field.Conclusion: Predominant parasitoids are D.isaea、N.formosa and Clos.lyonetiae,respectively.And D.isaea and N.formosa have significantly partial females in the field,which cause the external(host plants、host species、climate change and so on)and internal factors(existing thelytous strains).2.The distribution and coexistence of D.isaea and N.formosa in ChinaIn order to further explicit the distribution of D.isaea and N.formosa,we conducted the survey for important occurrence areas in China.The results showed that we have collected 7 species in total,respectively Chro.horticola(Goureau)、L.chinensis(Kato)、L.lutea(Meigen)、L.sativae(Blanchard)、L.trifolii(Burgess)、L.bryoniae(Kaltenbach)、L.huidobrensis(Blanchard).Chro.horticola and L.sativae were seriously damaged leafminers.Occurrence fastigiums of Chro.horticola preferred low temperature habitats,however,L.sativae occurred serious damage at the high temperature and others leafminers’ damage time was between Chro.horticola and L.sativae.D.isaea and N.formosa existed31 provinces/ municipalities in China.D.isaea were dominated parasitoids,occupying 87.3% when the hosts were Chro.horticola;the amounts of N.formosa were 19.3 times more than D.isaea when the hosts were L.sativae.It was almost equal to D.isaea and N.formosa numbers when other Lirimyza leafminers damaged.The sex of D.isaea and N.formosa were respectively 1.04-8.90 and 1.11-all females.Compared to emerged N.formosa from Chro.horticola,the sex of N.formosa from L.sativae was more biased toward females.Conclusion: D.isaea and N.formosa have wide distribution,and they can exist in sympatry.D.isaea occupy predominantly on Chro.horticola,while N.formosa are dominant on both L.sativae and L.trifolii.3.Competitive interaction of Diglyphus isaea and Neochrysocharis formosaDue to further explicate the interspecific competitive interaction between D.isaea and N.formosa,we have taken the late second to early third instar L.sativae larvae as a host,setting two host densities(low vs high)and three parasitoids release modes(release two pairs of D.isaea alone vs release two pairs of N.formosa alone vs a pair of D.isaea+ a pair of N.formosa).There were six treatments in total.Then we conducted the experiment using glass petri dishes,which put in the artificial climate chamber at 26℃,and observed them for continuous five days.The results showed: the control potential parameters(the number of parasitism,the number of host feeding and the number of host stinging)for parasitoids at the high density were significantly higher than low density,and the control potential parameters of combination release were between them.At the low density,the total mortality was the highest(96.2)when they were combination release,while the control effect was the best when release D.isaea alone at the high density.Whether at the low density or high density,the existence of N.formosa increased the oviposition of D.isaea,however the presence of D.isaea decreased the oviposition of N.formosa,and the oviposition of D.isaea were significantly higher than N.formosa when they were released simultaneously.Host-feeding ratio was the greatest in three host-killing mortality.Then at the case of same treatments,parasitoid adults were provided non-host food(20% glucose solution)at the same time.The results were as follows: the control potential parameters and competition in oviposition were the same as only providing host food.However,whether at the low density or high density,the total mean mortalities were the highest,but not be significant,respectively 91.6 and 175.1 when release D.isaea alone.Non-reproductive killing behaviors had made the greatest contribution for controlling the leafminers.Conclusion: It can’t decrease the control potential when two parasitoids were released simultaneously,and D.isaea have laying eggs competition superiority.Host-feeding behaviors play an dominant role in control potentials.In summary,the distribution of D.isaea and N.formosa were wide distribution and occurred in sympatry in China.They could alternate as the seasonal alteration and have partial females character at a certain extent.Interspecific competition interaction was not too strong between both parasitoids,so that they could release simultaneously to control agromyzidae leafminers in the field,and we could take ecological measures to enhance the control effect of parasitoids. |
