Screening Of The Optimal Trichogramma Strains To Control Conogethes Punctiferalis Guenée (Lepidoptera:Crambidae)

Corn is largest feed crop and also an important industrial raw material in China.In recent years,the yellow peach moth,Conogethes punctiferalis?Guenée?,has become one of the major pests at the corn ear stage in Huang-Huai-Hai region in China.Due to the adjustment of crop systems and climate changes,the pest severely affects the yield and quality of corn.C.punctiferalis is a kind of pest that needs to prevent and control timely.If the larvae bored into the host plants before the effective measures are not yet taken,it would have serious consequences.At the same time,long-term application of chemical control has caused a series of problems,such as environmental pollution and pest resistance,etc.So,it is urgent to develop an eco-friendly and efficient biological control techniques to manage C.punctiferalis.As we all known,Trichogramma is a kind of important egg parasitic natural enemy insect which is widely used to control many agricultural and forestry insect pests in the world.In this study,we compared the parasitic ability of 11 strains of T.ostriniae,T.dendrolimi and T.chilonis,which are widely used in biological control of lepidopterous pests via oviposition preference test under the laboratory conditions.Based on the results of oviposition preference,the effects of C.punctiferalis egg ages on parasitic ability,developmental fitness and parasitic behavior of Trichogramma were furtherly studied,and the functional response and parasitic potential of the candidate Trichogramma species?strains?to C.punctiferalis eggs were compared.In order to screen the optimal Trichogramma species?strains?for controlling C.punctiferalis,the control potential of the candidate Trichogramma species?strains?were evaluated comprehensively.The main results are as follows:1.Preference of different Trichogramma species?strains?to eggs of C.punctiferalisThe results from non-selection test were basically consistent with the results of the selection test that the So and Zo strains of T.ostriniae and Sd and Xd strains of T.dedrolimi showed higher preference and parasitic ablity to C.punctiferalis eggs than other strains of T.ostriniae,T.dendrolimi and T.chilonis.Therefore,So,Zo,Sd and Xd strains were used as candidate Trichogramma species?strains?to control C.punctiferalis for the further studies in the following experiments.2.Effect of C.punstiferalis egg ages on the parasitic ability and developmental fitness of four candidate Trichogramma strainsBy comparing the parasitic ability and developmental fitness of four candidate Trichogramma species?strains?to C.punctiferalis eggs in different ages?0²4h,24⁴8h and 48⁷2h?,we found that four candidate Trichogramma strains all preferred to parasitize the 0²4h eggs,and Xd strain of T.dendrolimi also showed better parasitic ability to the48⁷2h eggs than others.The parasitic ability of Xd strain of T.dendrolimi to the 0²4h,24⁴8h and 48⁷2h eggs were higher than that of the So and Zo strains of T.ostriniae.At the same time,the study also revealed that Xd strain of T.dendrolimi showed higher developmental fitness to 0²4h eggs than others.3.Effect of C.punctiferalis egg ages on parasitic behavior of four candidate Trichigramma strainsIn order to determine the effect of egg ages on the parasitic behavior of four candidate Trichogramma strains,the drumming,drilling and ovipositing time of four candidate Trichogramma strains to C.punctiferalis eggs in different ages were compared.The results indicated that the drilling duration of Xd strain of T.dendrolimi to C.punctiferalis eggs not increased with the egg ages.The Xd and Sd strains of T.dendrolimi spent less time in ovipositing behavior than that of the So and Zo strains of T.ostriniae,so did the total parasitic time.The total parasitic time of Xd strain of T.dendrolimi was the shortest.4.Functional response of four candidate Trichogramma strains to C.punctiferalis eggsBy studying the functional responses of four candidate Trichogramma species?strains?to C.punctiferalis eggs,it showed that the parasitic effects of four candidate Trichogramma species?strains?to C.punctiferalis eggs accorded with the Holling II type model.According to the model,the value of a/T_h of Xd strain was 19.22,that was the largest in all species?strains?.The density of four candidate Trichogramma strains appeared interference effects to their parasitic ability.The searching parameter?Q?of Xd strain was 0.2931,so that was the highest.5.Parasitic potency evaluation of four candidate Trichogramma species?strains?to C.punctiferalis eggsBy comparing the life table parameters of four candidate Trichogramma species?strains?to C.punctiferalis eggs,we found that the four candidate Trichogramma species?strains?all reached the parasitic peak at the first day of emergence,and the number of parasitized eggs in the first two days after emergence accounted for 90%of the total parasitized eggs.The net reproductive rate?R₀?,intrinsic growth rate?r_m?and the finite rate of increase???of Xd strain were all the highest,and that was 18.23,0.3120 and 1.3662respectively.However,there were no significant differences in the longevity and offspring emergence rate of the four candidate Trichogramma species?strains?on the C.punctifrealis eggs.These results imply that Xd strain of T.dendrolimi is the optimal strain among eleven strains could be used to control C.punctiferalis.