Screening The Trichogramma Parasitoids And Biological Control Potential For Eggs Of Soybean Pod Borer(Leguminivora Glycinivorella)

Legunminivora glycinivorella (Matsumura) is the most important pest of soybeanplantation in northern China. Currently, the chemical pesticides are still the onlyoption to control the soybean pod borer (SPB) in local regions. With a long-term andheavy use of pesticides, a series of negative question such as environmental pollution,resistance, resurgence and nature enemies killed, are rising. In this study, the eggparasitoids of SPB collected from main soybean producing region were identifiedfirstly. In order to select suitable biological control agents against SPB, we evaluatedtheir selections and suitabilities on L. glycinivorella eggs at different ages, andfunctional responses and life table parameters on host eggs in the laboratory. Themain results as followed:1. Identification of the egg parasitoids of SPBThe egg parasitoids of SPB collected were identified with morphology of malegenitalia and analysis of rDNA-ITS2sequences. Three natural populationsparasitizing SPB eggs in northeastern China were found: Trichogramma chilonis(collected from Jilin Province), and Trichogramma leucaniae and Trichogrammaostriniae (collected from Heilongjiang Province).3. Parasitism and suitability of three indigenous Trichogramma species on theirnatural host eggs of the soybean pod borer, Leguminivora glycinivorellaIn this experiment, we compared the parasitic capacity and suitability of threeindigenous Trichogramma species on SPB eggs at various ages. The results indicatedthat host eggs with various ages were accepted by T. chilonis, T. ostriniae and T.leucaniae. Trichogramma chilonis tended to parasitize0-to2-day-old eggs more thanthey did on3-to4-day-old eggs. There were no significant differences in parasitismbetween the0-to2-day-old eggs and the1-to4-day-old eggs for T. ostriniae and T.leucaniae. On variously aged eggs, T. chilonis parasitized the smallest number of eggs,while T. leucaniae and T. ostriniae exhibited similar parasitic capacities. On0-day-old host eggs, T. ostriniae took the longest to develop (8.7d), and T. leucaniae had the most female progeny (87.9%). Both T. leucaniae and T. ostriniae had similardevelopmental times, survival rates and percentages of female progeny on1-to3-day-old eggs.2. Host selection on SPB eggs at different ages by Trichogramma species fromdifferent natural host speciesThe parasitism abilities of T. chilonis collected from SPB eggs and other three Trichogrammaspecies (T. ostriniae, T. dendrolimi and T. japonicum) from Chilo suppressalis eggs on0-4-day-old SPB eggs were investigated. The results indicated that T. chilonis significantlypreferred0-2-day-old eggs with no difference between them, and T. dendrolimi preferred thenewly-laid fresh eggs. T. ostriniae exhibited similar parasitism ability on all aged host eggs,whereas T. japonicum hardly used SPB eggs at various ages. When0-2-day-old eggs were offered,the largest number of hosts was parasitized by T. chilonis (19.8-27.4eggs/24h), followed by T.ostriniae, T. dendrolimi. When3-4-day-old eggs were offered, the largest number of hosts(9.2-10.9eggs/24h) was parasitized by T. ostriniae, but was not significantly different from thatparasitized by T. chilonis.4.Functional responses and searching capabilities of three indigenousTrichogramma species on SPB eggsFunctional responses and interfering responses of T. leucaniae, T. ostriniae and T.chilonis were were studied at25℃. The results showed thathost egg densitysignificantly affected their parasitism abilities. The functional responses ofTrichogramma to SPB eggs could be described well by Holling’s type II mode1, whichwere Na=0.9757N/(1+0.0220N), Na=0.8470N/(1+0.0187N), and Na=0.6156N/(1+0.0135N) for T. leucaniae, T. ostriniae and T. chilonis, respectively. The theoreticalmaximum number of host eggs parasitized by three Trichogramma species, given bythe asymptote (1/Th) of the functional response curve, was44.4-45.7eggs per day perfemale. The own densities of Trichogramma exhibited interferring responses on theirparasitisms, which could be expressed as E=0.3289P0.6116, E=0.3270P0.6085andE=0.2906P0.4543based on Hassell-Varley model, for T. leucaniae, T. ostriniae and T.chilonis, respectively.5.Analyses of parasitism potential of three indigenous Trichogramma species onSPB eggs with life table technology The experimental population life tables on SPB eggs were established for eachtrichogramma species reared on the eggs of rice moth, Corcyra cephalonica, and thereproductive property parameters of the net reproduction rate (R0), mean generationtime (T), intrinsic rate (rm), finite rate of increase (λ), number of host eggs parasitizedper female, average longevity of female and emergence rate were compared andanalyzed. The results showed that the R0, T, rmand λ of T. leucaniae, T. chilonis and T.ostriniae on SPB eggs were24.75,23.78and21.13;9.46,10.34and10.37d;0.3393,0.3064and0.2941,1.4040,1.3585and1.3419, respectively. However, there were nosignificant differences in longevity of female wasps and emergence rate in SPB eggsamong the three Trichogramma species. Generally, the reproductive propertyparameters (R0, T, rmand λ) of T. leucaniae were more ideal than those of T. chilonisand T. ostriniae.Generally, based on comparisons of parasitic abilities, suitabilities, functionalresponses and the parameters of life table on SPB eggs by different Trichogrammaspecies, the present study indicated that T. leucaniae could be a suitable biologicalcontrol agent for controlling the soybean pod borer, L. glycinivorella.