| Plutella xylostella is one of the major pests of Brassicaceae vegetables.The frequent use of chemical insecticides has led to the development of resistance in Plutella xylostella,resulting in increasing difficulty in its control.The Trichogramma spp.is an important egg parasitic natural enemy of Lepidopteran pests.However,different Trichogramma species(strains)for the host eggs and their release environment vary,therefore,finding suitable Trichogramma species(strains)and field release methods is the key to the success of applying Trichogramma spp.to.Plutella xylostella.In this study,determined the period of field release of Trichogramma through a survey of the dynamics of Plutella xylostella occurrence;we screened Trichogramma species(strains)with high efficiency in parasitizing eggs of Plutella xylostella as the target pest;determined the release point of Trichogramma through a study of the dispersal distance of Trichogramma,clarified the technical points of field application of Trichogramma for controlling Plutella xylostella,and conducted field trials:1.In this study,18 local strains of Trichogramma spp.were tested in the laboratory for their ability to parasitize Plutella xylostella eggs.The parasitism rate,emergence rate,and female emergence rate of Trichogramma spp.were used as experimental parameters.One strain of Trichogramma spp.(strain 3)was found to be highly efficient in parasitizing Plutella xylostella.2.The occurrence peak of Plutella xylostella appeared in late June to early July,with a long occurrence period and severe overlapping generations.The occurrence time and characteristics of Plutella xylostella were determined to establish the appropriate release time of Trichogramma chilonis.The survey found a mixture of Plutella xylostella and Pieri srapae with large populations,so it is recommended that control of Plutella xylostella should be combined with control of Pieri srapae.3.Field tests were conducted using strain 3 of Trichogramma chilonis to determine the spread distance of Trichogramma spp.in cruciferous vegetable fields.The results showed that when the release quantity was 5,000 individuals per release point,the spread distance of Trichogramma chilonis was approximately 6 m in spring cabbage fields and 9 m in autumn cabbage fields.It was estimated that in spring cabbage fields,five release points per mu should be set for the release of Trichogramma chilonis to control Plutella xylostella.In autumn cabbage fields,three release points per mu can achieve the same effect.4.The effectiveness of Trichogramma strain 3 was tested in the field.The results showed that in spring cabbage fields,the parasitism rate of Trichogramma chilonis on Plutella xylostella eggs was 65%,the corrected parasitism rate was 53.33%,and the average control effect was 83.91%. |
