Abstract
Trichogramma dendrolimi, T. ostriniae, T. confusum and T. evanescens are the four most commonly occurring Trichogramma species with overlapping distribution in China. They are the most frequently used egg parasitoids for biological control of lepidopterous crop pests in China. It is difficult to differentiate Trichogramma species because of their small size and lack of differences in morphological characters. Different molecular markers were employed to molecularly characterize and differentiate these species, including direct amplification of the internally transcribed spacer 2 (ITS2) of ribosomal DNA by polymerase chain reaction (PCR), restriction fragment length polymorphism (RFLP), random amplified polymorphic DNA (RAPD) and species-specific primers. The results showed that direct amplification of ITS2 could not clearly discriminate these species, but they could be differentiated using RFLP pattern obtained with endonucleases EcoRI and HindIII. The banding pattern produced by RAPD is irreproducible so it is not a suitable way to identify Trichogramma species. Finally, the species-specific primers designed based on ITS2 sequences could unequivocally distinguish the four species. The species-specific primer-based protocol proved to be the most convenient and time saving method for the identification of Trichogramma species by creating a unique PCR product, which can be used in surveying natural populations of Trichogramma species. This is the first report of the prompt identification of the four most commonly occurring Trichogramma species in China.
Highlights
T. dendrolimi Matsumura, T. ostriniae Pang et Chen, T. confusum Viggiani and T. evanescens Westwood are the most commonly occurring Trichogramma species in China
The polymerase chain reaction (PCR) amplicons of internally transcribed spacer 2 (ITS2) from T. dendrolimi and T. confusum were nearly of the same size (~600 bp), and those from T. ostriniae and T. evanescens were sized (~630 bp). These results demonstrate that ITS2 itself cannot be used to differentiate the four species
ITS2 of T. dendrolimi was cut into two overlapping bands of similar size around 300 bp; ITS2 of T. confusum was excised into two visible bands (300 ± 40 bp)
Summary
T. dendrolimi Matsumura, T. ostriniae Pang et Chen, T. confusum Viggiani and T. evanescens Westwood are the most commonly occurring Trichogramma species in China. T. ostriniae is numerically dominant in cornfields, while T. confusum is the predominant Trichogramma species in cotton fields. T. dendrolimi mainly occurs in forests, whereas T. evanscens is often collected in vegetable fields. Their distribution ranges frequently overlap across the country. Over 80% of the samples collected from cornfields are of T. ostriniae, but T. confusum, T. evanescens, and T. dendrolimi can occur simultaneously in cornfields. It is always necessary to identify the samples collected from fields before further studies are undertaken
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