Early Detection and Identification of Parasitoid Wasps Trichogramma Westwood (Hymenoptera: Trichogrammatidae) in Their Host Eggs Using Polymerase Chain Reaction-Restriction Fragment Length Polymorphism.

Parasitoid wasps are invaluable agents in pest biological control. Early detection and identification of parasitoid immatures are vital in characterizing parasitoid-host interactions and for evaluating parasitism rates accurately in the field. Trichogramma is the most widely used parasitoid wasp, and several studies have been performed for its molecular identification. However, those studies were mainly focused on Trichogramma adults and rarely on immatures. Here, we report a method to detect and identify Trichogramma larvae in their host eggs. We designed a pair of Trichogramma-specific primers that amplified Trichogramma mtCOI sequences from Corcyra cephalonica (Stainton) eggs parasitized by any of eight Trichogramma species tested but not from nonparasitized eggs of four lepidopteran hosts. This PCR method reliably detected Trichogramma immatures in parasitized eggs as early as 1 h after parasitism. We further developed an RFLP (restriction fragment length polymorphism) assay using restriction enzymes SspI and VspI to differentiate eight Trichogramma species at their immature stage. Overall, we developed a sensitive and reliable PCR-RFLP method to detect and identify immature-stage Trichogramma in their lepidopteran hosts. This method shows promise for conveniently identifying Trichogramma in insectaries and accurately evaluating parasitism rates in the field.

Mitochondrial Genomes of Two Asexual Trichogramma (Hymenoptera: Trichogrammatidae) Strains and Comparison with Their Sexual Relatives.

Despite its substantial costs, sexual reproduction dominates in animals. One popular explanation for the paradox of sex is that asexual reproduction is more likely to accumulate deleterious mutations than sexual reproduction. To test this hypothesis, we compared the mitogenomes of two asexual wasp strains, Trichogramma cacoeciae and T. pretiosum, to their sexual relatives. These two asexual strains represent two different transition mechanisms in Trichogramma from sexual to asexual reproduction. Asexual T. pretiosum is induced by Wolbachia, while T. cacoeciae presumably originated from interspecific hybridization. We sequenced and assembled complete mitochondrial genomes of asexual T. cacoeciae and T. pretiosum. Compared to four sexual relatives, we found no evidence of higher mutation accumulation in asexual Trichogramma mitogenomes than in their sexual relatives. We also did not detect any relaxed selection in asexual Trichogramma mitogenomes. In contrast, the intensified selection was detected in Nad1 and Nad4 of the asexual T. pretiosum mitogenome, suggesting more purifying selection. In summary, no higher mitochondrial mutation accumulation was detected in these two asexual Trichogramma strains. This study provides a basis for further investigating mitochondrial evolution and asexual reproduction in Trichogramma.