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Corresponding author: Stefanos S. Andreadis ( stefandr@ipgrb.gr ) Academic editor: Petr Janšta
© 2023 Lucian Fusu, Stefanos S. Andreadis.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Fusu L, Andreadis SS (2023) Ooencyrtus mirus (Hymenoptera, Encyrtidae), discovered in Europe parasitizing eggs of Halyomorpha halys (Hemiptera, Pentatomidae). Journal of Hymenoptera Research 96: 1045-1060. https://doi.org/10.3897/jhr.96.109739
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Ooencyrtus mirus Triapitsyn & Power (Hymenoptera, Encyrtidae) is recorded for the first time in Europe. It was found parasitising eggs of the invasive true bug Halyomorpha halys Stål (Hemiptera, Pentatomidae). This parasitoid is part of the Ooencyrtus telenomicida species complex where accurate species identification requires molecular data. Using morphology, the identification of the Ooencyrtus species parasitising brown marmorated stink bug eggs in Greece is ambiguous, but the sequences of the standard DNA barcode region (COI) and ITS2 place them in O. mirus.
brown marmorated stink bug, DNA barcoding, egg mass, new record, parasitoid
The brown marmorated stink bug, Halyomorpha halys (Hemiptera, Pentatomidae), is native to eastern Asia but it was accidentally introduced into the United States in 1996 in Pennsylvania, and several years later in Europe, in 2004 in Switzerland (
In the native range of H. halys (north-eastern Asia), substantial control is provided by numerous natural enemies including parasitoids, predators, and entomopathogens (
To obtain large numbers of natural host eggs, captive H. halys were reared on green bean (Phaseolus vulgaris) pods and green bean plants in a mesh cage (30 × 30 × 30 cm) with vinyl window and zip closure (Raising Butterflies, UT, USA) and maintained at 26 °C, 60% RH under a 16:8 h light dark photoperiod. This colony was initiated in 2019 from mixed-sex adults collected from homes and fields in the area of central Macedonia, Northern Greece. Egg masses were removed carefully every other day, placed in Petri dishes (60 mm diameter), and labelled by date to monitor the age of host eggs. Moistened cottonwool was placed in the dishes to increase humidity.
Ooencyrtus mirus (Chalcidoidea: Encyrtidae) adults were obtained in the summers of 2020 and 2021 from parasitized H. halys eggs collected from the underside of apricot tree leaves and of green bean plant leaves, respectively, in Thermi, Thessaloniki, Northern Greece (40°32'17"N, 23°00'04"E and 40°32'12"N, 23°00'01"E, respectively). A colony of O. mirus was established for multiple generations at the Institute of Plant Breeding and Genetic Resources, Laboratory of Entomology at 26 °C, 60% RH and under a 16:8 h L:D photoperiod. The colony reported here is not exactly the same as in
Sex ratio (proportion of males) of O. mirus was measured on 1- and 3-days old eggs of H. halys. Freshly emerged male and female parasitoids from the colony were placed together in single pairs for 48 h to ensure mating. After this period, each female was offered 10 H. halys eggs, on the lid of a plastic Petri dish (3.5 cm in diameter) inside the plastic cups. After 24 h, the parent parasitoids were removed and the parasitized eggs were reared at 26 °C, 60% RH under a photoperiod of 16:8 h L:D until adult emergence for a total period of 30 days, to ensure all adults are accounted for. Emergent wasps were counted and identified by sex. Only replicates in which parasitoid attack by O. mirus occurred on at least one egg were included in the data analysis.
For this study specimens were sampled at two different moments from the laboratory colony, in February 2021 and January 2022. Live parasitoids were killed in 80% ethanol and kept at –20 °C until preparation. For examination, specimens were chemically dried using hexamethyldisilazane (HMDS) (
Identification of the specimens was done by comparing them with specimens from the same rearing event as the neotype of O. telenomicida (Vassiliev) (see
Gastral tergites are abbreviated as Gt1 to Gt3.
DNA was individually extracted from four whole specimens using a non-destructive method as described in
To our sequences we added those of Ooencyrtus mevalbelus Guerrieri & Samra, Ooencyrtus pistaciae Hayat & Mehrnejad, and Ooencyrtus zoeae Guerrieri & Samra (from
Separate phylogenetic analyses were performed for the two genes because the goal was to check congruence between mitochondrial and nuclear gene trees. The ITS2 sequences were analysed in an unpartitioned analysis while the COI sequences were partitioned by codon position. The best partitioning scheme and substitution models were selected during the phylogenetic reconstruction using IQTree v.1.6.12 (
The nuclear and mitochondrial sequences were not concatenated for a partitioned phylogenetic analysis because most of the published sequences for the two genes cannot be correlated. This analysis was performed by
In the investigated Greek population of O. mirus, a strongly female-biased eclosion sex ratio (proportion of males 0.39 ± 0.05) is observed (Independent Student’s t-test, p = 0.004).
Using
In
Following the designation of a neotype for O. telenomicida by
Body part | O. telenomicida (type locality) | O. telenomicida (Mediterranean) | O. mirus (type locality) | O. mirus (Greece) |
---|---|---|---|---|
Frontovertex | Dark with comparatively strong greenish-blue lustre | Black with weak bronze-green reflections | Black with weak bronze-green reflections | Black with weak bronze-green reflections |
Mesoscutum | Dark with comparatively strong greenish-blue lustre | Black with bronze-green reflections | Black with weak bronze-green reflections | Black with weak bronze-green reflections |
Scutellum | Dark with comparatively strong greenish-blue lustre apically | Black with weak bronze-green reflections apically | Black with weak bronze-green reflections apically | Black with weak bronze-green reflections apically |
Base of gaster | From only base of Gt1 yellow to Gt1 and Gt2 yellow | Gt1–Gt3 yellow | Gt1–Gt3 yellow | From only base of Gt1 yellow to Gt1–Gt3 completely yellow |
Hind coxa | Brown | Yellow | Yellow | Brown |
The extent of the yellow coloration on the base of the gaster varies in the Greek Ooencyrtus, from only the basal half of Gt1 to Gt1–Gt3 being yellow (basal half of the gaster up to the cercal plates). The least yellow specimens are thus similar in this respect to typical O. telenomicida, while the more yellow ones to O. mirus and the Mediterranean O. telenomicida (Table
One must take into consideration when comparing Ooencyrtus specimens that the yellow colour of the legs and base of the gaster is influenced by the treatment received by the specimen. Air dried specimens that have the gaster strongly collapsed will exhibit a darker base of the gaster compared to uncollapsed specimens in alcohol or specimens dried with hexamethyldisilazane. Specimens that had their DNA extracted through lysis, will have the basal tergites of the gaster and the legs of a pale brown colour instead of a saturated yellow colour (cf. Fig.
The divergence calculated using either the p-distance or the K2P distance was very similar, hence we discuss further only the p-distance. On both molecular markers the specimens from Greece are most similar to O. mirus. On the COI sequences the divergence between the Pakistani (type locality) and Greek Ooencyrtus is 1.3%, while on ITS2 it is 0.7%. The closest species to O. mirus in terms of genetic divergence is O. pistaciae with 6.2% on COI and 4.5% on ITS2 when compared to the sequences of O. mirus of Pakistani origin. On both ML phylogenetic trees (Figs
Two distinct COI haplotypes were identified for O. mirus in Greece. Because mitochondria are maternally transmitted in most animals, it means that the colony was founded by a minimum of two females, perhaps one from the 2021 and the other from the 2022 collecting events.
Ooencyrtus mirus is part of the O. telenomicida species group as first proposed by
The group includes O. telenomicida (the first described species), Ooencyrtus acastus described by Trjapitzin from the Russian Far East as part of the group (
Ooencyrtus acestes Trjapitzin, though originally included in the group by
Within this species group we define a subset of morphologically very close species that we name “O. telenomicida species complex”. These species are characterized by the sculpture of the scutellum consisting of elongate cells, cells more obviously elongate mesally and especially on sides (
The species within this complex differ only in the colour of the legs, the intensity and hue of the metallic shine on head and thorax (
In the case of O. mirus the divergence between the specimens from Pakistan and those from Greece is very small on both genes (1.3 and 0.7% on COI and ITS2, respectively). To put this into perspective, the smallest interspecific K2P distance on COI in the Ooencyrtus telenomicida species group is 5% (between O. mevalbelus and O. zoeae) (
When comparing O. mirus with O. telenomicida,
In conclusion, because of the high genetic similarity, we include the Greek Ooencyrtus in O. mirus even though the colour of the hind coxa disagrees and the gaster is as yellow as in typical O. mirus only in few specimens. The colour differences could be due to the geographic distance and to the thelytokous parthenogenetic reproduction of the Pakistan population used to describe the species. It is infected with a strain of Wolbachia and thelytoky appears to be irreversible: even if males are produced after curing the infection, the females are not receptive to their courtship behaviour (
We are grateful to Giuseppino Sabbatini Peverieri (Research Centre for Plant Protection and Certification, Florence) and Serguei V. Triapitsyn (Department of Entomology, University of California, Riverside) for sending the Ooencyrtus specimens from laboratory colonies used as comparative material. Acknowledgement is given to infrastructure support from the Operational Program Competitiveness 2014–2020, Axis 1, under POC/448/1/1 Research infrastructure projects for public R&D institutions/Sections F 2018, through the Research Center with Integrated Techniques for Atmospheric Aerosol Investigation in Romania (RECENT AIR) project, under grant agreement MySMIS no. 127324. This research has been partially co‐financed by the European and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH – CREATE – INNOVATE (MIS-5072510, KIWIPRO).