A modified DNA barcode approach to define trophic interactions between native and exotic pentatomids and their parasitoids

Abstract

The establishment of invasive Halyomorpha halys (Stål) outside of its native range may impact native species assemblages, including other pentatomids and their scelionid parasitoids. This has generated interest in defining species diversity and host-parasitoid associations in this system to better understand the impact of invasive alien species on trophic interactions in invaded regions. Information on scelionid-pentatomid associations in natural habitats is lacking, and species-level identification of these associations can be tenuous using rearing and dissection techniques. Naturally occurring pentatomid eggs were collected in areas where H. halys has established in Canada and were analysed using a modified DNA barcoding approach to define species-level trophic interactions. Identification was possible for >90% of egg masses. Eleven pentatomid and five scelionid species were identified, and trophic links were established. Approximately 70% of egg masses were parasitized; parasitism and parasitoid species composition were described for each species. Telenomus podisi Ashmead was the dominant parasitoid and was detected in all host species. Trissolcus euschisti Ashmead was detected in several host species, but was significantly more prevalent in Chinavia hilaris (Say) and Brochymena quadripustulata (Fabricius). Trissolcus brochymenae Ashmead and Tr. thyantae Ashmead were recorded sporadically. Parasitism of H. halys was 55%, and this species was significantly less likely to be parasitized than native pentatomids. The scelionid species composition of H. halys consisted of Te. podisi, Tr. euschisti and Tr. thyantae. Although these species cannot develop in fresh H. halys eggs, we demonstrate that parasitoids attempt to exploit this host under field conditions.

A molecular tool to identify Anastatus parasitoids of the brown marmorated stink bug

“…Given that the Anastatus primers are also within the DNA barcoding region, they could, if proven to be compatible, potentially be used in combination with the primer pair for Scelionidae (SCEL: SCEL-F1/HCO-2198) (Gariepy et al, 2014) to assess multispecies interactions in the Pentatomidae. However, in order to determine species-level interactions, DNA sequencing of both scelionid and Anastatus amplicons would be required for species-level resolution (as was done for scelionids and pentatomids in Gariepy et al, 2019). This type of DNA sequencing approach allows broad applicability of the technique, regardless of geography, as the same primers amplify Anastatus from North America, Europe, and Asia, and the DNA barcode library for these species (BOLD project NASTA) would allow species separation based on single-nucleotide polymorphisms in the DNA barcode region.…”

“…Recently, trophic interactions between Pentatomidae hosts, including H. halys, and their scelionid parasitoids were investigated in North America with a modified DNA barcode approach (Gariepy et al, 2019). Given that the Anastatus primers are also within the DNA barcoding region, they could, if proven to be compatible, potentially be used in combination with the primer pair for Scelionidae (SCEL: SCEL-F1/HCO-2198) (Gariepy et al, 2014) to assess multispecies interactions in the Pentatomidae.…”

“…With this molecular tool, recovered eggs from the field can be screened for the presence or absence of Anastatus species, and trace amounts of DNA can even be detected following parasitoid emergence. This forensic-style approach (screening of empty egg masses for traces of parasitoid DNA) can provide valuable information regarding the ecological host range and impact of a parasitoid on nontarget species, which is often a decisive factor in pre-and post-release assessments of biocontrol agents (Gariepy et al, 2008(Gariepy et al, , 2019. In the present study, field-exposed sentinel egg masses which had been stored for several months at 26°C nonetheless yielded Anastatus PCR products, despite the fact that storage conditions were less than ideal in terms of preserving DNA and preventing degradation.…”

“…First, species-level identification of the host eggs is challenging, as there are few distinguishing morphological characters in the egg stage (Esselbaugh, 1946;Bundy & McPherson, 2000;Gariepy et al, 2014). To overcome some of these difficulties, a modified DNA barcode approach was developed with general primers for Pentatomidae and Scelionidae in order to evaluate host-parasitoid associations in this system (Gariepy et al, 2014;Gariepy et al, 2019). Identifying the associated egg parasitoids after their emergence is similarly challenging.…”

“…Even if the parasitoid was still present inside the host egg, pre-imaginal mortality can prevent identification via rearing and even dissections are of little use once the parasitoids have disintegrated. To overcome some of these difficulties, a modified DNA barcode approach was developed with general primers for Pentatomidae and Scelionidae in order to evaluate host-parasitoid associations in this system (Gariepy et al, 2014;Gariepy et al, 2019). However, Anastatus species were not included in this analysis.…”