Identification of the parasitoid community associated with an outbreaking gall wasp,Zapatella davisae, and their relative abundances in New England and Long Island, New York

Abstract

Gall wasps (Hymenoptera: Cynipidae) are phytophagous insects that often go unnoticed; however, when they are introduced to a new area or released from their natural enemies, they have the capacity to outbreak and cause extensive foliar damage. One such outbreaking pest, Zapatella davisae (Cynipidae: Cynipini), causes significant damage and mortality to black oak, Quercus velutina, in the northeastern United States. In this study, we aimed to identify the parasitoid community associated with Z. davisae, compare differences in percent parasitism of Z. davisae in Cape Cod and Long Island, and determine which parasitoid species contribute most to parasitism in each region. From both locations, we reared parasitoids, identified morphological groups, analyzed percent parasitism rates for each group, and used DNA barcoding to provide species‐level identifications. On Long Island, there was nearly 100% parasitism in 2015 followed by a near total collapse of the population in 2016. In contrast, parasitism rates were lower and remained consistent on Cape Cod between 2015 and 2016, which may explain the greater canopy damage observed in that region. Species of Sycophila were the dominant parasitoids, with one species Sycophila nr. novascotiae representing ~65% of reared parasitoids from Long Island, and two species of Sycophila (S. nr. novascotiae and S. foliatae) with near equal representations on Cape Cod. In order to manage an insect pest, it is important to understand factors that influence its mortality and survival. An understanding of how these infestations progress overtime can help predict the impact that newer infestations in Nantucket, MA, and coastal Rhode Island will have on black oak populations and will aid in the management of this rapidly spreading gall wasp pest.

Delimiting the cryptic diversity and host preferences of Sycophila parasitoid wasps associated with oak galls using phylogenomic data

“…Nevertheless, it is clear that the North American Sycophila is in need of taxonomic revision, and while this is beyond the scope of the current study, the molecular evidence presented here and in previous studies (Davis et al, 2018;Smith-Freedman et al, 2019) has shown that body coloration or wing band shape that was used by Balduf (1932) can vary significantly among conspecifics, and are therefore not reliable diagnostic characters. This is especially evident in species with a small wing band (e.g.…”

“…Assessing species richness and revealing axes of host specialization for gall parasitoids requires a well-resolved and stable parasitoid taxonomy, which in turn requires an integrative approach. Single or multi locus approaches for taxon delimitation that use one or more genes such as the mitochondrial loci COI and Cytb have been used extensively to understand gall community diversity (Ács et al, 2010;Davis et al, 2018;Forbes et al, 2016;Gil-Tapetado et al, 2021;Kaartinen et al, 2010;MacEwen et al, 2020;Nicholls et al, 2018;Nicholls et al, 2010;Sheikh et al, 2021;Smith-Freedman et al, 2019;Ward et al, 2020;Weinersmith et al, 2020;Zhang Y.M. et al, 2014;2019a), often in combination with morphological and/or ecological data.…”

Delimiting the cryptic diversity and host preferences of Sycophila parasitoid wasps associated with oak galls using phylogenomic data

“…Assessing species richness and revealing axes of host specialization for gall parasitoids requires a well-resolved and stable parasitoid taxonomy, which in turn requires an integrative approach. Single or multi-locus approaches for taxon delimitation that use genes such as the mitochondrial loci COI and Cytb have been used extensively to understand gall community diversity (Ács et al, 2010;Davis et al, 2018;Forbes et al, 2016;Gil-Tapetado et al, 2021;Kaartinen et al, 2010;MacEwen et al, 2020;Nicholls et al, 2018;Nicholls et al, 2010;Sheikh et al, 2022;Smith-Freedman et al, 2019;Ward et al, 2020;Weinersmith et al, 2020;Zhang Y.M. et al, 2014;2019a), often in combination with morphological and/or ecological data.…”

“…Some described North America species have a wide host repertoire (e.g., Sycophila quercilanae = 19 gaLL types on various oak species, S. occidentalis = 12, S. varians = 11, S. dorsalis = 9), though lack of detailed study suggests that these host repertoires are probably underestimates, and they are low compared to some Western Palearctic species in oak galls (e.g., Sycophila biguttata = 80, S. variegata = 41; Askew et al, 2013; Balduf, 1932; Noyes, 2019). The high level of sexual dimorphism, morphological plasticity and poorly known biology have further confounded species delimitation within this group (Davis et al, 2018; Gómez et al, 2013; Li et al, 2010; Lotfalizadeh et al, 2008; Smith‐Freedman et al, 2019). An inability to reliably identify Sycophila greatly hampers our understanding of the ecology and evolutionary history of their interactions with host galls, and also limits our understanding of Sycophila serving as potential biocontrol agents of pestiferous gall wasps such as the invasive Asian chestnut gall wasp, Dryocosmus kuriphilus (Dorado et al, 2020), or the North American species Zapatella davisae , which damages black oaks in the New England area (Davis et al, 2018; Smith‐Freedman et al, 2019).…”

“…Assessing species richness and revealing axes of host specialization for gall parasitoids requires a well‐resolved and stable parasitoid taxonomy, which in turn requires an integrative approach. Single‐ or multilocus approaches for taxon delimitation that use genes such as the mitochondrial loci COI and Cytb have been used extensively to understand gall community diversity (Ács et al, 2010; Davis et al, 2018; Forbes et al, 2016; Gil‐Tapetado et al, 2021; Kaartinen et al, 2010; MacEwen et al, 2020; Nicholls et al, 2010, 2018; Nicholls et al, 2018; Sheikh et al, 2022; Smith‐Freedman et al, 2019; Ward et al, 2020; Weinersmith et al, 2020; Zhang et al, 2014; Zhang, László, et al, 2019), often in combination with morphological and/or ecological data. However, results from one or a few genes can be limited in resolution, and single‐locus mitochondrial COI barcodes are known to be misleading due to confounding factors such as incomplete lineage sorting and introgression within both gall wasps and their associated parasitoids (Nicholls et al, 2012; Rokas et al, 2003; Zhang et al, 2021).…”