Ecology and Genetic Structure of the Parasitoid Phobocampe confusa (Hymenoptera: Ichneumonidae) in Relation to Its Hosts, Aglais Species (Lepidoptera: Nymphalidae)

Abstract

The biology of parasitoids in natural ecosystems remains very poorly studied, though they are key species for their functioning. Here we focused on Phobocampe confusa, a Nymphalini specialist, responsible for high mortality rates in charismatic butterfly species in Europe (genus Aglais). We studied its ecology and genetic structure in connection with those of its host butterflies in Sweden. To this aim, we gathered data from 428 P. confusa individuals reared from 6094 butterfly larvae (of A. urticae, A. io, and in two occasions of Araschnia levana) collected over two years (2017 and 2018) and across 19 sites distributed along a 500 km latitudinal gradient. We found that P. confusa is widely distributed along the latitudinal gradient. Its distribution seems constrained over time by the phenology of its hosts. The large variation in climatic conditions between sampling years explains the decrease in phenological overlap between P. confusa and its hosts in 2018 and the 33.5% decrease in the number of butterfly larvae infected. At least in this study, P. confusa seems to favour A. urticae as host. While it parasitized nests of A. urticae and A. io equally, the proportion of larvae parasitized is significantly higher for A. urticae. At the landscape scale, P. confusa is almost exclusively found in vegetated open land and near deciduous forests, whereas artificial habitats are negatively correlated with the likelihood of a nest to be parasitized. The genetic analyses on 89 adult P. confusa and 87 adult A. urticae using CO1 and AFLP markers reveal a low genetic diversity in P. confusa and a lack of genetic structure in both species, at the scale of our sampling. Further genetic studies using high-resolution genomics tools will be required to better understand the population genetic structure of P. confusa, its biotic interactions with its hosts, and ultimately the stability and the functioning of natural ecosystems.

Rewiring of interactions in a changing environment: nettle‐feeding butterflies and their parasitoids

“…While in some systems parasitoid activity can increase with temperature (Mann et al 1990), which could lead to a higher activity period and oviposition rate in the parasitoids at lower and warmer latitude, the literature does not provide consistent evidence of such a pattern (Hawkins 2005). Further, the recorded differences in microclimatic conditions across sites do not align with the latitudinal pattern observed for parasitism (Supplementary material Appendix 1 in Audusseau et al 2020). However, we observed latitudinal differences in the parasitoid community.…”

“…From our study, we cannot rule out the possibility of other spatial confounds causing the differences in parasitism rates across counties. Among the factors not considered here, the differences in parasitoid population dynamics, habitat quality, parasitoids community or the variation in phenological synchrony between the butterflies and their parasitoids (Audusseau et al 2020), may all contribute to the observed decrease in parasitism rates along the latitudinal gradient. For example, the occurrence of other hosts for the parasitoids in the landscape, but not included in our study, may influence the population dynamics of parasitoids and mediate apparent competition (Davis 1991, Gaston et al 2005).…”

The mango seed weevil Sternochetus mangiferae (Fabricius) (Coleoptera: Curculionidae) is characterized by low genetic diversity and lack of genetic structure

“…Other population genetic parameters also indicated that S. mangiferae has low haplotype and nucleotide diversity (Table 2). For instance, the mtDNA nucleotide and haplotype diversity values observed in S. mangiferae are similar to that of a number of other species (Brusentsov et al, 2013;Garcia-Cisneros et al, 2016;Cao et al, 2017;Nakano et al, 2017;Kohli et al, 2018;Audusseau et al, 2020), which were also implicated as possessing low genetic diversity.…”

Larval parasitism in a specialist herbivore is explained by phenological synchrony and host plant availability

“…The overlap (i.e. temporal co‐occurrence) between the host and its two main parasitoids, Pelatachina tibialis and Sturmia bella , was estimated using the Overlap Parasitoid‐Host index (OPH), as described by Audusseau et al (2020). This index was calculated for all possible combinations of site and year in each region.…”