Evolution of Specialization of Cassida rubiginosa on Cirsium arvense (Compositae, Cardueae)

Abstract

The majority of herbivorous insects are specialized feeders restricted to a plant family, genus, or species. The evolution of specialized insect–plant interactions is generally considered to be a result of trade-offs in fitness between possible hosts. Through the course of natural selection, host plants that maximize insect fitness should result in optimal, specialized, insect–plant associations. However, the extent to which insects are tracking plant phylogeny or key plant traits that act as herbivore resistance or acceptance characters is uncertain. Thus, with regard to the evolution of host plant specialization, we tested if insect performance is explained by phylogenetic relatedness of potential host plants, or key plant traits that are not phylogenetically related. We tested the survival (naive first instar to adult) of the oligophagous leaf-feeding beetle, Cassida rubiginosa, on 16 selected representatives of the Cardueae tribe (thistles and knapweeds), including some of the worst weeds in temperate grasslands of the world in terms of the economic impacts caused by lost productivity. Leaf traits (specific leaf area, leaf pubescence, flavonoid concentration, carbon and nitrogen content) were measured as explanatory variables and tested in relation to survival of the beetle, and the phylogenetic signal of the traits were examined. The survival of C. rubiginosa decreased with increasing phylogenetic distance from the known primary host plant, C. arvense, suggesting that specialization is a conserved character, and that insect host range, to a large degree is constrained by evolutionary history. The only trait measured that clearly offered some explanatory value for the survival of C. rubiginosa was specific leaf area. This trait was not phylogenetically dependant, and when combined with phylogenetic distance from C. arvense gave the best model explaining C. rubiginosa survival. We conclude that the specialization of the beetle is explained by a combination of adaptation to an optimal host plant over evolutionary time, and key plant traits such as specific leaf area that can restrict or broaden host utilization within the Cardueae lineage. The phylogenetic pattern of C. rubiginosa fitness will aid in predicting the ability of this biocontrol agent to control multiple Cardueae weeds.

Symbiont Digestive Range Reflects Host Plant Breadth in Herbivorous Beetles

“…Consistent with the latter, an upgraded digestive capacity by Stammera appears to not only reflect a broader phylogenetic host plant coverage but also an expanded geographical distribution that extends beyond the tropical origins of the Cassidinae [17]. Beetles symbiotically endowed with rhamnogalacturonan lyase and polygalacturonase exploit host plants adapted for temperate climates, such as thistles [23][24][25], mints [22], and Maleae trees [21], in contrast to the tropical or subtropical distributions of lamiid host plants for cassidines relying solely on polygalacturonase [18][19][20]27]. This biogeographical pattern is notable, given that land plants enrich for RG-I in response to drier growth conditions [63,64].…”

Effects of Temperature and Photoperiod on the Immature Development in Cassida rubiginosa Müll. and C. stigmatica Sffr. (Coleoptera: Chrysomelidae)

“…Besides Carduus and Cirsium thistles, larvae and adults feed on a wide variety of other asteraceous plants from the tribe Cynareae (=Cardueae), such as species of Arctium , Cynara , Silybum etc . 8,27,28,37–39 .…”

Impact of the biocontrol beetle, Cassida rubiginosa, on the secondary weed target, marsh thistle (Cirsium palustre)

“…Utilisation of these plants was predicted by pre-release choice and no-choice host testing (Paynter et al 2015); however, the potential impact on individual plant, or population performance, is uncertain. As an initial step towards understanding the potential impact of Cassida rubiginosa on other thistle weeds, marsh thistle was selected as a test species, since it is closely related (congeneric) to Californian thistle, and the survival of the beetle is equivalent on this species (Cripps et al 2016). The objective of this study was to test the impact of different densities of Cassida rubiginosa larval feeding on growth and reproductive performance of marsh thistle.…”