Invasive moth facilitates use of a native food plant by other native and invasive arthropods

Abstract

Organisms that invade new habitats exploit new resources or niches and influence native species. Here, we examine how an invasive moth, the parsnip webworm (Depressaria radiella, formerly D. pastinacella), facilitates interactions with other arthropods in spatially separated populations of native cow parsnip (Heracleum maximum) in the Rocky Mountains (New Mexico and Colorado). We compare this with results on small hogweed (Heracleum sphondylium) in the Netherlands, where both the plant and herbivore are native. Larvae of D. radiella feed in webs on ripening fruits of their food plants. Mature caterpillars descend the hollow stems into which they chew a hole, enter the stem and pupate. Other arthropods enter the stems through these holes. Plants in all populations of cow parsnip/hogweed contained either moth pupae and/or webworms mummified by their main parasitoid, Copidosoma sosares that also been introduced into parts of the United States. In both countries, earwigs (Forficula auricularia), which are also invasive in the United States, were the dominant arthropod to utilize webworm‐perforated stems, although there was more within‐site variability in abundance of earwigs in the United States than in the Netherlands. The woodlouse, Porcelio scaber, which is native to Eurasia but also established in the United States, was abundant in stems of Dutch hogweeds but absent in stems of American cow parsnips. Other native herbivores (e.g., mirid bugs), were collected in stems at sites in both continents. Moreover, the number of various arthropods found in perforated stems correlate positively with the number of holes found in these stems.

Artificially perforated holes in stems of small hogweed mimic ecosystem engineering by a moth

“…In line with previous studies (i.e. Harvey et al, 2016;Harvey et al, 2019), stems of plants at site 3 that were naturally perforated by D. radiella caterpillars also contained woodlice and earwigs in numbers similar to those found in stems with artificially perforated holes. Species composition of the arthropod community within hogweed stems and in the vegetation surrounding the stems differed;…”

“…Moreover, both P. scaber and F. auricularia were also introduced into North America and are now widely distributed. A previous study conducted in the Rocky Mountains of Colorado and New Mexico found that native populations of the cow parsnip, H. maximum , that had been infested with D. radiella larvae also harboured variable numbers of earwigs (but not woodlice) that similarly entered the stems through the holes chewed by mature webworm caterpillars Harvey et al (2019). Remarkably, the authors even found a native North American Clubiona species inside several D. radiella ‐perforated stems of cow parsnip H. maxima plants.…”

“…Another shelter‐building insect is the parsnip webworm, Depressaria radiella Goeze (Lepidoptera: Depressariidae), a specialist‐feeding herbivore of the small hogweed, Heracleum sphondylium L. (Apiales: Apiaceae) and related species, that is native to Eurasia but is now introduced across much of the world (Berenbaum & Zangerl, 2006; Harvey et al, 2016; Harvey et al, 2019; Harvey et al, 2020; Ode et al, 2004). In the Netherlands, adult moths of D. radiella begin laying their eggs on leaves of H. sphondylium in early June.…”

Population- and Species-Based Variation of Webworm–Parasitoid Interactions in Hogweeds (Heracelum spp.) in the Netherlands

“…One of the major differences between native (European) and invasive (North American) interactions between webworms and their food plants is that populations of hogweeds and wild parsnips in the native European range have been constantly exposed to threat of webworm attack for millennia. In contrast, in the United States, where webworms are invasive, they attack the native cow parsnip (Harvey et al 2019) or invasive populations of wild parsnip (Lohman et al 1996). Cow parsnips do not have a long co-evolutionary history with webworms, whereas wild parsnips were re-acquainted with webworms after at least several decades of isolation from them.…”