Insect communities on experimental mugwort ( Artemisia vulgaris L.) plots along an urban gradient

Abstract

We studied the ability of insect herbivores and their natural enemies to colonize exposed, potted mugwort plants (Artemisia vulgaris L.) along a rural-urban gradient in 1994 in Hamburg (northern Germany). Ectophagous insects, leafmines and galls were monitored weekly from mid-May to mid-September. Endophagous insects were counted by harvesting and dissecting the stems at the end of the growing season. The rural-urban gradient was characterized by a gradient of vegetation-free areas and increasing proportion of ground covered in concrete, tarmac, paving and other impermeable surfaces surrounding the Artemisia plots, i.e. six different zones of increasing isolation. Numbers of insect species (herbivores, parasitoids and predators) decreased along the gradient from 43 to 12. Monophagous herbivores were not more affected than polyphagous herbivores, but parasitoids, especially rare species, were more strongly affected by isolation than predators. Some dominant herbivorous species were very successful colonizers and occurred in inner city sites devoid of all natural vegetation. Sometimes their abundance increased in the inner city to significantly higher densities than in the urban fringe. Isolation appeared to be the main reason for the observed patterns, since area and soil conditions were held constant in the experiment. Microclimate and pollution were considered to play a minor role.

Does urbanization explain differences in interactions between an insect herbivore and its natural enemies and mutualists?

“…However, a few trends have begun to appear. Urban areas are often characterized by reduced numbers of native vertebrate predators (McKinney 2002;Shochat 2004), an increased abundance of some urban-adapted species, which can potentially lead to increased competition and displacement (Hostetler and McIntyre 2001), altered behavior and phenology (Connor et al 2002;Neil and Wu 2006), high densities of herbivorous arthropods (Dreistadt et al 1990;Hanks and Denno 1993;Tooker and Hanks 2000), lower numbers of arthropod predators (Turrini et al 2016) and lower numbers of parasitoids (Denys and Schmidt 1998;Bennett and Gratton 2012;Burks and Philpott 2017). All these changes can potentially lead to altered trophic structure, and we must recognize that trophic dynamics cannot be understood based only on our knowledge of species composition (Shochat et al 2006).…”

Climatic variability and landscape heterogeneity impact urban mosquito diversity and vector abundance and infection

“…Cities also allow to test whether b-diversity differences, in this case understood as changes in species composition across the different habitats encompassing the urban landscape (Denys andSchmidt 1998, Zanette et al 2005), are driven by any of the main processes shaping diversity patterns: selection, drift, speciation and dispersal (Vellend 2010). A predominant role for drift can be revealed by habitat homogeneization leading to nested patterns, i.e., where differences in species richness are due to species loss (McKinney andLockwood 1999, Baselga 2010), the turnover of species can highlight the presence of selection/speciation processes, while dispersal limitation can be tested by comparing associations of b-diversity differences with the geographical distance between sites sampled (Baselga 2010, Vellend 2010.…”

The biology of Canadian weeds. 118. Artemisia vulgaris L.

“…A survey of A. vulgaris roadside populations in Germany revealed 65 species of insects, mites, and spiders residing on this weed (Denys and Schmidt 1998). Among the most abundant species were Liriomyza spp., Bucculatrix noltei, Macrosiphoniella artemisiae, Trypeta zoe, and Macrosiphoniella oblonga.…”