Invasive paper wasp turns urban pollinator gardens into ecological traps for monarch butterfly larvae

Abstract

Invasive species can be particularly disruptive when they intersect with organisms of conservation concern. Stabilizing the declining eastern migratory population of monarch butterflies (Danaus plexippus) is projected to require extensive habitat restoration across multiple land use sectors including metropolitan areas. numerous conservation programs encourage urban citizens to plant gardens with milkweeds, the obligate larval host plants of the monarch. Here, we show that predation by Polistes dominula, an invasive paper wasp that is particularly abundant in urban settings, can turn such sites into ecological traps for monarch larvae. Polistes dominula was the predominant paper wasp seen foraging in central Kentucky pollinator gardens. In 120 observed encounters with monarch larvae on milkweeds in gardens, most second to fourth instars were killed, whereas most fifth instars escaped by thrashing or dropping. The wasps bit and carried off second instars whole, whereas third and fourth instar kills were first gutted, then processed and carried away piecemeal. Predation on sentinel larvae was much higher in urban gardens than in rural settings. The wasps exploited ornamental butterfly "hibernation boxes" in pollinator gardens as nesting habitat. Polistes dominula is an under-recognized predator that may diminish the urban sector's contributions to monarch habitat restoration. Invasive species can be particularly disruptive when they intersect with organisms of conservation concern 1. Urban ecological restoration can sometimes create ecological traps by attracting native species to colonize patches of semi-natural habitat where they incur inordinately high mortality from exotic natural enemies 2,3. For example, songbirds drawn to naturalized suburban habitat for nesting may suffer heavy predation by (non-native) domestic cats 4,5. Urbanization itself can magnify such interactions by providing nesting sites or other resources for synanthropic invasive predators 6-8. As urban citizens increasingly plant gardens to support native pollinators and other biodiversity 3,9 , it is important those efforts do not inadvertently create ecological traps for species they are intended to benefit. Populations of the monarch (Danaus plexippus), an iconic migratory North American butterfly, are declining 10,11. To help offset this decline, conservationists are encouraging planting milkweeds (Asclepias spp.), the monarch's obligate larval host plants, across the breeding range 12. Despite the public's enthusiasm for monarch-friendly gardening 13,14 , and projections that restoring enough milkweed to ensure a stable monarch population will require participation by the urban sector 12,15 , the conservation value of urban milkweed gardens remains uncertain. Such gardens attract ovipositing adults, often with higher egg-loading per plant than occurs in natural milkweed stands 16-20 , but they could also be ecological traps if they expose monarchs to increased risk of predation, disease, or abiotic mortality factors. Polistes dominula, the...

Invasive paper wasps have strong cascading effects on the host plant of monarch butterflies

“…Densities of P. dominula were highest in suburban areas, which was in accordance with findings of previous research that these wasps prefer to nest on anthropogenic structures (Roets et al, 2019). A higher rate of caterpillar predation in urban gardens was observed in a similar study investigating the predatory effects of P. dominula on monarch caterpillars in differing habitat types (Baker & Potter, 2020). Coastal areas were found to contain comparatively fewer P. dominula nests than suburban areas, which appeared to be reflected in the lower mortality rates of caterpillars in these areas.…”

“…This lower mortality is unsurprising based on observations in the field of large caterpillars thrashing about or dropping to the ground when touched by P. dominula, resulting in the wasp searching elsewhere. Similar observations were made in previous studies focused on the predation of monarch caterpillars by P. dominula (Rayor, 2004;Baker & Potter, 2020). These findings suggest that if a caterpillar is able to survive through earlier instars, there is a size threshold where they are more likely to escape predation.…”

Mixed-Species Gardens Increase Monarch Oviposition without Increasing Top-Down Predation

“…Monarchs are somewhat protected from natural enemies because they sequester cardenolide toxins from their milkweed hosts, rendering them toxic and unpalatable to certain predators [ 53 ]. Despite this, many common generalist predators are able to eat monarchs, including ants (Formicidae) and paper wasps (Vespidae), as well as common monarch parasitoids including tachinid flies (Tachinidae) and chalcidid wasps (Chalcididae) [ 26 , 27 , 29 , 54 , 55 ]. We captured all four of those families on our sticky traps, but ants were by far the most abundant.…”

Giants are coming? Predicting the potential spread and impacts of the giant Asian hornet (Vespa mandarinia, Hymenoptera:Vespidae) in the USA

“…1,2 Invasive species have detrimental effects on the newly colonized areas, such as impoverishment of local species assemblages in terrestrial and aquatic ecosystems, 3,4 as well as the decline of key insects providing herbivore control and pollination services, such as ladybirds, butterflies and bees. [5][6][7] In this sense, invasive hornets and wasps are particularly problematic due to the effects they have on local bee assemblages as well as the possible negative human health implications derived from stings and their allergenic effects. 8,9 In Europe the accidental introduction of the yellow-legged or Asian hornet (Vespa velutina Lepeletier 10 ) has had serious consequences for honey bees (Apis mellifera Linnaeus 11 ), affecting their foraging activity and survival probability.…”

“…Biological invasions are one of the main problems of the 21st century for biodiversity and food production arising from pest introduction in different countries 1,2 . Invasive species have detrimental effects on the newly colonized areas, such as impoverishment of local species assemblages in terrestrial and aquatic ecosystems, 3,4 as well as the decline of key insects providing herbivore control and pollination services, such as ladybirds, butterflies and bees 5–7 . In this sense, invasive hornets and wasps are particularly problematic due to the effects they have on local bee assemblages as well as the possible negative human health implications derived from stings and their allergenic effects 8,9 .…”