Japanese beetles’ feeding on milkweed flowers may compromise efforts to restore monarch butterfly habitat

Abstract

The eastern North American migratory population of monarch butterflies (Danaus plexippus) is in serious decline. Habitat restoration, including adding millions of host plants to compensate for loss of milkweed in US cropland, is a key part of the international conservation strategy to return this iconic butterfly to sustainable status. We report here that Popillia japonica, a polyphagous, invasive beetle, aggregates and feeds on flowers of Asclepias syriaca, the monarch’s most important larval food plant, reducing fruiting and seed set by >90% and extensively damaging milkweed umbels in the field. The beetle’s ongoing incursion into the monarch’s key breeding grounds in the US Midwest is likely to limit pollination and outcrossing of wild and planted milkweeds, reducing their capacity to colonize new areas via seeds. Popillia japonica represents a previously undocumented threat to milkweeds that should be considered in models for monarch habitat restoration.

Not Just from Blood: Mosquito Nutrient Acquisition from Nectar Sources

“…pipiens and Ae. aegypti readily respond to the milkweed Asclepias syriaca [31], a common host plant to insects, including butterflies [32] and beetles [33].…”

Natural selection by pollinators on floral attractive and defensive traits did not translate into selection via fruits in common milkweed

“…Latex production is related to flowering time in this species (Parachnowitsch et al 2012), suggesting a relationship between the likelihood of herbivory and the production of latex defence. In A. syriaca, florivory by floral specialists and J Poll Ecol 36(6) generalist herbivores suggests there could also be a defensive function of floral latex (Matter et al 1999;Baker & Potter 2018). Florivory can also be costly, for example, floral damage by the Japanese beetle Popillia japonica, which preferentially feeds on the nectaries and ovaries, can reduce seed set by 90% (Matter et al 1999).…”

Japanese beetle feeding and survival on apple fruits

“…During routine inspections, conducted in 1916, in plant nurseries near Riverton, New Jersey, United States, this insect was observed and reported (DICKERSON;WEISS, 1918;FLEMING, 1976). Currently, P. japonica has colonized almost all of the eastern United States and is moving into the Western Region with increasing reports in the Midwest Region of the country, where considerable population growth has been observed HELD, 2002;BAKER;POTTER, 2018). For example, in Minnesota, United States, P. japonica has been included on the list of the state's most concerning invasive pests that are priorities for research (CFANRS, 2016).…”

“…A wide variety of host plants, exceeding 300 plant species, have been reported as viable food sources for adults (POTTER, HELD, 2002). Its voracity is another factor making this insect a major pest, because it can generate significant losses within a short period of time by skeletonizing leaves, injuring flowers (FLEMING, 1972;BAKER;POTTER, 2018), and even injuring fruits (DAVIS, 1920;FLEMING, 1972;HAMMONS et al, 2009). For example, P. japonica has been reported attacking fruits of grape, raspberry and apple (DAVIS, 1920;FLEMING, 1972;HAMMONS et al, 2009).…”