Biodiversity Highlight - Series #3: Scarabaeidae of the Bull Run Mountains

Biodiversity Highlight (Series #3: Part Two): Macrodactylus subspinosus (American Rose Chafer)
Virginia Outdoors Foundation - Bull Run Mountains Natural Area Preserve

American Rose Chafer (Macrodactylus subspinosus) - Adult specimens observed on the Northern Sections of The Preserve

Hello again everyone,

Welcome back the to our biodiversity highlight series on the Scarabaeidae of The Preserve at Bull Run Mountains. This week's entomological deep dive will be our second entry into the series investigating the Scarab beetles in our area. This large family illustrates some of the most diverse examples of diversity in color and appearance witnessed among Coleoptera. While somewhat mundane to the average gardener, this week's highlight is a remarkable example of the wonder found right under our noses. The rose chafer, or Macrodactylus subspinosus, is a small yellow/gold scarab beetle that may be the bane of any of our traditional English gardeners - but we'll circle back around to that shortly. This small, yellow/gold species of scarab measures about 7-11mm (or around a quarter inch) in length. It is more characterized by its appetite for roses but is physically distinct by sporting long, red legs lined with visible spines and long tarsal claws. The yellowish color of the elytra, thorax, and head are due to the integration of dense, broad setae (or hairs/scales) along the exoskeleton, which may wear off as the beetle ages. Like many other scarabs, this beetle sports a pair of short lamellate antennae terminating in a club of flat plates. In the traditional sense of insect sexual dimorphism, the females of this species are typically more robust than their male counterparts (the opposite of last week's highlight!). The rose chafer is ubiquitous across the Eastern United States and ranges from Quebec to Florida, east to Minnesota, and Texas.

The term chafer is one with a long history and is used colloquially for a variety of beetle species here in the United States and Europe. In the United Kingdom, the term Chafer can be used to describe several beetle species, including the European chafer and Cockchafer. While our rose chafer looks similar to these European examples of chafers, the colloquial descriptor falls short of the scientific classification as the three species are all in separate genera. When the species was first described in 1775, this wasn't the case, as our Macrodacytlyus subspinous was originally placed in the same genus as the Cockchafer (Melolontha melolontha) and listed as Melolontha subspinus. Generally, a chafer can mean any beetle found to be devouring the foliage of your garden or farm plants. Even more generally, chafer can loosely describe the entire subfamily to which our highlight species belongs, the Melolothinae. This subfamily includes the May beetles, June beetles, and ...well… chafers! It is one of the most diverse subfamilies in Scarabaeidae, consisting of about 750 genera and approximately 11000 species worldwide. Taking a closer look at the etymology of our subject's scientific name, Macrodactylus subspinosus. Both our genus and specific epithet take a literal approach to the description of the species. Macrodactylus means "big fingers", which fits well given the species' extended tarsi and claws. These exaggerated appendages make the species seem incredibly awkward while walking across your palm or on flower clusters. While our genus is a humorously blunt interpretation of the species, the specific epithet is a less interesting, but literal description of the organism - subspinous. This specific epithet is vaguely easy to interpret relating to the tarsal spines of the species, but this author would have liked to find the original description for more etymological history - the author did not find what he was looking for.

American Rose Chafer (Macrodactylus subspinosus) - A great visual example of the extended tarsi and tarsal claws of the rose chafer.

© Katja Schulz (@treegrow), some rights reserved (CC-BY)

The rose chafer is a common species that can be encountered across a variety of habitats, however, they are typically observed in old fields habitats, gardens, and forest edges (with specific regard given to their occurrence near vining plant species). They are most active as adults in the summer season between May and July. As mentioned above the rose chafer may rank up there with Japanese beetles (Popillia japonica) as far as garden nuisances go if you're a gardener. The species is notorious for targeting the foliage and flowers of roses, but can be found feeding on a great variety of native and ornamental plants - this list is by no means exhaustive, but demonstrates the adaptability of a hungry native species. Host plants include rose, peonies, grape, apple, birch, blackberry, cherry, dahlia, elder, elm, foxglove, geranium, hollyhock, hydrangea, pear, poppy, raspberry, Virginia creeper, and wisteria (Rosa spp., Paeonia spp., Vitis spp., Malus spp., Betula spp., Rubus spp., Prunus spp., Dahlia spp., Sambucus spp., Ulmus spp., Digitalis spp., Geranium spp., Alcea spp., Hydrangea spp., Pyrus spp., Papaver spp., Parthenocissus quinquefolia, Wisteria spp.). Damage can include the partial or total consumption of flower petals, and buds, and the skeletonization of foliage. Although not an invasive species, large quantities of beetles can descend on gardens and agricultural areas causing enough damage to warrant their classification as a pest species. Instances of dozens of beetles on one plant can be observed in extreme cases. This applied role as a pest species is assigned in varying degrees depending on your reference resource. Some classify the species as only a minor pest species, while others treat the species in a similar vein to more destructive species like the Japanese beetle. This harsher application of pests seems to have more roots in a time when the species was a greater nuisance and abundance.

As we have delved into in our other scarabaeoid species highlights, this species also includes a "white grub" form as a larva. Diverging from our previous trend, this species does not feed on decaying woody materials like the Dynastinae and Lucanidae but feeds on the living roots of grass species and non-crop plants. There are mixed references to the species damaging horticultural resources like turf. Unlike our previous entries, the rose chafer is a rather quick-lived species, hatching from its egg and completing its life cycle in about a year. Following the ingestion of all your garden plants (or more likely and commonly the flowers and foliage of the native plant species in our area), mating in sometimes large masses on plants, the female will lay her eggs in the soil near the host plant's base. The species prefers more sandy soils, which may account for them becoming horticultural pests as many gardeners mix sand into soils for better drainage. rose chafer grubs hatch after a few weeks and feed until the late fall when they pupate and overwinter. After emerging as adults in the following summer, adult beetles only live for about 4-6 weeks while searching for food and mates.

American Rose Chafer (Macrodactylus subspinosus) - Mating individuals; note the wore appearance of the female underneath [left]. Defoliation of host plant by individuals [Right]

In a final note about the species, we are going to explore one of the most interesting adaptations this species has for self-defense. In regards to our previous beetle highlights, our subjects did not have much beyond their size and maybe their mandible/horns to protect them from larger predators - evolutionary tools which may provide little defense when faced with a large bird or snake. In regards to the rose chafer, this beetle is armed with a chemical defense that may not provide much in preventing its demise but demonstrates to the predator that this species is not one to target for a quick snack. This chemical defense is cantharidin, a chemical more associated with the Coleopteran family Meloidae, or blister beetles. While the species has no external mechanism to discourage predation, ingestion of the beetle is toxic to predators like birds. In the Meloidae, the chemical is excreted from the joints via "reflex bleeding" and can cause blisters to appear on the skin of a person handling them. The rose chafer is harmless to handle because the chemical is an internal deterrent, similar to the poisons carried by other brightly colored insect species, which warn would-be predators of their toxicity.

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Publicado el septiembre 23, 2022 07:04 TARDE por

mjwcarr

Biodiversity Highlight - Series #3: Scarabaeidae of the Bull Run Mountains - Part Two

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