Beetles on Mallow
Common Mallow (Malva sylvestris L.) should be familiar to all coleopterists because it hosts a few beetles that are common and widespread and that are rarely found on other plants, and plants growing in just about any situation are likely to host at least one, and more likely several of these species. A few other members of the Malvaceae are also attractive to mallow-feeding beetles and so should always be inspected e.g. cultivated Hollyhocks (Alcea L.) are sometimes productive and, so far, this is the only host of Rhopalapion longirostre (Olivier, 1807), a species only recently recorded in the UK. Marsh Mallow (Althaea officinalis L.) is another example, in this case hosting the tiny monophagous brentid, Aspidapion sorror (Rey, 1895). Common Mallow is a perennial herbaceous plant that can be very vigorous and extremely tenacious, at best it forms magnificent banks of large flowering plants in the summer, at worst it persists as a low-growing weed in lawns that defies all attempts at eradication, but which generally grows individually or in small groups in a wide range of habitats. Common Mallow is the type species of a large genus, it is native to the Western Palaearctic region but has spread with trade throughout the world, and it has been used in all sorts of medicinal and culinary roles that should be of absolutely no interest to the coleopterist whatsoever. The species is common throughout England, Wales and most of lowland Scotland but is largely missing from Ireland; it can grow on any soil type in most situations and will often thrive on disturbed sites such as gardens, allotments and waste ground. It is adept at persisting in lawns and other hostile habitats for years without flowering or even producing much in the way of foliage, but once left alone it will soon produce a mass of stems and foliage over the course of a single season. In short, it can be a pain for gardening types but for coleopterists it is a delight.
Common Mallow is commonly grown as an ornamental plant in herbaceous borders, and to this end many cultivars have been produced, these have bred to produce larger flowers in a wide range of colours, they flower over a long season and often have modified foliage. Cultivar flowers range from Blue to pink, often with stripes of darker or paler colour; they are generally attractive to both humans and beetles, are easily identified and should always be examined. The wild form has purple or reddish-purple flowers with darker stripes which appear in irregular axillary clusters along stems and usually open in sequence from the base of stems. The leaves are deep green and weakly incised pentagonal-palmate (this varies widely) with the veins and fine pubescence radiating from a point at the base. Foliage forms near the soil surface in the spring, it soon forms a dense clump and from this stems grow rapidly from April or May, depending on the season, at this time the foliage is lush, dark and dense, but as the season progresses and the stems lengthen it becomes paler, leaves fall and the plants start to look straggly. By June or July they may reach more than a metre high and carry numerous flowers, and where several plants are growing together they make impressive displays. Stems lengthen and foliage falls during the summer so that by August or September the plants begin to look bare and unhealthy. Foliage often falls or turns black in response to frost and plants may die back but leaves usually persist close to the ground and, in these days of milder winters, it is not uncommon for plants to survive the winter intact. Because they are easily identified and may be found at any time, mallow plants should always be examined for beetles.
Two leaf beetles are associated with Mallow: Podagrica fuscicornis (Linnaeus, 1767) and P. fuscipes (Fabricius, 1775). The former is widespread and locally common across southeast England while the latter is much more local and mostly restricted to the Thames estuary although there are also coastal records from the south and a few from the midlands and East Anglia. Adults of both occur through the spring and summer but both overwinter as larvae. Two further species occur in Europe; P. malvae (Illiger, 1807) and P. menetriesi (Faldermann, 1837), and both are specialist Mallow feeders. Our other Mallow feeders are all brentids. Malvapion malvae (Fabricius, 1775) is common and widespread across southern England and Wales, adults occur over a long season during spring and summer and they are readily identifiable, even in the field. Pseudapion rufirostre (Fabricius, 1775) is also common across the south although more coastal in the west, it may be identified by the dark and slightly metallic body and red legs, and males may be distinguished in the field by the bicoloured rostrum. Our other mallow species are included in the genus Aspidapion Schilsky, 1901; this genus includes four European species of which three occur in the UK. All are mallow feeders. A. aeneum (Fabricius, 1775) is a large and dark species with bright metallic blue elytra which appear glabrous in the field; it is generally common across the southeast but otherwise widespread and very local. Adults occur from spring to autumn and overwinter among litter etc. near to host plants. Our two remaining species are small, black or with a slight metallic reflection, and distinctly pubescent. A. radiolus (Marsham, 1802) is generally common throughout England and Wales though more local in the north where it extends into Southern Scotland. Adults are active from spring to autumn and they overwinter near to host plants, the species is the most common of our mallow-feeders and by late spring adults are often present in large numbers. The Marsh Mallow feeder, A sorror (Rey, 1895) is similar to radiolus, and specimens will need to be examined very carefully for accurate identification, fortunately host-plant association is the best clue here. A. sorror is a very local and generally rare species of South East and Central England and South Wales.
Mallow in any situation should be examined, beating or sweeping usually reveals the beetles but by early summer the foliage usually shows signs of adult feeding and these are a good guide to the beetle’s presence. Larvae of Aspidapion feed within stems while those of Pseudapion and Malvapion develop and pupate within seed pods. Of course other beetles will be found on Mallow but our specialist Common Mallow feeders are all distinctive enough to be named with confidence from association with the plant.