Beetles on bittersweet

Solanum dulcamara L., more commonly known as bittersweet or woody nightshade, is a member of the Solanacaea and closely related to various cultivated crops and ornamental plants such as potato, tomato and petunia. It is native to the Western Palaearctic region and common throughout Europe and North Africa, it is also established in North America, Australia and New Zealand following accidental introductions. In much of Europe, including most of the UK and its islands, it grows as a weed in a wide variety of habitats; it thrives in wetlands, including floodplains that become regularly inundated, but is also common in drier habitats such as agricultural land, wasteland, and coastal dunes, it can tolerate wide range of soil types and is often common on nutrient rich top-soils in parks and gardens. The plant is a hardy perennial that will persist for many years under a wide range of conditions, the growing season is generally early March until October or November when the leaves drop and most of the stems and branches die back, those remaining will produce new growth the following spring. This wide tolerance of conditions may also be seen in the mode of growth; depending on nutrient and light conditions, among other things, it will either form a stable bush up to 2 metres high with sturdy woody stems, or it will climb fences or nearby trees and shrubs and form extensive masses of spindly growth reaching up to five metres. Various parts of the plant are poisonous, the roots, flowers and unripe fruits contain alkaloids which probably act against slugs and browsing animals; solanine (a complex glycoalkaloid found in the unripe fruits) is known to be poisonous to humans, lethal cases are rare but several have been recorded, and extracts have been used by herbalists since the Middle Ages against various maladies and were thought to be especially effective against witchcraft. Bumblebees are the most important pollinators as their buzzing is essential for releasing pollen from the anther cone, and dispersal is primarily by birds eating the fruits, especially thrushes that seem to be immune from the toxic effects.

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Bittersweet - Solanum dulcamara

The plants are very distinctive, especially when flowering or carrying fruit, and as they grow just about anywhere, the coleopterist should make a point of sampling them.  Leaves grow alternately along thin stems, they are up to 12 cm long, and cordate with a large apical lobe and several smaller lateral ones, the margins being either smooth or toothed, they are lime-green when fresh but turn darker with age. Flowers form in alternate or opposite clusters along the apical parts of thin woody stems, they are star-shaped with five attractive narrow petals and a ring of yellow anthers surrounding a yellow stigma, flowers at the base of a cluster tend to open first but eventually the whole cluster will be in flower at the same time, berries form after flowering, they are initially green but turn through orange to an attractive deep red, and it is not unusual to see red berries at the base of a stem while flowers are still developing at the apex. Both flowers and berries are present through the summer and into the autumn.

Despite the poisonous nature of bittersweet, it hosts a varied insect community, this involves only a very few beetles that consume the plant tissues, but through the spring and summer plants usually host large populations of aphids and whitefly, and these attract ladybirds that want to harvest them and ants that want protect them and harvest their honeydew. The leaves also secrete droplets of sugar when attacked and this further attracts and ladybirds and ants. Ants recorded from bittersweet include Myrmica rubra (Linnaeus, 1758), Formica fusca Linnaeus, 1758, Lasius niger (Linnaeus, 1758) and L. brunneus (Latreille, 1798), this last being a saproxylic (mainly associated with oak) and mostly nocturnal species which forages over a wide area. Among the ladybirds are the usual aphidiophagous species, Anisosticta novemdecimpunctata (Linnaeus, 1758), Coccinella quinquepunctata Linnaeus, 1758, C. septempunctata Linnaeus, 1758, Harmonia axyridis (Pallas, 1773), Exochomus quadripustulatus (Linnaeus, 1758), Propylea quattuordecimpunctata (Linnaeus, 1758), Adalia bipunctata (Linnaeus, 1758), A. decempunctata (Linnaeus, 1758) Stethorus punctillum (Weise, 1891) (feeding on psyllid eggs) and the infrequently-recorded Hippodamia tredecimpunctata (Linnaeus, 1758), the particular species likely to occur depending upon the habitat. Other insects using bittersweet as a host tend to be polyphagous on Solonaceae, these include a leaf-mining fly, Liriomyza bryoniae (Kaltenbach, 1858) (Agromyzidae), which is a horticultural pest only very rarely recorded in the UK and otherwise known as the Tomato Leaf-miner, several thrips, a few micro-moths and noctuids and the spectacular Acherontia atropos (Linnaeus, 1758) or Death’s-head hawk moth. Most of these species occur on cultivated Solonaceae and so the bittersweet acts as a refuge and source of infestation in arable areas.

Only a few beetles use bittersweet as a host and, again, these tend to be more widely polyphagous on Solonaceae, and most are leaf beetles included in Chrysomelidae. The Colorado Potato Beetle, Leptinotarsa decemlineata (Say, 1824)is native to the Nearctic region and has become established across Europe following several accidental introductions during the 20th century, most notably following the second world war, it is better known as a peat of cultivated potatoes, and to a lesser extent other crops such as tomato and aubergine (etc), it has been recorded in the UK on only a very few occasions and has never become established, but it is common across northern Europe and, given the obscene quantities of crops imported into the UK, it might occur here at any time. Adult lily beetles, Lilioceris lilii (Scopoli, 1763) occasionally eat the foliage but their larvae do not develop on bittersweet. Epitrix pubescens (Koch, J.D.W., 1803) is polyphagous on Solonaceae and bittersweet is the usual host; it is locally common across the south of England and should soon be found by sweeping as adults feed on host foliage. Epitrix Foudras in Mulsant, 1859 includes more than 100 species worldwide, 9 occur in Europe and 12 in the Nearctic region, and all are associated with Solonaceae; our other UK species, E. atropae Foudras, 1860 is associated with various species, especially deadly nightshade, Atropa belladonna L., but so far as is known does not occur on bittersweet. Ochrosis ventralis (Illiger, 1807) is a very local and mostly coastal species in Wales and southern England; it occurs on plants of various families including Lythraceae, Asteraceae, Primulaceae and Caryophyllaceae but bittersweet is the usual host. Two UK species of Psylliodes Berthold, 1827 are associated with various Solonaceae but will most often be found on bittersweet. P. affinis (Paykull, 1799) is generally common across England and Wales and is probably the most frequently encountered beetle on this plant; it occurs throughout the spring and summer and is easily identified by its distinctive colour. P. dulcamarae (Koch, J.D.W., 1803) is a more southern species, it is common in the southeast and the midlands but rare and mostly coastal in the west, the bright metallic blue and very convex form make it unmistakable. Various other widely polyphagous chrysomelids such as P. luteola (Müller, O.F., 1776) or Aphthona lutescens (Gyllenhal, 1808) may also swept from the foliage but they are not known to breed on the plant. The only other UK species known to use the plant as a host is the tiny nitidulid Pria dulcamarae (Scopoli, 1763), both adults and larvae feed on pollen and flower buds; adults fly well and may visit a range of other flowers to feed but the larvae develop only on bittersweet and black nightshade (Solanum nigrum L.) Pria occurs across Wales and southern England but tends to be very local, it may be abundant where it occurs and adults may sometimes be seen on warm afternoons swarming in flight around the hosts.

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