Gastrophysa Chevrolat in Dejean, 1836
This small Holarctic genus of leaf beetles is represented in Europe by four species in two subgenera, the two members of Gastrophysa s. str. are widespread and extent north into the UK while the two species of subgenus Exiguipenna Jolivet, 1951 have very restricted distributions , one is endemic to Portugal and Spain and one to Bosnia and Herzegovina. They are small, convex and brightly metallic species which may be recognized among our UK fauna by the following combination of characters: 4-6 mm, antennae separated by more than the length of the basal segment, pronotum only slightly narrower than the elytra, elytra confusedly punctured with an impressed groove adjacent to the suture in the apical quarter, epipleura without a small fringe of hairs towards the apex, apex of all tibiae wide, truncate and bearing a single apical spur. Our two species are easily identified by the habitus and the colour of the pronotum. Both are common and widespread and both occur on various Polygonaceae; G. viridula (De Geer, 1775) usually on Broad-leaved Dock (Rumex obtusifolius L.) and G. polygoni (Linnaeus, 1758) usually on Knotgrass (Polygonum aviculare L.)
Gastrophysa polygoni (Linnaeus, 1758)
This very widespread species is locally common throughout the Palaearctic region, extending from Portugal and North Africa to China, Korea and Japan and across North America where it is among the most common leaf beetles of cereal fields, it is present on the Mediterranean and Atlantic islands and extends north to the UK and far beyond the Arctic Circle in Fennoscandia. It occurs from lowlands to alpine altitudes and has been recorded at 2400, in Bulgaria. Here it is common across Wales and south and central England, less so Wales and further north to the Scottish Highlands, and sporadic and scarce in Northern Ireland. Adults are present year-round and are usually active between early April and October, they occur in a wide range of habitats including grassland, moorland, open woodland, scrub and roadside verges and occasional large populations occur on arable land after cereal crops have been harvested. Host plants include a range of Polygonaceae e.g. knotgrass (Polygonum arviculare L.), redshank (Persicaria maculosa Gray), sorrel (Rumex acetosa L.), Russian vine (Fallopia baldschuanica (Regel)), buckwheat (Fagopyrum sagittatum Gilib.) and various docks (Rumex L.) and adults commonly occur on flowers, especially hawthorn blossom. Adults overwinter among tussocks or litter, they emerge early in the year and disperse by flight to flowers or host foliage to feed before mating begins, they feed openly on foliage and produce small holes but generally do little damage to the plants. Females oviposit from late April until the end of August, each female ovipositing over a period of about forty, days but this can be confusing as two generations have been observed in the UK and the oviposition period will involve females from both, they lay several batches of eggs each day on the underside of host leaves and larvae emerge after a week or so. They are very fecund, each producing between 500 and 1000 eggs, and gravid females display physogastry-a state in which the abdomen becomes grossly swollen with eggs. Larvae feed openly, often alongside adults, they produce small holes in the leaves and these can be very extensive and cause whole leaves to die off, they pass through three instars, each lasting between three and seven days and when full-grown they drop and burrow into the soil to pupate. Fully grown larvae have been observed from June until early October but even the latest larvae will pupate and it is only the adult stage that will overwinter, it is likely that these late emerging adults are from a second generation produced from eggs laid in the spring, these produce adults from June that will feed for a month or so before ovipositing. Adults are easily sampled by sweeping suitable foliage, a close inspection often revealing them as they feed, they also occur flight-interception traps and appear through the winter in tussock and litter samples.
4-5 mm. Very distinctive among our leaf-beetles due to the colour of the body and the form of the tibiae; species of Podagrica are also bicoloured but here the head is the same colour as the pronotum. Head and elytra black with a metallic blue or, rarely, green reflection, pronotum orange, legs orange with darker tarsi, antennae dark with four basal segments variably orange. Head finely punctured between convex and prominent eyes, antennae inserted on the anterior margin, the insertions spaced further apart than the length of the basal segment, segments 1-5 elongate, 6-10 quadrate to very slightly elongate, and the terminal segment sinuate before a rounded apex. Pronotum transverse, broadest about the middle and narrowed to distinct angles, surface finely and diffusely punctured, without transverse or longitudinal impressions. Scutellum finely punctured, black or metallic as the elytra. Elytra randomly and more strongly punctured than the pronotum, without striae but with a fine line beside the suture, which is slightly raised, in the apical half. Legs robust, the hind femora longer but not substantially thicker than the others and all tibiae produced into a sharp external tooth just before the apex. Tarsi Pseudotetramerous; the small fourth segment hidden within the large lobes of the third.
Gastrophysa viridula (De Geer, 1775)
Green Dock Beetle
Native to the Palaearctic region and possibly also in North America where there a few widely scattered records but here it may have been mistaken for a closely similar species, it is represented in Europe by two subspecies; G. v. pennina (Weise, 1882) is restricted to Italy while the nominate subspecies is widespread and abundant throughout, reaching north to the UK and southern Fennoscandia and as far as the Arctic Circle in Russia, it is present as far south as Greece and Turkey but absent from North Africa. Until about 1920 it was common mostly in alpine areas in Europe, mostly around farms and other disturbed habitats, and was generally local and uncommon in lowland areas but since then it has spread along valleys and stream margins and by the 1950s it was widespread and generally common. Here it is abundant throughout England and Wales, including the islands, and more local though still generally common further north to Orkney and across Northern Ireland. It is among our most common leaf-beetles and might be expected wherever its host plants are common, generally all types of grassland, wasteland, wetland margins, woodland and verges etc, adults occur on a range of docks and other species of Rumex, they disperse by flight and sometimes visit flowers and during the summer should be expected from grass and foliage in the vicinity of the hosts. Adults are present year-round; they overwinter in tussocks or among litter or debris and become active in March or April although they may be found much earlier during mild winter spells, they peak during June and July and remain active until into October, they feed on host foliage, producing small circular holes which often unite and may extensively skeletonise entire plants. Mating occurs over a long season from early spring and it is likely that there are at least two generations each year. Following a period of feeding females lay batches of up to 60 small yellow eggs on the underside of larger or fully-expanded leaves, and larvae emerge after a week or so. Larvae consume their egg-shells and remain in tight groups for a few hours before dispersing, they feed openly on the foliage and reduce it to little more than the veins, they grow rapidly, passing through three instars and becoming fully grown in three to four weeks at which time they leave the host and burrow into the soil where they prepare a chamber for pupation. The pupal period generally lasts for about 10 days but may be prolonged at lower temperatures and at higher temperatures they may remain dormant for much longer. Freshly eclosed adults leave the soil and begin feeding immediately, they mate soon afterwards and females become greatly swollen before a prolonged period of oviposition which may continue into late summer, mating continues through the season, it always precedes eggs laying and males will often be seen trying to displace other males during mating. Notably large populations are common during the summer when whole plants can become skeletonised and larvae often become cannibalistic, especially in the first instar when they may consume numbers of unhatched eggs. Both sexes disperse by flight, this is seen mostly in teneral specimens and the dispersal distance tends to be small.
4-6mm. Body long-oval and moderately convex; entirely bright metallic green or with blue, coppery or brassy overtones, the dorsal surface glabrous and finely and randomly punctured. Head much narrower then the anterior pronotal margin, weakly impressed between small and convex eyes, antennae inserted laterally behind the mandibles, 11-segmented; 1-5 glabrous and 6-11 pubescent and slightly wider. Pronotum transverse, broadest and sub-parallel or slightly sinuate in the basal half and narrowed to distinct anterior angles, surface smoothly convex and without distinct depressions, a little more finely and sparsely punctured than the elytra. Scutellum transverse, curved laterally and shiny and punctured as the pronotum. Elytra with distinct humeral angles and smoothly curved to a continuously-rounded apical margin, surface randomly punctured, often finely wrinkled towards the base and lacking striae although there is a variously developed sutural stria in the apical half, epipleura flat, visible in side view and lacking the apical fringe of hairs seen in Chrysolina. Legs robust, tibiae expanded before the apex to an external tooth and tarsi with the third segment widely enlarged and entire or only weakly emarginate.