Picromerus bidens belongs to the subfamily Asopinae and can be separated from all other North American asopines as follows: humeri prominent, ending in a spine; humeri, lateral margins of pronotum, and the head often shining deep-blue; inner apical third of anterior femora with a short spine and inner apical third of anterior tibia with a short, acute spur; dorsal and ventral surfaces of the body with fine or deep, dark punctures; length 11.0-14.0 mm.
A detailed description of the adult is found in Mayne and Breny (1948b), Dupuis (1949), and Kelton (1972); the latter also includes a color photo of the adult. The egg was described by Butler (1923), Mayne and Breny (1948b), Cooper (1967), and Southwood and Leston (1959). First to third instar nymphs were described by Mayne and Breny (1948b), the fourth instar by Butler (1923) and Mayne and Breny (1948b), and the fifth instar has been described in detail by Butler (1923), Mayne and Breny (1948b) and Dupuis (1949).
Europe. Fresh, humid, even marshy areas, although sometimes in drier places where a certain freshness persists; among abundant vegetation in sunny places; in areas in flower, in humid copses and bushes; especially near woods and waters; more rarely in orchards, gardens, or coniferous forests (Schumacher 1911; Strawinski 1927; Mayne and Breny 1948b; Dupuis 1949; Southwood and Leston 1959). In western Europe, the species is linked more to forests (Southwood and Leston 1959). It is found on the vegetation within two meters above the ground (Mayne and Breny 1948b).
North America. In Quebec and also in the other states and provinces visited, P. bidens is found in wet and dry areas, but always in clear, sunny places; along hedges, in fields along the forest edge, along wooded roadsides, in openings of mixed, deciduous or coniferous forests, where it prefers shrubby areas rich in woody plants (trees or bushes, e.g., raspberry plants), but also on weeds such as goldenrods. The species is found on plants at a height of 1 to 2 m above the ground. It is found in flat open country as well as at altitudes of 1 ,000 to 1 ,200 m. We have found the species in Vermont on 7, 11, and 16.VIII.1987 at the summits of Mounts Jay Peak (1,251 m), Ascutney (1,019 m), and Equinox (1,236 m) respectively. Javahery (1986) reports that the species is rarely found in orchards.
The local distribution of P. bidens seems to be dictated by plant diversity and the resulting variety of prey used for its feeding. The following is a list of plants on which various stages of the species can be found. These are not necessarily the hosts used for reproduction.
Europe: Alnus glutinosa (L.) Gaert., Betula verrucosa Ehrh., B. pubescens Ehrh., Calluna sp., Carex sp., Corylus sp., Dipsacus sp., Fagus sylvestris L., Galeopsis sp., Galium sp., Genista sp.,Juniperus sp., Myrica gale L., Pinus sylvestris L., Polygonum sp., Populus alba L., Primula elatior (L.) Hill, Prunus avium L., P. cerosus L., Pyrus malus L., Quercus sp., Q. pedunculata Ehrh., Ranunculus acrisL., Rhamnus cathartica L., Ribes nigrum L., Rubus sp., R. idaeus L., Rumex sp., Salix nigricans Sm., S. repens L., S. caprea L., S. aurita L., Spiraea ulmaria (L.), Tilia sp., and Urtica sp. (Butler 1923; Mayne and Breny 1948b; Dupuis 1949; Thomas 1954). According to Schumacher (1911), the following plants are visited less frequently: Calluna sp.,Genista sp., Polygonum sp., Salvia sp., and Urtica sp.
North America. In Québec and Ontario, P. bidens has been collected on Ambrosia sp., Rubus idaeus, Malus sp.,Polygonum sp., Rubus sp., Solidago sp., Vaccinium sp., weeds, and forage legumes (Larochelle and Lariviere 1980; Javahery 1986).
We have also found P. bidens on 46 additional associated plants in Québec, Ontario, New York, and New England: Abies balsamea (L.), AInus sp., A. rugosa (DuRoi) Spreng, Amelanchier sp., Betula alleghaniensis Britton, B. glandulosa Michx., B. papyrifera Marsh., Clematis virginiana L., Comptonia peregrina (L.), Cornus stolonifera Michx., Corylus cornuta Marsh., Crataegus sp., graminaceous plants, Impatiens capensis Meerb., Juniperus communis L., Larix laricina (DuRoi) Koch., Osmunda claytoniana L., Ostrya virginiana (Mill.) K. Koch., Parthenocissus quinquefolia (L.), Picea sp., P. glauca ( Moench ) Voss, Pinus banksiana Lamb., P. resinosa Art., P. sylvestris L., Populus tremuloides Michx., Prunus serotina Ehrh., P. virginiana L., Quercus alba L., Q. macrocarpa Michx., Q. rubra L., Ribes sp., R. cynosbati L., Rubus idaeus L., Salix sp., S. fragilis L., Sambucus pubens Michx., Solidago sp.,Spiraea latifolia (Ait.), Thuja occidentalis L., Tilia americana L., Urtica procera Muhl., Vaccinium sp.,Viburnum lentago L., Vitis riparia Michx., and various undetermined species of weeds.
Although it appears that P. bidens does not favor any particular plant species, we have observed that the density of individuals was higher on and around raspberry plants when these were present in the habitat. In Québec, the occurrence of raspberries almost always assured the collection of P. bidens. We have observed the same phenomenon on goldenrods, which are blooming in August. This is probably related to the fact that both plants, at certain times in the season, are inhabited by larvae and adults of species fed on by P. bidens. The presence of all nymphal instars as well as adults was noted on goldenrods and raspberries.
Palearctic distribution. In the Old World, P. bidens is widely distributed in the western Palearctic Region and throughout Europe, from 64°N latitude south to North Africa in the west and China in the east; it occurs as far west as Ireland, and as far east as Siberia and China (Mayne and Breny 1948b; Dupuis 1949; Puchkov 1961; Southwood and Leston 1959; Zheng 1980).
Nearctic distribution. Until now, the known North American distribution of P. bidens has been limited to Maine, Massachusetts, New Hampshire, New York, Vermont, and the Province of Québec (Froeschner 1988). The first North American specimens were collected on 22.VII.1932 in Lincoln Co., Maine, and on 28.VII.1945 at lle-au-Haut (so called "Peaks Island") near Rockland, Maine (Javahery 1986). There seems to be no record of the voluntary importation of P. bidens for use as a biological control agent. Javahery (1986) suggests, and it is also our opinion, that the species may have been accidentally introduced from Europe, probably in the egg stage, with the importation of nursery stock or other horticultural plants.
The species has subsequently been collected at Union Village, Vermont, from 1962 to 1967 (Cooper 1967), at Durham, New Hampshire, in 1956 and 1967 (Lattin and Donahue 1969), and at Lennoxville and Ascot Corner in southern Québec in 1970 (Oliveira and Juillet 1971; Kelton 1972). In a previous paper (Larochelle and Lariviere 1980), we reported P. bidens in Berkshire Co., Massachusetts and Franklin Co., New York as well as in about 40 localities in Québec.
We now have collected over 1,500 adults and 300 nymphs in more than 180 localities from 10 northeastern states or provinces from 1978 to 1988 (states, provinces, and counties in bold face):
MAINE: Franklin: Weld. Wilton. Oxford: Sumner.
MASSACHUSETTS: Worcester: W. Brookfield
NEW BRUNSWICK: Kent: Cap-Lumiere. Pointe-Sapin. Restigouche: White Brook. Westmorland: Jolicure.
NEW YORK: Franklin: Duane, Fort Covington.
NOVA SCOTIA: Annapolis: Annapolis Royal. Cumberland: Middleboro. Lunenberg: Canaan. Queens: W. Caledonia.
ONTARIO: Glengarry: Alexandria. Prescott: Carillon Prov. Park.
PRINCE EDWARD ISLAND: Kings: Brudenell River Prov. Park. East Baltic. For- tune. Prince: Ellerslie, Norboro. Queens: Surrey, Wood Islands Prov. Park.
QUEBEC: 136 localities: north to Etangs-des-Caps (Ile-de-la-Madeleine). in the following counties: Abitibi, Bagot, Beauce, Beauharnois, Berthier, Bonaventure, Brome, Champlain, Charlevoix-Est, Charlevoix-Ouest, Chacfateauguay, Chicoutimi, Compton, Dorchester, Drummond, Frontenac, Gaspe-Est, Gaspe-Ouest, Gatineau, Huntingdon, Ile-de-Montreal, Iles-de-la-Madeleine, Kamouraska, Lac-Saint-Jean- Est, Lac-Saint-Jean-Ouest, L'Assomption, Levis, Lotbiniere, Maskinonge, Matane, Matapedia, Missisquoi, Montcalm, Montmorency No. 2, Nicolet, Papineau, Pon- tiac, Richmond, Rimouski, Riviere-du-Loup, Rouville, Saguenay, Saint-Jean, Saint- Maurice, Shefford, Sherbrooke, Soulanges, Stanstead, Temiscouata, Terrebonne, Vaudreuil, Vercheres Wolfe.
RHODE ISLAND: Providence: Chepachet.
VERMONT: Bennington: Mt. Equinox. Woodford. Essex: Bloomfield, E. Brighton. Grand Isle: E. Alburg, N. Hero. Lamoille: Belvidere Center. Belvidere Corners, Eden. Jef- fersonville. Lake Elmore, N. Wolcott. Wolcott. Wolcott Pond. Orleans: Albany. Hazens Notch, Jay. Washington: E. Montpelier, Maple Corner Montpelier, Worcester. Windham: Townshend St. Park. Wilmington. Windsor: Mt. Ascutney.
The northern limit of distribution (Fig. 1) is now Iles-de-la-Madeleine (47'14" N latitude), Québec, and the southern limit, Chepachet, Rhode Island. The species is recorded for the first time from Prince Edward Island, Nova Scotia, New Brunswick. Ontario, and Rhode Island.
Observations made inQuébecindicate a rapid colonization of the territory. It is possible thatQuébecpopulations are the result of successive colonizations by Maine populations. We have noticed, however, while collecting in Maine (June, July and September 1985, and August 1986) that the species is less abundant in fields and in general more difficult to find there than inQuébec, where it was common to find 10 to 15 individuals in 3 to 4 sweeps from the third week of July to mid-September in almost any of the fields surveyed. It seems likely that the species has been more recently introduced directly intoQuébec(i.e., possible multiple introductions in North America), as is probably the case of certain Palearctic coccinellids (Coleoptera) suchas Propylea quatuordecim-punctata (L.) (Gordon 1985) and Hippodamia variegata (Goeze) (Gordon 1987).
In 1975, P. bidens was known inQuébecfrom only three localities in the southern part of the province. An intensive survey of the St. Lawrence Valley south of Tadoussac (Saguenay Co.) in 1978 showed that it occurred in another three localities, which extended the known range more than 300 km north of Lennoxville (Sherbrooke Co.), the first record for the province. In 1979, a survey of the same region revealed its presence in more than 40 localities.
During July and August of 1980 to 1984, we surveyed the region from the southern part of the St. Lawrence Valley, north to Miquelon (Abitibi Co.), west to Abitibi-ouest and east around the Gaspe Peninsula; and from Sherbrooke (southeasternQuébec) west through Montreal and the Ottawa Valley to Temiscamingue. Picromerus bidens has been collected in 87 localities, north to Miquelon (Abitibi Co.), western limit of its range inQuébecat that time. A rapid survey of the same region in 1985 confirmed its presence in another three localities of Abitibi County. The known western limit of the range is now Manneville (Abitibi-Ouest Co.), about 30 km from the Ontario border. Picromerus bidens is now known from 136 localities inQuébec.
Picromerus bidens, the spiny shieldbug or spiked shieldbug, is a carnivorous species of shield bug in the family Pentatomidae.[2]
This species has a wide distribution in the Palaearctic, from 64°N to North Africa and from the British Isles to China. It has also been introduced, probably more than once, to North America, where it has been recorded from more than 180 sites.[3]
These bugs prefer deciduous and mixed forests, heathland, gardens, chalk downland and damp flower-rich meadows.[4]
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Picromerus bidens is a large (12 to 13.5 mm long) and distinctive predatory shieldbug. It shows a thick rostrum directed away from head. Body colour is quite variable, generally light to dark brown or bluish, with red-brown antennae and legs and two unmistakable thorn-like brown projections on the sides of the pronotum (hence the species name bidens, meaning "with two teeth"). Front femurs are armed with a ventral spine distally.[4][5] The early instar nymphs are commonly reddish, while the final instar nymphs are greyish black, with banded antennae and legs.[4]
Both adults and nymphs of the spiny shieldbugs are predatory, feeding on the larvae of other insects, especially on leaf bugs, beetles, aphids and caterpillars. The choice of the prey depend on the season and availability of food. However both adults and nymphs also suck sap from plants. The female lays eggs on tree trunks and leaves. In the spring the larvae hatch, growing to the adult bugs after five moultings. Nymphs become adults by July or August and adults can be found until November. This species usually overwinters as eggs and less frequently as nymphs.[4][6][7][8]
Picromerus bidens, the spiny shieldbug or spiked shieldbug, is a carnivorous species of shield bug in the family Pentatomidae.
