Picromerus bidens

(Linnaeus, 1758)

spiny shieldbug, spiked shieldbug

Picromerus bidens is a predatory shield bug in the Pentatomidae, notable for its large size and distinctive spiny pronotal projections. It is , with summer dormancy () ensuring synchronization of its with seasonal conditions. The is native to the Palaearctic region but has been introduced to North America, where it has established . Both and nymphs are predatory, feeding primarily on insect larvae, and the species has been investigated as a potential agent.

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Shield bugs, Picromerus bidens - geograph.org.uk - 2092577 by Lairich Rig . Used under a CC BY-SA 2.0 license.

Pronunciation

How to pronounce Picromerus bidens: /pɪˈkroʊmɛrəs ˈbaɪˌdɛnz/

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Identification

Distinguished from other shield bugs by the two prominent thornlike projections on the pronotum. The combination of large size (12–13.5 mm), variable brown to bluish coloration, red-brown appendages, and the distinctive 'spiny' pronotum separates it from and other Pentatomidae. Final instar nymphs can be recognized by their greyish black coloration with banded and legs.

Images

Habitat

Deciduous and mixed forests, heathland, gardens, chalk downland, and damp flower-rich meadows. In North America, has been recorded from more than 180 sites across varied .

Distribution

Native to the Palaearctic region, ranging from 64°N to North Africa and from the British Isles to China. Introduced to North America, probably on multiple occasions, with established recorded from more than 180 sites.

Seasonality

present from July or August until November. Nymphs become adults by July or August. laid on tree trunks and leaves; larvae hatch in spring. usually overwinters as eggs, less frequently as nymphs.

Diet

Both and nymphs are predatory, feeding on larvae of other insects including leaf bugs (Miridae), beetles, aphids, and caterpillars. Prey selection depends on season and availability. Adults and nymphs have also been observed sucking sap from plants.

Life Cycle

(one per year). Females lay on tree trunks and leaves. Larvae hatch in spring and develop through five moults to become by July or August. Summer dormancy () in early-emerging adults prevents early oviposition and maintains univoltinism. occurs primarily as eggs, less commonly as nymphs.

Behavior

Exhibits summer dormancy () induced by long-day photoperiodic conditions, which delays and prevents untimely hatching of nymphs. When attacking prey in protective silken webs, exhibit efficient including returning to previously attacked webs. varies with temperature and plant context.

Ecological Role

of insect larvae, including agricultural and forest pests. Can act as a substantial mortality factor in small insect . Investigated as a potential agent for defoliating caterpillars and the Colorado potato beetle (Leptinotarsa decemlineata).

Human Relevance

Investigated as a agent for pest insects, particularly as a potential alternative to the North American Podisus maculiventris in Europe. High rates at varied temperatures suggest value for biological control, though mass production obstacles remain. Climate change may reduce suitable , potentially limiting its effectiveness as a biocontrol agent.

Similar Taxa

Podisus maculiventrisBoth are predatory pentatomid used in ; P. bidens has longer nymphal development and greater voracity at temperature extremes, while P. maculiventris has higher rates at moderate temperatures.

More Details

Photoperiodic Response

Long-day conditions (L18:D6, L20:D4) induce , delaying oviposition; short-day conditions (L12:D12, L14:D10) result in synchronous -laying soon after .

Functional Response

Exhibits type II at 18°C and 23°C, but type III response at 27°C; and handling time vary significantly with plant and temperature.