Sitona hispidulus

(Fabricius, 1777)

Clover Root Curculio, Clover Weevil

hispidulus, the clover root curculio, is a weevil native to Europe that has been introduced to Asia and North America. The larval stage is the most damaging, feeding cryptically underground on root nodules and taproots of legumes, particularly alfalfa and clovers. feed on foliage with minimal damage. The species has been overlooked as a pest for decades but causes chronic issues including reduced stand establishment, shortened stand life, and increased winterkill in forage systems. levels are limited by availability of root nodules for early instars and taproot for later instars.

Sitona hispidulus by (c) Barry Walter, some rights reserved (CC BY), uploaded by Barry Walter. Used under a CC-BY license.

Sitona hispidulus by (c) Alexis Tinker-Tsavalas, some rights reserved (CC BY), uploaded by Alexis Tinker-Tsavalas. Used under a CC-BY license.

Pronunciation

How to pronounce Sitona hispidulus: //sɪˈtoʊnə hɪˈspɪdjʊləs//

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Images

Habitat

Agricultural fields and forage systems; specifically the rhizosphere of leguminous crops including alfalfa, clovers, peas, and vetches. Larvae occur in soil where they feed on root nodules and taproots. occur on foliage and in field margins where they overwinter outside of crop fields.

Distribution

Native to Europe; introduced to Asia and North America. Present across Europe including Austria, Belgium, Britain, Bulgaria, Corsica, Czechoslovakia, Denmark, Finland, France, Germany, Greece, Hungary, Italy, Netherlands, Norway, Poland, Portugal, Romania, Spain, Sweden, Switzerland, and Yugoslavia. In Asia: Cyprus, Iran, Israel, Japan, Syria, Turkey. In North America: Canada and USA, including North Carolina where seasonal reproductive has been studied.

Seasonality

overwinter outside of fields and migrate into fields in late spring to lay . Larvae develop underground through five instars before pupating. Adults re-emerge in summer and continue feeding. In the Palouse region, first- adults typically attack before pea aphids arrive, while second-generation adults attack after aphids and pea enation mosaic virus have arrived.

Diet

Larvae feed on nitrogen-fixing root nodules and taproot cortex of leguminous plants. First and second instars primarily consume root nodules; fifth instars feed on taproot . feed on foliage with minimal damage.

Host Associations

Medicago sativa - larval alfalfa; larvae feed on root nodules (early instars) and taproot (later instars)
Trifolium - larval clovers
Pisum sativum - peas
Vicia - vetches
Vicia faba - broad bean

Life Cycle

Complete with five larval instars. are laid in soil. First and second instar larvae feed on root nodules and are correlated with nodule availability and soil moisture. Third and fourth instars show no consistent correlation with measured rhizosphere components. Fifth instar larvae are associated with taproot . occurs in soil. emerge, feed on foliage, and overwinter outside of fields before migrating back in late spring.

Behavior

migrate into fields from sites in late spring. Larval feeding is cryptic, occurring underground, making detection and monitoring difficult. Larval feeding damage accumulates over time rather than killing plants outright.

Ecological Role

Herbivore and pest of leguminous crops. Larval feeding on nitrogen-fixing nodules may reduce nitrogen fixation in plants. are controlled by availability of root nodules, with -dependent mortality occurring when nodules are sparse. Serves as host for including Steinernema feltiae, S. bibionis, and Heterorhabditis bacteriophora.

Human Relevance

Significant agricultural pest of alfalfa and clover production in North America. Causes chronic damage including reduced stand establishment and , shortened stand life, increased winterkill, and decreased water and nutrient uptake. Synergism with secondary plant can decrease yield two- or three-fold compared to damage from the pest alone. No established , predictive models, or registered targeting larvae currently exist. Historical suppression by broad-spectrum insecticides used against alfalfa weevil ended when those insecticides were banned, leading to resurgence. using shows promise, with S. feltiae causing 100% larval mortality in laboratory tests.

Similar Taxa

Hypera posticaAlfalfa weevil; historically, used against H. postica indirectly suppressed S. hispidulus . Both are weevil pests of alfalfa but H. postica is more well-known and has characteristic foliage damage from larval feeding, whereas S. hispidulus larval damage is underground on roots.
Sitona lineatusPea leaf weevil; congeneric also a pest of legumes, but feeds on pea leaves with tiny feeding bites rather than root nodules. S. lineatus has been studied for its effects on plant defense signaling when attacking before or after pea aphids.

More Details

Population Dynamics

First-instar larval mortality is high (66-81%) due to lack of available root nodules. of early instars is significantly related to nodule number and . Fourth-instar abundance is associated with taproot biomass independently of nodule effects, suggesting taproot surface area may limit levels.

Entomopathogenic Nematode Susceptibility

Third instar larvae are more susceptible to than first, second instars, pupae, or . Steinernema feltiae is the most aggressive tested, causing complete larval mortality in 6 days at 30 L3 nematodes per insect. All three nematode species (S. feltiae, S. bibionis, Heterorhabditis bacteriophora) multiply sufficiently in S. hispidulus, which is considered among the best for these nematodes.