Profile

The weevils(Otiorhynchus spp.) are a genus of beetles from the weevil family (Curculionidae) that feed on the roots and above-ground parts of soft fruit, vines and various ornamental plants, causing damage. Common species are the furrowed weevil(Otiorhynchus sulcatus F.) and the strawberry root weevil(Otiorhynchus ovatus L.)

Biology

Depending on the species and temperature, the beetles appear from the end of April to October and usually undergo a one-year development cycle outdoors. The flightless beetles are nocturnal, hide in cracks or crevices in plants or in the ground during the day and feed on above-ground plant parts.

From the end of May, the female beetles lay several hundred eggs over a period of two to three months at the root necks of the host plants in the soil or under plant debris, from which the larvae hatch after around 14 days. From the end of August, the young larvae can be found in the soil of the root area or in the rhizomes of the infested plants.

The beetle larvae overwinter after a short period of feeding in the root area and pupate after maturing in the following spring from the end of March. After a pupal dormancy of three to six weeks, the adult beetles emerge.

There may be deviations from the one-year development cycle because, depending on the temperature, two-year development cycles can occur in some species of weevil outdoors, or because adult beetles can overwinter alongside the larvae in greenhouses or conservatories. Therefore, several developmental stages of the weevil may occur simultaneously throughout the year.

Host plants

Chiggers occur on approximately 150 host plant species and infest grapevines, bush fruit, strawberries, and ornamentals, especially various container plants and nursery stock such as yews(Taxus), rhododendrons, cherry laurels, privet, and dwarf loquats(Cotoneaster), as well as cyclamen in greenhouses.

Distribution

The pine weevil is native to Europe and occurs worldwide, but mainly in Europe and North America.

Propagation and transmission

The flightless beetles can migrate distances of 2-3 m on average, but also up to 70 m.

Economic importance

Larval feeding on roots and rhizomes causes wilting and death of infested plants and can lead to total yield loss and uprooting of strawberry plants, as well as destroying the entire shoot in nurseries and young plant nurseries.

Prevention and control

• Only infestation-free planting material should be planted (check the root balls for larval stages in nursery stock).
• Perennial strawberry crops or the repeated planting of strawberry crops in succession in the same area should be avoided.
• Control of adult beetles is difficult and usually ineffective due to the long hatching period from the pupa and the hidden lifestyle of the nocturnal beetles.
• Optimal control is directed against the larvae. Treatments should be carried out in spring (mid-April to the end of May) or autumn (September to mid-October) for a one-year outdoor development cycle, or in both periods in the case of heavy infestations.
• Insect-pathogenic nematodes(Heterorhabditis sp., Steinernema sp.) or insect-pathogenic fungi(Metarhizium anisopliae) are suitable for biological control (see list of plant protection products authorised in Austria)
• Chemical control is currently only authorised for pot and container plants for ornamental plants.

Specialized information

Publications

Blümel, S., Kaserer, H., 1989. studies on the control of Otiorrhynchus sulcatus F. on vines and ornamental plants, Mitteilungen Klosterneuburg, 39, 124-129.

Blümel, S., 1989. is it possible to successfully control "thickmouth weevils"? New Harvest, 3, 10-11.

Blümel, S., 1989. autumn control of the thick-mouthed weevil on strawberries. Better Fruit, 34(9), 251-252.

Blümel, S., 1989. is it worthwhile to use Heterorhabditis nematodes against largemouth weevils? Horticultural Economics, 44(8), 14-15.

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