Black Vine Weevils (Otiorhynchus sulcatus) are a serious insect pest of many broad leaf plants, both woody and non-woody. Although the genus Otiorhynchus consists of hundreds of species, Otiorhynchus sulcatus (the black vine weevil) is believed to be the most destructive and widely spread, especially in the home landscape. The adult beetles feed on foliage, but their feeding damage is only considered to be cosmetic. The larvae (grub) stage however is highly destructive, as they live in the soil and feed on roots and the base of the stems, often going undetected until the plant is in distress.

Host Plants

In the ornamental landscape, black vine weevils are particularly fond of container grown plants and can cause extensive damage to the roots. Some popular container grown plants that may be at risk are Rhododendrons, Azelia’s, Yew topiary, Cyclamens, Impatiens, Asters, Strawberries, Hosta, Primula, Japanese holly, Hydrangea, Heuchera, Hemlock bonsai and Spruce topiary. Plants grown in the ground usually require higher populations to kill the plants, but all these same plants can be seriously damaged, as well as Euonymus, Sedum, Bergenia, Grapes and many others. Visit CABI digital library for a more extensive list of host plants for Otiorhynchus sulcatus (vine weevil).

Identifying Black Vine Weevils and Their Damage

Adults are small matt black beetles measuring about 1 cm long. They have hard forewings that fold over its back (top of abdomen) that consist of beaded rows, giving them a ribbed appearance. These wing covers (elytra) also have tufts of whitish or yellowish hair-like scales giving them a spotted appearance. Their thorax (the middle body segment) is highly beaded and covered in short hairs that can only be seen through magnification. Other distinguishing characteristics include the prominent snout with elbow like antennae that end in a club shape. Although they have wings, this insect is unable to fly, as their wing casings are fused. When they first emerge from pupae, they are whitish in colour, but turn black within a few days. The adults feed on the outer margins of foliage at night creating halfmoon shaped notches. Like lily beetles and Japanese beetles, they drop to the ground on their backs when disturbed, making them extremely difficult to spot.

Eggs are laid in the soil, garden debris or may be inserted into bark and crevices on woody plants. The eggs are very tiny, less than 1mm. When first laid the eggs are whitish, but viable eggs change to a brownish colour within 3 days and camouflage well with the soil and bark.

Larvae live in the soil feeding on roots and bases of stems. They have a grub like appearance, whitish in colour with a hard reddish-brown head capsule and curl into a C-shape when disturbed, but unlike scarab beetles like Japanese beetle, June beetle and European chafer, they are legless, and smaller up to 12mm (1/2″) in length. Their feeding damage causes the girdling of roots and lower stems which prevents the flow of water and nutrients to the plant. Above ground plants may show decline and begin wilting, browning and dying.

Pupae are typically found within the first 5 cm (2inches) in the soil. The insect is enclosed in an earthen cell consisting of excreted gut contents and soil, which hardens. Inside the insect (prepupae) first appears white and legless, then develops obvious legs, antennae and turns a yellowish brown as pupation takes place. For an excellent photo of this earthen cell check out figure 6 in entomologist, Floyd F. Smith’s article entitled BIOLOGY AND CONTROL OF THE BLACK VINE WEEVIL

Look-a-likes include several root weevils from the same Otiorhynchus genus, especially the strawberry root weevil Otiorhynchus ovatus which looks almost identical but is about half the size.

Life Cycle

Outdoors the insect overwinters as larvae in the soil (occasionally as an adult), below the frost line in temperate climates. When the soil warms again the larvae resume feeding then pupate in the soil. Pupation time varies a bit, depending on temperatures it appears, but ranges from about 2-3 weeks. The adults, in temperate North American climates, begin emerging from the soil in May and June. The adults feed on the margins of foliage for 3-4 weeks at night, hiding in cool dark places during the day, then begin producing eggs parthenogenetically (non-sexually, no males required). Hundreds of eggs can be laid over a period of 2-3 weeks in the soil, garden debris or bark and crevices on woody plants. These eggs are very sensitive to drying out. Note: if the insect over wintered as an adult egg laying will occur earlier. The eggs begin hatching in 10-14 days (Hoover G.A. Sr., (Updated: February 28, 2017)), and the larvae feed on roots and bases of stems until ground freeze, then resume feeding again the following spring. In all they will pass through 6-7 instar stages before pupating in spring. The adult continues to feed after egg laying and lives on average 90 to 100 days (Shetlar D. J. and Andon J. E., (Apr 20, 2015 revised).

Managing Black Vine Weevils

Natural Predators: There are many naturally occurring predators of black vine weevils in their various life stages such as birds, frogs, toads, lizards, shrew and other beetles like ground beetles and rove beetles.

Physical Controls include hand picking the adult beetles after dusk and/or applying a sticky barrier to trunks to catch the adult beetles as they climb up to feed at night or climb down to hide in the day.

• Black vine weevils prefer a moist environment and removing mulches in problem areas, cleaning up garden debris and reducing watering may all help to reduce this pest.
• The abrasive particles in diatomaceous earth applied to the base of affected plants may help control vine weevils by scraping them up and causing them to dehydrate and die.

Biological Controls like parasitic nematodes can be fairly useful in controlling black vine weevils at the larvae stage, especially in sandier lighter soils. The microscopic worm-like nematodes are watered into the soil, and they parasitize the larvae killing them. Species include Heterorhabditis bacteriophora and Steinernema spp.

• The entomopathogenic fungi Beauveria bassiana can also be affective at parasitizing black vine weevils (Hu B., Deer C. and Rebek E., (Feb. 2021)). Note: These entomopathogenic fungi do not appear to be available in Canada for home use.

For more information I recommend this excellent article posted online by Virginia Tech BLACK VINE WEEVIL BIOLOGY AND MANAGEMENT written by Richard S. Cowles. In the article he discusses at length various control options for black vine weevil.

References:

CABI, (Nov. 2021). Otiorhynchus sulcatus (vine weevil). https://www.cabidigitallibrary.org/doi/10.1079/cabicompendium.38071

Cowles R.S., (Modified March 06, 2013). BLACK VINE WEEVIL BIOLOGY AND MANAGEMENT. Virginia Tec. https://scholar.lib.vt.edu/ejournals/JARS/v49n2/v49n2-cowles.htm

Hoover G.A. Sr., (Updated: February 28, 2017). Black Vine Weevil. https://extension.psu.edu/black-vine-weevil

Hu B., Deer C. and Rebek E., (Feb. 2021). Fungi Used for Pest Management in Crop Production. Oklahoma Cooperative Extension Service, HLA-6038. https://extension.okstate.edu/fact-sheets/print-publications/hla/fungi-used-for-pest-management-in-crop-production-hla-6038.pdf

Koppert, (n.d.). Black vine weevil. https://www.koppert.ca/challenges/pest-control/beetles/black-vine-weevil/

Masaki, M. (Japan. Ministry of Agriculture, Forestry and Fisheries, Yokohama. Yokohama Plant Protection Station); Ohto, K.;. Effects of temperature on development of the black vine weevil, Otiorhynchus sulcatus (F.) (Coleoptera: Curculionidae) [1995]. Research Bulletin of the Plant Protection Service (Japan). ISSN : 0387-0707. https://agris.fao.org/agris-search/search.do?recordID=JP9602418

Missouri Botanical Garden, (n.d.). BLACK VINE WEEVIL. https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/insects/beetles/black-vine-weevil

Natural History Museum, (n.d.). Vine weevil (Otiorhynchus sulcatus) identification guide. https://www.nhm.ac.uk/take-part/identify-nature/common-insect-pest-species-in-homes/vine-weevil-otiorhynchus-sulcatus-identification-guide.html

Oregon State University, (n.d.). Grape-Black vine weevil. A Pacific Northwest Extension Publication. https://pnwhandbooks.org/insect/small-fruit/grape/grape-black-vine-weevil

Phillip P. A., (1989). Simple monitoring of black vine weevil in vineyards. CALIFORNIA AGRICULTURE, MAY-JUNE 1989. ucanr.edu/repository/fileAccessPublic.cfm?fn=ca4303p12-171635.pdf

Royal Horticultural Society, (n.d.). Vine weevil. https://www.rhs.org.uk/biodiversity/vine-weevil

Shetlar D. J. and Andon J. E., (Apr 20, 2015 revised). Department of Entomology Ohio State University Extension, Black Vine Weevil (and Other Root Weevils) https://ohioline.osu.edu/factsheet/ENT-49

Smith F. F., BIOLOGY AND CONTROL OF THE BLACK VINE WEEVIL. UNITED STATES DEPARTMENT OF AGRICULTURE
WASHINGTON. D. C.. TECHNICAL BDLLETIN NO. 325. https://naldc.nal.usda.gov/download/CAT86200319/pdf

Van Tol R. W. H. M., Van Dijk N., Sabelis M. W., (2004). Host plant preference and performance of the vine weevil Otiorhynchus sulcatus. https://resjournals.onlinelibrary.wiley.com/doi/10.1111/j.1461-9555.2004.00232.x

Wikipedia, (last edited on 8 August 2022). Vine Weevil. https://en.wikipedia.org/wiki/Vine_weevil