Strawberry root weevil
- French common name: Charançon de la racine du fraisier
- Other common names: Crown girdler
- Scientific name: Otiorhynchus ovatus (L.)
- Kingdom: Animalia
- Phylum: Arthropoda
- Class: Insecta
- Order: Coleoptera
- Family: Curculionidae
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Partial list of synonyms:
- Brachyrhinus ovatus Linnaeus
General information and importance
Strawberry root weevil is an introduced beetle that feeds on a wide variety of plants. Adult root weevils feed on the aboveground parts of plants. As larvae, it feeds on the roots of the same plants. As its name suggests, it is a pest on strawberries. Strawberry root weevil, however, also affects coniferous trees in nurseries. This is detrimental because outbreaks in nurseries can cause significant economic loss. More recently, it has been found in natural hardwood forests, but the impact of this invasive root weevil and other related species is unclear.
Distribution and hosts
Strawberry root weevil is native to Europe. It was first found in Canada in the late 19th century and was associated with agriculture. It is now distributed throughout much of Canada, mostly in temperate regions and the more southern portion of the boreal zone. It has been observed, however, in both the Yukon and the Northwest Territories. It is considered a generalist, as it feeds on a wide range of host trees, shrubs, and plants. Damage from larvae and adults of this weevil has been reported on true fir (Abies), spruce (Picea), cedar (Thuja), and hemlock (Tsuga). Adults have also been observed feeding on maples (Acer), birch (Betula), ironwood (Ostrya), and basswood (Tilia). It is uncertain whether larvae feed on the roots of any of these latter deciduous host species.
Tree parts affected
Adults feed on leaves and needles.
Larvae feed on roots.
Symptoms and signs
Strawberry root weevil feeding damage on trees is not readily apparent unless populations are high enough to cause tree mortality. Evidence of infestations can be found by excavating at the base of weakened trees and observing the absence of fine roots. Other sources of evidence include bark stripped from larger roots and stems below the soil surface. Adults feed on needles, leaves and twigs, but this damage is often inconspicuous unless numbers are high. Feeding damage on leaves and needles appears as notches or irregularities in the leaf or needle margins. Adults are most active at night and usually fall to the ground if disturbed during feeding.
Eggs of strawberry root weevil are laid singly in the soil. The small (0.25 millimetre in diameter), oval eggs are milky white when laid. They change to a pale brown colour as they age. Recently hatched larvae are about 0.5 millimetre in length, creamy white in colour, and are found in the soil associated with host roots. Full-grown larvae are up to 10 millimetres in length and about 3 millimetres in diameter, C-shaped, covered with minute hairs, and creamy white with pale brown heads. Mandibles (chewing mouth parts) of the larvae are usually a darker brown than the rest of the head. Pupae are located within earthen cells. They are about the same size as adults and are a creamy white colour. They have conspicuous black eyes, wing pads, legs, and antennae. Adult weevils are snout-nosed, dark brown to black in colour, and flightless. They are about 5 to 6 millimetres in length and 2 to 3 millimetres in width. The thorax and abdomen of weevils are deeply pitted and the elytra are fused (these weevils cannot fly). They are striated (marked with parallel, fine, impressed lines) and covered with sparse, fine, yellowish setae. The adult weevils’ antennae are segmented and hairy, elbowed, and tapering to a slight enlargement at their tips.
Life cycle
In its native European range, there is some debate about whether both female and male strawberry root weevils occur. For example, Warner and Negley (1976, see references below) indicate that both occur in its native range. In some of the original literature written in German (i.e., Jahn, 1941; Holdhaus, 1929; Holdhaus and Lindroth, 1939; see references below), however, only females of this particular species of Otiorhynchus have been reported and reproduction is asexual. Regardless, only asexually reproducing (parthenogenetic) female weevils have spread more widely elsewhere in Europe and Asia. In North America, only females have been introduced and reproduction occurs asexually. There is one generation per year. Adults emerge from the soil during a protracted period from late May to early July. After feeding on foliage for 4 to 5 weeks, female weevils lay 60 to 70 eggs on average, beginning in July. Most adults live for about two months, but a small percentage can live and continue to lay eggs for up to 10 months. Egg production appears to be higher for weevils feeding on strawberry plants (150 to 200 eggs) than those feeding on coniferous trees. Eggs hatch after about 14 to 16 days. Larvae are found in the shallow rooting zone of seedlings and young trees. They continue to grow during the late summer and early fall. The insect moves deeper into the soil before winter and usually overwinters as larvae. As the soil thaws in the spring, larvae begin to feed again until maturity. Pupation occurs in late spring to early summer, closer to the soil surface.
Damage
Strawberry root weevil is considered primarily an agricultural pest. It causes significant damage to strawberry, cranberry, currant, alfalfa, and clover. The damaging impacts of this insect, however, are also widely recognized in tree nurseries. The weevil’s damage to seedlings and young trees negatively impacts seedling production in forestry and nurseries growing ornamental landscape trees. During outbreaks, seedlings and small trees up to 2 metres in height can be killed or severely damaged. The most critical damage is to the root system of affected trees, which decreases efficiency of water uptake, affects the overall vigour of the host, and lowers the aesthetic quality of the trees (critical for landscape tree value).
In recent studies, strawberry root weevils have been observed widely in eastern North American deciduous forests, but their ecological and economic impacts are not well understood.
Prevention and management
Pest management strategies for a particular pest vary depending on several factors. These include:
- the population level of the pest (i.e., how numerous the pest is on the affected host[s]);
- the expected damage or other negative consequences of the pest’s activity and population level (either to the host, property, or the environment);
- an understanding of the pest’s life cycle, its various life stages, and the various natural or abiotic agents that affect population levels;
- how many individual host specimens are affected (an individual tree, small groups of trees, plantations, forests);
- the value of the host(s) versus the costs of pest management approaches; and
- consideration of the various silvicultural, mechanical, chemical, biological, and natural control approaches available and their various advantages and disadvantages.
Decisions about pest management strategies require information about each of these factors for informed decision-making. These various factors should then be weighed carefully in terms of costs and benefits before action is taken against any particular pest.
The larval stages of strawberry root weevil feed in the soil and are difficult to control with conventional pesticides. A promising approach for controlling larvae is offered by entomopathogenic nematodes of the families Heterorhabditidae and Steinernematidae. Nematodes are microscopic worms and some species of nematodes are parasitic on a wide range of soil-inhabiting insects. A number of nematode species are commercially available as biocontrol agents across Canada. Warm and moist soils are more conducive to nematode efficacy. Late August and early September applications are ideal because larvae are smaller and closer to the soil surface, and the soil is usually moist from late summer rains.
Adults are somewhat easier to control because they are not in soil and are exposed in host trees. The control of adults should be timed to coincide with peak emergence (late June to early July) to prevent egg laying. More than one pesticide application may be necessary, depending on the number of adult weevils and the duration of emergence, and should be done at night when weevils are actively feeding. Careful monitoring of adults is required to determine the proper timing and number of applications.
Pesticides registered for use against strawberry root weevil under specific situations may change from year to year. Therefore, please search Health Canada’s Pesticide Product Information Database for currently registered pesticides and product information for use against this weevil. The application of any registered product should be based on population size and applied only when necessary and against the approved life stage. It is also recommended to consult a local tree care professional. Chemical pesticides may be toxic to humans, animals, birds, fish, and other beneficial insects. Apply registered products only as necessary and according to all directions and precautions noted on the manufacturer’s label. In some jurisdictions and situations, only a licensed professional can apply pesticides. Consulting relevant local authorities to determine local regulations that are in place is recommended.
Photos
White spruce seedlings with bark stripped near the root collar by strawberry root weevil larvae.
Thérèse Arcand
A spruce seedling with bark stripped near the root collar by strawberry root weevil larvae.
Thérèse Arcand
Close-up view of a spruce seedlings with bark stripped near the root collar by strawberry root weevil larvae.
Thérèse Arcand
Teneral adult (left), mature adults (second from left and right), and larva (between two mature adults) of strawberry root weevil.
Adult strawberry root weevil on a leaf.
Carole Germain
Adult strawberry root weevil on a leaf (dorsal view).
Carole Germain
Spruce seedlings damaged or killed by strawberry root weevil.
An excavated spruce seedling revealing bark stripped near the root collar by strawberry root weevil larvae.
Selected references
Anderson, R.S. 1997. Weevils (Coleoptera: Curculionoidea, excluding Scolytinae and Platypodinae) of the Yukon. Pages 523–562 in H.V. Danks and J.A. Downes, editors. Insects of the Yukon. Biological Survey of Canada (Terrestrial Arthropods). Ottawa, Ontario. 83 p.
Brandt, J.P. 1993. The strawberry root weevil, Otiorhynchus ovatus (L.) and other important root weevils. Pages 3–4 in Forest Insect and Disease Note A-023. Forestry Canada, Northwest Region. Edmonton, Alberta. https://ostrnrcan-dostrncan.canada.ca/entities/publication/a6d73ad5-9d4e-4a7d-93a3-ce1b210ef9d3?fromSearchPage=true
Brandt, J.P.; Smith, S.M.; Hubbes, M. 1995. Bionomics of strawberry root weevil adults, Otiorhynchus ovatus (L.) (Coleoptera: Curculionidae), on young ornamental trees in southern Ontario. The Canadian Entomologist 127(4): 595–604. https://doi.org/10.4039/Ent127595-4
Brandt, J.P.; Smith, S.M.; Hubbes, M. 1996. Distribution and sampling of root weevil larvae in young ornamental conifer plantations. The Canadian Entomologist 128(6): 1125–1133. https://doi.org/10.4039/Ent1281125-6
Bright, D.E.; Bouchard, P. 2008. The insects and arachnids of Canada, Part 25: Coleoptera, Curculionidae, Entiminae. Weevils of Canada and Alaska Volume 2. National Research Council of Canada (NRC) Research Press. Monograph Publishing Program. Ottawa, Ontario. 327 p.
Coyle, D.R.; Mattson, W.J.; Raffa, K.F. 2008. Invasive root-feeding insects in natural forest ecosystems of North America. Chapter 8. Pages 134–149 in S.N. Johnson and P.J. Murray, editors. Root feeders: an ecosystem perspective. Commonwealth Agricultural Bureau International. Cambridge, Massachusetts, United States.
Fisher, J.R. 2006. Fecundity, longevity and establishment of Otiorhynchus sulcatus (Fabricius) and Otiorhynchus ovatus (Linnaeus) (Coleoptera: Curculionidae) from the Pacific North-west of the United States of America on selected host plants. Agricultural and Forest Entomology 8(4): 281–287. https://doi.org/10.1111/j.1461-9563.2006.00309.x
Gambrell, F.L. 1938. The strawberry root weevil as a pest of conifers in nursery plantings. Journal of Economic Entomology 31: 107–113.
Georgis, R.; Poinar, G.O. Jr.; Wilson, A.B. 1982. Susceptibility of strawberry root weevil, Otiorhynchus ovatus, to neoaplectanid and heterorhabditid nematodes. IRCS Medical Science 10: 42.
Gothro, P.; Rosetta, R.; Mankin, R. (editors). 2007. Proceedings of the North American root weevil workshop. 1–2 November 2001. Oregon State University, Department of Entomology, Integrated Plant Protection Center, and the North Willamette Research and Extension Center. Aurora, Oregon, United States. 40 p.
Holdhaus, K. 1929. Die geographische Verbreitung der Insekten (The geographical distribution of insects). Pages 592–1058 in C. Schröder. Handbuch der Entomologie (Handbook of entomology), Band II (Volume II). Gustav Fischer Verlag. Jena, Germany.
Holdhaus, K.; Lindroth, C.H. 1939. Die europäischen Coleopteren mit borealpiner Verbreitung (The European Coleoptera with a boreal-alpine distribution). Annalen des Naturhistorischen Museums in Wein 50: 123–129.
Jahn, E. 1941. Über Parthenogenese bei forstschädlichen Otiorrhychsarten in den während der Eiszeit vergletsscherten Gebieten der Ostalpen. (On parthenogenesis in forest-damaging Otiorhynchus species in the areas of the eastern Alps that were glaciated during the Ice Age). Zeitschrift für Angewandte Entomologie 28(3): 366–372. https://doi.org/10.1111/j.1439-0418.1941.tb01027.x
McDaniel, E.I. 1930. The strawberry root weevil as a pest in conifer nurseries. Quarterly Bulletin of the Michigan Agricultural Station 12(3): 102–105.
Proctor, E.; Anderson, R.S.; Nol, E.; Girard, J.M.; Richmond, S. 2010. Ground-dwelling weevil (Coleoptera: Curculionidae) communities in fragment and continuous hardwood forests in south-central Ontario. Journal of the Entomological Society of Ontario 141: 69–83.
Smith, C.C. 1972. Strawberry root weevil. Fisheries and Environment Canada, Forestry Service, Maritimes Forest Research Centre. Fredericton, New Brunswick. Tree Pest Control Leaflet.
Warner, R.E.; Negley, F.B. 1976. The genus Otiorhynchus in America North of Mexico (Coleoptera: Curculionidae). Proceedings of the Entomological Society of Washington 78(3): 240–262.
Wheeler, A.G. Jr. 1999. Otiorhynchus ovatus, O. rugosostriatus, and O. sulcatus (Coleoptera: Curculionidae): exotic weevils in natural communities, mainly mid-Appalachian shale barrens and outcrops. Proceedings of the Entomological Society of Washington 101(3): 689–692.
Zervos, S.; Eidt, D.C.; Weaver, C.A.A.; Tosh, K.J. 1994. Control of black vine weevil in forest nurseries with entomopathogenic nematodes. Natural Resources Canada, Canadian Forest Service, Maritimes Region. Fredericton, New Brunswick. Technical Note 289. 5 p.