The most serious damage caused by the Black Vine Weevil (Otiorhynchus sulcatus) comes from its larvae, which feed extensively on plant roots. As the root system is destroyed, the larvae often continue feeding into the corms, rhizomes, and stem bases, and in some cases, may even move above ground into the stems. Both larvae and adult weevils are polyphagous, feeding on a wide variety of plant species. In high numbers, larvae can devastate crops, particularly under field conditions. Young plants and recently planted cuttings are especially vulnerable, while well-established crops tend to be more resilient to damage. Adult beetles are nocturnal and typically feed at night, creating distinctive round notches along the edges of leaves. While this leaf damage is generally not a concern in fruit or vegetable crops, it can significantly reduce the market value of ornamental plants due to aesthetic damage.

The life cycle of the Black Vine Weevil (Otiorhynchus sulcatus) includes an egg stage, six or seven larval instars, a pupal stage, and the adult beetle. In temperate regions of the Northern Hemisphere, adult weevils typically emerge in May. These beetles are about 7–10 mm long, brownish-black in colour, with dull yellow spots on their backs. Their wing covers are grooved and fused to the body, which means they cannot fly but are capable of walking considerable distances. Vine weevils are strictly nocturnal, hiding during the day in sheltered locations such as between a plant pot and the soil, under debris, in dense vegetation, or beneath planks.

Egg laying begins in early July and continues through late October. The eggs are small (about 0.7 mm), spherical, and white. Once hatched, the larvae are white to pinkish with reddish-brown heads and no legs. They start out around 1 mm long but grow up to 12 mm. These larvae feed on roots within the soil and are often found curled into a characteristic C-shape when disturbed. Their bodies are covered in stiff, curved white to light brown hairs. Overwintering typically occurs in the larval stage, usually as medium-sized instars. As temperatures rise in spring, the larvae resume feeding before pupating in the soil. Pupation occurs at depths of 2–20 cm, and the pupae are white to cream-coloured and 7–10 mm long.

Outdoors, there is generally one generation per year. Notably, all individuals in a population are female, and reproduction occurs via parthenogenesis, meaning no males are required. This reproductive strategy allows even a single female to establish a new infestation. Since Black Vine Weevils cannot fly, their natural dispersal is limited. Long-distance spread most often occurs through the movement of infested plants, making sanitation and monitoring of nursery stock critical for preventing outbreaks.

Preventing Black Vine Weevil (Otiorhynchus sulcatus) infestations requires a proactive approach that targets both the adult beetles and their soil-dwelling larvae. Since the larvae cause the most significant damage by feeding on plant roots, prevention efforts should focus on excluding the pest from planting areas and interrupting its life cycle before populations become established.

Sanitation and inspection are essential first steps. Because this pest is commonly spread through the movement of infested plant material, it is critical to inspect incoming nursery stock—especially potted plants—for signs of larvae in the root zone. Avoid accepting or planting any material that shows evidence of root damage or weevil presence. Maintaining a clean growing environment by removing plant debris and weeds will reduce adult beetle sheltering options. Regularly inspecting under pots and around containers can help detect adults, which often hide in these protected areas during the day.

Physical barriers and cultural practices can also be effective. Using pot toppers or sticky traps on greenhouse benches or around pots may help limit adult movement into production areas. Since adult weevils cannot fly, controlling their movement by elevating plants or using clean benches can reduce infestation pressure. Additionally, minimizing the use of overhead irrigation late in the day and avoiding excessive plant density can help discourage the moist, shaded conditions that favour weevil activity.

Crop rotation and careful plant placement are useful in outdoor settings. Avoid planting known host plants, like rhododendrons and strawberries, in the same area year after year if Black Vine Weevil is a known problem. Where possible, avoid reusing potting media, and sterilize containers before reuse. Since established plants are more resistant to larval feeding than young plants or cuttings, ensuring strong root development early on can also increase resilience.

Because the species reproduces parthenogenetically—where each female can produce viable offspring without mating—even a single adult can start a new population. This makes early detection and strict quarantine procedures for incoming plant material essential. By combining sanitation, inspection, physical exclusion, and environmental management, growers can significantly reduce the risk of Black Vine Weevil infestation and protect the health and quality of their crops.

Biological control of Black Vine Weevil (Otiorhynchus sulcatus) can be effectively achieved using the entomopathogenic nematode Heterorhabditis bacteriophora, which is available in Larvanem. This microscopic roundworm targets the larval stage of the weevil in the soil, where the most damaging feeding occurs.

Larvanem is applied as a soil drench to target actively feeding larvae. Once introduced into moist soil, the nematodes actively seek out larvae, enter their bodies through natural openings, and release symbiotic bacteria that kill the host within 24–48 hours. The nematodes then reproduce inside the dead larva, releasing new generations into the surrounding soil to continue the infection cycle. This makes Larvanem particularly effective for curative control during periods of high larval activity.

Timing and environmental conditions are key to success. Larvanem should be applied when soil temperatures are consistently above 12°C and when larvae are actively feeding near the root zone—typically from late summer into early autumn and again in spring, depending on local climate. The soil must be moist before, during, and after application to ensure nematode survival and mobility. Irrigation before and after application helps carry the nematodes deeper into the root zone where the larvae are located.

As with all biological controls, Larvanem is most effective when integrated into a broader pest management strategy that includes sanitation, inspection, and exclusion. It offers a natural, residue-free option that is safe for plants, beneficial insects, and the environment, making it especially suitable for use in ornamental crops and environmentally sensitive production systems.