Otiorhynchus sulcatus Family: Curculionidae
Life cycle: Generations per year: one in the Pacific Northwest
Description & Life Cycle: This weevil overwinters in the soil as immature larvae. In early spring, when the larvae have reached their mature sixth instar stage at 0.4 – 0.6 inches (10 – 15 mm) long, they enter the pupating stage. They are white and have the rough outline of the adult weevil. This last roughly 10 days after which the adults emerge. This is usually from late May through June. Adult weevils require 3 – 4 weeks of active foliage feeding before they start laying eggs. As many as 500 eggs are laid in the soil around the base of host plants over a 2 – 3 week period. The legless white larvae with a brown head will hatch in 10 – 14 days and begin feeding on the plant roots. In the fall, when the temperatures start to decrease, the larvae will move deeper into the soil where they will overwinter.
Special Notes: Native to Europe, this weevil species was discovered and identified in Connecticut in 1910. Since that date, it has become widespread throughout North America.
It is interesting to note that only female adult weevils are produced in North America. They reproduce parthenogenically. Adults feed on host plant leaves during the night leaving a multitude of half-round notches along the edges of the leaves. In a particularly high weevil populated area of the garden, this can look quite unsightly on your targeted evergreen plants.
Remedial Action: There are some insect killing nematodes available which will control root weevils in their immature, larval stage. These are applied as a soil drench and best used when the soil temperatures are 12 °C (55 °F) or higher in late summer and early fall. Soil must be very wet at time of application and never in direct sunlight. The UV rays will quickly kill the beneficial nematodes.
Unfortunately, there is not much data on the effectiveness of this treatment.
Posted on May 17, 2022