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Isochnus rufipes (Formerly Rhynchaenus rufipes)

Adult willow flea weevil. Photo: Therese Arcand, Natural Resources Canada.
Scientific Name: 
Isochnus rufipes (Formerly Rhynchaenus rufipes)
Common Name: 
Willow Flea Weevil
Growing Degree Days (GDD's): 
363–618 GDD's; 707-1029 GDD's, Base 50F, March 1st Start Date (Source: Robert Childs, UMass Extension and Cornell Cooperative Extension.)
Host Plant(s) Common Name (Scientific Name): 
Apple (Malus spp.)
Aspen (Populus spp.)
Birch (Betula spp.)
Black willow (Salix nigra) (Anderson, 1989)
Cherry (Prunus spp.)
Elm (Ulmus spp.)
Narrowleaf cottonwood (Populus angustifolia) (Anderson, 1989)
Pussy willow (Salix discolor) (Anderson, 1989)
Red maple (Acer rubrum)
Red oak (Quercus rubra)
Serviceberry (Amelanchier spp.)
Shining willow (Salix lucida) (Anderson, 1989)
Willow (Salix spp.) *Primary adult weevil host.
Insect Description: 

The willow flea weevil is a type of snout beetle. Adults are small (approximately 2.3 mm), black in color, with red/yellow legs. Adults are broad in shape, with large eyes, elbowed antennae, and thick hind femurs for jumping. It is known to occur in Massachusetts and other cooler areas of North America (Johnson and Lyon, 1991). Adults overwinter in sheltered areas, such as the leaflitter and under debris. Adults emerge as spring temperatures warm and feed on host plant buds, and eventually on the tips of new shoots and host plant foliage. Adult weevils chew tiny, circular pits in the host plant parts that it feeds on. In Southern Quebec and Maine, flights of the willow flea weevil were frequent in June and July following adult emergence in May. Adults also mated in early June with new generation adults in August (Levesque and Levesque, 1995). Eggs are white in color and tiny (0.3-0.4 mm in size). Following egg laying, larvae emerge in early summer. They feed in small blotch mines in willow leaves. Leaf mines eventually turn dark brown and dry out. Once mature, the larvae pupate within their leaf mines. Pupae change from whitish in color to black as they mature within their leaf mines. Adults from the current season's generation emerge by August and begin feeding on host plant leaves. Adults will gather in large groups on the sides of buildings as cool fall weather approaches. 

Damage to Host: 

Larvae create blotch type mines in the upper surface of willow foliage. Mines may cause the leaves to brown or drop prematurely from the host plant by August or September. The adults chew holes/small pits in the foliage in late summer upon emergence and again in the spring after they overwinter and when warm spring temperatures allow. Adult feeding may be enough to kill new shoots in the spring. Pit-like feeding in host plant leaves becomes a hole after the surrounding foliage browns and drops from the leaf. Holes are less than 1 mm in diameter. Historically reported as an important forest pest (Craighead, 1950).


Visually search for the circular pits on the upper surface of host plant foliage created by the adults any time between May and August. Search for blotch mines in host plant leaves approximately in June. 

Cultural Management: 

Large, otherwise healthy host plants are likely to sustain willow flea weevil feeding. Proper planting and maintenance to promote tree health can help reduce the impact of insect feeding. 

Natural Enemies & Biological Control: 

Natural enemies of the willow flea weevil are not readily discussed in the scientific literature. Parasites, predators, and fungal pathogens of other weevil species exist, so it is likely that this native insect also has natural enemies that help keep their populations below outbreak levels.

Chemical Management: 

Abamectin (NL)

Acephate (NL)

Acetamiprid (L)

Azadirachtin (NL)

Bifenthrin (NL)

Chlorpyrifos (N)

Clothianidin (NL)

Cyantraniliprole (NL)

Dinotefuran (NL)

Emamectin benzoate (L)

Flonicamid+cyclaniliprole (N)

Gamma-cyhalothrin (adults) (L)

Horticultural oil (L)

Imidacloprid (L)

Lambda-cyhalothrin (adults) (L)

Neem oil (NL)

Permethrin (L)

Pyrethrin+sulfur (NL)

Spinosad (NL)


Active ingredients that may be applied systemically include: Abamectin (injection), acephate (injection), acetamiprid (injection), azadirachtin (injection, soil drench), clothianidin (soil drench), cyantraniliprole (soil drench, soil injection), dinotefuran (soil drench), emamectin benzoate (injection), imidacloprid (soil drench), and neem oil (soil drench).

When used in a nursery setting, chlorpyrifos is for quarantine use only.

Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.

Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.

Read and follow all label instructions for safety and proper use. If this guide contradicts language on the label, follow the most up-to-date instructions on the product label. Always confirm that the site you wish to treat and the pest you wish to manage are on the label before using any pesticide. Read the full disclaimer. Active ingredients labeled "L" indicate some products containing the active ingredient are labeled for landscape uses on trees or shrubs. Active ingredients labeled "N" indicate some products containing the active ingredient are labeled for use in nurseries. Always confirm allowable uses on product labels. This active ingredient list is based on what was registered for use in Massachusetts at the time of publication. This information changes rapidly and may not be up to date. If you are viewing this information from another state, check with your local Extension Service and State Pesticide Program for local uses and regulations. Active ingredient lists were last updated: January 2024. To check current product registrations in Massachusetts, please visit: .