Raspberry sawfly—Monophadnoides geniculatus
Raspberry sawfly (family Tenthredinidae) is an uncommon, leaf-feeding pest of raspberry along California's Central Coast. Less commonly it feeds on other caneberries including blackberry and loganberry.
Identification
Larvae of raspberry sawfly are pale green with fine, pale bristles (hairs). Some individuals have a lengthwise dark stripe on top. They grow up to 2/3 inch long and can occur on the underside of leaves singly or in a scattered group.
The larvae resemble caterpillars (larvae of butterflies and moths, Lepidoptera) but are distinguished by the number of leglike appendages (prolegs) on the middle of abdomen. Caterpillars that feed openly on plants have four or fewer pairs of prolegs in the middle of the abdomen. Larvae of sawflies that feed openly have at least six pairs of prolegs, those on abdominal segments two to seven.
Adults are black, broad-waisted wasps with a yellow band on the abdomen, yellow legs, and clear wings. They are about 1/4 inch long. The whitish pupal cocoons are about 1/4 inch and hidden in topsoil.
Life cycle
Adult sawflies emerge from pupae in the soil or organic litter on the ground in April or May. After mating, adult females lay their eggs in or on caneberry leaves, usually raspberry. Larvae feed for about 2 to 3 weeks, generally in May and June. They chew and feed from the underside of the leaves. Mature larvae (prepupae) drop to the ground and form a silk cocoon in which they overwinter. In spring, they pupate and the adult wasp emerges.
There is generally one generation per year. However a portion of the population may have a second generation that causes leaf chewing later in the summer.
Damage
Larval feeding causes scattered holes in raspberry leaves which can be seen beginning in May. It is uncommon that larvae are so abundant that only veins are left on chewed leaves by late June and the leaves may drop prematurely.
Otherwise, healthy raspberry plants tolerate significant chewing on their leaves. This pest generally does not warrant control.
Solutions
Larvae can be handpicked and disposed of or infested leaves can be clipped from the plant and disposed of in covered containers. If feeding by raspberry sawfly has been problematic during previous years, inspect caneberry leaves in early June. If the larvae and their damage are not tolerable, the underside of foliage can be thoroughly sprayed with spinosad. Adding horticultural oil to the spray mix can increase the efficacy persistence of spinosad.
Note that spinosad is toxic to bees and certain beneficial predatory insects for several hours after its application. If raspberries are flowering when foliage spraying is planned, make the application late in the day when honey bees are no longer active.
Adapted from Raspberry Sawfly in Central Coast Raspberries and Raspberry Sawfly, University of California Agriculture and Natural Resources.
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