Raspberry cane maggot—Pegomya rubivora
Larvae of raspberry cane maggot, a fly (family Anthomyiidae), bore and feed in caneberry shoots. This causes caneberry terminals to wilt, discolor, and die.
Identification
Because larvae feed hidden inside canes, their damage is generally the first observed clue to their presence. A hole about 1/25 inch (1 mm) in diameter is present near the tip of the cane where the larva (maggot) bored inside to feed and tunnel. There is a swelling in canes where the larvae are or have been feeding inside.
Larvae of raspberry cane maggot are white, legless, and up to 1/3 inch long. The adult is a hairy, gray fly about 1/5 inch long with 1 pair of clear wings. The puparium (covering of the pupa) is oblong, about 1/5 inch long, and occurs in topsoil.
Raspberry horntail (a sawfly, or broad-waisted wasp, family Cephidae) causes virtually identical drooping and wilting of caneberry tips and swelling of canes where its larva tunnels and feeds inside. However, its pale larvae have three pairs of true legs, which larvae of raspberry cane maggot lack. Raspberry horntail larvae also grow up to 9/10 inch long, more than twice the length raspberry cane maggots. It may not be important to distinguish these species because their management is the same.
Life cycle
Adult flies emerge from the soil in late April and lay eggs on the tips of new caneberry shoots. Larvae hatch and tunnel into the young shoots. They bore downward inside the cane and girdle the terminal. After feeding, the mature larva (prepupa) drops and overwinters and pupates in topsoil. There is one generation per year.
Damage
Larvae of raspberry cane maggot chew, feed, and tunnel inside stems of blackberry, loganberry, and raspberry. Infested stems wilt, droop, and discolor blackish to purple. This pest kills canes but does not appear to reduce fruit yield even when abundant.
Solutions
Parasitoid (parasitic) wasps help to keep the abundance of this pest low if broad-spectrum, persistent insecticides are not applied to caneberries for any pest. Regularly inspect cranberries and prune off infested (drooping and wilted) canes and shoots several inches below the wilted area and where any tunneling is apparent inside the stem. Dispose of prunings in covered containers. Destroying any nearby wild blackberries may help to reduce the abundance of this pest in caneberries grown for fruit production.
To make plants more tolerant of this pest's damage, provide caneberries with optimal growing conditions. Appropriate irrigation is especially important to keep caneberries growing vigorously. No insecticide application is recommended for this occasional pest.
Adapted from Raspberry Cane Maggot Pegomya rubivora (Coquillett) (PDF), University of New Hampshire. |
Shoot tip wilted from the feeding and tunneling of a larvae of raspberry cane maggot.
Stems blackened and wilted from tunneling of larvae of raspberry cane maggot.
Larva of raspberry cane maggot exposed in its frass-filled tunnel.
Adult raspberry cane maggot.
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