Plum Curculio

Plum Curculio

Plum curculio, Conotrachelus nenuphar, is native to Eastern North America where it is a problem in commercial pome and soft fruit orchards. It belongs to a large group of beetles called snout beetles or weevils. The pest has not been detected in British Columbia. The closest infestation to BC is in the NW corner of Utah (see http://ceris.purdue.edu/napis/pests/pc/imap/pcall.html for distribution in US).

Introduction of the plum curculio to BC could result in increased use of pesticides at a time when industry is reducing usage through new softer/non-chemical tactics against existing pests. Increased use of pesticides would adversely impact current IPM programs that rely on biological control organisms, and would also increase the cost of production for growers.

Life Cycle and Appearance

The plum curculio overwinters in the adult stage under ground litter, in woodpiles and other protective sites adjacent to orchards. When apple trees are in the pink stage, the adults begin to fly into the orchards to feed on the buds, flowers, leaves and young fruit for up to 4 weeks. During this time females chew small cavities in the developing fruit in which they lay eggs (one egg/cavity). At each site they make a crescent-shaped cut next to the cavity. The eggs hatch in about 7 days and larvae develop in the fruit for 10 to 16 days, then drop to the ground to pupate in the soil. After about 2-3 weeks the new adults emerge and fly into the trees to feed on the fruit. No eggs are laid at this time. The adults feed until the cooler and shorter days of fall signal time to leave the orchards in search of suitable overwintering sites.

An adult curculio is about 4-6 mm long, dark grey to brown with grey and white patches on the back. It has 4 bumps on the back and their snout is about ¼ of their body length. Mature larvae are 7-9 mm long, white, legless, grub-like with a brown head.

plum curculio plum curculio damage

Plum curculio.
Photo courtesy OMAFRA. Copyright Queen's Printer for Ontario, 2001. Reproduced with permission. Plum curculio sting on fruit at harvest.
Photo courtesty OMAFRA. Copyright Queen's Printer for Ontario, 2001. Reproduced with permission.

Hosts and Damage

Plum curculio attacks all pome and soft fruits as well as gooseberry and chokecherry. Early varieties with dense foliage and yellow-skinned apple cultivars are preferred. However survival of eggs and larvae is least in apple because they are often crushed by the firm tissue as the fruit grows. Summer-generation adults prefer smooth-skinned fruit such as apples and plums.

There are three kinds of damage caused by this pest:

Small irregular feeding holes and D-shaped russeted scars on the young fruit characterizes early season feeding injury. Leaves and blossoms may show irregular notching along the margins as a result of adult feeding.
Crescent-shaped scars around egg laying sites on the fruit. Injured fruit that remains on the trees until harvest will be misshapen if heavily attacked.
Small holes and cavities characterize summer feeding injury by adults. These wounds are often darkened by the activity of decay organisms attacking the exposed tissue.

Monitoring

Visual and olfactory traps have not proven very successful in detecting the presence of plum curculio adults. Limb tapping of border trees as well as inspection of blossoms, leaves and developing fruit for feeding injury will assist in detecting the immigration of adults in the spring.

A very similar insect, the apple curculio, is present in the BC Interior where it has occasionally attacks pear, apple and cherry. The saskatoon (Amelanchier alnifolia) is its native host. It has a similar appearance and life cycle, but does not leave characteristic crescent-shaped scars on young fruit. See the description of apple curculio on the BCMAL website at http://www.al.gov.bc.ca/cropprot/tfipm/applecurculio.htm.

Further information on Plum Curculio:

Return to Non-native and Invasive Pests
Return to Pest Management Home