Ambrosia Beetle Complex
Ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) represent a large number of native and exotic species that live in association with Ambrosia fungi. Ambrosia fungi digest wood and provide nourishment to adult beetles and larvae. The beetles are the only dispersal vehicle for these fungi. More than 50 exotic ambrosia beetle species have been reported in North America. Granulate ambrosia beetle (Xylosandrus crassiusculus), black stem borer (Xylosandrus germanus), and camphor shot borer (Cnestus mutilates) are listed as the major pests to the nursery crop industry.
Damage and Hosts
Ambrosia beetles mainly attack stressed plants; however, they can affect healthy trees as well. Severely damaged plants show wilting, branch dieback, and occasionally death of small plants. In general, injury is irreparable; in consequence, plants must be removed from production and destroyed because they are source of further infections and lack marketable value.
Ambrosia beetles can cause great economical loses on the following species of interest for the ornamental industry: aspen, beech, cherry, Chinese elm, crapemyrtle, dogwood, golden rain tree, hickory, magnolia, maple, mimosa, oak, peach, persimmon, Prunus, red bud, sweet gum, tulip, poplar, and walnut.
There is no effective chemical control, unless it is applied preventively to control flying adults emerging from plants. In general, permethrin insecticides are recommended.
Survey and Trapping in 2016
Monitoring is a key practice to control Ambrosia beetles in nursery crops since these species are very difficult to observe unless the damage is already done and visible as toothpick-like strands on trunks or branches. This year, ambrosia beetle monitoring began in late winter in western Kentucky using Baker traps. The traps were built using a transparent 2-liter soda bottle with three to five rectangular holes on the top and a transparent 500 milliliter water bottle on the bottom; they were attached together with a male-to-male hose connector (Figure 1).
The lure was either denatured 95% ethanol or ultra-high release ethanol (Contech Enterprises Inc. Canada). The catching solution was a commercial coolant.
A total of ten traps were deployed in March 2016. Seven traps were placed in tree farms located in Hazel (Marshall County) and Elkton (Todd County). Natural wooded areas surrounding nursery crops were preferable when possible. Three traps were located at the University of Kentucky’s Research and Education Center at Princeton (Caldwell County) in apple and peach orchards and the woods. Traps were monitored biweekly.
Species Currently Found
Preliminary identification has shown that at least eight Scolytinae species have been captured; among them were Camphor shot borer (Cnestus mutilatus) and Granulate ambrosia beetle (Xylosandrus crasiusculus) (Figures 2 & 3).
These two species have been the most abundant in the three sites (Figure 4), and the highest populations were recorded in Princeton and Hazel on April 19 and 28, respectively. In Elkton, ambrosia beetles were first detected on May 4 in low numbers compared to the other two sites. Granulate ambrosia beetles and Camphor shot borer are identified as very damaging pests in the nursery crop industry. So far, no damage has been observed on nursery trees.
- Ambrosia Beetles (Clemson Cooperative Extension, Entomology Insect Information Series) (link)
- Biology, Injury, and Management of Maple Tree Pests in Nurseries and Urban Landscapes (Journal Integrate Pest Management 4(1): 2013) (link)
- Camphor Shot Borer: A New Nursery and Landscape Pest in Tennessee (Tennessee State University) ANR-ENT-01-2012.
- Granulate Ambrosia Beetle (Division of Agriculture Research and Extension, University of Arkansas) (FSA-7064)
By Zenaida Viloria, Extension Associate; Winston Dunwell, Extension Horticulturist; and Virginia Travis, Horticulture Technician