Ambrosia Beetle

Ambrosia beetles have a broad range, but are most abundant in the southern and eastern regions of the United States.  The term ambrosia beetle refers to a number of species of the insect, 40 of which are native.  Several are destructive, but there are non-native species as well.  Native ambrosia beetles prefer stressed and weakened trees, while non-native species attack both stressed and healthy trees.

The following species are considered “ambrosia beetles”

  • Corthylus punctatissimus – pitted ambrosia beetle
  • Xyleborus saxenseni  – lesser shothole borer
  • Xyleborus crassiusculus – Asian (or granulate) ambrosia beetle
  • Xyleborus dispar – European shothole borer
  • Xyleborus sayi – ambrosia beetle
  • Xylosandrus germanus  – alnus ambrosia beetle or black stem borer
  • And many others

Treatment Strategy

Prevention is the most reliable method available when it comes to the ambrosia beetle.  The beetle does not feed on the host tree, so systemic insecticides are not effective.  Bark sprays are the only way known to prevent trees from attack.

Maintaining tree vigor can help.  Most native species will not attack healthy trees, but attack weakened, dying, or dead trees with enough wood moisture to support their symbiotic fungal growth.  Some exotic species will attack both weakened and healthy trees.

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Ambrosia Beetle Treatment Option 1

Mulching

Maintain a 3-inch-deep mulch ring around the trunk of the tree to help keep the roots moist and increase the important fibrous root system. The optimal size for a mulch ring is one foot for every inch of trunk diameter. However any size mulch ring is beneficial.

Fertilizing

Apply a complete LOW NITROGEN fertilizer every 2-3 years. This can be helpful in urban or non native soils.

Watering

Periodic watering of your trees in drought-like and hot conditions will help the trees’ defense system and keep invading pests out.

Remove Infested Trees

Some species of ambrosia beetle feed on dead or dying wood.  Removal of infested material near the treated tree may help reduce local beetle activity. 

Application Type - Cultural Practices

DIY Equipment Needed:

• Soaker hose (for watering)

• Mulch

• Rake and shovel

• Low nitrogen fertilizer

Ambrosia Beetle Treatment Option 2

When mulching and watering are not enough, the use of trunk-applied insecticides can provide control of ambrosia beetles.  Several applications are required to maintain protection throughout the growing season.  First applications should begin in March and continue every 30 days until August.

Application Type Trunk and Limb Spray

DIY Product/Equipment Needed:

• Tengard

• Gloves and safety glasses

• Pump up sprayer with wand

Ambrosia Beetle Treatment Option 3

When mulching and watering are not enough the use of trunk-applied insecticides can provide control of ambrosia beetles.  Several applications are required to maintain protection throughout the growing season.  First applications should begin in March and continue every 30 days until August.

Application Type Trunk and Limb Spray

DIY Product/Equipment Needed:

• UpStar EC TT&O

• Gloves and safety glasses

• Pump up sprayer with wand

Ambrosia Beetle DIY Kit

Option One:

Application Type - Cultural Practices

DIY Equipment Needed:

• Soaker hose (for watering)

• Mulch

• Rake and shovel

• Low nitrogen fertilizer

Option 2:

Application Type Trunk and Limb Spray

DIY Product/Equipment Needed:

• Tengard

• Gloves and safety glasses

• Pump up sprayer with wand

Option 3:

Application Type Trunk and Limb Spray

DIY Product/Equipment Needed:

• UpStar EC TT&O

• Gloves and safety glasses

• Pump up sprayer with wand

How Is It Spread?

In general, adult ambrosia beetles are most active in March, though they are active year-round.  Females excavate galleries within the host plant just beneath the bark where eggs are laid.  Newly hatched females mate with their brothers, then move to other host trees.  Males are wingless and are used only for mating.  The life cycle takes around 50-55 days and two generations are possible each year.

These beetles work symbiotically with fungi such as Fusarium species and Ambrosiella species.  The fungi that are consumed (sometimes referred to as “Ambrosia”) are grown in galleries created by the beetles.  These fungi may be responsible for the death of the tree, though the beetles introduce multiple fungi species, some apparently inadvertently.

Susceptible Trees

Many.   Persea americana (avocado), P. borbonia (redbay), P. palustris (swampbay), Sassafras albidum (sassafras), Litsea aestivalis (pondspice), Lindera melissifolia (pondberry), Cinnamomum camphora (camphor tree), Carya (pecan), Prunus persica (peach), Diospyros (persimmon), Koelreuteria (golden raintree), liquidambar (sweet gum), Quercus (oak), Ulmus parvifolia (Chinese elm), magnolia, and others.  Many ambrosia species will preferentially attack smaller trees , orchard or new plantings in particular.

Symptoms

Vascular wilt symptoms are a tipoff for ambrosia bark beetles.  These symptoms include flagging and dieback of entire branches.  As the beetles attack their host they introduce vascular fungi that eventually kill the tree.  These effects can be seen best in mid to late summer after trees have leafed out and been exposed to summer stress.   Blue or brown staining in the vascular tissue will also be seen.  Eventually dieback and tree death will occur.

  • 1.4 mm-4 mm dark brown to black beetle.
  • Eggs are larvae, are minute (smaller than a pencil tip) and are rarely seen.
  • 1” to 2” long frass tubes the thickness of pencil lead are a dead giveaway.  They are rare though: being weak they will break in wind and rain.  Some species begin feeding at the bottom of the trunk, while others can attack near the base of twigs and branches.
  • “Sawdust” that is actually frass can accumulate at the base of the tree.
  • Pencil-lead-sized holes called “shotholes” at the base twigs where the brood has exited the host.

Lookalikes

Vascular wilt symptoms could look similar to an advanced ambrosia beetle attack.  Ambrosia beetles introduce fungi to the vascular system of trees as they excavate their galleries.

Related/Similar Problems

Laurel Wilt

Timing

Spring

Urgency

High

Risk of Spreading

High

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