Contents: By Damage and Image
In progress
Contents: Alphabetical

alder flea beetle
aphid management
apple and thorn skeletonizer
apple ermine moth
ash whitefly
azalea bark scale
azalea lace bug
azalea sawfly
Bagrada bug
bark lice
Barypeithes root weevil
Beneficial nematodes
biocontrol of root weevils
birch aphid
black bean aphid
black cherry aphids
black stem borer
bluegum psyllid
Boisduval scale
branch and twig borer
brown marmorated stink bug

bronze birch borer
boxwood leafminer
boxwood psyllid
bulb flies
cabbage whitefly
carnation tortrix
carpet beetle (images)
Calligraph californica

Ceanothus stem gall moth
cereal leaf beetle
cherry ermine moth
chilli thrips
cinnabar moth
clay colored weevil
cottony camellia scale

crane flies
cypress tip moth

dogwood sawfly
Douglas fir sawfly
Douglas fir twig weevil
elm leafminer
European pine sawfly new
European pine shoot moth
European wool carder bee
emerald ash borer
Fall webworm
fir coneworm new
flatheaded cedar borer
ground beetle gallery
Hemerocallis gall midge new
hollyhock weevil
honeylocust plant bug
honeylocust pod gall midge
Heliothis phloxiphaga
holly bud moth
huckleberry root aphids
ground mealybug
Japanese beetle
lady beetle gallery
leaf weevil
light brown apple moth
Linden aphid new
lupine aphid new
Macrosiphum rhamni new
maple aphids
maple tip moth
maple midge
March flies
mountain ash sawfly
Myzocallis sp. on red oak new
Narcissus bulb fly
natural enemies gallery
oak ambrosia beetle
oak slug
oak twig gall wasp
obscure root weevil
Pacific flatheaded borer
peach tree borer
peach twig borer
pear blight beetle
pear psylla
pear leaf-curling midge
pear sawfly
pine needle scale
pine and cone spittlebug
poplar and willow borer
Psyllopsis fraxinicola
rose curculio weevil
rose midge
rove beetle gallery
rose stem girdler new
sequoia pitch moth
soldier beetle gallery
snakefly gallery
speckled green fruitworm
meadow spittlebug
spotted asparagus beetle
spruce twig aphid
tent caterpillars
viburnum leaf beetle
violet gall midge
western poplar clearwing
western spotted cucumber beetle
white pine weevil
woolly alder aphid new
woolly ash aphid
woolly beech aphid

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Cynipid gall wasps on oak- Bassettia ligni, Andricus californicus, Besbicus mirabilis, and Neuroterus saltatorius

There are several cynipid gall wasps that make galls on oaks in the PNW. One potentially damaging cynipid gall wasp in nursery production is Bassettia ligni, a native insect that causes twig galls on Oregon white oaks.

This species has alternate asexual and sexual generations. B. ligni wasps overwinter in stem galls and adult wasps emerge in spring (by mid-April in 2016) leaving tiny holes in the gall. These wasps, all female, lay their eggs in oak leaves causing inconspicuous galls. A sexual generation hatch from the leaf galls in June through mid-July. The mated females from this generation lay eggs in oak twigs, which form twig galls later in the fall.

In forest landscapes, this damage becomes obvious as squirrels debark white oak twigs in search of a wasp larvae meal. This debarking girdles the oak twigs causing a striking dieback of white oak branches. This damage generally will not kill an oak tree but can be an aesthetic issue.

In nurseries, the damage is more impactful. Twig galls caused by the B. ligni, cause the affected terminal to die, stimulating lateral branches to grow. While in some cases, this might provide a preferred bushier tree, sometimes this damage is a less appealing witches broom or other distortions, requiring retraining of another terminal.


Abraham, Melika, G. 2007. Review of the Nearctic gallwasp Species of the Genus Bassettia Ashmead, 1887, with Description of New Species (Hymentoptera: Cynipidae: Cynipini). Acta zool. hung. 53, 2007

Larew, H. and J. Capizzi. 1983. Common Insect and Mite Galls of the Pacific Northwest. Oregon State University Press.

Shaw, Dave. 2015. Summer 2015 DROUGHT! And heat. A Forest Health Report. Tree Topics. Oregon State University Extension. Posted September 2 2015. <18 July 2016>

Shaw, Dave. 2013. Oregon white oak in the Willamette Valley, 2013 . . . Some in your face issues. Tree Topics. Oregon State University Extension. Posted 2013. <18 July 2016>

Garry oak leaf and twig gall. PNW Insect Management Handbook.

Original version: <18 July 2016)

Last revision <19 July 2016>

Author: R.L. Rosetta, Extension Nursery Integrated Pest Management, Department of Horticulture, Oregon State University/NWREC.



Cynipid gall wasp, Bassettia ligni, [tentative ID] damage on white oak
Bassettia ligni [tentative ID] larva and stem gall on white oak

Cynipid gall wasp, Bassettia ligni, damage on white oak (note emerging was on underside of gall)
Bassettia ligni damage to white oak twig

Bassettia ligni (tentative ID) larva in stem gall on white oak.
Bassettai ligni [tentative ID] larva and stem gall

Emergence holes from Bassettia ligni gall wasp on white oak
Bassettia ligni emergence holes

Bassettia ligni ovipositing on white oak twig
Bassettia ligni ovipositing on white oak twig

Bassettia ligni male and femaleBassettia ligni


Cynipid wasp on bur oak leaf
Cynipid wasp on bur oak

Cynipid wasp on bur oak leaf
cynipid wasp on bur oak

Close up of a cynipid wasp inserting egg (ovipositing) on bur oak
cynipid wasp inserting egg into bur oak leaf

Website editor:
Robin Rosetta

Page last modified 7/19/16


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