Subanguina picridis (Nematoda: Tylenchidae) 
Photos: Photo by: Norman E. Rees
subanguina picridis

Origin: Turkey and the former USSR (1).
Type of Agent: Gall-forming nematode (Nematoda: Tylenchidae) (1).

Life cycle:
Over wintering stage: The second stage larval in the upper levels of soil (1).
Egg stage: Larval nematodes are born from the females (1).
Larval stage: The infective stage larvae are activated by moisture to leave the deteriorating galls, in early spring.  They enter young leaves and stems of the new shoots.  Galls develop at the sites that are infected, eventually.  Nematodes grow in these galls until August, when the developed galls have primarily second-stage larvae.  Because the galls are deteriorating, the larvae leave the galls and go into the soil.  These larvae can become infective only if there is at least a month of moisture in the soil.   The larvae (essentially microscopic) look long and slim and have a translucent appearance (1).
Pupil stage: There is none (1).
Adult stage: They are about 1.5 mm (0.06 in) in length and appear in the summer (1).

Destructive stages: They are only destructive during their larvae and adult stages (1).
Plant species attacked: Russian knapweed (Acroptilon repens); diffuse knapweed (Centaurea diffusa) (1).
Damage to host: With permitable weather, this nematode can cause severe damage to the plant.   The best incidence that supports this is the USSR (1).

First introduced into the United States: 1984,  Washington
Now established in: Colorado, Montana, Oregon, Utah, Washington, & Wyoming (1)
Habitat:  With enough moisture during the winter and spring infection periods S. picridis does very well.  In dry areas S. picridis is less effective (1).
Availability: Limited (1).
Stage to transfer: Larval, in infected plant material (1).
Redistribution: In the fall, galls can be gathered and put on the soil to let the nematode larvae come out from the wet, disintegrating galls and go into the young shoots of knapweed when they emerge from the soil in the spring.  If the galls are taken care of properly, they can be stored for several years (1).

Comments:  In the former USSR, Canada, and the United States, S.  picridis was the first organism to be studied for biological control against Russian knapweed.   It was also the first nematode to be brought into North America as a biological control agent for a weed (1).


(1) Rees, Norman, et, al., Ed., Biological Control of Weeds in the West, Western Society of Weed Science, in cooperation with USDA, ARS, MT Dept. of Ag, and MT State Univ., Bozeman, Color World Printers, Bozeman MT, Feb., 1996.

By: Cody O'Donnell, Forrest Lewton, & Whit Smith, 03/2003. 
Updated by: Hans 02/11/2008. HOME     Back to Biological Control Agents, by Weed