Location: Invasive Species and Pollinator HealthTitle: Biological control of arundo with the arundo wasp in the Central Valley
|BITUME, ELLYN - Us Forest Service (FS)|
|ROGERS, DYLAN - University Of California|
Submitted to: California Invasive Plant Council
Publication Type: Abstract Only
Publication Acceptance Date: 8/26/2020
Publication Date: N/A
Technical Abstract: Arundo or giant reed (Arundo donax L.) has invaded over 2,200 acres of riparian habitats in California’s Central Valley. Arundo consumes water, blocks flood control channels and creates fire hazards. In 2017, USDA-ARS scientists released a proven biological control agent, the shoot tip-galling wasp Tetramesa romana, at nine sites. Three plots per site were pre-cut to ground level, 1 m height, or left uncut, and cut plots allowed 1 month to regrow. In 2018, arundo shoot exit holes, made by wasps emerging from galls, were 25-fold more abundant in ground-cut plots. Surveys in 2019 found exit holes at 56% of 99 survey points at a site on Stony Creek near Orland in the northern Sacramento River watershed, and at 90% of 30 points at a site on Cottonwood Creek near Madera in the southern San Joaquin River watershed. Wasps dispersed 200 m from release plots, and young main shoots were galled, suggestive of emerging wasp impact. Observations in 2020 found wasps at two additional sites in Madera and in the Delta. Moisture was important in wasp establishment. Death of arundo shoots due to seasonal drought hindered establishment, and humidity level in greenhouse cages influenced wasp reproduction. Impact monitoring is ongoing and requires five years. The arundo wasp can be a key biological control tool in integrated management of arundo in the Central Valley. Its use is best combined with pre-cutting of release plots, and it is most likely to establish populations at sites with year-round water supply.