Tiny predatory wasps to combat citrus-damaging insect

Published on May 25, 2017

The efforts against agriculture-harming pests are a continual battle for Placer County. Inspectors are in the field every day, whether visiting shipping companies or nurseries or checking the more than 1,000 insect traps that are strategically placed throughout the western slope of the Sierra Nevada.

Last fall, the Asian citrus psyllid was discovered in citrus trees in two adjacent private residences in the Lincoln area. The psyllid can carry a disease called Huanglongbing, or HLB, that is fatal to citrus plants. Although the insects found in Placer County last year did not carry the disease, the county’s agricultural commissioner’s office and the California Department of Food and Agriculture have stepped up efforts to ensure the psyllids that were found were the only ones in county.
As part of those efforts to protect commercial orchards and homegrown trees, staff from the county’s agriculture commissioner’s office is working with the California Department of Food and Agriculture on the use of biological insect controls. Tiny, non-stinging black wasps (Tamarixia radiata) were recently released at sites in Lincoln, Rocklin, Loomis and Penryn. The wasps only attack the Asian citrus psyllid. Neither the wasp nor the psyllid are indigenous and they both originate in Pakistan. The wasps pose no threat to humans, and only attack the Asian citrus psyllid.
“Placer County is always diligent in our efforts to protect our prized agricultural products, including our beloved Satsuma mandarins,” said Joshua Huntsinger, agricultural commissioner. “We are incredibly fortunate that the California Department of Food and Agriculture was able to release predatory wasps here in Placer County. The beauty of the wasps is that they are able to find and destroy Asian citrus psyllids more easily and effectively than humans can.”
The release of the wasps is dependent on weather, and they were not released until rains stopped. The release is a one-time event and follows a pesticide application last year around the site where the psyllids were discovered. The disease that psyllids can carry, HLB, has only been found in Los Angeles, but it can be spread to healthy citrus trees throughout the state, including Placer County’s famed mandarin trees and the Central Valley, where much of California’s commercial citrus is produced. The disease attacks all varieties of citrus trees. There is not a known cure once a tree is infected.
The wasps are kept in a container and then sprinkled on citrus trees where they lay eggs in the psyllid’s nymphs. When the eggs hatch the larvae feed on and kill the nymph. While the use of biological control agents such as the wasps alone cannot contain the psyllid, they are effective when used in conjunction with conventional treatments. The wasp can reduce up to half of the psyllids.
After the discovery last year of the psyllid in Lincoln, a 118-square-mile quarantine area was established surrounding the discovery site. The quarantine prohibits the movement of citrus and curry leaf tree nursery stock, including all plant parts except fruit, out of the quarantine area and requires that all citrus fruit be cleaned of leaves and stems prior to moving out of the quarantine area. The quarantine boundary area can be seen by following this link: Psyllid (PDF). For additional information: Citrus threat and ACP.