USDA-APHIS officials are asking for public comments before the Oct. 20 closing date concerning a preliminary environmental assessment on a plan that would release endoparasitoid predator wasps in select citrus-growing regions as part of a proposed strategy to help control Asian citrus psyllids (ACP) and Huanglongbing (HLB) disease that threatens the U.S. citrus industry.

HLB is a bacterial pathogen spread by the psyllid (moth), which prefers citrus trees on which to feed and lay their eggs. HLB, caused by strains of the bacterial pathogen Candidatus Liberibacter asiaticus, attacks the vascular system of host plants. The disease causes yellow shoots to develop, blotchy mottling and chlorosis, reduced foliage, and tip dieback of citrus plants.

Inevitably, HLB greatly reduces production, destroys the economic value of the fruit, and kills the tree. Without quick preventive measures it can spread quickly from tree to tree and grove to grove.

For the latest on southwest agriculture, please check out Southwest Farm Press Daily and receive the latest news right to your inbox.

ACP is currently present in Alabama, American Samoa, Florida, Georgia, Guam, Hawaii, Louisiana, Mississippi, the Northern Mariana Islands, Puerto Rico, Texas, the U.S. Virgin Islands, and portions of Arizona, California, and South Carolina. The Animal and Plant Health Inspection Service (APHIS) is proposing to issue permits for the field release of a parasitic wasp, Diaphorencyrtus aligarhensis, to reduce the severity of infestations of ACP in the United States and control the spread of HLB.

APHIS' review and analysis of the potential environmental impacts associated with this proposed release are documented in an environmental assessment entitled “Field Release of Diaphorencyrtus aligarhensis for the Biological Control of the Asian Citrus Psyllid in the Contiguous United States,” dated June, 2014. The environmental assessment is currently available to the public for review and comment.

HLB, also known as citrus greening disease, first arrived in Florida in 2005. Florida is the largest citrus producer in the United States and, behind Brazil, the second largest producer of orange juice in the world. But research indicates the presence of HLB increases Florida production costs by as much as 40 percent and has resulted in the loss of nearly $8 billion in industry revenue in recent years as well as the economic loss of thousands of jobs.

Serious citrus disease

It is one of the most serious citrus diseases in the world. So far it has significantly shrunk citrus production in Florida, Asia, Africa, the Arabian Peninsula and Brazil. In areas of the world where HLB is endemic, citrus trees decline and die within a few years after infection. The disease specifically attacks citrus plants, but presents no threat to humans or animals. In spite of extensive research by APHIS and multiple universities, no cure for HLB has been discovered.

Researchers say good evidence exists to show that reducing psyllid populations via insecticide application not only slows the rate of HLB spread but also reduces severity of the disease once established. However, they say eliminating HLB from an area has never been successful and would not be possible with vector control alone.

Since the arrival of Asian psyllid and HLB in the Texas Rio Grande Valley in early 2012, an aggressive, industry-wide spraying regime of commercial citrus groves has proven effective in limiting the spread of both the ASP and the disease. But research indicates pesticide control can also have a negative impact on beneficial insect populations and cannot by itself provide complete control, making additional control methods necessary.

Foliar insecticide applications should only be used as necessary to minimize the impact on natural enemies that maintain psyllids and other pests at lower levels later in the year. While a single female psyllid can lay as many as 800 eggs, studies in Florida and Puerto Rico have shown that over 90 percent of psyllids that hatch in the field do not survive to become adults. Many are consumed by predaceous insects such as ladybeetles.

Currently, all possible vector and disease control methods are being employed to manage HLB in Florida and in other states where HLB has been detected, including biological control with Tamarixia radiata and Diaphorencyrtus aligarhensis, two different types of predator wasps.

Researchers appear divided over which of the two species of wasps provide the best defense against ASP. One Florida study indicated Tamarixia radiata is presumed superior to Diaphorencyrtus aligarhensis based on previous reports of high psyllid parasitization rates and rapid establishment in new areas. But not all researchers agree.

But the release of predator wasps, in general, are known to have revived the citrus industry in Reunion Island after its introduction from India in 1978, and the parasitoids caused substantial decline in ASP populations in Guadeloupe Island within one year of release.

Interested individuals can file comments by either of the following methods: