Bursaphelenchus coccophilus | Pest Rating Proposals and Final Ratings

California Pest Rating for

Bursaphelenchus coccophilus (Cobb) Baujard 1989

Pest Rating: A

PEST RATING PROFILE

Initiating Event:

In 2011 the detection of the South American Palm Weevil in San Ysidro, a potential vector of the Red ring nematode, Bursaphelenchus coccophilus, led to laboratory examination of in-State detected weevils for the presence of the nematode. Bursaphelenchus coccophilus is a federally regulated nematode pest. Herein is proposed an official and permanent State rating for the nematode species.

History & Status:

Background: Red ring nematode (RRN) causes red ring disease of palms. The nematode parasitizes the South American Palm Weevil, Rhynchophorus palmarum which in turn transmits it to palms. Symptoms of red ring disease were first described on Trinidad coconut palms in 1905. Although RRN has never been detected in California, its insect vector was first detected in the State in 2011 thereby marking a first U.S. find.

Life cycle: The life cycle of RRN is intimately associated with the palm weevil. The palm weevils are attracted to wounds or cuts in the trunks of the palms. At an infected palm, a weevil ingests dispersal third stage juvenile nematodes or picks them up on the surface of its body. When palm weevils disperse and invade healthy or stressed palms, the associated nematodes are usually deposited by the insect as it lays its own eggs. Only a few nematodes are needed for a successful transmission. Nematodes feed and reproduce in the palm tissue, causing the death of infected trees. When the weevil eggs hatch, immature nematodes associate with immature weevils. As many as 10,000 juveniles of B. cocophilus remain within a weevil through the latter’s metamorphosis, apparently without molting or reproducing, and appear to aggregate around the genital capsule of the adult weevil. Adult weevils emerge from their cocoons and disperse to healthy or stressed and dying palms carrying new batches of third-stage juvenile nematodes with them, completing the life cycle. The life cycle takes nine to ten days.

Hosts: Several species of tropical palms are hosts including date, Canary Island date and Cuban royal, but it is most common in oil and coconut palms, and date palm. Over 17 species belonging to the family Palmae can be infected by the nematode.

Symptoms: Symptoms of red ring disease vary greatly with palm species, cultivar, age of palm, and environmental conditions. Palms younger than two and a half years are not infected with the nematode. Most often 3-10 year old coconut palms and 5 year old African Oil palms are attacked by the nematode and die 2-4 months after nematode infection. Older trees may live longer – up to 20 weeks or several years. However, infested trees never fully recover from red ring nematode infestation. Those few that do recover have a recurrence of the disease in later years.

The main internal symptom is the presence of a red ring – seen as such in a cross section cut through the trunk of an infested palm, 3-5 cm wide, and found 1-7 ft above the soil line. The color is commonly red but may vary from light pink or cream to dark brown. The tissue of a healthy palm is creamy white. Internal symptoms are visible within 2-3 weeks after the nematode enters a healthy plant. External symptoms in infested coconut palms include dwarfed, deformed, and yellow-bronzed leaves that turn deep reddish brown. This color change starts at the tip of leaves, beginning in older leaves and progressing to younger ones. Leaves eventually die and will often break close to the petiole or remain hanging from the stem. In African oil palms and older coconut palms, small, deformed leaves remain green initially. Similarly new leaves are also dwarfed and the central crown of the tree resembles a funnel. This is a sign of little leaf disease, a chronic disease that can lead to red ring disease. Eventually these little leaves become necrotic and often stop producing fruit. External symptoms take up to 2 months to appear after infection.

Damage Potential: The disease kills palm trees. Losses of 80 and 35 percent in coconut and oil palm production respectively are reported in the tropics. Palms are cultivated mainly for landscape, and date palms in particular are also grown for fruit production in California. Red ring nematode is not present in the USA. Introduction of the red ring nematode would devastate landscape/ornamental, tourism, date fruit palm industries, as well as domestic and international trade.

Transmission: RRN is spread mainly by the Palm Weevil, R. palmarum. Studies on red ring disease conducted in Grenada showed that 22.3 percent of coconut palms were infected with the disease. Of those infected, 92 percent had been invaded by palm weevils – and it was estimated that 72 percent of those weevils had vectored the nematode (Esser & Meredith, 1987). Other vectors reported include ants, spiders, and other potential weevil vectors such as Metamasius hemipterus and Rhynchophorus cruentatus. It can also be spread by tools used to cut down infested trees, and roots.

Survival: The red ring nematodes survive less than a week in soil or on the body of a weevil. They can survive 16 weeks in nut husks and 90 weeks in seedling tissue. They can survive for long periods within an infected weevil.

Location/recovery of the nematode: 1. From the Palm weevil. Male and female Palm Weevils are infested internally and externally with RRN juveniles. Newly emerged weevils from cocoons carry high numbers of RRN. Fewer nematodes have been found on the body of the insect than inside of it. Empty cocoon (after weevil emergence) are rarely infested with the nematode. 2. From Coconut palm. RRN is located in the reddish tissue of the ring and immediately adjacent to it, especially in the inner circle. As many as 50,000 individuals have been found in 10 grams of infected stem tissue. They can also be recovered from the top part of the trunk where the necrotic spots appear, and from petioles and necrotic lesions of older leaves. 3. From Oil palm. RRN is located in the discolored ring and the internal tissue adjacent to the ring. Recovery from other plant parts: necrotic lesion on trunk, petioles, etc, is variable as the nematodes may be absent there. 4. From palm roots and soil. Usually numbers of RRN in palm roots and soil are variable (low to absent). In the soil they have been found as deep as 80 cm, however, most nematodes are found 30-40 cm deep.

Worldwide Distribution: Central America, South America and many Caribbean islands: Belize, Brazil. Colombia, Costa Rica, Ecuador, El Salvador, French Guiana, Grenada, Guatemala, Guyana, Honduras, Mexico, Nicaragua, Panama, Peru, Saint Vincent and the Grenadine Islands, Surinam, Tobago, Trinidad and Venezuela. Reports of the presence of the nematode in Bahamas, Barbados, Dominica, Dominican Republic, Haiti, and Jamaica have not been confirmed. Earlier reports of the nematode in Puerto Rico have been negated following targeted surveys. In certain regions, mainly from Mexico to South America and in the lower Antilles, the red ring nematode is co-distributed with its primary vector the South American Palm Weevil (Brammer & Crow, 2008).

Official Control: The following countries include Bursaphelenchus coccophilus on their ‘Harmful Organism Lists’: Antigua and Barbuda, Chile, China, Dominica, Honduras, Jamaica, Saint Lucia. In the USA, B. coccophilus is a federally regulated pest per Federal Order issued January 25, 2010.

California Distribution: Bursaphelenchus coccophilus has not been detected in California.

California Interceptions: Bursaphelenchus coccophilus has never been detected in host palm trees imported into California.

Consequences of Introduction:

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is High (3) – RRN is able to establish a widespread distribution in California in regions where its palm tree host is able to grow and its insect vector is able to establish.

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Medium (2) – Several species of tropical palms are hosts, most commonly oil and coconut palms, and date palm. Over 17 species belonging to the family Palmae can be infected by the nematode.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (3) – High numbers of RRN is spread mainly by its insect vector. It is also spread through infested trees, tools used to cut down infested trees, roots, and possibly other insects including ants, spiders, and other weevils moving from infested to non-infested plants.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is High (3) – RRN kills palm trees. Introduction of the red ring nematode would devastate landscape/ornamental, tourism, date fruit palm industries, as well as domestic and international trade. As a result quarantines against this nematode pest would be implemented, normal cultural practices would be altered due to the detection and destruction of infested trees, and production costs would be negatively affected. The pest is vectored by the pestiferous South American Palm Weevil.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is High (3) –RRN infestations of palm trees would have significant impact on the environment by disrupting natural communities or changing ecosystem processes, significantly affect ornamental plantings, alter cultural practices, and trigger additional official or private treatment programs.

Consequences of Introduction to California for Bursaphelenchus coccophilus:

Add up the total score and include it here. (Score)

-Low = 5-8 points

-Medium = 9-12 points

–High = 13-15 points

Total points obtained on evaluation of consequences of introduction of Bursaphelenchus coccophilus to California = (14).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

–Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is not established (0). Bursaphelenchus coccophilus has never been detected in California.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score: Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 14

Uncertainty:

As the biology, introduction and distribution of Bursaphelenchus coccophilus is closely associated with that of its palm weevil vector, diligent survey for detection of the vector is critical for detecting the nematode species in palms. The discontinuation or lack of a palm weevil detection survey program will hinder any knowledge gained about the possible introduction of the weevil-associated red ring nematode.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for red ring nematode, Bursaphelenchus coccophilus, is A.

References:

Esser, R.P. and J. A. Meredith. 1987. Red ring nematode. Nematology Circular No. 141, Florida Department of Agriculture and Consumer Services, Division of Plant Industry, Gainesville.

USDA APHIS-PPQ. 2011. Detection of South American Palm Weevil (Rhynchophorus palmarum) in California. Notice to State and Territory Agricultural Regulatory Officials, for Information and Action. DA-2011-45.

Brammer, A. S. and W. T. Crow. 2008. University of Florida IFAS Extension. EENY-236, published September 2001, reviewed March 2008.

Chinchilla, C. M. 1991. http://www.asd-cr.com/ASD-Pub/Bo101/b01c1.htm.

Giblin-Davis, R. M., P. S. Lehman and R. N. Inserra. http://nematode.unl.edu/pest1.htm.

Gerber, K. and Giblin-Davis, R. 1990. Journal of Nematology 22 (2):143-149.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.