New World palm/Palmetto; Palm (coconut palm, oil palm, etc.)

Bursaphelenchus cocophilus parasitizes the South American palm weevil Rhynchophorus palmarum, which serves as a vector. This weevil was found in the area of San Diego, California in May of 2011 and Alamo, Texas in May 2012. Delimitation surveys were initiated and other finds have been made in the same general geographic areas within 2.5 miles and 5 miles of the United States/Mexico Border.

Other Rhynchoprinae beetles, including Dynamis borassi and Metamasius hemipterus, are also reported to vector the red ring nematode.

To date the geographic areas of the nematode-carrying weevils have not overlapped with the U.S. native palmetto weevil, R. cruentatus, or with the invasive red palm weevil, R. ferrugineus. These beetles are not known to vector the nematode but the possibility exists as other species of Rhynchorpinae serve as hosts.

Host samples or extracted nematodes should be sent to Dr. Lynn Carta:

No specific signs are present.

Two distinct types of symptoms are caused by B. cocophilus : "red ring" and "little leaf disease".

Red ring:
The nematode causes reddish lesions to form in the stem. These lesions gradually enlarge and often form the primary and most characteristic internal symptom of the disease for which the disease was named, a "red ring" when the cut stem is viewed in cross section. The ring may vary in color from bright red to light pink, or cream to dark brown in Elaeis guineensis (African oil palm). The ring can be 3 to 5 cm wide (1.18 to 1.97 in) from the periphery, but the width may vary depending on tree size. The red ring can usually be seen when the infected palm is cut crosswise from 0.3 to 2.1 meters (1 to 7 ft.) above the soil line. The ring may not be continuous throughout the trunk length. The ring may also be found in the cortex of the host roots and in the petioles. When diseased, the soft, white cortex of the roots becomes orange to faint red in color and dry and flaky in texture.

With red ring disease, established leaves become short, deformed, and turn yellowish-bronze before turning deep reddish-brown in color. The change in color typically starts at the leaf tip spreading towards the base. Older leaves will show symptoms before younger leaves. Leaves will eventually wilt and die. The oldest leaves usually break at the petiole, close to the trunk and can remain hanging down for a long period of time. In coconut palm (Cocos nucifera), fruit typically drop prematurely (before mature). This usually happens around the same time that leaf symptoms develop or slightly before. Four to six weeks after symptom development, the palm crown will often topple over; this is associated with severe internal damage caused by the larvae of the weevil vector.

Little leaf:
Some African oil palms and older coconut palms will produce small, deformed leaves, which remain green with no initial necrosis. "Little leaf disease" is a chronic condition that can lead to red ring disease development. These trees usually stop producing fruit. Nematodes can be found in high numbers in young leaves, when the leaves are elongating. These leaflets eventually become partially necrosed and remain partially folded along the rachis.

The approved identification method is morphological. B. cocophilus is a relatively long, vermiform nematode with long tapering tails, about 1 mm for both females and males, but are also very thick. The vulva is positioned one-third of a body length from the tail tip. Stylets are small, 11 to 13.5m long and are often obscure.

Detailed descriptions of the adult male and female as well as larva can be found in Dean (1979). Giblin-Davis et al (1989b) also provides information on the morphological features of B. cocophilus.

The only other known nematode known to cause severe damage in Cocos nucifera (coconut) is Radopholus similis (burrowing nematode). In coconut palms, R. similis causes non-specific general decline symptoms including: stunting, yellowing, reduction in number and size of leaves and leaflets, delay in flowering, button shedding, and reduced yield. Infestation by R. similis produces small, elongate, orange-colored lesions on tender creamy-white roots.

Bursaphelenchus gerberae was also found recently to be in association with the vector of red ring nematode Rhynchophorus palmarum in Trinidad and could potentially be confused with B. cocophilus (Giblin-Davis et al., 2006).

Culture: Giblin-Davis et al. (1989a) showed that B. cocophilus can survive longer than 70 days in autoclaved red ring stem tissue infusion water that was unsupplemented or supplemented with D-glucose, lactose, or Bacto-lactose broth and D-glucose.