The coconut mite, Eriophyes guerreronis keifer, belongs to a group of mites that feed exclusively on plants. The mites are important pests since they cause plant abnormalities and transmit virus. The coconut mite is a relatively recent pest in the Caribbean and Latin America, being first reported in Mexico just over 20 years ago.
The coconut mite is microscopic in size (0.2 mm) and can achieve very high population levels on the host. It is creamish-white, with worm-like rings on the back, and has two pairs of legs.
DISTRIBUTION AND DISPERSAL
The drier parts of a country are potentially more susceptible to mite infestation than the wetter more humid areas, therefore closer attention is needed there. In addition, the drier Caribbean countries have to be more closely monitored for mite infestation than the water more humid countries.
Exposed mites on the fruit surface are dispersed by wind during the dry season. Dispersal by wind during the dry season. Dispersal is limited during the rainy season when the mites are washed off the surface. Prevailing winds pattern influence mite distribution. Dry, cool, windy nights present the best conditions for dispersal.
DAMAGE DONE AND ECONOMIC IMPORTANCE
Mites do not kill their host. However, very high population levels on the host, in very severe attacks, cause serious economic loss. Infestation begins on the inflorescences (cluster of flower). In mild cases, initial damage begins on the newly formed nuts and is seen as whitish, triangular blotches on the exocarp (outer surface) of the young fruit, near the calyx (cap over top of fruit). These blotches indicate the position of mite colonies. The mite feeds on the liquid content of the fruit cells, and interaction of mite saliva with plant auxins (chemicals) produces a range of damage in the fruit.
In severe attacks, the fruit’s outer surface becomes brown and corky, often cracking to leave a number of scars. The fruit looks unattractive and hinders the green nut trade. Gum is often exuded. Also, complete fruit malformation and or reduced fruit size occur resulting in up to 60 percent copra losses. There is premature nut fall and as much as a thirty percent reduction in the number of nuts per inflorescence.
Control can be achieved by chemical means. However chemical control is difficult for a number of reasons:
- The mites is a fast reproducer
- It is well protected beneath the floral bracts of the calyx
- The palms are often extremely tall
Control by spraying is ineffective due to the location of the mites under the calyx. Successful chemical control involves injecting 50 to 100 ml Vamidothion (Kilval R) 4 to 6 inches deep into the trunk of infested trees. The distance allows for chemical movement all around the trunk and to all developing inflorescences. To inject the chemical, a 7/8 inch auger is used to make holes in the trunk. The holes are made 4 to 6 inches deep at a 45 degrees angle to the base and at a convenient height for the worker. Measure the chemical volume using a measuring cylinder and pour into the tree trunk via a funnel. Block the hole with a cork to prevent pam weevils and other insects from entering. The injecting is done at the end of the wet season when the mite population is at the lowest. All the mature nuts must be removed and used before injection to eliminate the possibility of pesticide residues in the fruit, and it helps to prevent the development of mite resistance to the chemical.
Highly infested trees are injected to remove pockets of the pest and to control epidemic. In mild attacks the infested nuts are removed and the pests in the nuts soon die off. If several fields in an area are infested, all farmers should treat at the same time to control the pest and prevent further spread. (Injecting is a rather tedious affair. While this is the recommended practice, work is ongoing to determine residual effects, if any of the chemical in the fruit.)
Laboratory experiments on biological control (the use of a live agent that feeds on the pest) have shown the fungus Hirsutella thomsonni to be a potentially good candidate. However, field trials so far have proven inconclusive.
AGRONOMIC CONTROL PRACTICES
Experiments indicate that the application of 2 pounds of high nitrogen and potassium fertilizer per tree twice a year, assist plants in escaping severe damage. The fertilizer application encourages nuts to produce more auxins. As a result, bigger and more nuts are produced per bunch, thereby compensating for any damage done by mites.
Coconut mite attack is increasing in the Caribbean. There is no preventive control of the coconut mite at present, but fertilizer application and injection of heavily infested trees can keep losses to a minimum.