It has been reported in almost all countries affected by LY (see Damage and Economic Importance), but its range extends far beyond the current geographical range of this disease. The auchenorrhynchous fauna of palms in the Bahamas is poorly known, but M. crudus may be presumed to be present there. In a survey of planthoppers and their taxonomic relatives on palms in the Dominican Republic (Hispaniola), M. crudus was not found, but a morphologically similar undescribed species was collected from coconut palms (Cocos nucifera L.).
The adult female of M. crudus at rest with posteriorly extended wings is about 5 mm long from the vertex of the head to the tip of the wing. The head and body are straw colored. The frons is bordered on each side by a ridge (carina). The wings are transparent, with brown veins that have numerous pustules bearing setae.
The prominent ovipositor distinguishes the female. The male is slightly smaller and similarly straw-colored, but often paler, and the light green abdomen is more acutely tapered than that of the female. The eyes may have the straw color of the head and body, or a deep maroon color, depending on light conditions (see Biology).
The nymphs are tan to grey colored with a reddish blush on the head. The legs also are reddish, grading to bright red distally. Unlike in the adult, the maroon colored eyes do not change color with changes in light intensity. The nymphs are covered with a thin waxy bloom produced by numerous wax glands in the cuticle. The tibiae of the forelegs are flattened, a possible adaptation for digging beneath the soil surface.
Upon maturing to the adult stage, the insects fly to palm foliage, where they feed and mate. The adults feed on palm foliage, inserting their stylets into leaf tissue and sucking plant juices. As in fulgoroids in general, they tend to feed in the phloem. The females return to grasses to lay eggs.
The adults are active diurnally and nocturnally. In the field, an observer may be puzzled that the eyes of some M. crudus adults are straw-colored, while those of other individuals are maroon-colored. This is because the eyes are light/dark adapted. Movements of pigments within the compound eye in response to changing light conditions are seen by the observer as changes in eye color. They are maroon-colored when adapted to darkness and turn straw-colored in response to increased light. The change from one condition to the other takes place in about 15 to 60 minutes depending on several factors. Thus, at night or in the early morning, the eyes of most individuals are maroon-colored. As light intensity increases during the rest of the day those of most individuals are light-colored. But M. crudus with dark-adapted eyes can sometimes be seen during daylight hours on deeply overcast days, or when an insect has been resting in a darkened site. Following the discovery of this adaptation in the eye of M. crudus, it was described in additional species of Hemiptera.
Myndus crudus is also commonly seen resting and presumably feeding on some arborescent monocotyledonous plants other than palms, e.g., common screw-pine (Pandanus utilis Bory). Interestingly, cases of LY have been diagnosed in P. utilis.
Myndus crudus has been collected from almost all of the species of palms in Florida that are susceptible to LY, the exceptions being mostly palm species that are rare here and thus have not been adequately examined. Many of the species that are attractive to M. crudus are not susceptible to LY. It can be surmised that in these cases either the insect does not feed on the palm, feeds but does not transmit the pathogen, or the pathogen is transmitted but does not induce the disease.
The nymphs have been reared for research studies on the roots of many different species of grasses, including species cultivated as turf or forage. There is great variability in the suitability of different species of grasses as hosts of M. crudus. Some species are highly favorable to the development of the nymphs, while other species are poor developmental hosts of this insect or do not serve as hosts. St. Augustine grass (Stenotaphrum secundatum (Walter) Kuntz) is one of several species that are highly favorable hosts. The popularity of this turf grass in southeastern Florida possibly may have been a factor in promoting dense populations of M. crudus in this region during the epidemic of LY in the 1970s and 1980s. This grass species remains the principal turf grass of this region, but the incidence of both LY and of M. crudus have subsided in recent years for unexplained reasons. Similarly, Guinea grass (Panicum maximum Jacquin), which is a favorable host and was the most widespread grass in coconut plantations in Jamaica, may have contributed to the development of high populations of M. crudus during the LY epidemic there in the 1950s through the 1980s.
Lethal yellowing is a name for a palm disease that was known by different names in different Caribbean countries for more than 100 years. In the 1800s the disease seems to have been most prevalent in Cuba, and repeated epidemics have devastated that island's coconut industry. In Jamaica it was endemic on the west end of that island in the latter 1800s, but spread from there and became epidemic in the 1960s, ultimately spreading throughout the entire island and killing an estimated four million coconut palms by the 1980s. It was reported early in the 20th Century in Hispaniola and some islands of the Bahamas.
Lethal yellowing was diagnosed in coconut palms in Key West, Florida, in the 1950s and in Miami on the Florida mainland in 1971, from where it spread throughout the southeast coast of the peninsula and by 1983 had killed about 300,000 of perhaps 1.0 to 1.5 million coconut palms, as well as many thousands of palms of other species. The epidemic began to subside in most areas of southeastern Florida in the latter years of the 1980s, but cases of LY continue to occur in this region.
In the late 1980s, LY was reported near Fort Myers on the southwest coast of Florida. From there the disease spread north and south on Florida's west coast, but the extent and level of destruction has been somewhat less than on the southeast coast.
initial case of LY, Fort Lauderdale, Florida
Florida was the only locality on the mainland of the Americas affected by LY until the early 1980s, when it was reported in Quintana Roo, Mexico. It has since practically eliminated coconut palms from the Caribbean Coast of most of southern Mexico and much of Central America, causing a serious impact on the agricultural economies of this region.
Although it is sometimes suggested that additional species of insects may transmit LY, researchers have found no evidence that any species other than M. crudus is a vector of this disease. Transmission experiments have successfully shown this insect to be a vector in Florida, where conditions for conducting this type of experiment were especially favorable, but M. crudus is most probably a vector in all countries of Tropical America where LY is present. It is also recognized, however, that insect diversity tends to increase relative to decreasing latitude, and indeed there are more species of auchenorrhynchous insects on palms in the tropics than in Florida. Little is known concerning the biology and vector potential of most of these species.
Lethal yellowing infects and is lethal to at least 36 species of palms. These include the economically important coconut palm and date palm (Phoenix dactylifera L.), as well as many palms that are important as ornamentals or as local sources of food or fiber in tropical countries. In southern Florida, hundreds of thousands of palms were killed by this disease during the epidemic of the 1970s through the 1980s, identifying LY as one of the most destructive diseases affecting the landscape in the history of the US, along with such notorious tree diseases as Dutch elm disease, beech bark disease, and chestnut blight.
Lethal yellowing has been most intensely studied as a disease of coconut palm because of that species economic importance. In fact, the coconut palm is considered one of the 20 most important crop plants in the world, and is a basic element in the agricultural economies of many tropical countries, as well as a source of important products in the world economy. Coconut palm is also one of the most important palms for aesthetic enhancement in southern Florida and in many tropical countries.
There are several other diseases of coconut palm present outside of the Caribbean region that were formerly thought to be identical to LY of the Caribbean, and thus were referred to as LY. But LY is currently recognized as a distinct disease of palms in the Caribbean Region. Similar diseases, most of which attack coconut palms in various parts of Africa, are currently known by other names.
The prospects for controlling LY via biological control of the vector are not promising. The insect is native to Florida and the Caribbean Region, and is already under a degree of natural control. Several natural enemies of M. crudus have been identified, but these do not appear to reduce the populations of this insect sufficiently to significantly reduce the spread of LY.
In an experiment, biweekly applications of an insecticide to foliage of susceptible palms over large areas for 18 months slightly reduced the incidence of LY, but it was concluded from this same experiment that chemical control of M. crudus was not a feasible method of reducing the spread of LY over large areas for long periods. Insecticide treatments of palms and grasses have been used as quarantine treatments to attempt to prevent M. crudus from being transported to new localities.
Based on experiments, populations of M. crudus can be reduced by planting ground covers that do not support development of the immature stages. Various grass species that are suitable as ground-cover in coconut plantations have been shown to be poor hosts or non-hosts of the immature stages of M. crudus. Certain legumes, e.g., tropical-kudzu, Pueraria phaseoloides (Roxburgh) Bentham, and perennial peanut, Arachis pintoi Krapov & W. C. Gregory, have been shown experimentally to not support the development of the immature stages of M. crudus. The latter species are used as ground cover in coconut plantations for soil improvement and erosion control. Their negative impact on the suitability of the environment for M. crudus may be an additional advantage. This would reduce the potential for transmission of LY, and where LY-resistant palms are planted would provide the advantage of reducing the disease pressure on the palms, thus delaying the development of a strain of the pathogen that can overcome the defenses of the resistant palm. This prospective method of managing LY has been investigated in experiments in small research systems, but not on farms or other large areas.
During the 1970s-1980s LY epidemic in Florida, researchers noticed that the disease tended to spread fastest on golf courses and other areas with intense horticultural maintenance. Tentative explanations for this were that the higher levels of irrigation and fertilization may have (1) supported higher insect vector populations, (2) resulted in a physiological condition that increased the palms' susceptibility to the disease, or (3) promoted both vector populations and LY susceptibility of the palms. In contrast, LY spread more slowly through plantings of coconut palms on seaside beaches and on paved automobile parking areas. This observation seemed compatible with any of the tentative explanations above. However, it was additionally considered that the relatively higher rate of survival of coconut palms on beaches and paved areas might be related to the lack of grass, which in turn would reduce the vector populations. Effects of salt spray, wind patterns, and albedo (i.e., reflectivity of solar radiation from sand or pavement) have been suggested as constituting the "beach factor". An experiment to compare M. crudus populations on palms growing in sand and in grassy areas was inconclusive.
In summary, observations suggest that in areas where LY is present, excessive irrigation and application of fertilizer may result in a higher incidence of the disease. The relatively slow spread of LY on sandy beaches and other grassless areas compared to nearby grassy areas may be due to differences in the ability of the habitats to support the development of the disease vector.
Authors: F. W. Howard, University of Florida
Photographs:F. W. Howard and James V. DeFilippis, University of Florida
Map: Jane Medley, University of Florida
Project Coordinator: Thomas R. Fasulo, University of Florida
Publication Number: EENY-389
Publication Date: September 2006
Copyright 2006 University of Florida
Featured Creatures
Department of Entomology and Nematology
Division of Plant Industry
Electronic Data Information Source
adult
antenna
prothorax
hind leg
wing veins
adult female
abdomen of female
male
abdomen of male
nymph
light adapted eyes
dark adapted eye
LY distribution
LY in Hollywood, Florida
early effects of LY
LY aftermath, Florida
LY in Mexico
Coconut palms, Dominica
spraying
perennial peanut
Tropical-kudzu
coconut palms, Florida