Prospects for Control of the Vector of Lethal Yellowing on Small Coconut Farms F. W. Howard University of Florida Institute of Food & Agricultural Sciences Fort Lauderdale Research and Education Center 3205 College Avenue Fort Lauderdale, Florida 33314 Recent experimental evidence has implicated a planthop- per, Myndus crudus Van Duzee, as the vector of lethal yellow- ing (LY). It may be inferred from experimental results that chemical control of LY would not be practical on small coconut farms. The fact that the immature forms ofM. crudus utilize grasses as hosts may be a key to controlling this insect. The potential use of ground covers that are unattractive to M. crudus is discussed. Keywords: Myndus crudus, palms, mycoplasma, Cocus, grasses. Suggested running head: Lethal yellowing vector con- trol: Howard. Lethal yellowing (LY) of palms is one of the most destructive diseases faced by tropical agriculturists. It is present in seven countries of the Caribbean and in parts of Africa. The impact of the disease was particularly severe in Jamaica during the 1960's and 1970's, during which period an estimated four million coconut palms were destroyed by the disease (Eden-Green, 1978), and devastating epidemics have occurred in Cuba, Florida, and most recently in Quintana Roo, Mexico. Most of the world's coconuts are produced on small farms. Coconuts were listed among 20 major crops upon which a large portion of the human population depends (Mangelsdorf, 1966). The disease is believed to be caused by mycoplasma-like organisms (MLO) since these are consistently found in phloem sieve tubes in diseased palms, but not in healthy palms (Beakbane, et al., 1972; Heinze et al., 1972; Parthasarthy, 1974; Plavsic-Banjac et al., 1972; Thomas, 1979; Thomas and Norris, 1980), and oxytetracycline treatments cause a remission of symp- toms (Hunt et al., 1974; McCoy, 1972; McCoy and Gwin, 1977; Steiner, 1976). Myndus crudus Van Duzee (Homoptera: Cixiidae) became suspect as a vector of LY when it was found to be the most abun- dant auchenorrhynchous insect on coconut palms in two LY- affected areas, viz. Jamaica (Schuiling, 1976) and Florida (Woodiel, 1976). In Florida, M. crudus was collected on all but the rarest LY-susceptible palm species (Howard and Mead, 1980) and was found to occur in higher numbers in the LY-affected areas than in LY-free areas (Howard, 1980). Insecticidal control of M. crudus reduced the apparent rate of spread of LY (Howard and McCoy, 1980). Replicated transmission experiments were conducted in which MLO were transmitted inside cages, ap- parently by M. crudus, to Veitchia merrllii (Becc.) H.E. Moore (Howard and Thomas, 1980), Pritchardia thurstonii F. Muell. & Drude and coconut palms (Howard, Norris and Thomas, 1983). Two means of combating LY are the use of resistant palms (Harries, 1970; Harries and Romney, 1974; Shaw, 1971; Smith, 1970) and antibiotic treatments (McCoy and Gwin, 1977). This paper discusses the prospects for developing methods of control- ling LY by controlling the insect vectors of the disease. 144 Chemical Control In view of the evidence that M. crudus transmits LY, can insec- ticides applied to palms protect them from LY? There is little possibility that insecticidal control on small coconut farms would be practical and effective. In one experiment we sprayed foliage of Manila palms, Veitchia mer/ilii, with insecticides biweekly for 15 months and carried out observations for 18 months (Howard and McCoy, 1980). The experiment compared treatments of dimethoate 400 at 2.6 ml/1, diazinon Ag 500 at 1.3 ml/1, and an untreated check. About 500 palms were in each treatment at the beginning of the experiment. Each treatment was divided into six replicates. Each replicate consisted of a 1.5 ha plot with 80-90 palms. The incidence of LY was not significantly different in the three treatment areas during the first 12 months of spraying. We had anticipated this, because the incubation period (the time period between inoculation of the pathogen and expression of symp- toms) of LY has been determined to be as long as 360 days (Dabek, 1975). Thus, in an area where LY is active it must be assumed that an unknown portion of the symptomless palms are actually infected. Spraying these palms cannot save them, but may help to protect uninfected palms by interrupting disease transmission. At the beginning of the experiment 12.9% of the Manila palms had LY symptoms. At the end of the first 12 months of spraying, losses of palms due to LY in the three treat- ment areas were as follows: dimethoate 64.2%, diazinon 49.1%, and untreated check 37.7%. There was no significant difference in disease incidence in the three treatments. It can thus be in- ferred that if a coconut farm manager were to discover that about 10% of his palms had LY symptoms, an intensive insecticide spray program might make no impact during the first year. We compared the apparent rate of spread in different treatments during the 12th to the 18th month of the experiment. Any differences in the rates of disease spread in the different treatments would probably be related for the most part to treatments applied during the first 12 months of the experiment. We found that the rate of spread (based on symptoms) rose in the untreated check and declined in the two insecticide treatments (P <0.05). Losses of palms in the different treatments during the latter 6-month period were as follows: dimethoate 23.4%, PROCEEDINGS of the CARIBBEAN FOOD CROPS SOCIETY-VOL. XX