History and Importance of Diaprepes to Florida
David G. Hall, Ph.D.
Research Department, United States Sugar Corporation
P.O. Drawer 1207, Clewiston, FL 33440
dghall@ussugar.com
863-983-8121
The History of Diaprepes in Florida
Much of the information presented on the early history of Diaprepes in Florida was taken from Beavers (1981) and Woodruff (1968).
Diaprepes abbreviatus (L.) was first reported in Florida during 1964, when a single adult male specimen was found in a citrus nursery at Apopka in Orange County during September. No additional specimens were found, but entomologists kept the nursery under surveillance. In 1968, several larvae were found at the nursery. Additional surveys were initiated immediately, and several hundred adults were found in citrus within the vicinity of Apopka. Recognized as a potential threat not only to citrus but also to other crops of economic importance in Florida, federal and state regulatory agencies established a quarantine area of approximately 2,500 acres around the infestation to prevent spread. The agencies attempted to eradicate the pest during 1969 using aerial applications of heptachlor (3 lb a.i. per acre). Adult weevils were observed again during 1970 and 1971, and during each of these years the agencies applied carbaryl (2.5 lb a.i. per acre) at 10-day intervals during the adult weevil emergence season. These applications suppressed population levels of adult weevils, but the regulatory agencies suspended the applications because carbaryl killed honeybees and was stimulating resurgence of purple scale problems. The agencies applied granular dieldrin to infested trees during 1973-74 at a rate of 10 lbs a.i. per acre (split application). Citrus growers simultaneously tried to control adult weevils using various registered insecticide applications. Eradication efforts were dropped by the regulatory agencies thereafter due to the loss of effective registered insecticides, but the quarantine was maintained. The weevil spread. By 1981, the quarantine area had been increased to the point that it encompassed 61,700 acres across 3 counties in central Florida (Orange, Seminole and Lake), with a total of 4,950 acres of citrus groves reported to be actually infested.
Diaprepes was discovered in Broward County near Davey Palms (southeast Florida) during the late 1970s. No commercial citrus was found to be infested in the county, but 6,000 acres were placed under quarantine and 17 acres of ornamental nurseries were identified as being actually infested. Due to the likely spread of Diaprepes in plant material from ornamental nurseries to other areas in the state, ornamental nurseries within the quarantine area were required to treat potting soil with heptachlor or dip potted plants in chlorpyrifos. Foliage sprays of carbaryl were required 2 weeks prior to shipping plants, and the nurseries had to hold the plants for at least 7 days after spraying. Citrus nurseries with infestations of Diaprepes were required to treat foliage with carbaryl 14 days prior to shipment and to spray every 2 weeks during the adult emergence season.
By 1975, more than 3,000 acres of citrus were known to be infested in the Apopka-Plymouth area; approximately 26,240 acres were under State quarantine (USDA, 1975). By 1978 or 1979 (year not clear), Diaprepes infested around 5,000 acres of commercial citrus in Florida (Schroeder et al., 1979). During 1982, the weevil was discovered in Palm Beach County in an ornamental nursery near Boca Raton. Two years later, adult Diaprepes were discovered in several citrus groves near Ft. Pierce in St. Lucie County during June 1984. (The Palm Beach Post, June 29, 1984). By the early 1990s, infestations of Diaprepes were known to be present in Lake, Orange, Polk, St. Lucie, Palm Beach, Broward and Indian River counties (Futch and McCoy, 1994; Beavers, 1981). By the mid 1990s, Diaprepes had spread to all major citrus growing areas of Florida (Hall, 1995).
Infested nurseries continued to have strict quarantine regulations placed upon them during the 1980s and 1990s. A total of 94 commercial plant nurseries were known to be infested in Florida during 1995 (Hall, 1995). An estimated 23,000 acres of commercial citrus were thought to be infested by the weevil by 1995 (Romander, 1995). An infestation of the weevil was found on citrus in eastern Palm Beach County in the vicinity of sugarcane during 1996. The Florida Department of Agriculture & Consumer Services, Division of Plant Industry, reported that by 3/18/97 a total of 161,280 acres across 252 sections of land were known to be infested in Florida; included among these infested acres were 28,532 acres of commercial citrus and 1,047 acres of ornamental sites. A 1997 map of sections of land known to contain infestations of the weevil is presented in Figure 1. Lapointe et al. (1999) reported that, by 1997, around 163,000 acres in Florida were considered to be infested by Diaprepes, of which about 20% (32,600 acres) were commercial citrus plantings.
A report during June 1999 indicated that Diaprepes had spread to 20 counties in Florida, infesting approximately 164,000 total acres and around 30,000 acres of commercial citrus (Adair et al., 1999). According to records maintained by the Florida Department of Agriculture & Consumer Services, Division of Plant Industry, a total of 21 counties in Florida were known to contain infestations of Diaprepes by November, 1999. These counties were Broward, Collier, Dade, DeSoto, Glades, Hendry, Hillsborough, Indian River, Lake, Lee, Marion, Martin, Orange, Osceola, Palm Beach, Pasco, Polk, Seminole, St. Lucie, Sumter and Volusia.
The original introduction of Diaprepes into the State of Florida may have been associated with the introduction of ornamental plants into Florida from the Caribbean. Scientists and regulatory personnel agree that Diaprepes is more likely spread by man moving infested plants than by the insect moving by itself. It has been for this reason the regulatory agencies (primarily the Division of Plant Industry) have established quarantine areas and required that infested citrus and ornamental nurseries to adhere to compliance agreements with respect to shipping plants.
The Importance of Diaprepes as a Pest in Florida
The weevil's impact on citrus is primarily discussed here, but Diaprepes can have a serious, similar direct impact on other crops grown in Florida as well as an indirect impact on nurseries marketing citrus or ornamental plants.
Diaprepes is an important pest of citrus primarily because feeding damage by larvae to the roots of trees kills young trees, reduces the vitality and productivity of bearing trees, and in some cases causes death of older trees (perhaps more so if the foot/root rot fungus Phytophthora is present).
Adult D. abbreviatus feed on leaves, usually along the edges of new tender leaves resulting in a characteristic notching. Unless extensive, feeding by adults is generally considered to have an insignificant effect on citrus. Adult females glue their eggs between leaves, and neonate larvae emerge from the eggs and drop to the soil. The neonates dig their way into the soil to feed on roots. The entire larval cycle may last from 6 to 24 months. Feeding by larvae on roots can result in significant damage to citrus and sugarcane. An infestation of larvae can rapidly kill a young citrus tree. As few as 2 or 3 weevil larvae can remove the entire bark from the root system of a containerized citrus seedling within 4-5 weeks. Older trees may also be killed if enough larvae are present. Little is known regarding economic injury levels of larvae in citrus, but there is some evidence that relatively few larvae may sometimes cause substantial yield reductions and death of mature trees. Older citrus trees infested by larvae sometimes do not die but simply become unthrifty. Old signs of adult feeding on older leaves coupled with a thinning appearance of a tree canopy are good indications D. abbreviatus has attacked a citrus tree. The weevil is thought to greatly enhance infections of Phytophthora in citrus if this fungus is present in the soil. When large citrus trees in Florida with symptoms of damage by D. abbreviatus have been excavated, large feeding channels along the bark and into the cambium layer and woody portion of major lateral roots have been observed. No citrus rootstock appears to be resistant to larval feeding, although 'Swingle' sometimes tends to standup better against larval infestations than other rootstocks. There appears to be no larval feeding preference among rough lemon, sour orange, 'Carrizo', 'Milam' or 'Cleopatra' (Futch and McCoy, 1994). The annual impact of D. abbreviatus in Florida citrus was estimated at more than $75 million (USA) in 1997 (Diaprepes Task Force, 1997).
Yield projections for citrus groves infested versus non-infested by Diaprepes suggested that, if there is no effective control tactic available to fight the weevil, significant yield reductions would occur within 3 to 5 years after a 3-year-old grove becomes infested by the weevil (Figure 2) (Hall, unpublished data). These projections (which are based on the assumptions that a 10% annual increase occurs in infested trees, that 5% infested trees die annually, and that a 40% production loss occurs in infested trees not killed) have not been substantiated, but empirical observations indicated the estimates may not be unrealistic, at least in some situations. A citrus grower confronted with a Diaprepes infestation will be inclined to try to control the weevil. Unfortunately, a definitive control program for the weevil has yet to be developed. A combination of the following management tactics together in an IPM program has potential for reducing economic losses to the weevil: foliage treatments to control adults; foliage treatments to control eggs; soil surface treatments to control neonate larvae; nematode treatments to control larvae; and fungicidal treatments to control Phytophthora. Cost estimates for an IPM program utilizing all of these components have run as high $250 to $300 or more per acre. Unfortunately, even under a complete program employing these tactics, researchers expect the weevil will still cause losses. One estimate of the total per-acre economic loss to an infestation of Diaprepes in a citrus grove (including the cost of a full IPM program, replants, and expected reductions in tree productivity) was $1,250 per acre. Here within lies the present importance of Diaprepes to a citrus grower.
Citrus and ornamental nurseries in Florida have suffered economic losses to Diaprepes. The weevil has a very wide range of plant hosts and may cause significant damage to some. Although nurseries infested by Diaprepes undoubtedly suffer some direct losses to Diaprepes, more important are the economic losses associated with compliance agreements.
Plants most likely to be infested and damaged by Diaprepes larvae in Florida may include: aloe, coralberry, citrus, croton, false-aralia, waxplant, shore juniper, red cedar, lilyturf, prayerplant, and sugarcane (Schroeder et al., 1979).
References
1. Adair, R. C., H. N. Nigg, S. E. Simms, and L. Le Fevre. 1999. Observations on the oviposition process of Diaprepes abbreviatus (Coleoptera: Curculionidae). Florida Entomologist. 82 (2):362-365.
2. Beavers, J. B. 1981. Diaprepes abbreviatus: a sugarcane root weevil infesting citrus and other hosts in Florida. Proceedings Second Inter-American Sugar Cane Seminar, Insect and Rodent Pests. 2:67-69.
3. Diaprepes Task Force. 1997. Diaprepes Root Weevil Workshop Report and Strategic and Operational Plan. October 15, 1997. Winter Haven, FL.
4. Futch, S. and C. W. McCoy. 1994. Citrus Root Weevils. University of Florida, IFAS, SP 157. 8 pp.
5. Hall, D. G. 1995. A revision to the bibliography of the sugarcane rootstalk borer weevil, Diaprepes abbreviatus (Coleoptera: Curculionidae). Florida Entomol. 78(2):364-377.
6. Lapointe, S. L., J. P. Shapiro and K. D. Bowman. 1999. Identification of sources of plant resistance to Diaprepes abbreviatus (Coleoptera: Curculionidae) by three bioassays. J. Econ. Entomol. 92(1):999-1004.
7. Romander, L. 1995. Diaprepes: more effective control tools now available. Citrus Industry. October. 30-31.
8. Schroeder, W. J., R. A. Hamlen and J. B. Beavers. 1979. Survival of Diaprepes abbreviatus larvae on selected native and ornamental Florida plants. Florida Entomologist. 62(4):309-312.
9. Selhime, A. G., and J. B. Beavers. 1972. A new weevil pest of citrus in Florida. Citrus Industry. 53(1):4-5.
10. U.S.D.A. 1975. West Indian Sugarcane Root Borer. Plant Protection and Quarantine Programs, Animal and Plant Health Inspection Service, U. S. Department of Agriculture Program Aid No. 1120. 4 pp.
11. Woodruff, R. E. 1968. The present status of a West Indian weevil (Diaprepes abbreviata (L.)) in Florida (Coleoptera: Curculionidae). Florida Dept. Agriculture, Division of Plant Industry. Entomol. Circ. No. 77. 4 pp.
