History and Importance of Diaprepes to Agriculture in the Carribean Region
Stephen L. Lapointe
Research Entomologist
USDA-ARS, U.S. Horticultural Research Lab
2001 South Rock Road
Ft. Pierce, FL 34945
The species Diaprepes abbreviatus was described by Carl Linnaeus as Curculio abbreviatus in the tenth edition of his Systema Naturae in 1758 from specimens collected in the West Indies. Today, D. abbreviatus is found on Puerto Rico and Hispaniola and in the Lesser Antilles from Grenada and Barbados in the south to the Virgin Islands in the north. Curiously, the species has not been reported from Trinidad and Tobago nor from Jamaica (related weevils of the genera Exophthalmus and Pachnaeus are serious pests of citrus in Jamaica). Several species of Diaprepes have been described based on coloration that have since been synonymized with D. abbreviatus. A questionable species, D. rohrii is reported only from St. Croix, U.S. Virgin Islands, while D. abbreviatus is apparently absent from that island. D. rohrii may simply be another color morph of D. abbreviatus. By 1933, it was recognized that the various forms of Diaprepes found throughout Hispaniola, Puerto Rico, and the Lesser Antilles were most likely a single species, fundamentally similar both structurally and behaviorally (Wolcott, 1933a). Puerto Rico is clearly the center of diversity of D. abbreviatus, and seems the most likely center of origin for the species because of the high degree of stable phenotypic diversity on the island.
The Reverend N. B. Watson worked out the basic biological cycle of D. abbreviatus in 1899 and 1900 on Barbados (Watson, 1903). He described it as whitish with stripes and recalled playing with it as a youth, thereby placing the weevil on Barbados as a common insect at least as early as the later half of the 19th century. He reported that it was considered a minor pest until recent years but that since 1901 its numbers had increased despite the fact that sugarcane has been cultivated in the West Indies and Puerto Rico for close to 500 yrs. Interestingly, Watson attributed the increase of Diaprepes to the introduction of the mongoose for control of rats. Although the mongoose failed to control its intended victims, apparently it was more effective at destroying species of reptiles and birds that preyed on insects. D. abbreviatus was a common insect on Barbados for many years prior to 1912 but only recorded as a pest of sugarcane in 1912 (Ballou, 1912). By 1921, D. abbreviatus was considered a serious pest of sugarcane on Barbados and massive collection of adults by hand was recommended as a control method (Bourne, 1921).
In 1900, Diaprepes was reported in large numbers in Puerto Rico attacking guava and young coffee plants (Watson, 1903 citing Bulletin No. 30, New Series of the U.S. Department of Agriculture, Division of Entomolgy). In 1915, it was reported to be generally distributed over the island of Puerto Rico (Jones, 1915) but causing particular damage to sugarcane on the south coast. He noted that the jobo plant (Spondias lutea, a species of Mombin in the Cashew Family, Anacardiaceae) was preferred by adults. It was also noted at this time that the weevil was found throughout the island of Puerto Rico, and that distinct phenotypes occurred within defined geographic regions on the island. The populations were marked by varying colors and patterns of stripes on the elytra (wing covers). On Puerto Rico, western lowland populations of D. abbreviatus tend to have whitish elytra. They are brownish in southern and eastern lowlands including Culebra and Vieques. In the western central mountains, there is a larger weevil often with yellow elytra and an additional strip per elytron; in the eastern mountains, a smaller, grayish, sometimes greenish variety prevails (Hantula et al., 1987). On Barbados, Ballou (1912) described the weevil as pale-green with dark, bronze stripes.
The variability of phenotypes was noted early on. Diaprepes adults are largely black but covered with colored scales that range from ashy white to dull orange to bright yellow. On the elytra, the length and number of raised ridges devoid of scales varies between populations. On St. Lucia and Puerto Rico, there is subspecific variation in color and elytral ridges linked by intergrades. The genetic basis for this variation has not been determined but may provide clues to the origin of Florida's infestation(s).
By 1917, Hutson (1917) described the increasing importance of Diaprepes root borer as a pest of sugar-cane, corn, limes, cotton, sweet potatoes, onions, and ground nuts in the Caribbean. Again, he suggested collection of adults and egg-masses as the best control method. On St. Kitts, 40,000 adults were collected in a short time in a cotton field during April 1914. On Antigua, during the early part of 1916 some 70,000 adults attacking limes were caught and destroyed on one estate.
From these reports and others, there is no indication of the possible introduction of Diaprepes nor traces of possible spread from island to island. Rather, the most parsimonious explanation of the origin of Diaprepes is that it evolved in the Caribbean on the islands where it is most numerous today. The greater diversity of color and elytral patterns found on Puerto Rico argue in favor of Puerto Rico as the center of origin although repeated genetic exchange between island populations in recent history cannot be excluded. Any search for agents of classical biological control must, therefore, focus on the Caribbean archipelago.
Damage Caused
Few efforts have been made to quantify the damage caused by Diaprepes. Myers (1931) wrote that D. abbreviatus had increased to the extent that it rivaled Diatraea as the most serious pest of sugar-cane in Barbados. Apparently, the weevil, an indigenous insect, did not infest sugarcane for centuries despite its extensive cultivation on the island. Its attacks on sugarcane and sweet potatoes, according to Watson (1903) were not observed prior to 1901. By 1904 it had become fairly abundant, but not serious until 1909 (Ballou, 1912) and since that date it increased in virulence every year. Myers (1931) cited an estimated loss of 3.5 tons of cane per acre on Barbados in 1922.
Tucker (1929) estimated loss due to larval predation of sugarcane on Barbados was equivalent to 5 to 6 tons of cane/acre. Tucker (1936) reported that no parasites of any stage of D. abbreviatus were present on Barbados prior to 1931. He released 22,000 Tetrastichus haitiensis (an egg parasitoid) imported from Puerto Rico in 1931 and 11,000 in 1932. No parasitoids were recovered from the field on Barbados and Tucker observed that no parasitoids were recovered from cane fields on Puerto Rico. He concluded that T. haitiensis cannot attack Diaprepes eggs when laid between leaves of sugarcane. By 1939, Tucker was advocating a system of cash payments for collection and destruction of adult weevils.
George Wolcott, working at the University of Puerto Rico at Rio Piedras, observed that nurseries and young trees just set out were more damaged that mature trees (Wolcott, 1936). He recorded oviposition, described the life cycle, and noted the high degree of variability in development time. Wolcott suggested that variability in development was a strategy by the weevil to avoid parasitoids that were seasonally abundant on Puerto Rico. He noted that parasitization of eggs was heavy in the spring but absent the rest of the year. Eggs, however, were found throughout the year (Wolcott, 1934). Wolcott (1933b) guessed that larval molts and pupation are timed by sudden contact with liquid water (rains). While this is probably accurate, it has not been sufficiently elucidated to this day. Wolcott also described the intriguing preference of adult females for ovipositing between strips of paper (Wolcott, 1933c).
By 1987, D. abbreviatus was being described as the most serious insect pests of agriculture, horticulture, and silviculture on Puerto Rico (Hantula et al., 1987).
History of Efforts to Control Diaprepes abbreviatus
Ballou (1912) noted that continuous cropping of cane increased damage from Diaprepes. In 1911, school children on Barbados were enlisted to collect and destroy adults - 30,000 were captured and destroyed on one estate over a month. Similar efforts on St. Kitts and Antigua were already mentioned. Adult weevils were reported from pigeon pea, sweet potato, corn, bean, and sweet potato (considered an especially good host for the weevil). Bourne (1921) also describes efforts to collect adults on a massive scale and this appears to have been effective when systematically applied over large regions. Cooperative campaigns over a decade to reduce Diaprepes populations on Barbados were deemed successful due to the fact that the island is small, densely populated, and had a minimal amount of uncultivated land (Tucker, 1953). Manual collection of newly emerged adults, especially from cane fields, was facilitated by planting attractive host plants such as pigeon pea (Cajanus cajan) or other fast-growing shrubs or trees on field borders (Wolcott 1933a, 1933d). The toad, Bufo marinus, was imported to Puerto Rico from Barbados in 1920 and again from Jamaica in 1924 to control white grubs (Phyllophaga spp.) and Diaprepes. It was recommended to plant "gandules" (pigeon pea, Cajanus cajan) or bananas along ditches and banks to attract adult beetles that will then fall prey to the toads (Dexter, 1932).
Nowell (1912) recommended pulling cane stumps after harvest to expose the grubs and suggested "a few head of poultry" be kept on hand during the operation. He observed that fully developed larvae disperse from the cane stools in search of moist soil to pupate, sometimes moving a considerable distance in the soil. Large numbers emerged after the first heavy rains of May/June.
The interaction between larval feeding and root pathogens was noted by Nowell (1913). He observed that rotation of cane with cotton greatly reduced damage even though larvae survived in the soil through the rotation. He suggested that reduction of inoculum of the pathogen Marasmius sacchari reduced damage due to the complex of weevil and pathogen.
R. G. Fennah was hired to investigate the mysterious death of lime trees on Montserrat and of citrus in general on St. Lucia. He described several aspects of Diaprepes biology including the preference of younger leaves for feeding and older leaves for oviposition. He showed that oviposition was deterred when the female's tarsi were covered with various substances that destroyed the suction mechanism. He also suggested that leaf age was detected by means of chemoreceptors on the antennal club. Fennah described three methods of control then considered practical for use in the Lesser Antilles: application of lead arsenate close to the roots, the bare-root method, and growing of a repellent cover crop between the trees. The bare root method consists of removing the soil around the base of the cane stools, thereby exposing the most susceptible part of the plant to the air and avoiding feeding or boring by the grubs on the crown. In this way, damage to the most susceptible part of the tree is avoided. Another approach was cultivation of a repellent cover crop. Apparently, the legume Tephrosia candida repels adult weevils and may be of use in deterring Diaprepes (Fennah, 1940a, 1940b, 1942). However, no reference of subsequent investigation into this possibility could be found in the literature.
Relatively few references to chemical control of Diaprepes are to found during the 1950's and 1960's. Para-dichlorobenzene and chlorinated hydrocarbon insecticides were used in Jamaica as barriers to neonate weevils (not Diaprepes) with some success (Dixon, 1954). DDT, chlordane, barium fluosilicate, lead arsenate, aldrin, and dieldrin, were all proposed as adulticides (Fennah, 1942; Wolcott, 1948; Wolcott, 1933a). I suspect aldrin and dieldrin were widely used for control of both adult Diaprepes by foliar sprays and larvae as soil insecticides during the period when those compounds were marketed (Wolcott, 1954). On Puerto Rico, D. abbreviatus attacking date palm was controlled by foliar sprays of aldrin (Jackson, 1963). The waning of the era of persistent insecticides coincided with the introduction of Diaprepes into the United States. Bullock (1971) tested 24 adulticides and identified 10 as capable of controlling adult Diaprepes. However, because of the short residual effectiveness of foliar sprays and the prolonged period of adult emergence, no evidence is available to indicate the value of adulticides.
Since the introduction of Diaprepes into Florida, an increasing awareness of the severity of the damage caused by Diaprepes and the difficulty of controlling a long-lived subterranean insect on a tree crop such as citrus, has stimulated considerable research into the biology, physiology, host-plant relations, and methods for control. The results of these efforts will be detailed in the sections that follow.
References Cited
1. Ballou, H. A. 1912. Insect pests of the Lesser Antilles. Imperial Dept. Agric., Barbados, West Indies. Pamphlet ser. 71:66-69.
2. Bourne, B. A. 1921. Insect attacks reported or observed. Annu. Rep. Dep. Agric., Barbados 1919-1920, pp. 12-13.
3. Bullock, R. C. 1971. Effectiveness of foliar sprays for control of Diaprepes abbreviatus (L.) on Florida citrus. Trop. Agric. 48:127-131.
4. Dexter, R. R. 1932. The food habits of the imported toad Bufo marinus in the sugarcane sections of Puerto Rico. Proc. Internat. Soc. Sugar Cane Technologists 1935. 4th Entomol. Congress P.R., pp. 1-6
5. Dixon, W. B. 1954. Fiddler Beetles. Natural history notes of the Natural History Society of Jamaica No. 69:166-167.
6. Fennah, R. G. 1940a. Rep. Dept. Agric., St. Lucia 1939, pp. 25-28.
7. Fennah, R. G. 1940b. Observations on behaviour of citrus root-stocks in St. Lucia, Dominica and Montserrat. Trop. Agric. 17:72-76.
8. Fennah, R. G. 1942. The citrus pests investigation in the Windward and Leeward Islands. B.W.I. Imp. Coll. Trop. Agric. Trinidad, 1937-1942.
9. Hantula, J., A. Saura, J. Lokki, and N. Virkki. 1987. Genic and color polyorphism in Puerto Rican phyllobiine weevils Diaprepes abbreviatus (L.) and Compsus maricaco Wolcott. J. Agric., Univ. P. R. 71:391-397.
10. Hutson, J. C. 1917. Insect notes. Some weevils of the genus Diaprepes in the West Indes. The Agricultural News 16:186-187.
11. Jackson, G. C. 1963. Diaprepes abbreviata Linnaeus on Phoenix dactylifera L. J. Agric., Univ. Puerto Rico 47:290.
12. Jones, J. H. 1915. The sugar-cane weevil root borer (Diaprepes spengleri L.). Insular Exp. Sta. (Rio Piédras, Puerto Rico) Bull. 14:1-19.
13. Myers, J. G. 1931. A preliminary report on an investigation in the biological control of West Indian insect pests. Empire Marketing Board 42:1-173.
14. Nowell, W. 1912. Field investigations of beetle grubs attacking roots of sugarcane. Rep. Local Dept. Agric., Barbados 1911-12, pp. 50-51.
15. Nowell, W. 1913. Report of the assistant superintendent of agriculture on the entomological and mycological work carried out during the season under review. Rept. Local Dept. Agric., Barbados 1911-1913, pp. 34-45.
16. Tucker, R. W. E. 1929. Sugar-cane borers. Tropical Agric. 6:224-226.
17. Tucker, R. W. E. 1936. Parasites introduced into Barbados for control of insect pests. Dept. Sci. & Agric., Barbados Agric. J. 5:1-22.
18. Tucker, R. W. E. 1953. Biological control of insect pests in Barbados. Proc. Int. Soc. Sugarcane Tech. 8:573-581.
19. Watson, N.B. 1903. The root-borer of sugar-cane. West Indian Bull. 4:37-47.
20. Wolcott, G. N. 1933a. An economic entomology of the West Indes. Entomol. Soc. P. R., San Juan. 1-688.
21. Wolcott, G. N. 1933b. The larval period of Diaprepes abbreviatus L. J. Agric., Univ. Puerto Rico 17:257-264.
22. Wolcott, G. N. 1933c. Otiorhynchids oviposit between paper. J. Econ. Entomol. 26:1172.
23. Wolcott, G. N. 1933d. The changed status of some insect pests in Puerto Rico. J. Dept. Agric. Puerto Rico 17:265-270.
24. Wolcott, G. N. 1934. The diapause portion of the larval period of Diaprepes abbreviatus L. J. Agric., Univ. Puerto Rico 18:417-428.
25. Wolcott, G. N. 1936. The life history of Diaprepes abbreviatus L., at Rio Piedras, Puerto Rico. J. Agric., Univ. Puerto Rico 20:883-914.
26. Wolcott, G. N. 1948. The insects of Puerto Rico: Coleoptera. J. Agric., Univ. P.R. 32:225-416.
27. Wolcott, G. N. 1954. Residual effectiveness of insecticides against soil-inhabiting insects. J. Agric., Univ. P. R. 38:108-114.
