Diaprepes abbreviatus Linnaeus Coleoptera Curculionidae

Natural History

Distribution. Diaprepes abbreviatus is found widely in the Caribbean Islands, and was discovered in Florida in 1964. It has since then spread slowly, but occurs throughout southern and central Florida. It is thought to have been introduced with ornamental plants shipped to Florida from Puerto Rico, and there fore has the potential to spread again by this means, particularly to other warm weather regions such as southern Texas and California. In Puerto Rico these pests are known as "vaquitas."

Host Plants. Although first reported to be a pest of sugarcane, this weevil has since been found to attack many other plants. In Florida, it is a serious pest of citrus and woody ornamentals. However, it has been known to cause serious injury to okra in the Virgin Islands, to yam, pepper and lima bean in Puerto Rico, and to potato in Florida. The adults have been found on numerous shrubs and flowers (Griffith, 1975), and sometimes trees are defoliated by adult feeding. However, adult-feeding behavior is not truly indicative of host suitability, because it gives no indication of suitability for larval development. Schroeder et al. (1979) evaluated over 70 plants for larval suitability, and indicated that in addition to citrus and sugarcane, larvae could develop on aloe, coralberry, croton, false aralia, waxplant, shore juniper, red cedar, liriope, and prayerplant. Eggs are deposited on ornamental plants such as ficus and cornplant (Abreu-Rodriguez and Perez-Escolar, 1983).

Natural Enemies. Predation rates of young larvae are quite high as they drop from their point of hatch on foliage and crawl along the surface of the soil seeking a suitable site to enter the soil. Within Florida citrus groves, several species of ants account for nearly 50% destruction of young larvae (Whitcomb et al., 1982). The ants, Pheidole dentata Mayr, P. floridana Emery, and Tetramorium similimum Roger (all Hyme-noptera: Formicidae) are most effective. The ant, Cre-matogaster ashmeadi Mayr (Hymenoptera: Formicidae) also attacks weevil egg masses on foliage. In the absence of ants, the earwig Labidura riparia (Pallas), is an important predator (Tryon, 1986).

Several egg parasitoids of D. abbreviatus are known, but Tetrastichus haitiensis Gahan (Hymenoptera: Eulo-phidae) is the most important parasitoid in the Caribbean areas and it has been introduced into new infestations in the Caribbean areas and Florida (Beavers et al., 1980). In Florida, performance has been erratic.

The larvae are affected by such fungi as Metarhizium anisopliae, Beauveria bassiana, Paecilomyces lilacinus, and Aspergillus ochraceous, and the nematodes Steinernema carpocapsae (Nematoda: Steinernematidae) and Hetero-rhabditis sp. (Nematoda: Heterorhabditidae). The nematodes cause higher levels of mortality than the fungi in Florida, often about 50% (Beavers et al., 1983).

Life Cycle and Description. A life cycle requires about a year for completion, but development time is highly variable and diapause apparently is variable. Adults can be found throughout the year, but there are two periods of peak emergence—June and September. Adult males are active for about two months, whereas females are active for four months.

  1. The eggs are deposited in clusters between leaves. An adhesive secreted by the female causes the leaves to stick together and glues the eggs to the leaves. Old rather than young leaves are selected as oviposition sites, presumably because adults tend to feed on young leaves, which would endanger the eggs. Egg clusters normally contain 30-100 eggs, but up to 300 they have been observed in some clusters. They are deposited in a single layer. Over the course of their life, females produce about 5000-6500 eggs. The eggs are elongate-oval with a length of about 1.2 mm and a width of 0.4 mm. Initially white in color, the eggs turn brownish before hatching. The egg hatching occurs in about 7-8 days. (See color figure 261.)
  2. Young larvae, upon hatching, drop from the foliage to the soil. Larvae are not effective at burrowing, rather entering the soil through cracks. They feed initially on small roots or rootlets, and do not acquire the burrowing habit as suggested by the their common name, until they attain the third or fourth instar. Larvae are whitish to yellowish-brown, with a brown head. At hatching they measure only about 1 mm long, but attain a maximum length of about 20 mm. They normally display eight instars, but individuals have been observed with as few as six instars or as many as 18. The larval growth is rapid for the first 3-4 months, but total larval development usually requires about 370 days (Beavers, 1982). The period of larval development is variable, in part, because it may include a 2- to 13-month period of diapause. The period of diapause is defined by Wolcott (1936) as a period when feeding, growth and molting do not occur; however, the larva continues to move in the soil. Wolcott speculated that this kept the larva from being infested by mites and fungi.

Quintela et al. (1998) studied larval development on artificial diet and citrus roots. This study suggested that larvae can have 10-11 instars, though it is not clear that all larvae display this pattern of growth. Mean head capsule widths were 0.26, 0.35, 0.47, 0.65. 0.99, 1.39, 1.81, 2.22, 2.64, 3.03, and 3.31mm for instars 1-11, respectively. Mean duration of each instar was 7.9, 5.1, 4.0, 9.4, 3.7, 4.8,11.9, 11.1, 37.2, 35.1, and 18.0 days, respectively. Total larval development time, about 148 days, was relatively short in this study, probably because a period of diapause was absent. Larval growth, as reflected by head capsule width and larval weight, was rapid for the first 75 days, but there was little increase thereafter.

West Indian sugarcane rootstalk borer weevil larva.
  1. At larval maturity a pupal cell is formed in the soil. Pupation may occur at any time during the year though spring and autumn are predominant. The pupa is waxy white in appearance and its form resembles the adult except the wings that are twisted ventrally. Duration of the pupal period is about 15 days.
  2. The adults are grayish green to black dor-sally, and usually bear light tan or orangish scales on the elytra. A striped pattern usually occurs on the elytra, where 3-7 black stripes traverse about two-thirds the length of the elytra. The ventral surface and legs are dark gray. This species has distinctly long legs and antennae, and the snout is moderately long. Adults measure 9-15 mm long. Females were reported to commence oviposition 3-7 days after they emerge from the soil by Wolcott (1936), but Beavers (1982) reported a mean pre-oviposition period of 21 days. The difference is attributable to the period of time the adults spend in the soil before emergence. Adults are capable of strong flight, but of short duration. Thus, natural spread is slow. When disturbed, adults tend to drop to the soil (Beavers and Selhime, 1978). Adults often aggregate on certain trees, and though tender young foliage is involved in attraction, there is also evidence of an aggregation pheromone (Beavers et al, 1982). (See color figure 133.)

The West Indian sugarcane rootstalk borer weevil, including its color forms, was described by Pierce (1915). The most complete biology was given by Wolcott (1936). Methods of culture, including an artificial diet, were presented by Beavers (1982). A bibliography was published by Hall (1995).

Damage

Adults injure plants by feeding on foliage. Initially they feed along the edge, creating a notched appearance. Eventually, however, they may consume the entire leaf, even defoliating trees. The larvae feed below-ground on roots. They will consume rootlets and remove the outer layers of larger roots, often girdling them. The larvae also burrow into soft below-ground plant tissue such as the base of sugarcane stalks and the tubers of yam and potato. However, vegetable

Diaprepes Abbreviatus
Adult West Indian sugarcane rootstalk borer weevil.

crops are not normally injured by this weevil. Injury occurs to vegetables mostly when planted in soil previously occupied by sugarcane or ornamental crops.

Management

  1. Because these beetles are not usually vegetable pests, specific monitoring practices have not been developed for use in vegetables. In citrus, adult populations are monitored by visual examination of trees for adults and leaf notching, and with screen traps that capture adults as they emerge from the soil. Visual and odor-based traps are under development (Schroeder and Beavers, 1985), but as yet they are unproven.
  2. Application of insecticide to soil can reduce tunneling in tubers (Oramas et al., 1990). Adult suppression is commonly practiced in citrus and ornamental crops by application of insecticide to foliage (Wong et al., 1975), but oil sprays to foliage can also reduce survival of eggs (Schroeder and Green, 1983).

Biological Control. Larvae of D. abbreviatus are susceptible to infection by Steinernema and Heterorhab-ditis spp. entomopathogenic nematodes (Nematoda: Steinernematidae and Heterorhabditidae) (Figueroa and Roman, 1990a,b, Downing et al., 1991, Shapiro et al., 1999). Under field conditions, Heterorhabditis bacteriophora significantly reduced adult emergence (Downing et al., 1991).

0 0

Post a comment