Urbanus proteus Linnaeus Lepidoptera Hesperiidae

Natural History

Distribution. Bean leafroller is a tropical species, but apparently is a native to the southeastern United States. It is found throughout Florida and in coastal areas from South Carolina west to eastern Texas. It also invades most of the southeastern states, even attaining New England during warm years, and regu larly invades the southernmost areas of the Southwest. It cannot tolerate prolonged freezing temperatures, however, and in the United States it persists only in the southern coastal plain, perhaps only southern Florida. The range of bean leafroller also includes Mexico, Central America and the Caribbean, and south to Argentina.

A closely related species, Urbanus dorantes Stoll, has expanded its range from the tropical Americas to include the permanent range of U. proteus in the United States. Found throughout Florida, and southern Texas and Arizona, it is readily confused with bean leafroller, particularly because it also feeds on legumes, including bean (Heppner, 1975). Thus far, however, it is not particularly abundant. (See color figure 21.)

Host Plants. Bean leafroller feeds exclusively on legumes, and normally is found inhabiting open, disturbed habitats. Vegetable hosts include cowpea, lima bean, pea, and snap bean. Other hosts include soybean; wisteria, Wisteria sp.; trefoil, Desmodium spp.; butterfly pea, Clitoria spp.; and hog peanut, Amphi-carpa bracteata.

Natural Enemies. Natural enemies are poorly documented. Wasp and fly parasitoids were observed in Colombia (van Dam and Wilde, 1977). Two tachi-nids with a very wide-host range, Lespesia aletiae (Riley) and Nemorilla pyste (Walker), have been reported from bean leafroller (Arnaud, 1978). In Florida, Chrysotachina alcedo (Loew) (Diptera: Tachinidae) was reared from larvae, and predation was observed by a Polistes sp. wasp (Hymenoptera: Vespidae) and Euthyrhynchus floridanus (Linnaeus) stink bugs (Hemi-ptera: Pentatomidae). Also, a nuclear polyhedrosis virus was found to infect and to kill up to 40-50% of larvae late in the season when larvae were numerous (Temerak et al, 1984).

Life Cycle and Description. The bean leafroller can complete its life cycle in about 30 days during warm weather. They breed in southern Florida throughout the year, but are relatively infrequent in northern Florida until June, and only become abundant late in the season, usually September-October. The number of generations is not known, but has been estimated at 3-4 in Florida. In the northern areas invaded during the summer months there usually is only a single generation. In Florida, large numbers of adults are frequently observed migrating southward in the autumn (Balciunas and Knopf, 1977); they make a similar northward migration in the spring and summer, but it is less apparent.

  1. The eggs of bean leafroller may be deposited singly on the lower epidermis of foliage, but often are found in small clusters of 2-6 eggs. Also, clusters of up to 20 eggs have been observed, and on occasion they may be stacked upon one another to form a column. Initially the eggs are white, but soon turn yellow. The egg is a slightly flattened sphere, and marked with about 12 vertical ridges. It measures about 1 mm in diameter and about 0.8 mm long. Eggs hatch in about 4.5 days when held at 24°C and 2.8 days at 29°C.
  2. The larva of bean leafroller increases in size from about 2 mm at hatching to 30 mm at maturity. Initially the larva cuts a small triangular patch at the edge of the leaf, folds over the flap, and takes up residence within this shelter. The larva leaves the shelter to feed, and lines the shelter with silk. These flaps are used until the third or fourth instar, when the larva constructs a larger shelter formed by folding over a large section of the leaf or webbing together two separate leaves. Larvae feed nocturnally. Eventually, the larva pupates within the leafy shelter. There are five instars. Mean head capsule widths (range) for the five instars are 0.6 (0.5-0.7), 1.1 (1.0-1.2), 1.8 (1.5-2.1), 3.2 (2.9-3.5), and 4.7 (4.2-5.2) mm, respectively. When maintained at 24°C the mean duration is about 2.8, 3.1, 3.5, 5.6, and 15 days, respectively, for instars 1-5, whereas instar duration at 29°C is about 2.0, 1.7, 2.2, 2.8, and 5.9 days.

Initially the larva is yellowish with a brownish-black head and prothoracic shield, and this general color pattern is maintained though the markings become more distinct as the larva matures, and the larva may also acquire considerable green color. With the molt to the second instar the dorsal surface of the insect is marked with numerous small black spots. Beginning with the third instar, lateral yellow lines become quite distinct. The last two instars are similar to the preceding: brownish-black head, black prothor-acic shield, yellowish body sprinkled with black spots but lighter below, and yellow lateral lines. Also evident are orange spots on the head near the base of the mandibles, and red on the ventral portion of the thoracic segment. The body tapers sharply toward both the anterior and posterior ends. Perhaps the most striking attribute of this insect, but a character shared with other members of the family Hesperiidae, is the greatly enlarged head, which is connected to the body by a narrow "neck." (See color figure 96.)

Urbanus Proteus Larva
Bean leafroller larvae.
Bean leafroller pupa, partially encased in leaf.
  1. The larva pupates on the plant within the shelter formed by the larva from leaf material. The pupa measures about 20 mm long and about 6 mm wide. The pupa is yellow to brown, and is covered by a bluish-white pubescence. Duration of the pupal stage is about 17.1 day at 24°C and only 8.7 days at 29°C.
  2. The bean leafroller moth is fairly large for a hesperiid, measuring about 50 mm in wingspan. The most pronounced feature is the prolonged extensions or "tails" of the hind wings. Not surprisingly, the butterfly is commonly known as "long-tailed skipper." The front and hind wings are chocolate brown dorsally and pale brown ventrally. The front wings also are marked with 5-7 squares or rectangular white spots. Green iridescent scales are found dorsally on the wings and body. The presence of green scales serves to differentiate bean leafroller from the other bean-feeding skipper, Urbanus dorantes. Skippers are active principally at dawn and dusk, often seen darting from flower to flower seeking nectar. (See color figure 202.)

This insect has not been well studied. The most complete description was provided by Quaintance (1898a), but Young (1985) provided valuable observations. Phenology and developmental biology were given byGreene (1970a, 1971a). Greene (1970b) made reference to culture on standard bean-based artificial diet, but the relative success of this approach is not clear.

Damage

Larvae are defoliators, feeding only on leaf tissue of legumes. Greene (1971b) determined that larvae consumed about 0.5, 1.3, 5.1, 26.1, and 162.4 sq cm of foliage during instars 1-5, respectively. Beans can tolerate up to about 30% leaf loss without reduction in yield, so Greene estimated that about 4.4 larvae must complete their development on a "typical" bean plant with 2175 sq cm of foliage to inflict a damaging level of defoliation. As about one-half of the individuals perish in each life stage, Greene estimated that densities of

Lepidoptera Proteus
Adult bean leafroller.

140 eggs or 70 first instar larvae per plant must occur to cause damage.

Management

  1. The distribution of eggs and larvae is clumped (Shepard, 1972). Populations are normally sampled by visual observation because the larvae are sheltered within leaf folds and are difficult to dislodge by sweeping, and as the leaf damage caused by shelter-building activity is readily apparent.
  2. Insecticides applied to the foliage at the first sign of damage are very effective for leafroller suppression. This should only be necessary for late-season bean crops. The microbial insecticide Bacillus thuringiensis currently is not recommended.
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