Agroiconota bivittata Say Coleoptera Chrysomelidae

Natural History

  1. These native species are distributed widely in eastern North America, west to Iowa and
  2. Most also have a broader range, with D. guttata found in Mexico and South America, A. bivittata in Arizona and Mexico, and C. cassidea and J. nigripes in western states and Mexico.

Host Plants. The aforementioned species of tortoise beetles are associated with sweet potato and related species such as morningglory, Ipomoea spp., and bindweed, Convolvulus spp. Argus tortoise beetle is reported from other plants such as cabbage; corn; milkweed, Asclepias sp.; sunflower, Helianthus sp.; and dodder, Cuscuta. However, most records indicate Convolvulaceae as the host, and other records are suspect.

Natural Enemies. Several wasp parasitoids are known, including Emersonella niveipes Girault (Hyme-noptera: Eulophidae) and Brachymeria russelli Burks (Hymenoptera: Chalcididae) from argus tortoise beetle, and Tetrastichus cassidus Burks (Hymenoptera: Eulophidae) from golden tortoise beetle and mottled tortoise beetle. Fly parasitoids include Eucelatoriopsis dimmocki (Aldrich) from striped tortoise beetle and golden tortoise beetle, and Eribella exilis (Coquillett) and Eucelatoriopsis dimmocki from argus tortoise beetle (all Diptera: Tachinidae).

Numerous predators are reported to feed on tortoise beetle larvae, including lady beetles such as Coccinella spp. and Coleomegilla spp. (Coleoptera: Coccinellidae) but especially insects with piercing-sucking mouth-parts, such as damsel bugs (Hemiptera: Nabidae), shield bugs (Hemiptera: Pentatomidae), and assassin bugs (Hemiptera: Reduviidae). The "shield" carried by larvae (see description of larvae below) is somewhat effective against small predators, but large predators, especially those with long piercing-sucking mouth-parts, are not deterred (Olmstead and Denno, 1992, 1993).

Life Cycle and Description. Very little biological information is available on these species, probably reflecting their slight economic importance. In the northern states, there usually is only one generation annually. In New Jersey, the beetles first appear in May or June, commence feeding on weeds, and deposit eggs soon thereafter. A new population of adults is evident in July. New adults feed briefly before entering diapause until the following spring. In argus tortoise beetle a few beetles deposit eggs in August, which successfully develop into a second generation. Development time from egg to adult requires about 40 days.

Egg. The eggs of most species are attached singly to the underside of leaves or on stems, and usually are white. Eggs are oval and flattened, but sometimes decorated with sharp angles or spines. They measure

Argus tortoise beetle eggs.

only about 1 mm in length and hatch in 5-10 days. In argus tortoise beetle, the eggs are elongate-spherical and attached to the leaf by a stalk or pedicel. Each egg of argus tortoise beetle bears a small pointed cap. Eggs are deposited in clusters of about 20 eggs. The eggs of this species are slightly larger than the others, measuring about 1.6 mm long. Fecundity is not well documented, but Rausher (1984) reported ovi-position of 50-90 eggs by argus tortoise beetle in a two-week period.

  1. The larvae are broad and flattened and adorned with branched spines. Their thoracic legs are short and thick, and unlike many chrysomelids they lack an anal proleg. The color of the larva varies among and within species. Most are yellowish, but larval color may be reddish brown in golden tortoise beetle (see color figure 114), and greenish in mottled tortoise beetle. There are three instars. Larvae display the habit of carrying their cast skins and fecal material attached to spines arising from the posterior end of their body, a structure called an "anal fork." The anal fork is movable, and is usually used to hold the debris over the back of the body, forming a "shield" which deters predation. Striped tortoise beetle differs from the other species in not carrying debris on the anal fork. Larvae of tortoise beetles mature in 14-21 days.
  2. When mature, the larva attaches itself to the leaf by its anal end and pupates. Pupae are brownish, except that in mottled tortoise beetle the pupa is greenish. As is the case with larvae, the pupae bear spines. The fecal material and other debris carried by the larval stage may also remain attached to the pupa. The pupa measures 5-8 mm long. Duration of the pupal stage is usually 7-14 days.
  3. The adult beetles are distinctive in that the margins of the prothorax and elytra are expanded,
Argus tortoise beetle larva.
Argus tortoise beetle pupa.

largely concealing the head and appendages. The expanded margins usually are not heavily pigmented. The beetles are fairly small, measuring 5.0-7.0 mm long. Argus tortoise beetle is a notable exception, measuring 8.0-11.5 mm. The beetles vary in color, but invariably are brightly colored, often metallic, and are sometimes called "goldbugs." Argus tortoise beetle is reddish or yellowish, and usually it has six black spots on the pronotum and on each elytron, plus one spot dorsally that overlaps each elytron. Blacklegged tortoise beetle is red to yellowish, and bears several (usually three) conspicuous black spots and several inconspicuous small spots on each elytron. A distinctive feature of this species is the black legs, the basis for its common name. Golden tortoise beetle is, as its name suggests, particularly golden-metallic (see color figure 113). When the adult first emerges, however, the beetles are orangish with six spots, but this soon fades and the golden color is acquired. Mottled tortoise beetle usually bears considerable black pigment, especially at the base of the pronotum and dorsally on the elytra. The periphery of the beetle is mostly transparent, however. The black pattern on the beetle often resembles a shield, but is highly variable. Striped tortoise beetle, perhaps the most distinctive of the sweet potato-feeding species, is yellow with two black stripes on each elytron.

Complete description of these interesting beetles is lacking. Riley (1870b), Smith (1910), and Barber (1916) gave useful observations, and Chittenden (1924) described argus tortoise beetle. Downie and Arnett (1996), and Riley (1986) provided keys to the genera and brief descriptions of the species.

Damage

Both larvae and adults feed on the foliage of sweet potato. The typical form of injury is creation of numer-

Adult argus tortoise beetle.
Adult golden tortoise beetle.
Adult mottled tortoise beetle.

Adult striped tortoise beetle.

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