Tortoise Beetles
Argus tortoise beetle, Chelymorpha cassidea (Fabricius); Blacklegged tortoise beetle, Jonthonata nigripes (Olivier); Golden tortoise beetle, Metriona bicolor (Fabricius); Mottled tortoise beetle, Deloyala guttata (Olivier); Striped tortoise beetle, Agrioconota bivittata (Say), Chrysomelidae, COLEOPTERA


DESCRIPTION

Adult - These oblong-oval beetles are basically gold in color with various black and/or red markings depending upon species. Slightly flattened and squared at the shoulders, tortoise beetles' bodies are somewhat shell-like in appearance. Body margins extend in a roof-like manner over much of the head and legs. Most species are 5 to 8 mm long.

Egg - Tortoise beetle eggs usually occur in masses. Each individual egg is stalked, the long stalk being attached on the plant surface by gelatinous substance. The beige or white eggs of some species have a reddish tubercle on the upper end. Eggs are about 1.6 mm long.

Larva - The spined larvae may be basically dull yellow, brown, or green depending upon the particular species. They all have black heads, prothoracic shields (area behind head), legs, spots, spine-like setae, and anal forks. The anal forks are long spines near the tip of the abdomen which hold large masses of excrement. Fully grown larvae are 10 to 12 mm long.

Pupa - Pupae are oblong-oval in shape like adult beetles but have spines along the abdomen like larvae. They are approximately the same size as adult beetles.


BIOLOGY

Distribution - Argus and mottled tortoise beetles occur in all arable sections of the U.S. and Canada. The golden and blacklegged species are most common from the Rocky Mountains eastward.

Host Plants - Most tortoise beetles feed on sweet potato and closely related plants such as morning glory and bindweed. Argus tortoise beetles also infest cabbage, corn, raspberry, strawberry, milkweed, and plantain. Golden tortoise beetles have been found on eggplant.

Damage - Both larvae and adults feed on leaves causing them to be riddled with holes. This type of damage is most threatening to seedlings or newly set plants.

Life History - Tortoise beetles overwinter as adults under bark, in leaf litter, or in other dry, protected places. In spring, beetles emerge and feed on weed hosts until sweet potato plants are available. Female adults deposit clusters of 15 to 30 eggs on the undersides of leaves. Larvae emerge 7 to 10 days later. After feeding for 2-1/2 to 3 weeks, larvae transform into pupae. About a week later, a new generation of beetles emerges. Several generations may occur each year in southern states.


CONTROL

Tortoise beetles and other leaf-feeding insects do not affect sweet potato production if growing conditions are satisfactory. Cultural practices such as adequate fertilization, good weed control, and well-timed planting effectively deter excessive tortoise beetle injury. Generally, chemical control is not necessary.

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