28 Tortoise beetle [EIF

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This leaflet is produced by the Ministry of Agriculture & Livestock, Solomon Islands, with support from IPPSI:
Improved Plant Protection in Solomon Islands, a project financed by ACIAR, the Australian Centre for
International Agricultural Research, Canberra. Authors: Helen Tsatsia, MAL & Grahame Jackson, TerraCircle
Inc.
.

Extension Fact Sheet 54:

Sweet Potato Tortoise

Beetle

Common name: Sweet potato tortoise
beetle; sometimes known as Golden
tortoise beetle

Scientific name: Cassida papuana

Hosts: Feeds on sweet potato, kangkong (Ipomoea aquatica), and related Ipomoea species
(plants in the morning glory family). Possibly, the beetles feed on crops and weeds in other
families.

Damage

Adults feed on leaves, making small to medium-sized holes (photo, left). The larvae at first
eat the leaf surface; latter they eat their way through the leaf. The effect on storage root yield
is not known in Solomon Islands, but it is unlikely to be large.

Biology and Life Cycle

The oval eggs (1-2 mm long) are laid individually on the leaves in a small papery parcel. The
larvae have spines, and an anal fork. The anal fork is made up of long spines near the tip of
the abdomen, and these hold the old skins (which are not shed completely) mixed with
excreta (faeces or droppings). The ‘tail’ of old skins is carried over the back of the body, and
can be moved about by the anal fork, probably to deter predators. The larvae pass through
five moults, before a pupal stage develops. The pupae are attached by the tail end to the
underside of the leaf.

The adults are about 5 mm diameter, oval and slightly flattened and squared at the shoulders
(photo, right). The head and appendages of the adult are mostly hidden by transparent parts of
the thorax and the wing covers.

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Detection and Inspection

Look for the golden round beetles, and the clearwing margins that cover most of the head and
thorax, and extend beyond the body, covering legs and other appendages.

Management

Tortoise beetles are attacked by (chalcid) wasps in other countries, parasitic flies, and lady
beetle larvae. It is likely that these parasites and predators attack Tortoise beetles in Solomon
Islands, although it is not known for certain. However, it is not common for Tortoise beetles
to become a serious pest.

Resistant varieties:

• None known, but fast-growing varieties are more likely to outgrow the damage caused by

the beetles.

Cultural control:

•  Avoid planting new crops next to those already infested with the beetles; or
•  Harvest the infested crop, collect the vines and destroy them, and then plant the new crop;
•  Provide conditions for healthy, rapid plant growth, especially for vine cuttings after

planting; these may include manures, mulches and/or commercial fertilizers, and
adequate water;

• Remove weeds (especially those in the Convolvulaceae family) around the gardens to

reduce the beetle numbers.

Chemical control:

Ashes may be effective in the control of the Tortoise beetle. Apply them to the crop as soon
as the pest is seen; do not wait until the population is high. See Fact Sheet no. 56 on PDPs,
Plant Derived Pesticides, for details of how to make and apply the ash.

• Use synthetic pyrethroid insecticides, such as lambda cyhalothrin or permethrin. The

choice of chemical is important: use those that are least persistent in the environment, and
have low toxicity against bees. READ THE INSTRUCTIONS BEFORE USING ANY
PESTICIDE.

• Derris (rotenone) may be effective against the beetle. A local variety of Derris, originally

from Papua New Guinea, with a high concentration of rotenone, is being multiplied by
MAL and the Kastom Gaden Association. [See these organisations for cuttings.]