Photo 2. Aspidimorpha deusta on sweetpotato (Solomon Islands). It is also a common species on Ipomoea pes-caprae.
Sweetpotato tortoise beetle
Cassida and Aspidimorpha species.
Widespread. Asia and Oceania. There are many Cassida and Aspidimorpha species in Pacific island countries, almost all feeding on Convolvulaceae. The following have been recorded on sweetpotato: Cassida compuncta (Fiji); Cassida diomma (Fiji and Samoa); Cassida papuana (Papua New Guinea and Solomon Islands), and Cassida species on Merremia peltata (Solomon Islands).
Sweetpotato, kangkong (Ipomoea aquatica), and related Ipomoea species (plants in the morning glory family). Possibly, the beetles feed on crops and weeds in other families.
Adults feed on leaves, making small to medium-size holes (Photos 1-3). The larvae at first eat the leaf surface; later, they eat their way through the leaf.
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, frass 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 a leaf.
The adults are about 5 mm diameter, oval and slightly flattened and squared at the shoulders (Photos 4&5). The head and appendages of the adult are mostly hidden by transparent parts of the thorax and the wing covers (Photos 2-5).
The effect on storage root yield is not known in Solomon Islands, but it is unlikely to be large. It is uncommon for tortoise beetles to become a serious pest.
Look for the golden round beetles, and the clear, wing margins that cover most of the head and thorax, and extend beyond the body, covering legs and other appendages.
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 Pacific island countries, but this is not known for certain.
The following is important:
None known, but fast-growing varieties are more likely to outgrow the damage caused by the beetles.
If chemical control is needed, do the following:
AUTHORS Helen Tsatsia & Grahame Jackson
Photo 2 Graham Teakle, Canberra. Information from Chris Reid, Australian Museum, Sydney.
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.
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