Aspidomorpha tecta (Fool’s Gold Beetle)

Life > Eukaryotes > Opisthokonta > Metazoa (animals) > Bilateria > Ecdysozoa > Panarthropoda > Tritocerebra > Arthopoda > Mandibulata > Atelocerata > Panhexapoda > Hexapoda > Insecta (insects) > Dicondyla > Pterygota > Metapterygota > Neoptera > Eumetabola > Holometabola > Coleoptera (beetles) > Polyphaga > Superfamily: Chrysomeloidea > Family: Chrysomelidae > Subfamily: Cassidinae

The larvae and adults of Fool’s gold beetles feed on leaves of Morning Glory Ipomoea spp. creepers and solonaceous plants such as potato and tomato. The adult has golden metallic coloration on its elytra that is caused by reflection and interference of light on the different layers of cuticle (skin). There are evidently two generations a years and they are most conspicuous on plants in spring and late summer. If you find a morning glory creeper with feeding damage to the leaves, try searching beneath the leaves and you will have a good chance of finding one or more of the life stages of this beetle.

Eggs are laid in packets, about 3 mm long, on the underside of Morning glory leaves. The larvae hatch from the eggs after 10-12 days and start feeding on the leaves, leaving small puncture marks where they have eaten. Tortoise beetle larvae are distinguished by the fork-like process on the end of the abdomen.

Final instar larva. Larvae pass through 5 instars – in other words they pass through five stages, moulting (shedding) their old skin at the end of each instar. The final (5^th) moult takes them into the pupal stage. Unlike most insects but common in tortoise beetles, Fool’s gold beetles do not discard the shed skins from moults but instead pile them up into a tail on the tip of the abdomen together with some of their excreta. Larvae wave this tail around when disturbed so possibly it is used for warding off predators and parasitoids. Once the larva grows big enough it stops just eating the surface of the leaf and instead chews away at the whole leaf margin.

 The final instar larva attaches itself to the underside of a leaf by digging the claws of its legs into the leaf tissue and moults into a flattened pupa. The adult beetle is formed within this pupa and eventually emerges.

Predators and parasitoids

 A parasitic wasp of the family Chalcididae (probably Brachymeria sp.) parasitises the pupal stage by laying an egg in the pupa which hatches into a grub-like larva that feeds on the contents of the pupa, passes into its own pupal stage inside the remains of the beetle pupa and then hatches into an adult which exits the beetle pupa by boring a neat round hole in the dorsal surface.

Find a population of these beetles on morning glory creepers and try to locate the different life stages by examining the underside of leaves. In mid-winter you are only likely to find adults as these are the overwintering stage.

Find the pupae on the underside of the leaves. Some of them might have a neat round hole in the dorsal surface where a parasitic wasp has emerged. Collect some of the intact pupae (without holes) and put them into separate small bottles or vials. Examine these pupae regularly (about once a day) and eventually you will find that either an adult beetle or a small wasp will emerge. The wasp might be the same one as pictured above but there are probably other species as well. Sometimes nothing will emerge because the pupa has been damaged. If you collect enough of the pupae, you will be able to work out the percentage parasitism (the number of pupae parasitised divided by the total number of pupae multiplied by 100).

The Spotted tortoise beetle Conchyloctenia punctata also occurs on morning glory creepers.

• Skaife, S.H. 1979. African Insect Life. C. Struik Publishers, Cape Town (see pages 130 – 132).

• Annecke, D.P. and Moran, V.C. 1982. Insects and Mites of Cultivated Plants in South Africa. Butterworths, Durban (see page 212). 

 Text by Hamish Robertson