Leaf Eating Ladybirds

Pests of Field Crops in Southern Africa

LEAF-EATING LADYBIRDS

(Coleoptera: Coccinellidae)

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Text Box: Most of the ladybirds are beneficial insects, preying upon such common pests as aphids and scale insects. There is a group of them, however, the genus Epilachna, which is plant-feeding. Several species occur in Zimbabwe, on crops such as maize, potatoes and cucurbits. The beetles are very similar in appearance to the beneficial ladybirds, usually being red or orange with a series of black markings, but unlike them, the harmful species usually have a dull rather than a shiny surface. This sort of “matt finish” is due to a fine pubescence over the elytra. The common species on cucurbits is Epilachna chrysomelina, which is 6 – 8 mm long and has six black spots on each reddish-brown elytron. The larvae are elongated but quite broad, pale yellow at first, but become darker as they develop, and have long, branched spines covering the body. TOP

Text Box: E. chrysomelina attacks most cucurbits but has also been found on various solanaceous plants such as potato and spinach, beetroot and a number of weeds. TOP

Text Box: Both adults and larvae are voracious feeders and may cause considerable damage. They favour the leaves, but may also eat flowers and fruit. Feeding results in the leaves being skeletonised, and only the veins and the epidermis on the farther side of the leaf remain intact. The appearance of this sort of damage is very characteristic and can be recognised immediately as ladybird damage. The presence of yellowish drops of excreta on the damaged tissue is also indicative of their presence. Fortunately, serious levels of damage by this pest are not common, and usually only a small number of them is seen on a crop. TOP

Text Box: The eggs are pale yellow, spindle-shaped and laid upright in batches on the lower surface of the leaf. In general, after a pre-oviposition period of some weeks, the female lays 100 – 200 eggs in small batches over a period of three to four weeks. The larvae hatch after four or five days and feed in groups, mainly on the undersides of the leaves, only later dispersing on the host plants. After four moults occupying about a month, the last larval instar is reached and pupation then takes place on the leaf. To do this, the larva attaches itself to the leaf by its hind end, the skin splits down the back and is folded at the rear of the body, and the yellowish pupa is exposed. This gradually darkens with age and adult beetles emerge after five or six days. The whole cycle thus takes five to six weeks. Eggs may be laid on a crop as early as November, and this would allow three generations to be completed by March. Beetles from the last brood do not mate at once, but leave the plant and pass the winter congregated in a state of semi-hibernation, usually in sheltered places such as narrow, shaded valleys, where they cluster along the branches of trees or in crevices between rocks. TOP

Text Box: Hand-picking of the adults and larvae may be practised in small plots, but is a tedious and time-consuming activity. If low numbers are present, the amount of damage would hardly warrant any control measures, but the pest can attack the fruits. Fortunately there are few records of serious infestations of leaf-eating ladybirds, but if an insecticide is required, malathion as a wettable powder formulation has been used successfully for years, and no doubt there are numerous other contact insecticides which would do a suitable job. The only proviso is to ensure good under-leaf coverage, since a large part of the population feeds there. TOP

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Epilachna leaf eating ladybird.