CMR beetle

Pests of Field Crops in Southern Africa

CMR BEETLE OR BLISTER BEETLE

(Coleoptera: Meloidae)

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Text Box: These beetles are well known as the slow-flying, bright yellow or red and black beetles, which cause blisters when the poison they contain in their bodies comes into contact with human skin, giving them one of their common names. The name CMR beetle is derived from the similarity of one species (Mylabris oculata) to the uniform of the historic South African Cape Mounted Riflemen. Not all Meloidae have these bright colours, however. The most well-known types are Mylabris and Decapotoma spp., but Cyaneolytta spp. are metallic blue-black, and Epicauta spp. are dull grey. They are medium sized beetles, ranging from 10-40 mm long, with elongated bodies and large clubbed antennae. Several other beetles mimic the striking colours of Meloid beetles in an attempt to put off would-be predators that may have learned to associate these colours with the toxin in their bodies. TOP

Text Box: Mylabris and Decapotoma spp. are commonly seen eating the flowers of the bean family, but also Hibiscus flowers, roses and some other ornamentals. Cyaneolytta and Epicauta spp.can be found eating the foliage of grasses, cereal seedlings, potatoes and lucerne. Meloid larvae, unlike the adults, are predacious on the eggs of other insects. TOP

Text Box: The beetles seldom do serious damage, mainly having nuisance value, but their habit of chewing the flowers may reduce a potential bean crop. Another form of damage is the urticaria the beetles can inflict on human skin. Their bodies contain a toxin known as cantharidin, which they can release when they are disturbed. This is a very strong blistering agent when applied externally, but a very small dose taken internally can be fatal, causing damage to the intestinal tract and internal bleeding. TOP

Text Box: The life cycle of Meloid beetles is rather remarkable in that they undergo hypermetamorphosis – a situation in which the larva transforms into markedly different stages between moults. The first stage (the triungulin) is small, active and runs around on the soil surface seeking out grasshopper egg pods that have been pressed into the soil. On finding one, it burrows into the soil and soon moults into quite a different type of larva, which is stouter with smaller legs, and moves more sluggishly. The next two or three stages are in the form of fleshy C-shaped grubs that continue to feed on the eggs. The last of these burrows deeper into the soil before forming a resting stage at the end of the summer. When the warm weather again arrives, another active stage appears after another moult, and this soon pupates. The beetles are commonly seen from November to April, and may often be seen emerging and feeding in areas where locusts or grasshoppers are known to breed. TOP

Text Box: Application of insecticides to control CMR beetles will seldom be economic, and if numbers are numerous, it would be a relatively simple matter to hand-pick them (carefully!). However, normal contact insecticides from the organophosphate and carbamate groups are registered for their control if necessary, although care should be taken not to spray if bees are pollinating flowers. TOP

CMR beetle eating young beanpod.

Blister beetle eating bean flower.

Blister beetle.

CMR beetle entering locust egg pod.