Armoured Bush Crickets

Pests of Field Crops in Southern Africa

ARMOURED BUSH CRICKETS

(Orthoptera: Tettigoniidae)

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Text Box: In the hotter, lower-lying areas, armoured crickets of the genus Acanthoplus seem almost to break out in plague proportions in some years and can be a substantial pest of sorghum and millets. Three species have been identified – A. armativentris, A. jallae and A. speiseri. They are all large ungainly crickets, with very long antennae, and formidable thorny projections on the prothoracic plate. The males have their wings reduced to stubs with which they produce their rasping call. They are usually green to brown in colour. TOP

Text Box: These crickets are more or less omnivorous, consuming grasses (particularly seed heads) and broad-leaved plants, and may often be seen feeding on the bodies of their own species, which are killed on the roads by passing traffic. TOP

Text Box: The crickets are not specific pests of sorghum or millets, but can cause havoc in outbreak years. The early instars feed primarily on wild grass seed heads, but later instars migrate in great numbers into maturing sorghum and millet fields and consume the grains, particularly in milk to hard dough stage. With their powerful jaws, they rapidly eat through the maturing seeds, and depending on population density, losses of 20-30% have been reported. TOP

Text Box: Some research has been carried out on the life cycle of these pests. Like crickets, the males attract the females by their high-pitched, rasping call. After mating, oviposition takes place from April to June in the shade of shrubs in the natural bush or in the fields, eggs being laid in the soil in small pods of up to 15 eggs. The eggs remain in a diapause state through the dry winter months, and only develop and hatch after good rains have fallen in the spring. If a drought season follows, the majority of the eggs will not hatch at all, but remain quiescent. Development of the nymphs through six instars takes about two months, and if the rains are very heavy, many of these fail to reach maturity. The juvenile stages are more or less miniature versions of the adults. As they approach maturity, the bush crickets have a greater need for more protein-rich food, and this coincides well with the heading and flowering stage of the crops. It is not known why populations are so large in some years, but major outbreaks are thought to occur when good rains follow drought seasons. TOP

Text Box: Since this pest is not able to fly, control measures could include band sprays around the edges of crops in outbreak years to prevent the crickets from immigrating into the field. Once there however, sprays of a contact chemical, such as carbaryl or a synthetic pyrethroid, would have to be applied to the heads of the crop. The success of this, however, is likely to be only partial since they are such large, robust creatures. In addition, more than one spray may be necessary since the crickets will continue to invade the crop over several weeks. TOP

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Armoured bush cricket.

Armoured bush cricket on Sorghum.