Crickets

Pests of Field Crops in Southern Africa

CRICKETS

(Orthoptera:Gryllidae)

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Text Box: A number of species of crickets cause damage to seedlings and turf or lawns. They are recognised by their robust, broadly flattened, dark bodies, long antennae, large biting mandibles, hindlegs that are modified for jumping, varied chirping calls and, in the females, long ovipositors at the rear of the body. The following species are commonly damaging: Acanthogryllus fortipes – large (50+ mm) and brown; Gryllus bimaculatus – medium-sized (about 25 mm), shiny black with yellow band on thorax at base of wings; Brachytrupes membranaceus – large “giant” or “sand” cricket (50+ mm), brown with spiny legs and strong jaws; Gryllotalpa africana – the medium-sized “mole” cricket (about 25 mm), velvety brown, with broad forelegs modified for digging and shortened, sculptured forewings. TOP

Text Box: Crickets seem to show little host specificity. The seedling stage of many crops is affected by the species described above. B. membranaceus and G. africana have been recorded feeding on tobacco and maize seedlings, vegetable seedlings and young nursery plants, such as Eucalyptus seedlings. A. fortipes and G. bimaculatus are the main culprits in lawns and turf, “grazing” and damaging them particularly when they are stressed in dry periods. TOP

Text Box: Crickets are usually locally sporadic pests, but may be very destructive. They remain in their subterranean burrows during daylight hours, but are active at night, foraging above ground level for suitable plant material. Seedlings may be cut off and carried back to the burrow, leaving just a stump behind. It appears that plants that have been cut off and left by cutworms are also readily collected by some species of crickets. In lawns, large bare patches where the grass has been removed may surround the burrows, although the crickets are always careful to leave a concealing tuft or two over the entrance to the burrow. TOP

Text Box: The life cycle of the various species is likely to be very similar. For the giant cricket, breeding is in the underground burrows, where large, elongated eggs are laid singly or in batches in February and March. These hatch in about April and the tiny crickets leave the burrow and start to excavate their own nests in the immediate vicinity. They develop through four nymphal instars in a period of about eight months, and resemble the adults except in size and lack of wings. The early instars are relatively slow to develop, as they have to cope with the scarcity of suitable food through the dry months. With the giant cricket, the depth of the burrows increases from about 10 cm or less for the young nymphs, to up to 80 cm for the adults. The burrow may be quite a complex structure with a number of tunnels, more than one entrance/exit, and an expanded food storage and living chamber. The burrows are usually found in greatest concentration on the borders of relatively small cultivated areas. Adults appear in early December, coinciding with young crops, or grass that has become lush from the rains. TOP

Text Box: The most effective control method for crickets in field crops is by application of poisoned baits, either pre-formulated, or home-manufactured with chemicals such as trichlorfon added to moistened maize meal. The bait should be applied as late in the day as possible so that it is still moist in the evening when the crickets emerge. A problem with this control method, however, is that it is very non-specific and while it is also an effective control method for cutworms and dusty surface beetles, it may be attractive to birds or even domestic animals. For crops in seedling stage, such as tobacco, collection and soaking of discarded, partly wilted plants with an approved insecticide can also be an effective baiting method. The plant bait can be scattered between the rows, and the crickets drag the wilted plants down into the burrows for storage and later consumption. In lawns and turf, application of insecticides (such as synthetic pyrethroids, carbaryl, and in South Africa chlorpyrifos, imidachloprid, thiamethoxam) can be made as a general spray in plenty of water. In lawns sprays should preferably be applied directly to the burrows themselves, which is more environment-friendly than general spraying, although laborious. TOP

Juvenile cricket at entrance to burrow.

Mole cricket.