Biological Notes on the Tobacco Cricket, Brachytrupes membranaceus (Dru.) (Orthopt., Gryllidae), in Southern Rhodesia

Abstract

The Tobacco Cricket, Brachytrupes membranaceus (Dru.), is a pest of young plants of tobacco, maize and other field and garden crops in Southern Rhodesia. During the period of investigations, 1949–52, it was found to be widely distributed in the Territory, the heaviest attacks occurring in areas of light sandy soil of granitic origin. All stages are nocturnal and each individual excavates and inhabits a permanent burrow in the soil, that of an adult averaging 50 to 80 cm. in depth. The burrow has an enlarged chamber in which the cricket lives and stores food.There is one generation a year. Oviposition takes place in February and March, the average number of eggs per female, as shown by dissection, was 216. Incubation takes about 30 days and development of the young nymphs is at first rapid. From June to October, the period of dry and often scarce food, development is retarded but increases rapidly during the third and fourth (the last) nymphal stages in November. From November to May, when young and succulent food abounds, development is rapid. The adults start appearing early in December.The eggs are laid in the burrows and the young nymphs on hatching crawl away from the parent burrow, in all directions, in search of suitable places in which to start digging. The mandibles are used to excavate the soil which is thrown outwards by the forelegs, and the mounds formed by the time the adult stage is reached may attain a height of as much as 30 cm. When an adult is evicted from its burrow, as soon as it finds a suitable place to dig, it will disappear within the space of a minute.The burrows may be found in virgin land or in cultivated land, or along the borders of cultivated fields. The food consists of succulent or dry vegetable matter, according to the time of year, and is carried to and stored in chambers in the burrows. In the virgin veld it consists mainly of lush grasses, seedlings and root suckers of trees such as Brachystegia and Isoberlinia in the rainy season and of dried material of a similar nature during tha dry months. In cultivated land, tobacco, maize, field beans, garden vegetables, seedlings and young transplants are cut and stored.Although the food is compacted in chambers in the burrows it has not been found in a mouldy or fermenting condition. It is thought that it is conditioned before storage, the more succulent material being allowed to wilt before being taken into the burrow and the dry material when softened by dew.