Mexican Jumping Bean Moth

Tortricidae, Cydia deshaisiana. Spanish: Brincador (Mexico, bean with larva). Jumping beans, Devil's beans (seeds with larva).

In the region of the Rio Mayo in southern Sonora and Chihuahua, Mexico, a species of tropical shrub called yerba de flecha (Sebastiana pavoniana, Euphorbiaceae) produces angular beanlike pods, some of which become infested with the larvae of this moth (Berg 1891) (fig. 10.12d). Females place the eggs on the pod early in its development, in the spring. The pods, each containing a single larva, later dry and fall to the ground. The larva lines the pod's interior with silk, and as the sun heats it, it becomes agitated and grasps the wall with its legs and snaps its body. This causes the pod to jerk. The higher the temperature, the more vicorously it jerks. The action apparently allows the larva to find a suitable crack or crevice out of the heat, which might kill it. The larva weighs about the same as the shell of the bean, so it can generate sufficient momentum to move it.

These "jumping beans" (Hutchins 1956) are collected in quantities by local entrepreneurs and exported to southern California, Arizona, New Mexico, and Texas where they are sold as curios during the jumping season, May or June. Games of chance have even been devised, with the beans used as pawns.

Just before maturing (when they reach a length of 3—5 mm), the larva cuts a circular door in the end of the pod, leaving an edge in place, like a trapdoor. The emerging moth later pushes it out of the way to escape. Beans with pupae do not jump.

The adult (fig. 10.12c) is a small (WS 20 mm), dark brown moth with broken, zigzag bluish-gray lines traversing the fore wings, the tips of which are abruptly marked with a broad dark triangular area.

The species formerly went under the name "Laspeyresia saltitans."

References

Berg, C. 1891. Sobre la Carpocapsa saltitans Westw. y la Grapholitha motrix Berg, n. sp. Soc. Cient. Argentina An. 31: 97-110. Hutchins, R. E. 1956. The jump in the jumping bean. Nat. Hist. 65: 102-105.

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