Mexican Jumping Bean Moth

Description:

The Mexican Jumping Bean moth from Mexico (Family Olethreutidae) is most widely known for it’s larva, which inhabit the carpels of seeds from several species of the desert shrub genus Sebastiania (S. pavoniana or S. palmeri). These seeds are commonly known as Mexican Jumping Beans. The moth lays the egg on the young pod. The hatched larva gnaws into the seed, closing the minute hole during its growth. The larva attaches itself to the bean with many silken threads by hooks on its anal and four hind abdominal prolegs. When ripe, the beans are dropped to the ground. When the bean is abruptly warmed, for instance by being held in the palm of the hand or under warm lights, the larva twitches and spasms, pulling on the threads and causing the characteristic hop. "Jump" is often an exaggeration, but the beans nonetheless do move around quite a bit. The biological purpose of the movement is to reach shade. The larvae inside the seeds on the ground will die in the hot desert sun. The larva may live for months inside the bean with varying periods of dormancy. It eats away the inside of the bean, making a hollow for itself. If the seed is cut, the larva will repair the hole with silk. If the larva has adequate conditions such as moisture, it will live long enough to go into a pupal stage. In preparation to this, it eats a circular hole through the shell (to form a trap door) in February and closes it again with a silken plug. This is to enable the jawless adult moth to escape from the seed. After completion of the exit hole it spins a cocoon within the seed with a passage way leading to the door. During the following pupal stage the larva will not move any more. Normally in the spring, the moth will force its way out of the bean through the round "trap door", leaving behind the pupal casing. The small (about 7 mm), mouthless silver and gray-colored moth will live for only a few days, for breeding and laying eggs.

Habitat:

Several Jumping Beans were purchased in September of 2012 in the market of Oaxaca, Mexico. They came from Alamos, Sonora in the northern desert of the country. They were kept at about 28º C. This moth emerged on May 10th of 2013.

Notes:

In the 4th picture, you can see the interior silk inside the seed through the trap door.