18 March 2010

Jumping-ball Moths and the Glossy Wild-currant

Glossy Wild-currant, Shiny-leaved Rhus, Blinktaaibos
Searsia lucida (formerly Rhus lucuda) ANACARDACEAE (the mango family)
At the moment the fruits on the Glossy Wild-currant can be seen on the Common.
A fascinating insect-plant relationship plays itself out with the Glossy Wild-currant Rhus lucida and the Jumping Gall Moth Scyrotis athleta. In the sand and leaf-litter beneath Searsia lucida one can sometimes see small (about 6 mm) oval balls that jump. In the ball is the larva of a moth, Scyrotis athleta (family Cecidosidae). The movement and jumping is a response to heat and facilitates repositioning of the ball into ideal pupating conditions in the soil and leaf-litter. It is quite a mystery how such a small larva in such a confined space is able to exert the force required to jump (up to 10 cm). Janse (1920) concluded that it is done by careful positioning inside the ball and rapid contracting and relaxing of muscles.
The balls start off as bumps (galls) that form on the leaves of Searsia lucida. A female moth lays her egg probably by inserting her ovipositor into the leaf. The gall is formed around the hatched larva possibly as a result of the feeding action inside the leaf. This is still being investigated. The larva feeds inside the gall and when mature the external layer of the gall bursts open and the ball falls to the ground. Jumping can continue for up to 6 weeks and the moth emerges a few months later. (Information and more photos on the website biodiversityexplorer.)