Quadrastichus Mendeli: Is this species a friend or a foe?

FABI (Forestry and Agricultural Biotechnology Institute) has recently discovered a natural enemy of the invasive wasp species, Leptocybe Invasa in South Africa.


Leptocybe Invasa

The pest Leptocybe Invasa is native to Queensland, Australia, but has spread to Africa, Asia, the pacific, Europe and Latin America. In fact, any country that has Eucalyptus trees can fall victim to this gall wasp.

In South Africa, Eucalyptus plantations are being infested by this pest. They insert their eggs into newly sprouted leaves, petioles and stems of the Eucalyptus tree, and, as the tree develops, the larvae grow and deforms the attacked area. This deformed mass of tissue is called a gall, hence the term, gall wasp.

Each gall has multiple chambers and each chamber hosts a developing insect, drawing nutrients from the deformed plant tissue surrounding it. At a high enough infestation rate, the growth of trees can be stunted. They can even be killed. This insect can cause major devastation of the Eucalyptus tree population resulting in various management strategies like the selection and deployment of resistant eucalypt genotypes and the introduction of biological control species like the Selitrichodes neseri.


Quadrastichus Mendeli

Having this little wasp in South Africa is good news. It is hoped that the Q.Mendeli will control and eventually end the spread of Leptocybe Invasa.

The Q. Mendeli is indigenous to Australia, is about 1mm and directly attacks the developing L. Invasa larvae. The Q. Mendeli was deliberately introduced by Israel and India and they have seen very good results in the control of the L. Invasa.

The situation is being monitored buy collecting samples of galls for research on a regular basis, but for now, all we can do is wait for the Q. Mendeli to do it’s job!