Seed Beetle May Check Spread of Jerusalem Thorn

Agricultural Research Service scientists in Argentina have recently completed basic research on the usefulness of the Parkinsonia seed beetle as a biological control agent for Parkinsonia aculeata--the Jerusalem Thorn tree.

Researchers at ARS’ South American Biological Control Laboratory in Buenos Aires, Argentina, have found that the Parkinsonia seed beetle--Penthobruchus germaini--may be able to control the spread of this invasive tree by depositing its eggs in the tree’s seedpod. Once the eggs hatch, the larvae burrow into the tree’s seeds to feed and complete their development.

The Jerusalem Thorn tree is native to northern Argentina, where natural controls keep it in check. In the southwestern United States, however, it has no natural enemies and has spread across rangelands from southern Texas to Arizona and northern Mexico. In Australia, the tree was imported as an ornamental. Now it’s become an invasive weed in Australian pastures and rangelands, as well as in the country’s most productive grasslands in low areas and along streams.

Preliminary indications are that P. germaini appears to have the necessary characteristics to be an effective biological control agent for the Jerusalem Thorn tree. In field studies, the beetle was found to infest one out of every four seeds in one season.

Since P. germaini develops in the relatively short time period of 48 days, two generations of beetles would be available as biological control agents each year. Its cold tolerance, high egg fertility and low rate of natural parasitism are also highly desirable attributes. The tests also indicate that the beetle is host specific to Parkinsonia aculeata. Preliminary field evaluations in Australia--where P. germaini was introduced in 1995--indicate that the beetle is destroying a high percentage of P. aculeata seeds.

This study is part of the Agricultural Research Service’s effort to find nonchemical pest control alternatives. ARS is the U.S. Department of Agriculture’s chief scientific research agency.

Scientific contact: Juan Briano, USDA-ARS South American Biological Control Laboratory, Buenos Aires, Argentina, phone 54-11-4662-0999, fax ext. 104, jabriano@mail.retina.ar