Biological Control  

For the last 15 years, the focus in our laboratory has been on classical biological control by the introduction of a small eulophid egg parasitoid, Oomyzus gallerucae [D]. These small wasps may parasitize 50 - 90% of the eggs in a cluster in addition to host-feeding on other eggs, essentially destroying the entire egg cluster.

Program Overview 1984-1999:

  • We have released approximately 400,000 O. gallerucae in 28 locations in California, representing at least seven strains from several European sources (Fig. 3) (Dahlsten et al 1998).
  • Studies with the egg parasitoid have been frustrating. Parasitism during the year of release may be as high as 95% of ELB eggs. However, the parasitoids apparently do not overwinter well in California, as they are normally not recovered the year after release.
  • Parasitoids have occasionally been recovered in years subsequent to field release, indicating that enough parasitoids survive to keep populations established, but not to impact ELB levels significantly.
  • Laboratory studies have confirmed that a low percentage of parasitoids possess the longevity to successfully overwinter in our climate. (Dreistadt and Dahlsten, 1991).


[D] Oomyzus gallerucae parasitizing elm leaf beetle eggs.


Fig 3. Release sites in northern and central California for different strains of Oomyzus gallerucae, 1984 - present.