Swiss Federal Research Station for Agroecology and Agriculture, Zurich-Reckenholz

Ecological risks due to biological control of the European corn borer with Trichogramma

The exotic egg parasitoid Trichogramma brassicae, which originates from the northern part of the Black Sea area, is successfully used for biological control of the European corn borer (Ostrinia nubilalis). In a four years project, we evaluated if mass releases of the parasitic wasp may pose a risk to non-target insect populations, in particular to butterflies and natural enemies. Overwintering experiments and monitoring showed that T. brassicae survives cold winters north and south of the Alps. However, only low numbers of T. brassicae, released in the previous year, were recovered the next spring. Dispersal experiments have shown that part of the released wasps leave the field and disperse to non-target habitats. Eggs of many lepidopteran species were successfully attacked under laboratory conditions, however, low parasitism rates were found in field experiments. Natural enemies like coccinellids, syrphids, or lacewings were not attacked at all or showed low parasitism rates in semi-field or field experiments. The two most important spring hosts of the endemic tachinid fly (Lydella thompsoni), a natural enemy of the European corn borer, were not parasitised by T. brassicae. Therefore, no competition between the tachinid fly and the parasitoid wasp exists. Based on our results, we conclude that the risk for non-target insects due to mass releases of T. brassicae is very low.

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