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Post-release monitoring

Monitoring methods

Direct effects on non-target, beneficial or valued species

In preparation for post-release studies, pre-release opportunities can be taken to enhance robust post-release investigations:

Then post-release

If non-target impact is identified in the field

If non-target impact is not identified in the field

Longer term impacts

There have been a small number of studies carried out to determine the longer-term impacts of introduced biological control agents but few have considered impacts in natural environments. A study was carried out in New Zealand to look at impacts of the parasitoid Microctonus aethiopoides, a biological control agent for the Lucerne weevil, Sitona discoideus in native grassland Ferguson et al. 2016. The parasitoid also attacks New Zealand native weevil species both in pasture, and to a lesser extent in native grassland. The study sought to determine whether non-target parasitism in native grassland was a result of spill-over parasitism from lucerne areas near native grassland, or whether the parasitoid had become established in native weevil populations in the higher altitude natural grassland ecosystems (see figure).

Schematic illustration of the processes hypothesized to lead to non-target parasitism of New Zealand native weevils by Microctonus aethiopoides in tussock grasslands.

© Copyright AgResearch, used with permission.

The results of the study indicated that non-target parasitism was probably a result of both mechanisms. Native weevils at the study site were shown to support the development of the parasitoid at very low levels, but they could overwinter in native weevil hosts. However, modeling predicted that at low temperatures the number of generations possible would be limited. The authors concluded that spillover parasitism would probably be required to maintain parasitoid survival in this environment.


Ferguson C.M., Kean J.M., Barton D.M. and Barratt B.I.P. (2016). Ecological mechanisms for non-target parasitism by the Moroccan ecotype of Microctonus aethiopoides Loan (Hymenoptera: Braconidae) in native grassland. Biological Control 96: 28-38.

Hoogendorn M. and Heimpel G.E. (2003). PCR-Based gut content analysis of insect predators: A field study. Pp. 91-97 In: Proceedings of the 1st International Symposium on Biological Control of Arthropods, R. Van Driesche (Ed.) Forest Health Technology Enterprise Team, Morgantown, West Virginia.

van Lenteren J.C., Cock M.J.W., Hoffmeister T.S. and Sands D.P.A. (2006). Host specificity in arthropod biological control, methods for testing and interpreting the data. Pp. 38-63. CAB Publishing, Delemont.