These examples demonstrate some of the issues that have to be considered when deciding whether a potential biological control agent should be released or not. The results from host-testing should determine the risk if any to non-target plants, but the decision whether the possible damage outweighs the benefits depends on the importance of the various factors involved. The decision reached will vary in different situations and may not be the same for different countries.

It is important to remember that weed biological control has an excellent safety record, with only eight instances of damage to non-target plants recorded in 100 years of agent introductions (McFadyen 1998). Of these, in five the damage was anticipated but considered not to be important. Two were the result of inadequate host-testing, and in the remaining instance, Zygogramma bicolorata on sunflower, the impact of very high populations was underestimated. However, in not one case were there significant economic losses, and the benefits gained from the introductions far outweighed any damage caused.

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