Reconsidering the IOBC Toxicity Classification System: Problems and incompatibilities arising from its use. Introduction of the Predator/Prey or Parasitoid/Host ratio as a new, more realistic classification system


Abstract: The IOBC Toxicity Classification System is a tool for categorizing the toxicity, or
effects such as parasitation rate, of Plant Protection Products (PPP) on beneficial organisms.
Adopting this rating system and the IOBC guidelines brought cases of discordance between the suggested experimental results and the feedback from horticulture. Examples of false
positive/negative results, differences in conclusion between beneficial release methods, cases
of mortality due to prey/host scarcity, and other cases of misguidance have been recorded.
Furthermore, the combination of the broad percentage range of each IOBC Class, the ineffective sorting of marginal PPP ratings, and the difficult interpretation led to this reconsideration of the Classification System.
Consequently, a study methodology closer to practice techniques and testing on existing
populations rather than on fresh residue has been adopted. A new IOBC Class 5 (Eradication), which excludes implementation in Integrated Pest Management (IPM) schemes, is suggested. However, as IPM focuses on the long-term prevention of pests and their damage, efficacy should also be considered. Therefore, before making conclusions about the PPPs’ toxicity, the availability of the pests and the PPPs’ ability to control them should be contemplated.
Thus, a new formula to calculate the predator/prey and parasitation/host ratio has been
introduced, considering both toxicity or parasitation rate, in the case of parasitoids, and the
efficacy of the tested PPP. The ratio’s rating indicates the tested PPP’s compatibility with IPM
strategies under applied conditions, on protected crops, or in the field. The formula has already been implemented, and examples will be presented.

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