4.7. Randomization

Random application of treatments to test larvae may be used to improve dose-effect curves in toxicity studies (Pierrick Aupinel, unpublished data). We recommend randomizing larvae within a study in order to avoid an eventual bias due to the minor differences of age and then a difference of susceptibility to the test pathogen or compound. Randomization can be conducted at different moments according to the applied protocol. Randomization is easily accomplished when determining the acute toxicity of a test compound. For example, one can randomly exchange queen cups on microtiter plates on day four, just before one ordinarily provides larvae with contaminated diet in an acute toxicity test. If testing in chronic conditions, cup randomization must be done at the grafting stage because larval exposure to test compounds begins at this moment. Larvae can be randomly dispatched directly from the comb to the plastic cups.