A comparison of rate–response toxicity tests with Aphidius rhopalosiphi (Hymenoptera: Aphidiidae) using glass, leaves and whole plants as substrate

Rate–response toxicity tests on Aphidius rhopalosiphi were carried out with seven plant protection products using three different test systems. The first type of test system conformed to the standard laboratory testing guidelines and consisted of two treated glass plates fitted into a metal frame, which created an enclosure for the wasps. In the second type of test system, the plant protection products were applied to two bean-leaf disks mounted on agar filled dishes, which were fitted to a transparent plastic frame. The third type of test system consisted of potted barley plants, which were treated and covered with an acrylic cylinder. Adult wasps were exposed to the dried residues of the products for 48 h before wasp mortality was assessed. For each product and test system, the LR 50 value (application rate at which 50% mortality of the wasps occurs) was determined with a Bayesian Probit analysis. Technically, rate–response testing was feasible with all three test systems, and rate–response relationships could be established. The results support a sequential testing scheme, as the LR 50 values increased from `glass plate test' to `excised leaf test' to `whole plant test' with all tested products. The LR 50 values were 7.8–340 times higher on whole plants than on glass plates. Because of the variability of this factor, a numerical safety factor cannot be used to substitute extended laboratory testing for regulatory purposes.