Results of 2-Year Ring Testing of a Semifield Study Design to Investigate Potential Impacts of Plant Protection Products on the Solitary Bees Osmia Bicornis and Osmia Cornuta and a Proposal for a Suitable Test Design

Abstract

There are various differences in size, behavior, and life history traits of non-Apis bee species compared with honey bees (Apis mellifera; Linnaeus, 1758). Currently, the risk assessment for bees in the international and national process of authorizing plant protection products has been based on honey bee data as a surrogate organism for non-Apis bees. To evaluate the feasibility of a semifield tunnel test for Osmia bicornis (Linnaeus, 1758) and Osmia cornuta (Latreille, 1805), a protocol was developed by the non-Apis working group of the International Commission for Plant-Pollinator Relationships, consisting of experts from authorities, academia, and industry. A total of 25 studies were performed over a 2-yr period testing a replicated control against a replicated positive control using either a dimethoate or diflubenzuron treatment. Studies were regarded to be valid, if ≥30% of released females were found to occupy the nesting units in the night/morning before the application (establishment). Thirteen studies were regarded to be valid and were analyzed further. Parameters analyzed were nest occupation, flight activity, cell production (total and per female), cocoon production (total and per female), emergence success, sex ratio, and mean weight of females and males. Dimethoate was a reliable positive control at the tested rate of 75 g a.i./ha, once >30% females had established, displaying acute effects such as reduction in flight activity, increase in adult mortality (shown by nest occupation), and reproduction ability of the females (total cell and cocoon production). On the other hand, no effects on larval and pupal development were observed. The growth regulator diflubenzuron had statistically significant effects on brood development, causing mortality of eggs and larvae at a rate of approximately 200 g a.i./ha, whereas fenoxycarb did not cause any significant effects at the tested rates of 300 and 600 g a.i./ha. In conclusion, the ring-test protocol proved to be adequate once the study comprised a well-established population of female Osmia bees, and the results improved in the second year as the laboratories increased their experience with the test organism. It is noted that the success of a study strongly depends on the experience of the experimenter, the crop quality, the quality of the cocoons, and the weather conditions. Based on these finding, recommendations for a semifield study design with Osmia spp. are proposed. Environ Toxicol Chem 2021;40:236-250. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Keywords: Ecotoxicology; Non-Apis; Osmia; Pesticides; Risk assessment; Semifield test design.

Figure 1

Life cycle of Osmia bicornis. Adults are emerging from cocoons in spring and females start the deposition of eggs after mating. Larvae are hatching from eggs and start feeding on the pollen provision in the brood cell. Before hibernation the larvae spin a cocoon, in which they overwinter and complete their maturation. In the next spring, the adult bees emerge from cocoons.

Figure 2

Boxplot of the percentage of released female bees nesting at the time of application in the ring test with the test items dimethoate and the bee species Osmia bicornis and Osmia cornuta. The median and 1st and 3rd quartile are presented; whiskers represent minimum and maximum values. For quality criteria, it was defined that a study was regarded valid if ≥30% of released females were found to occupy the nesting units in the night/morning before the application. (A) Data from 2016: 4 replicates/treatment group C and T (except for Lab 8: 3 replicates only). Lab 3, Lab 6, and Lab 7 are valid. (B) Data for 2017: 6 replicates/treatment group C and T (except for Lab 1: 4 replicates only). Lab 1, Lab 4, Lab 6, and Lab 8 are valid.

Figure 3

Boxplot of the mean number of nesting female bees (mean of 3 highest numbers) after the application of 75 g dimethoate/ha in all valid studies in the ring test with the bee species Osmia bicornis and Osmia cornuta. The bees were counted in the nesting units at night or early in the morning. In 2016, 4 replicates and in 2017, 6 replicates (except for Lab 1: 4 replicates only) were used per treatment group C and T.

Figure 4

Boxplot of the mean flight activity of female bees (entering the nesting unit in 3 min) at the first assessment after the application of 75 g dimethoate/ha in all valid studies in the ring test with Osmia bicornis and Osmia cornuta. In 2016, 4 replicates and in 2017, 6 replicates (except for Lab 1: 4 replicates only) were used per treatment group C and T.

Figure 5

Boxplot of the mean number of cells (A) and cocoons (B) produced/female bee (calculated based on the mean of the 3 highest numbers counted during nest occupation assessments) after the application of 75 g dimethoate/ha in all valid studies in the ring test with Osmia bicornis and Osmia cornuta. In 2016, 4 replicates and in 2017, 6 replicates (except for Lab 1: 4 replicates only) were used per treatment group C and T.