Large-scale Field Studies to Assess Side Effects of the Insecticide Spirotetramat to Honey Bee Colonies Under Realistic Field Scenarios

STADLER, T.; MAUS, CH.

Pensacola

Workshop; Pellston Workshop on Pesticide Risk Assessment for Pollinators; 2011

SETAC

AIM OF THE STUDY: The study was aimed to determine potential effects of two different application scenarios of a foliar systemic insecticide (test item) under realistic field conditions in a melon crop to honey bee (Apis mellifera) colonies. A special focus was made on potential brood effects. The GLP study was based on the EPPO 170 protocol. LOCATION OF THE STUDY AND CROP DESCRIPTION: The study was carried out in the surroundings of San Juan City (province of San Juan, Argentina). Nine plots of approx. 1 ha each were used in this study. All experimental plots were approximately 3 km distant from each other. There were no other flowering, bee attractive crops in the surroundings of the study plots. The crop used was melon Cucumis melo (Cucurbitaceae) sown at 15,000 seeds/ha. Appropriate plant density and space between the plants was achieved by young melon picking after emergence. The number of melon blossoms on the plots was counted on different assessment days. TEST ORGANISMS: In total 18 bee colonies (hives), 2 colonies per plot, were brought to the experimental plots. The bee colonies were randomly selected and assigned to the treatment groups. Each hive was comprised of 7 frames for brood of all ages and 1 honey frame and contained a colony of approximately 18,000 bees (Apis mellifera mellifera L.) plus a queen of the same maternal origin (sister queens) at the start of the study. TEST PRODUCT AND APLICATION: The applications of the test item were performed simultaneously on each plot by specially trained people using previously calibrated backpack sprayers and adapted hand lances, equipped with commercially available spray nozzles. The applications were performed after adjusting the walking speed of the people conducting the spray application, to the amount of test item solution to be applied per area to be sprayed within a given time. Subsequently, an extra sprayer calibration was performed in order to check possible deviations from the nominal volume, while the operator walked a distance equal to the length of the area to be applied on each plot. The spray time and remaining volume in the sprayer tank were gauged in order to calculate the mean walking speed, the mean applied volume and the deviation from the nominal volume. The test item was applied during bee flight in flowering melon fields. There were 3 treatment groups, each with 3 replicates, receiving 0, 2 and 4  applications with spray intervals of 7 days.  The hives remained opened during the application but it was made sure that the hives were not exposed to direct overspray with the test item. ASSESSMENTS: The assessments were performed in the framework of a strict, previously planned, time schedule. Due to the great distances between the plots and the generally large-scale dimensions of the study, not all treatment groups and replicates could be assessed for the endpoints given below within one day at the respective assessments. Therefore, assessments were staggered in treatment groups, in order to create work units which can logistically and technically be handled in one day. Five in-field brood assessments were conducted with 7 days interval. Thereafter, the colonies were transferred to an area of less intensive agricultural use. The last brood assessment was conducted 2.5 weeks after the last application had been conducted. Control colonies were assessed in parallel to the assessment dates of the respective treated groups. Meteorological data (non-GLP data) were recorded at the time of applications and at the bee activity assessments throughout the study. Temperature and relative air humidity were measured and cloudiness was estimated. OBSERVATIONS ON THE HONEYBEE COLONIES : a.- Brood Development. The percentages of the comb area in each hive occupied with cells containing eggs, larvae (worker brood unsealed cells) or pupae (worker brood sealed cells) were separately assessed by visual estimation of an trained expert beekeeper; b.- Colony Strength. The number of adult bees living in each hive was visually estimated during the assessments. Likewise, the percentage of each comb side covered by adult bees was assessed while extracting the comb of the hive. c.- Weight of the Bee Hives. The bee hive weight was determined gravimetrically for each treatment group during the assessments. d.- Pollen and Nectar/Honey Stores. The percentage of comb area occupied by stored pollen and nectar/honey in each hive was visually estimated during the assessments. e.- Foraging Activity of the Bees in the Crop. Foraging activity on the plots was determined by counting the number of melon blossoms, on which honeybees were found foraging and the number of melon blossoms without foraging bees was determined along 10 times 10 m rows impartially selected within each plot. Assessments were carried out in 48 h intervals in each treatment group. f.- Mortality. The mortality of adult bees (worker and drones), larvae and pupae was recorded by collecting and counting their numbers found in the dead bee traps attached to the hive. Dead bees, drones, larvae and pupae were immediately removed from the dead bee trap after having been recorded. Special attention was paid to larvae, pupae and malformed bees that were expelled from the hive. Assessments were carried out in 48 h intervals in each treatment group. g.- Returning of Foraging Bees to the Beehives. Bees entering the hives with and without pollen loads were counted when they arrived at the landing board for a 1-minute interval. Assessments were carried out in 48 h intervals in each treatment group. h.- Behaviour. Possible behavioural anomalies of the bees were observed and recorded at the same times as the observations of foraging activity were conducted. Additionally, the number of foraging bees, returning to the hive with and without pollen loads, as well as mortality in front of each hive were assessed in 48-hour intervals throughout the study. Furthermore (according to the same time table) the number of melon blossoms was counted exemplarily for 10 x 10 m rows on each plot throughout the study. Concurrently, the number of blossoms visited by bees was assessed. The validity criteria given in the study plan were fulfilled by using the above described methodology.