7.8.3. Feeding a liquid test substance to groups of caged adult workers in the laboratory
In contrast to feeding a liquid test substance to individuals, group-feeding has fewer logistic and time constraints. It mimics consumption and transfer of food among honey bees in a colony via trophallaxis because food is typically consumed by only a small proportion of workers but ultimately shared among nearly all worker nest-mates within 24 hours (Nixon and Ribbands, 1952; Crailsheim, 1998).
Although not well studied, the primary disadvantage of group feeding a test substance is its potential unequal distribution among individuals over time (Furgala and Maunder, 1961). Although many factors may influence food consumption, such as parasitism (Mayack and Naug, 2009), quantity of honey bees and level of starvation will most importantly dictate volume of test substance to provide. Generally, ten workers can consume 100 - 200 µl of 50% sucrose solution in 3-4 hours (OECD, 1998), or at an individual rate of 2.5 - 6.6 µl per hour. To group feed workers a known quantity of inoculum, a single feeding device containing a minimal amount of test substance should be used to ensure all contents are consumed in a timely fashion. Generally, the entire volume should be consumed in less than 24 hours, but exact duration of consumption should be determined by the specific experiment. The test substance should be replaced with standard food when the total volume of the test substance is ingested; constant vigilance is required to ensure that workers do not go without food. One should assume equal consumption by all caged workers when determining ingestion of test substances. For example, 660,000 N. ceranae spores are required to inoculate 20 workers with 33,000 spores each.