7.7. Controlling for water evaporation from food provided to caged adult workers in the laboratory

Food consumption is determined by calculating the difference between food provided and food remaining (sections 7.2.3 and 7.3.3). In most cases, evaporation does not need to be considered because all experimental variables should be conserved among treatment groups except for the variable of interest, thereby creating systematic conservative errors among cages.

If water loss from both carbohydrate or protein diets needs to be measured during the course of a study, it can be calculated:

  1. Prepare three ‘mock’ cages (MOCKCAGE) cages in the same incubator used to hold experimental cages for food of interest (i.e. carbohydrates or protein). All conditions for these evaporative control cages should be identical to experimental cages (e.g. type of food provided, frequency of food replacement, type of cage used, incubator maintained in, etc.).
  2. Within each MOCKCAGE, one ‘mock’ feeder (MOCKFEEDER) should be protected by a breathable mesh; whereas, a second feeder is only provided to allow workers to feed.
  3. For each MOCKCAGE, calculate average daily mass reduction of MOCKFEEDER feeding device per worker (MOCKBEE) according to methods described in sections 7.2.3 and 7.3.3 for measuring carbohydrate consumption.
  4. Determine average daily mass reduction per worker among all three cages (MOCKTOTAL) using the three MOCKBEE values.
  5. Determine loss via evaporation by subtracting MOCKTOTAL from daily per worker food consumed per cage (DAILYWORKER) as determined according to sections 7.2.3 and 7.3.3 for all experimental cages of interest; negligible negative adjusted consumptions should be set to zero.

Interestingly, licking or moistening of protein patties by honey bees can adulterate consumption (Fig. 21). At this time, we do not know how to include this behaviour into calculations of food consumption, although it likely has little influence.