Here we describe our detailed protocol for the preparation of single-cohort honeybee colonies – a useful tool for analyzing the role-associated worker physiology. We also describe detailed protocols for treating workers with juvenile hormone and ecdysone to evaluate the involvement of these hormones in the regulation of worker behavior and/or physiology.
The overall goal of these procedures is to examine the physiology of worker honeybees in association with the workers'role and the status of their endocrine system. It's a method which has been widely used for the analysis of worker behavior, can also help answer key questions about the relationship between physiology and the role of worker honeybees. The main advantage of this technique is that it is relatively easy to perform.
To create two single-cohort colonies, begin with three standard colonies and collect newly-emerged worker bees from each of the three. Using tweezers, regularly inspect the colonies for the appearance of puby in the capped peripheral cells with brown eyes and pigmented cuticles. Once found, most of the puby will emerge in the next few days.
Then brush the adults off the combs and remove the combs from the colony. Combine one such comb from each of the three colonies into an empty nuclear hive box. Establish two such hive boxes and incubate them at 33 degrees Celsius with a relative humidity of at least 60%Over the next three days, collect about 3, 000 newly-emerged workers from each new hive box.
To approximate the number of bees in each collection, weigh five randomly selected newly-emerged workers and use their average mass compared to the mass of the collected workers to estimate the number of bees. Prepare new hive boxes with a comb that is loaded with honey and pollen from an unmanipulated colony and another comb that is empty. Next, label the thoraxes of approximately 900 workers in each new colony using water-based poster paint markers.
Then transfer the collection of worker bees into these new hive boxes and add one queen. Six to eight days after setting up the single-cohort colonies, collect some of their nurse bees and precocious foragers for analysis. To collect the nurse bees, use tweezers to select bees that put their heads into comb cells to care for the brood.
Pick them up by the thorax. To collect foragers, use an insect net to capture workers that return to their hives with pollen loads on their hind legs. To classify the HPGs of honeybees, transfer a collection of 10 to 15 bees to an insect cage and anesthetize them at four degrees Celsius for 10 to 15 minutes until the bees cannot fly or walk.
Then transfer the bees onto ice to cool them into a completely anesthetized state after about five minutes. Then leave the bees on ice until needed. Now, dissect their heads from their bodies with scissors and tweezers.
In a Petri dish, fix the heads into dental wax using insect pins. To do this, use two pins inserted into the base of the antennae. Now, soak the fixed heads in insect saline and transfer the dish to a stereoscope.
Using fine tweezers and a surgical knife, remove the anterior cuticle from the head to access the areas around the brain. Next, remove the white membranous tracheal tissue under the cuticle to expose the HPGs. Then dissect the HPGs from the head by slowing pulling them out using tweezers.
Classify the HPGs with large and circular aseni developed and consider them to be from nurse bees. Classify HPGs with small and distorted aseni as shrunken and consider these to come from forager bees. Classify HPGs corresponding to neither developed nor shrunken as intermediate.
Use the developed and shrunken HPGs for RNA extraction to compare their gene expression. Collect nurse bees from typical colonies as previously described. Anesthetize the nurse bees at four degrees Celsius for about 30 minutes.
Then using tweezers, immobilize the bees on dental wax on a Petri dish. Once immobilized, inject the heads of the nurse bees with one microliter of 20E solution. To do this, use a calibrated capillary micropipette.
Connect the injection tip to a rubber tube and connect the 200 microliter micropipette tip to the opposite end of the tube. Next, load one microliter of 20E solution onto a piece of parafilm. Then use mouth aspiration to draw the solution into the injection tip.
Next, insert the injection tip into the base of the antennae and inject the solution by exhaling on the tube. Alternatively, use an automated injection machine if available. Rear the injected bees in insect cages at 35 degrees Celsius under dark and humid conditions.
Include honey water for nourishment and track survivorship as needed. Collect combs containing puby from a colony and incubate them at 35 degrees Celsius with 60%or more relative humidity for up to one day. Collect the newly-emerged bees from the combs and apply paint marks to their thoraxes using poster paint.
Then return these bees to their colonies. After six days, collect the painted workers from the colonies and anesthetize them at four degrees Celsius for 30 minutes. Once anesthetized, immobilize the bees using tweezers and dental wax as previously described.
Then apply one to five microliters of methoprene and acetone onto their heads using a micropipette resistant to acetone. Rear the bees in cages as previously described. If a high mortality is observed, reduce the volume of acetone to one microliter.
Workers that satisfy the behavioral criteria for nursing behavior or foraging behavior were collected from single-cohort colonies and their HPG development was estimated. Based on the HPG RNA extractions and quantitative RTPCR, expression of MRJP2 was enriched in nurse bees and Hbg3 was enriched in precocious foragers. Selected workers were injected with 20E and surviving bees were counted.
Seven days after injection, approximately 60%to 80%of injected bees were alive. The control injection had similar results. Quantitative RTPCR analysis show that the 20E injection decreased expression of MRJP2 in the HPGs.
The same occurred with Hbg3 in the HPGs. In addition to 20E, the effect of topical methoprene application on MRJP2 and Hbg3 expression in the HPGs was examined. After topical application, most bees survived to seven days.
RNA harvested from these survivors show that application of methoprene inhibited the expression of MRJP2 and enhanced the expression of Hbg3. After watching this video, you should have a good understanding of how to prepare single-cohort colonies and treat the bees with hormone in order to analyze the worker physiology associated with roles and endocrine system. Once mastered, the and the classification of HPG can be done in five minutes if it is performed properly.
While attempting the injection for hormone solution, it's important to remember to minimize the damage of bees by anesthesia and injection in order to keep bees alive when reared. Don't forget that working with honeybees can be hazardous and precautions such as wearing bee suits and gloves should always be taken while performing collection of bees and manipulation of colonies.
