Honey bee Case A. Effect of pesticides on virus infection
Honey bees are keystone species that play an important part in everyone’s day-to-day life. Approximately one third of our agricultural crops depend on honey bee pollination, amounting to about $15 billion of the food supply nationwide. For example, 100% of almond crops are pollinated by honey bees, which requires over one million bee colonies to be trucked into California from other parts of the country each year.
Since about 2006 there has been a major decline in the number of honey bees and other pollinators, which so far has no definitive cause. One aspect of this decline in honey bees is called colony collapse disorder (CCD), where the bees have simply disappeared or abandoned their hives, almost overnight. The cause of CCD is complicated; focus has been on pesticide use, mite levels, and virus levels, however global warming and habit loss are also thought to play a part. Researchers are investigating all aspects of honey bee health and hive management in order to determine the best strategies for ensuring that honey bee populations continue to thrive rather than decline.
Honey bees are commonly exposed to pesticides as they forage for pollen and nectar. Some pesticides are known to disorient bees and thus affect their behavior. Sub-lethal exposures of some pesticides are considered possible contributing factors to Colony Collapse Disorder (CCD). Dr. Muskiver was curious if pesticide exposure was linked to virus infection, another possible contributing factor to CCD.
To test this question, Dr. Muskiver set up four test hives, and fed the honey bees either with untreated pollen or pollen treated with sub-lethal doses of the pesticide Imidocloprid, a neonicotinoid. Samples of 20 bees from each hive were collected, RNA was extracted, and cDNA synthesized in order to run PCR. Multiplex PCR was performed using primers specific for 4 viruses, and also for the bee actin gene as a control. PCR products can be identified based on the size of the product:
|Primers||PCR product size|
|Deformed wing virus (DWV)||203 bp|
|Black queen cell virus (BQCV)||322 bp|
|Sac brood virus (SBV)||487 bp|
|Israeli acute paralysis virus (IAPV)||719 bp|
DNA samples for testing:
Negative control – bee sample with no viruses present
Positive control – bee sample containing all four viruses
Hive 1 – exposed to pesticides
Hive 2 – exposed to pesticides
Hive 3 – no pesticides exposure
Hive 4 – no pesticide exposure
- What are the results for each experimental hive, in terms of viruses that are detected?
- Do the control sample produce the results you expected?
- Is there any correlation between pesticide exposure and viruses detected? How would you explain these results to Dr Muskiver?
- What are some other tests that could be done to address this question? What would you suggest that these researcher do next?
- What changes would you suggest in the experiment design if this were to be repeated?