Honey bees experience varroosis, a viral disease caused by the ectoparasitic mite, Varroa destructor. These mites attack all life cycle stages of honey bees, and infects three different subspecies of honey bees, the Apis cerana (Asiatic), Apis koschevnikov, and the Apis mellifera (European). The Varroa mite attaches itself to the honey bee’s body and sucks up hemolymph, and infects the bee with a virus. The virus then causes the bee to become weak, have deformed wings, and die early, and can eventually take down a colony. Spread of the disease is partly caused by translocation of infected worker, thus introducing this disease to various regions of the world.
Research conducted by Invernizzi, Zefferino, Santos, Sanchez, and Mendoza, published in the Journal of Apicultural Research, investigated the grooming behavior of Italian and Africanized (hybrids of A. m. scutellata) honey bees at the individual, group, and colony levels, in order to assess their resistance against Varroa destructor. Honey bees display resistance by dislodging Varroa mites via autogrooming or allogrooming. They found that there were five behaviors that the bees displayed: cleaning their antennae and body with their legs, shaking their abdomen, biting the mite, rolling to in an attempt to find the mite, and flying. These behaviors are resistance mechanisms for parasitized bees to dislodge mites. The researchers ran three experiments to observe the bees’ behavior, and hopefully find new tools to control the mites.
Experiment 1: Individual Level Grooming Behavior
Experiment 1 evaluated behavior at the individual level, using 24 Italian bees and 24 Africanized bees (also known as “killer bees”), with the addition of a mite on each individual’s thorax. It was found at the individual level that cleaning and shaking were the most frequently used methods by both subspecies of bees. Additionally, it was seen that across all five behavioral resistance mechanisms, Africanized bees were reported to have an overall higher reaction to the mites than the Italian bees. This more intense grooming behavior displayed by the Africanized bees might contribute to this subspecies having a higher resistance than Italian bees.
Experiment 2: Group Level Grooming Behavior
Experiment 2 evaluated bees’ behavior at the group level, using 13 Italian bee colonies and 13 Africanized bee colonies. In this experiment, 20 mites were added into a small sample of 30 bees that were placed in a petri dish. In order to assess the grooming behavior, the researchers used an indirect method by counting the number of fallen mites collected on the hive floor. It was seen that both subgroups of bees were able to remove approximately 60% of the mites, with no significant difference observed between the two subspecies.
Experiment 3: Colony Level Grooming Behavior
Experiment 3 looked at the grooming behavior at the colony level, using 10 colonies of each bee species. Unlike experiment 1 and 2, which were under laboratory conditions, experiment 3 took place in under natural conditions.The result for experiment 3 showed that the Africanized bee colonies had a larger number of mites with mutilated legs than the Italian bee colonies. The analysis of the data concluded that there was no correlation between experiment 2, which assessed the number of mites that were dislodged, and experiment 3, the percentage of injured mites collected.
It was proposed that many of the mites that were dislodged and fell to the floor were not injured, and thus could potentially walk up the hive and make direct contact with the bees. This can be supported by an observation made in the laboratory, where Varroa mites were able to walk vertically and reach the nest with seemingly little struggle. On the other hand, the injured bees were predicted to be less successful at doing this, because even if they did succeed in attaching to another bee, they would most likely be easily dislodged and die from the injuries.
Why should you care about honey bees’ resistance to Varroa mites?
This disease poses as a tremendous environmental, economic, and social threat. It is an even larger concern considering mites are developing resistance against the various synthetic acaricides being used to treat mite infestations, making it harder to control the mites.
The punctures that the mites create on the bees from sucking hemolymph could lead to secondary infections and subsequent declines in honey bee populations. Honey bees also greatly impact the floral biodiversity; therefore with the decline of honey bees, we will also experience a decline in floral diversity.
European honey bees pollinate approximately 80% of the insect pollinated foods that humans consume. With a third of the food we consume being insect pollinated, this is a huge threat to the agricultural industry, because there would most likely be a decrease in crop yields as well as a decline the crop quality.
Not only with this disease impact the economy and environment, it will also have an impact on society. There are many that depend on apiculture for income. Due to the decline of honey bee populations and the growing resistance of mites to acaricides, beekeepers will have a difficult time producing and selling various bee products. It will also negatively impact the food industry at both the corporate and local levels, thus effecting the daily lives of billions of individuals.
Additionally, if varroacides are used, the bee products might contain varroacidal residues, which could result in a decline for the demand these products. These products are sold in various industries, such as the food and beauty industries.
IS THERE HOPE?!
This research provided additional knowledge about resistance mechanisms in honey bees, and can aid in the search for bees resistant to Varroa mites. It appears that Africanized bees are more efficient at grooming and therefore more resistant to mites than European strains. Future attempts of cross-breeding mite resistant strains of bees should take into consideration that European strains are not ideal for reproducing efforts. Hopefully, a hybrid subspecies of honey bees will be created to combat these issues resulting from Varroa destructor.
The article can be found here.