SMR - Suppression of Mite Reproduction
At Ohio Queen Breeders, we have been working with several lines that are showing signs of resistance to Varroa mites. While this is a promising step, it takes time to incorporate the mite resistant genes into a productive and economically valuable stock. However, we are one step closer to providing a economically viable honey bee that can survive with Varroa Mites.
SMR â€“ The Next Step towards Surviving with Varroa Mites
Recently, there has been a large research interest in the area of Varroa Mites. Researchers are involved in determining how different geographic populations of mites are related genetically, how mites reproduce, what influences their population growth and how beekeepers can control Varroa Mites, or more realistically, survive in their presence. During the past few years, there has been exciting research in the area of influencing mite reproduction to ultimately control the population growth of Varroa Mites. Drs. Harbo and Harris of the USDA laboratory in Baton Rouge, Louisiana, have identified a promising trait, which they refer to as Suppression of Mite Reproduction (SMR). With the recent release of queens that posses a compliment of genes to influence mite reproduction, beekeepers are faced with the task of introducing the genes into a population and selecting the most economically productive and mite resistant colonies.
As the title implies, SMR genes offer the next step towards surviving with Varroa Mites. As beekeepers, we have used chemical applications in an attempt to reduce mite populations in our colonies, or in the minds of some, eradicate them completely. Many years later, I think most of us realize that eradication is unrealistic and chemical applications have a limited life span with regard to their level of effectiveness. SMR offers beekeepers an alternative to chemical applications, while this does not imply that chemical applications are entirely unnecessary down the road; however, it does offer the hope that we may reduce our dependency on chemical applications. How does SMR work
â€”or better yetâ€”what is SMR? As stated earlier, SMR is an acronym for Suppression of Mite Reproduction, which is a trait that suppresses the ability of mites to reproduce inside a worker cell. When the queen lays an egg in a cell, it develops for approximately three days until it hatches into a larva. After approximately five days as a larva, the attending nurse bees will seal or cap the cell containing the developing larva so that larva can continue its development into a pupa and finally emerge as an adult. During the larval stage, shortly before the attending nurse bees seal or cap the cell, a female Varroa Mite will enter the cell and burry herself at the bottom of the cell and wait. The female mite is waiting for the nurse bees to seal the cell, so that she can begin her reproductive cycle in the safety of the sealed cell. Shortly after the cell is sealed, the female mite migrates from the bottom of the cell up onto the developing worker. During the miteâ€™s reproductive cycle in the cell, she relies on the developing worker for food by feeding on the â€œbloodâ€ of the developing bee. Under most circumstances the first offspring that the female mite will produce is a male, and subsequent offspring are females. At the end of their development, the original female mite and the new female mites will emerge with the bee and move on to repeat the cycle.
The SMR trait is effective for controlling the population growth rate of Varroa Mite because it disrupts the reproductive cycle, thus reducing the number of viable offspring produced per female mite. There is an interaction that takes place in the cell that reduces the number of offspring each female mite is able to produce. Some female mites may not produce any viable offspring and others may begin producing offspring too late in the beeâ€™s development. If the young mites do not complete their development by the time the new worker emerges, they die when the worker leaves the cell. However, the original female mite does not appear to be harmed, as she can leave the cell when the worker emerges and go off in search of another cell to invade.
It is one thing to have a colony that expresses the ability to control Varroa Mite levels in a research setting with a bee that has been selected primarily for reducing mite levels; however, it is another situation entirely to control mite levels in a production setting. Drs. Harbo and Harris addressed this issue by evaluating open mated queens from their lines to determine how effective the SMR trait is in a production environment. Good news, their research has shown that SMR is a heritable trait, which means it has a genetic component that can be passed from mother to daughter so that by rearing queens from a breeder queen that has been selected for the SMR trait, open mated daughter queens will also express the SMR trait. Given that some genes come from the queen and some come from the drone, the open mated queens express, on average, a lower level of the SMR trait than the selected breeder queens; however, it appears that the open mated queens retain a significant level of the SMR trait to be economically viable.
What does this mean for the future and how do we get these genes distributed? Here at Ohio Queen Breeders we have been fortunate enough to work with Drs. Harbo and Harris on their research and they have supplied us with the SMR genes to incorporate into our lines. The next step, so to speak, involves incorporating SMR genes into economically productive stock, while retaining the desirable characteristics of the original stock. It is important to remember that one specific trait does not make for a productive bee, in other words, too much emphasis on a good thing can be bad. For this reason, we have made many crosses with the original stock supplied by Drs. Harbo and Harris with our Aurea and Karnica lines. We are now left with the task of evaluating these new crosses to select the breeder queens which have retained a high level of their economically desirable traits that we have selected for over the years and those which also express a significant level of the SMR trait. This is not an easy task; however, with the use of instrumental insemination and large colony numbers, we are able to select queens that present the best of both worlds, one that is gentle and productive, as well as one that can control Varroa Mite populations.
This is a time consuming effort, but one that we feel is well worth our while. Drs. Harbo and Harris have taken the initiative in providing the preliminary research and have indicated that by allowing bees a â€œnaturalâ€ defense against Varroa Mites, with a reduced or eliminated use of chemical applications, we may also see the development of additional resistance mechanisms. We have not allowed our honey bees to develop their own natural defenses to the Varroa Mite, instead, beekeepers have provided protection from the mites in the form of chemical applications. In order for honey bees to develop resistance against the Varroa Mites, honey bees must have some exposure to the mites. However, with our current use