Migration of bees
Tropical bees migrate in search of forage. It is a common strategy employed by tropical bees to help them to survive the dearth period or to move away from adverse weather conditions. For temperate bees the migration strategy is almost never used as it is likely to be fatal to the colony. Tropical bees, African and Africanised bees and all Asian species of Apis may utilise either the hoarding or the migrating strategy to survive dearth periods and may show high levels of seasonal migration. It is not clear why colonies migrate in some years and not in others.
Migration should not be confused with absconding. Migration is planned and is largely driven by varying patterns in resource scarcity and abundance. The term absconding is used when referring to an unplanned move in response to a shock e.g. pest attack.
Migration appears to occur due to scarcity of nectar, pollen or water and occurs primarily during the dearth periods found in tropical conditions. Migration tends to be seasonal and differs from disturbance-induced absconding in that colonies start preparing to move up to one month in advance of actually leaving. Firstly, the queen will reduce her egg laying rate so that very few larvae will be reared during this period. Those few eggs that are laid will be eaten by the workers. Most of the stored pollen and honey is also consumed by the bees. As soon as the last young brood has emerged the colony will leave. By doing this they ensure they have a good number of relatively young bees and the consumption of pollen ensures their fat bodies will be full of stored protein, ready to start rearing new workers in the new place.
Apis dorsata and Apis laboriosa are the bees that have the best recorded migration behaviour although a great deal is still unknown about it. In this instance there is a planned movement of all the colonies in a given area to a predetermined alternative migration site. According to Oldroyd and Wongsiri (2006) Asian honey bees do not usually store great amounts of honey. Their survival strategy is to put their effort into developing reproductive swarms rather than storing surplus food stuff that may be taken at any time by predators. This leaves the bees vulnerable to starvation if there is a prolonged shortage of nectar or pollen. Consequently, the response to diminishing resources is to move to an area where food is more abundant. In most cases open nesting bee species will migrate twice each year.
In Africa, Apis mellifera's migration patterns are largely determined by altitude and rainfall patterns.
Broadly, a common seasonal pattern is for colonies to arrive at the end of the wet season. Then combs are built, there is a period of rapid colony growth and the strongest colonies produce reproductive swarms. By the end of the dry season, pollen availability is reduced, brood rearing diminishes and the adult population declines. Combs may be attacked by wax moths and predators while parasitic mite populations will be at the maximum. At this point colonies will move from the site and start a long migration to a new locality.
It is not clear how far migrating colonies can travel but it has been shown to be over 100km. As it travels the colony will settle in trees for rest periods. During this time the workers will forage for stores although a quiescent colony will have minimal energy needs. The colony will only move again once it has gathered sufficient stores for the next part of the journey. The movement is preceded by waggle dances on the surface of the colony that indicate the direction of movement. However, it is not known whether parts of the dance refer to the whole journey of just the part to be undertaken on that day. Under the right circumstance, a colony can move up 20kms each day. Nor is it understood how the bees find their intended new nest site since none of the workers who are travelling will have done the journey before and it is unlikely that the queen passes on this information. The probability is that the bees follow an environmentally beneficial trajectory determined by sufficient forage and optimum temperatures.
Once they near the new nesting site it is possible that the remains of last years combs offer some scent indication that the migration is complete. Despite this, Apis dorsata colonies are always started from scratch even if they are quite close the last season comb although Apis florea may take wax from another comb and reuse it in a new site. Apis florea migrations track abundant forage and other suitable physical conditions such as shade in summer and warmth in winter. Apis mellifera move away from some locations to avoid a heavy rainy season or to avoid a long dry season.
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- Author Bees for Development
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- Published Date October 2016
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