Effects of Brood Pheromone Modulated Brood Rearing Behaviors on Honey Bee (Apis mellifera L.) Colony Growth
Ramesh R. Sagili
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Tanya Pankiw
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T. Pankiw Department of Entomology, Texas A&M University, College Station
,
TX 77843-2475, USA
1
) Department of Horticulture, Oregon State University
, Corvallis,
OR 97331-7304, USA
A hallmark of eusociality is cooperative brood care. In most social insect systems brood rearing labor is divided between individuals working in the nest tending the queen and larvae, and foragers collecting food outside the nest. To place brood rearing division of labor within an evolutionary context, it is necessary to understand relationships between individuals in the nest engaged in brood care and colony growth in the honey bee. Here we examined responses of the queen, queenworker interactions, and nursing behaviors to an increase in the brood rearing stimulus environment using brood pheromone. Colony pairs were derived from a single source and were headed by open-mated sister queens, for a total of four colony pairs. One colony of a pair was treated with 336 g of brood pheromone, and the other a blank control. Queens in the brood pheromone treated colonies laid significantly more eggs, were fed longer, and were less idle compared to controls. Workers spent significantly more time cleaning cells in pheromone treatments. Increasing the brood rearing stimulus environment with the addition of brood pheromone significantly increased the tempo of brood rearing behaviors by bees working in the nest resulting in a significantly greater amount of brood reared.
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Social insect brood rearing systems present a unique set of evolutionary models
because workers that rear young do not generally reproduce. Additionally, brood
rearing labor is divided among the existing workforce, such that some individuals
work outside the nest foraging to meet the nutritional needs of the colony, and others
work inside the nest directly caring for young and maintaining the nest. Much like
individual whole organisms, honey bee colonies undergo a process of growth,
development, and reproduction. For social insect colonies, colony-level growth and
reproduction are the principal sources of fitness. As such, much of individual worker
and colony behaviors are ultimately related to colony growth leading to colony level
reproduction. A honey bee colony has only one queen and the majority of her eggs
develop into functionally sterile workers. Colony growth is achieved through
increased queen-egg laying rate and intensity of brood rearing labor. Houston et al.
(1988) presented a model investigating the amount of effort individual workers
should devote to foraging to maximize colony fitness. The model predicts that
individual workers and colonies should respond to an increased demand for
resources by working harder. Houston et al. (1988) also predicted that manipulating
the amount of brood should increase the brood rearing efforts of colonies.
The labor of honey bee brood rearing may be viewed as divided among bees that
forage for food outside the nest and those that work in the nest. Foraging effort
associated with changes in colony demand for food resources has been investigated
in depth. Increasing the amount of larvae results in increases in the number of pollen
foragers and pollen load weights returned (Al-Tikrity et al. 1972; Free 1979; Eckert
et al. 1994). Pollen foraging activity level decreases in response to the addition of
stored pollen and increases in response to the removal of stored pollen (Free 1967;
Danka et al. 1987; Camazine 1993; Dreller and Tarpy 2000). Increasing the amount
of stored pollen in colonies concurrently increases brood rearing and decreases
pollen foraging (Fewell and Winston 1992). Colonies also show corresponding
responses to the fatty acid esters extractable from the surface of larvae, called brood
pheromone, apparently estimating amount of larvae from amount of brood
pheromone. Adding brood pheromone to colonies increases number of pollen
foragers by up to 150%, significantly increases pollen load weight returned by
individual pollen foragers, significantly increases the number of pollen grains
extractable from the bodies of non-pollen foragers, and brood pheromone
significantly increases the number of pollen forager trips per unit time (Pankiw et
al. 1998; Pankiw and Page 2001; Pankiw 2004a; Pankiw 2004b; Pankiw et al. 2004;
Pankiw 2007). Addition of brood pheromone to colonies increases amount of
incoming pollen through a number of behavioral mechanisms, while colony rate of
growth concurrently increases over a 4 week period measured as amount of brood
area reared (Pankiw et al. 2004; Pankiw et al. 2008). This strongly suggested that
along with increased pollen foraging effort, there was increased brood rearing effort
by workers in the nest.
Change in brood rearing effort by bees working in the nest with change in amount
of brood has received far less attention than that of foraging effort. In the nest,
workers regulate queen egg laying rate through the quantity and quality of food
wo (...truncated)