to in a bee tree (Mitchell 2016). Our modern beekeeping practices – launched in 1852 with the invention of the movable frame hive, by Lorenzo L. Langstroth – have created new challenges for honey bee colonies, which are adapted for living without human management (interference). For the remainder of this chapter, we will explore the lifestyle features that help wild colonies of honey bees thrive despite their pests, parasites, and pathogens. We will also draw lessons that beekeepers and bee doctors can employ to help promote the health of the managed colonies living in apiaries.
Part 1: The Environment of a Wild Colony
Cavity Size
A good place to begin our exploration of wild honey bee health is understanding the home of a honey bee colony found in nature (Figure 1.4). Wild honey bees predominately make their homes inside the cavities of hollow trees, though any cavity of appropriate volume and specific characteristics will do, and this includes manmade structures, rock crevices, and other spaces. Wild colonies choose small cavities, with an average volume of just 45 l (range 30–60 l: Seeley and Morse 1976; Seeley 1977). When honey bee colonies choose their nesting sites, they seek cavities of this size, which is substantially smaller than the typical Langstroth hive in an apiary, with a volume of 120–160 l (Root and Root 1908; Loftus et al. 2016).
Nest cavity size has a major impact on honey bee health through its effect on mite population dynamics. A brief review of the Varroa life cycle will help us understand the role of nest cavity size on a colony's mite population. Varroa mites have two different life phases: the phoretic phase in which adult mites feed on the “fat bodies” of honey bees and the reproductive phase in which mites reproduce in the cells of sealed brood of workers and drones (Rosenkranz et al. 2010). Only adult female mites are phoretic; both the tiny males and the nymphal stage females remain within the capped brood cells. Honey bee larvae are essential for the mite because it has no free‐living stage off the host – the mite is entirely dependent on honey bee brood for its own propagation. Honey bee colonies living in large hives hold more brood than those living in natural nest cavities, so colonies in large hives are especially favorable for mite reproduction.
Table 1.1 Characteristics of wild honey bees (Apis mellifera) that differ from managed honey bees and their impact on bee health.
| Characteristic | Wild colonies | Reference | Managed colonies | Reference |
|---|---|---|---|---|
| Colony lifespan | Long‐lived 5–6 yr once established | Seeley (2017b) | Short‐lived; 2–3 yr without miticides | Rosenkranz et al. (2010) |
| Annual survival | High survivorship 84% (established) 20% (founder) | Seeley (2017b) | Low survivorship (0–50%) | Ellis et al. (2010) |
| Cavity size of home | Small cavity; 45 l (30–60 l) | Seeley and Morse (1976) | Large cavity; 120–160 l | Loftus et al. (2016) |
| Swarming frequency | 87% annual queen turnover in established colonies | Seeley (2017b) | Swarming suppressed, so low queen turnover | Oliver (2015) |
| Propolis barrier | Complete barrier “propolis envelope” | Seeley and Morse (1976) | Incomplete barrier smooth hive walls | Hodges et al. (2018) |
| Colony spacing | Colonies far apart (~1 km) | Seeley and Smith (2015) Radcliffe and Seeley (2018) | Colonies close together (~1 km) | Root and Root (1908) |
| Virulence level | vertical transmission of mite‐vectored pathogens, via swarming | Seeley and Smith (2015) | Virulence favored by horizontal transmission of mite‐vectored pathogens, via drifting/robbing | Seeley and Smith (2015) |
| Nest insulation | Thick‐walled (20 cm/8‐in.) well insulated tree cavity | Seeley and Morse (1976) | Thin‐walled (2.5 cm/1‐in.) poorly insulated Langstroth | Root and Root (1908) |
| Immune Function | Strong social immunity, Immune genes downregulated | Simone et al. (2009) | Weak social immunity, Immune genes upregulated | Borba et al. (2015) |
All honey bee populations that have survived for more than a decade without miticide treatments share a common feature: their colonies are small (Locke 2016). Small colony size relates directly to the dynamics of brood development and swarming. Having relatively few brood has two significant impacts on mite reproduction. First, since Varroa mites only reproduce within the cells of sealed (pupal stage) brood, the reproduction of these mites is hampered by the relatively small brood nests of wild colonies. Second, a small nest cavity size shortens the time before the sealed brood fills a colony's brood nest, and this brood nest congestion is one of the primary cues for swarms and afterswarms (Winston 1980). When colonies living in large hives (two deep hive bodies plus two honey supers) were compared to colonies living in small hives (just one deep hive body, to mimic the nest cavity size in nature), it was found that the small‐hive colonies had reduced mite loads and improved colony survival, as a result of more frequent swarming and lowered Varroa infestations (Loftus et al. 2016).
Wall Thickness and Thermoregulation
Seeley and Morse (1976) reported that the average wall thickness of natural nest cavities is approximately 20 cm (~8 in.). The wall thickness of a standard Langstroth hive is just 1.9 cm (0.75 in.), hence some 10 times thinner than the nest cavity wall of a bee tree. The reduced wall thickness in Langstroth hives creates a large reduction in nest insulation, possibly resulting in adverse effects on colony energetics. Large temperature fluctuations inside a hive exacerbate colony stress by increasing the demands on colony nutrition and hydration (more nectar and water foraging trips), by impairing a colony's ability to maintain thermal homeostasis (more fanning and “bearding” when it is hot, and more metabolic heat production when it is cold), and by hastening entry into a winter cluster – all of which increase the physiological demands on the colony (Mitchell 2016).
Coombs et al. (2010) found that natural tree cavities buffered environmental temperatures such that tree cavities were cooler than ambient during the day and warmer than ambient during the night. During the day, the tree diameter at breast height was the most important variable determining cavity temperature. At night, diameter and tree health were important with large living trees offering the most stable thermal environment. We compared the ambient temperatures inside two tall, man‐made cavities; one was inside a rectangular wooden box (built of 1.9 cm thick pine boards, as used for Langstroth hives) and the other inside a living sugar maple
