**Why Enhancement of Floral Resources in Agro-Ecosystems Benefit Honeybees and Beekeepers?**

Decourtye Axel1, Alaux Cédric1, Odoux Jean-François2, Henry Mickaël1, Vaissière Bernard E.1 and Le Conte Yves1 *1UMT PrADE, INRA – UMR Abeilles et environnement, Site AgroParc, AVIGNON Cedex 9 2INRA, Unité expérimentale d'entomologie Le Magneraud, Surgères France* 

#### **1. Introduction**

370 Ecosystems Biodiversity

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Honeybee (*Apis mellifera* L.) populations have experienced serious losses in Europe and North America (Neumann & Carreck, 2010; Oldroyd, 2007). These losses highlights the potential risks for our natural and agricultural landscapes through lack of pollination, and the repercussions these would have for human activities and nutrition (Aizen & Harder, 2009; Gallai et al., 2009; Klein et al., 2007; Rader et al., 2009; Ollerton et al., 2011). There is a great deal of concerns about the decline of honeybees across the world and what has been termed colony collapse disorder in the USA. Honeybee health is influenced by biotic factors such as availability of resources, competitors, pathogens, parasites, and predators, and abiotic factors such as climate and pollutants. Colony losses are likely due to multiple factors (Oldroyd, 2007), and most research to date has focused on epidemiological studies affecting honeybee health (Cox-Foster et al., 2007; Johnson et al., 2009; Le Conte et al., 2010), and on the negative effects of agricultural pesticides (Decourtye & Devillers, 2010; Desneux et al., 2007; Johnson et al., 2010; Kevan, 1977). Although the putative causes of this decline are still being investigated, it has long been recognized that a lack of food, and particularly a dearth of pollen, within intensively farmed agricultural landscapes has contributed to the loss of colonies (Mattila & Otis, 2006; Maurizio, 1950; Naug, 2009). Beekeepers have frequently cited starvation and poor foraging conditions as the principal causes of the recent bee losses (Allier et al., 2010; vanEngelsdorp et al., 2007). Naug (2009) suggested that nutritional stress due to habitat loss has played an important role in honeybee colony collapse, and thereby stressed the usefulness of protecting and enhancing the availability of flower resources by using rules and policies for efficient management of agricultural farmlands. Decourtye et al. (2010) reviewed potential approaches to provide and maintain diverse floral resources in a landscape, giving particular consideration to herbaceous plants, to sustain bee populations, and support honeybee health and beekeeping. These approaches include the cultivation and maintenance of large strips (6-12 m in width) of native or non native melliferous plants maintained between crop fields, fallow areas, field margins, and conservation buffer strips. To set up an favourable landscape for honeybees,

Why Enhancement of Floral Resources in Agro-Ecosystems Benefit Honeybees and Beekeepers? 373

will be quickly abandoned to the expense of a more profitable type of flower, if the food

Under experimental conditions, honeybees prefer nectar containing saccharose (Waller, 1972) and are able to assess differences in sugar concentrations in the order of 5% (Jamieson & Austin, 1956). They prefer concentrated nectars that range in sugar content between 15% to 50% (Jamieson & Austin, 1956; Sigurdson, 1981a, 1981b; Waddington & Kirchner, 1992; Waller, 1972), but they avoid nectars which are too viscous and thus make their collection difficult. Nectar accessibility also influences floral choice by nectar foragers as nectar has to be within reach given their proboscis length. Honeybees have an average tongue length of 6 mm and can often gather little nectar from flowers with deep corolla such as those of red

For pollen, the protein content does not seem to be detected by the foragers (Maurizio, 1954). Pollens which have the highest protein content are not necessarily those which are the most sought after or the most appetizing. Thus, the fact that a pollen is collected by honeybee foragers does not provide information about its nutritive value. Indeed, pollen from female kiwifruit vines is readily collected by honeybees while its nutritive value is very low (Jay & Jay, 1993). It is not easy to establish a link between the protein content and the nutritive value of a given pollen, because pollen grains contain many other elements besides proteins, and also because their proteins are more or less digestible. Digestibility essentially depends on the thickness and ornementation of the pollen wall. Moreover, a lack of rich pollen in the environment can result result in workers collecting pollen completely deficient of any nutritive value (Louveaux, 1959; Maurizio, 1954; Wille et al., 1985). Also accessibility is an important factor for pollen collection since honeybees cannot harvest large pollen grains which are echinate with long spines such as those of cotton and several other Malvaceae (Vaissière & Vinson, 1994). And the overall appetence of pollen is also influenced by the presence or absence of phago-stimulants or repulsive

Honeybees respond to groups of stimuli and rewards that are characteristic of each floral type. Both pollen and nectar gathering by a forager are made more efficient by the fact that the bee learns the handling of a floral type that it finds profitable and then remains loyal to this type for as long as it is available. Indeed, one can observe specialized foraging positions on most flower types (Robinson, 1989) and a strong area loyalty. Indeed, the individual

Yet one must not confuse the foraging area of an individual forager with that of the colony as a whole. Within the colony, different foraging groups target different sites. In an environment where nectar is abundant, the foraging area of a colony is on average ca. 2 km radius around the hive. And 90% of bees dancing gather pollen in a radius of less than 5 km from the hive (Beekman & Ratnieks, 2000; Steffan-Dewenter & Kuhn, 2003), that is a survey area of about 80 km2. When needed, a colony can expand considerably its foraging area. Beekman & Ratnieks (2000) noted that 50% of the foraging bees foraged at > 6 km, and 10% at > 9 km. Based on these results, the flowering areas targeted at the honeybees could be safely created and protected within a 1 km radius around the hive. But in intensively farmed landscapes that are flower-poor, the foraging activity can take place

foraging area of honeybee foragers is limited to an area of ca. 100 m2 (Singh, 1950).

clover (*Trifolium pratense* L.) and several other Fabaceae (Jablonski, 2001).

supply in the environment allows it (Winston, 1987).

compounds (Pernal & Currie, 2000).

**2.4 Flower loyalty and foraging areas** 

it is essential to understand the relationship between this insect and the melliferous or polleniferous flora in their environment. This is the main goal of this review and we also describe some available data on the effects of diet on some biological functions of bees so as to build a scientific background for agro-environmental measures protecting floral resources and benefiting the beekeeping industry.
