4.7.3. Nectar collection
Foraging behaviour of honey bees is closely linked to colony needs and nectar production (volume and quality/ sugar concentration). Plants not only display particular rhythms of nectar secretion, but also nectar reabsorption (Nicolson et al., 2007). In general nectar secretion is influenced by a variety of environmental factors e.g. humidity and temperature (Pacini and Nepi, 2007). Knowledge of these factors is essential for a proper understanding of the relationship between plants and honey bees.
Nectar secretion varies between plants, time of day and is even influenced by age of flowers (Pacini and Nepi, 2007). Nectar volume varies enormously between species; from less than a microlitre to thousands of microlitres (Pacini et al., 2003). Similarly there is an extreme variation in nectar sugar concentration of plants (between and within species); from 7-70%. An example for between species variation is the low sugar concentration of less than 10% in Aloe castanea (Aasphodelaceae) (Nicolson and Nepi, 2005, Fig 34) and an average of 66.5% in Carum carvi (Apiaceae) (Langenberger and Davis, 2002). It is generally known that the plants producing more concentrated nectar are the ones being visited and pollinated by insects, including bees (Pyke and Waser, 1981; Baker and Baker, 1982).
The method used for nectar collection will be determined by the intended
use as well as by flower size, volume and concentration of nectar. Calibrated
micropipettes/ micro-capillary tubes (1-20µl) (Fig. 35) are commonly used to
extract nectar with volumes >0.5µl and concentrations lower than 70%.
Calibrated syringes (Hamilton
microsyringes) and filtered paper wicks are other methods for nectar collection
and Inouye, 1993) for more detailed descriptions of the various techniques). We
here described those most commonly used for collection from honey bees (section
220.127.116.11.) and from flowers (see section 18.104.22.168.). Refractometers (Fig. 35) are
normally used for the measurement of sugar concentration (% weight/ weight). In
the case of very small amounts of nectar alternative methods are required
(Kearns and Inoye, 1993; Dafni et al.,
2005). There are various techniques for measurements of nectar volume and
concentration is discussed by Dafni (1992) and Kearns and Inoye (1993) and the
more common methods used in honey bee research will be discussed here.
Fig. 34. Nectar (arrows) in base of Aloe castanea flowers. Photo: M Nepi.
Fig. 35. Calibrated micropipettes/ micro-capillary tubes and refractometers used for measurements of nectar concentration and volume. Photo: A Switala.