4.7.3.2. Nectar collection from flowers

It is necessary to prevent insect visitation to flowers before measuring their nectar production/ secretion since consumption by insects will reduce the volume available. Nectar is collected from flowers in disposable micro capillary/ hematocrit tubes (length 75 mm, capacity 75 µl) through capillary action (e.g. Human and Nicolson, 2008; see references therein) (Fig. 36). It is standard procedure to measure both volume and concentration of nectar (the minimal information required) in any nectar/ foraging studies since this information is crucial.

  1. Cover flowers to be examined with gauze (2mm mesh size) to exclude visitation of any pollinators.
  2. Remove flower petals gently to reveal nectar at the base of the flowers.
  3. Withdraw/ collect the nectar from the flower in disposable micro-capillary tubes (length 75 mm, capacity 75 µl) by capillary attraction.
  4. Determine volumes of nectar from column length in the micro-capillary tubes (75 mm is equivalent to 75 µl).
  5. Release the nectar onto the prismatic surface of a pocket refractometer.
  6. Measure the nectar concentration as percent (w/w) sucrose equivalents.
  7. Depending on the purpose of nectar collection, samples should either be used immediately in the field or transported to the lab on either dry ice or on filter paper (Whatman no 1) (Dafni et al., 2005) after which it should be stored in 15 ml centrifuge tubes at -20˚C until ready for composition or residue analysis.

Pros

-  This is a cheap and easy way of nectar collection.

Cons

- These methods are very tedious because of the small quantities of nectar that may be available per flower, and thus several hundred flowers may need to be extracted to collect the required quantities for analysis.

Fig. 36. Collection of nectar from (Aloe zebrina) through capillary action into micro-capillary tubes. The clear nectar is visible in the lower part of the tube. Photo: A Switala.

figure36

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