8.5. Limited food resources
The amount of nectar and pollen provided by a crop in an enclosure is generally insufficient for long-term maintenance of honey bee colonies (Free, 1993). Moreover, adverse effects may express in a honey bee colony restricted to a greenhouse monofloral pollen source (Herbert et al., 1970); pollination activity is curtailed, and colonies may deteriorate in the space of a few weeks and eventually collapse (Kalev et al., 2002). There are different solutions for these nutritional deficits (Dag, 2008). One is to allow the honey bees to forage in the open and in the enclosures on alternating days (Butler and Haigh, 1956). Another is to use double entrance hives with one entrance leading into the enclosure and the other leading outside the enclosure to allow bees to forage and feed on the surrounding flora (Free, 1993). A third possibility is to artificially feed the colony (section 7.2.). This was shown to be efficient in a sweet pepper greenhouse (Kalev et al., 2002).