Apis sets record red clover seed: a climatic aberration | Apis establece un récord de semilla de trébol rojo: una aberración climática
2015
Stephen, William P
Western Oregon, USA is one of the better red clover seed-producing areas in the world, having an average yield of 676 kg/ha; individual growers report yields of over 1000 kg/ha. Bloom normally lasts from late June through to the third week in August in well-managed fields. From late June through the third week of July, Apis mellifera is the predominant pollinator. By early August, Apis is usually displaced by very large populations of workers and males of several species of Bombus, especially B. vosnesenskii Radoszkowski. However, 2009 was unique in that the last 16 days in July the max–mean temperature was 35.4 °C, with a max of 41.0 °C. Apis responded by changing its pollen collection in red clover from ±1% in previous years, to 41.5% during the 16 days of extreme heat, resulting in a yield of 1045 kg/ha in the first 30 days of red clover bloom. It is postulated that the extreme heat in that year reduced the turgidity of the clover floret and that the accompanying low humidity increased the sugar content of the nectar, making the floret more accessible and attractive. Reference is made to the parallels between high temperatures and Apis pollination of alfalfa in California, and our observations on red clover in Oregon.
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