INSECTS AND THEIR POLLEN LOADS AT A HYBRID HERACLEUM SITE

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Abstract
SUMMARY: Insects were caught at a site where Heracleum sphondylium and Heracleum mantegazzianum occur together, along with a few hybrid individuals. Fifty‐nine species of insect were caught on flowers of H. sphondylium and 48 from H. mantegazzianum. Only 23 species of insect were common to both. Pollen grains taken from individual insects were identified on the basis of size. Insects caught on H. sphondylium carried H. sphondylium pollen almost exclusively and those from H. mantegazzianum carried mainly H. mantegazzianum pollen. Very few individual insects carried both types of pollen. It is concluded that the selective foraging behaviour of insects is a main barrier to gene flow between the two species of Heracleum in Britain.