Ames • Pollination of Orchids through Pseudocopulation 



39 



Oakes Ames 



Pollination of Orchids through Pseudocopulation 



Reprinted with the permission of the Botan- 

 ical Museum of Harvard University from 

 Leaflet V{1), 1937. 



Within comparatively recent years, 

 biologists have been made aware of 

 a peculiar relationship between certain 

 orchids and the hymenopterous insects 

 which pollinate them. A wholly unex- 

 pected trend in biological behavior has 

 been revealed and it has been proved 

 that the motives leading to pollination 

 are much more complex than formerly 

 had been supposed. It is now known 

 that certain insects are attracted by or- 

 chids for a purpose wholly apart from 

 the search for food and that there are 

 aspects of pollination presenting new 

 and practically unexplored fields for 

 research. 



Scotia ciliata is a member of the 

 Scoliidae, a family of burrowing 

 hymenoptera, whose burrows are made 

 in sandbanks exposed to the sun. The 

 males emerge from the burrows about 

 a month earlier than the females, usu- 

 ally in March. The females lead an 

 almost subterranean existence and leave 

 the burrows chiefly in search of food. 

 While waiting for the females to make 

 their appearance (mating takes place 

 only in the open air) , the males may be 

 seen exploring in sinuous flight the 

 ramparts of Algerian fortifications and 



exposed railroad embankments. And it 

 is just such places as these for which the 

 plants of Ophrys speculum exhibit a 

 predilection. The flowering season of 

 the orchid coincides with the appear- 

 ance of the males of Scolia ciliata and 

 during the long wait for the coming of 

 the females, the male insects visit the 

 orchid flowers, seeming to find in them 

 a compelling attraction. There were 

 questions here demanding deep 

 thought. In the first place, why the 

 indifference of the females? And in 

 the second place, what attributes pecu- 

 liar to Ophrys speculum were of a na- 

 ture to attract one sex and not the 

 other of an insect seeking food? 



Pouyanne established beyond any 

 doubt that the flowers of Ophrys specu- 

 lum are not visited for nectar or edible 

 tissues, because when the males of 

 Scolia ciliata enter a flower the suc- 

 torial apparatus is not used and the 

 proboscis of the insect does not come 

 in sustained contact with any part of 

 the labellum of the orchid. The insect 

 assumes a position lengthwise of the 

 labellum with the head directed toward 

 the column, just beneath the rostellum, 

 and inserts the rip of the abdomen 



