SWEET-CLOVER SEED. 



21 



Table VII. — Influence of the weather at blossoming time upon the yield of sweet -clover 

 seed, at Ames, Iowa, in 1915. 



Date, 

 1915. 



Weather conditions. 



Insect visitors. 



Number 



of 

 flowers 



that 

 opened. 



Pods 

 formed. 



Percent- 

 age of 

 flowers 

 that 



matured. 



Aug. 16 

 Aug. 17 

 Aug. 18 

 Aug. 19 

 Aug. 20 

 Aug. 21 

 Aug. 22 

 Aug. 23 

 Aug. 24 



Cloudy and showery 



Rain all day 



Cloudy most of the day. . . 



Clear and cool 



Mostly clear and warm . . . 



Clear and warm 



Partly cloudy and warm. 



do 



Cloudy till mid-afternoon. 



Very few. . 



None 



Very few. . 

 Numerous. 



....do 



....do 



|....do 



Tew 



102 

 69 

 60 

 94 

 61 

 81 



18 

 4 

 20 

 53 

 38 

 44 



100 



12 



17.6 

 5.7 

 33.3 

 56.3 

 62.2 

 54.3 

 55.2 

 32.4 



The data given in Table VII show that the percentage of effective 

 pollination is much higher in clear weather, when insects are active, 

 than in cloudy or rainy weather, when but few insects visit the 

 flowers. 



INSECT POLLINATORS OF SWEET CLOVER. 



On account of the ease with which the heavy flow of nectar of 

 sweet-clover flowers may be obtained many insects visit the flowers, 

 thereby pollinating them. While the useful insect visitors of flowers 

 of red clover are limited to a few species of Hymenoptera, those 

 pollinating sweet-clover blossoms are many and belong to such 

 orders as Coleoptera, Lepidoptera, and Diptera, as well as to the 

 Hymenoptera. However, in the United States the honeybee is the 

 most important pollinator of sweet clover. In many parts of the 

 country the different species of Halictus, commonly known as sweat 

 bees, rank next in importance. The margined soldier beetles 

 (CJiauliognaihus mar ginatus Fabr.) were very active pollinators at 

 Arlington, Va,, in the latter part of June and first part of July, 1916, 

 but the woolly bear (Diacrisia virginica Fabr.) was the only night- 

 flying insect found working on sweet clover at Arlington. 



Insects belonging to the genera Halictus, Syritta, and Paragus 

 were very active pollinators at Ames, Iowa, in 1916, and ranked 

 next in importance to the honeybee. In fact, the results obtained 

 in the cage where the plants were protected from visitation by 

 insects that could not pass through a screen having 14 meshes to 

 the linear inch showed that these small insects were able under 

 the conditions of that experiment to pollinate practically as many 

 flowers as larger insects. 



The insects listed below were collected while visiting Melilotus 

 alba and M. officinalis flowers in 1916. 



