INFLUENCE OF THE WEATHER AT BLOSSOMING TIME UPON SEED PRODUCTION.
The seed production of sweet clover is seldom satisfactory when rainy or muggy weather prevails during the flowering period. In order to obtain data as to the relation existing between the visits of insects and the prevailing weather conditions, a record of insect visits and of the number of flowers that opened each day was kept for a period of nine days at Ames in August, 1915.
In this experiment the racemes were marked early each morning just above the last flowers which had opened the previous day, and early the following morning the number of flowers which had opened the previous day was noted. The number of flowers that were pollinated was determined by the number of pods that formed. [Table VII] gives in detail the results obtained.
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. | Percentage of flowers that matured. | |
| Aug. 16 | Cloudy and showery | Very few | 102 | 18 | 17.6 | |
| Aug. 17 | Rain all day | None | 69 | 4 | 5.7 | |
| Aug. 18 | Cloudy most of the day | Very few | 60 | 20 | 33.3 | |
| Aug. 19 | Clear and cool | Numerous | 94 | 53 | 56.3 | |
| Aug. 20 | Mostly clear and warm | do | 61 | 38 | 62.2 | |
| Aug. 21 | Clear and warm | do | 81 | 44 | 54.3 | |
| Aug. 22 | Partly cloudy and warm | } | do | 181 | 100 | 55.2 |
| Aug. 23 | do | |||||
| Aug. 24 | Cloudy till mid-afternoon | Few | 37 | 12 | 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 (Chauliognathus marginatus 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.