Factors Influencing the Effectiveness of Insect Pollinators of Alflfa in California

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Abstract
On the basis of field observations in California in 1945 and 1946, California alfalfa seed production appears to be dependent upon the pollinating activities of both honey bees and wild bees. Population trends of solitary bees are frequently more stable than pollen-collecting honey bees. The solitary bees reach a peak later in the season than do the honey bees and are not subject to manipulation by man. The important spp. of solitary bees involved in alfalfa pollination fly more rapidly than a honey bee, trip more flowers per minute, and visit a smaller % of the flowers on any one plant, thus accomplishing more pollination and probably a greater transfer of pollen from plant to plant per individual bee. The honey bee appears to spend more time in the field than the wild bees, and begins collecting pollen earlier in the morning and continues later in the day. If honey bees are to be used to increase alfalfa pollination, calculations as to the number of colonies per acre should be based on an area as a whole rather than on individual fields. Elimination of competing plants such as sweet clover, mustard and sun flower should increase the number of pollinating honey bees in alfalfa as well as that of certain of the spp. of wild bees. Wherever possible, competition with other seed crops, especially carrots, should be avoided. The abundance and effectiveness of pollinating bees can be increased by lygus bug control, thus reducing blossom injury by these bugs, provided the measures employed do not themselves injure the bees.

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