Flow chart of Alfalfa Pollination Model

Slide 16 of 21
Notes:

This flow chart helps conceptualize what is happening in alfalfa seed production as a system. It’s not important that you understand all the details; just some important points.

The model consists of two components, the flower pollination component and the bee offspring component. Basically what happens is that a bee population is introduced, flowers are pollinated for some period of time, bees produce offspring, and the result is a seed yield and a bee yield for the next season.

In the flower component, buds come into bloom as open flowers, i.e., the “standing crop” of open flowers, what is available to the bees at a given point in time. If not pollinated within about a week, flowers wilt and leave the system. When flowers are tripped they are also removed from the pool of open flowers, and quickly begin to develop pods, from which we can calculate a seed yield. The rate of flower visitation depends on the number of bees that have been introduced to the field, and the search and handling time of individual bees and some other factors affecting the bees.

In turn, the number of flowers visited by the bees determines how much pollen and nectar they collect which determines how many offspring they make.

Note the feedback loop connecting pods and buds. This is an exponential decline in rate of bud opening as pollination increases. This is consistent with a source-sink model for flower development, where the sink shifts from raceme production to pod development as flowers are pollinated. The exponential decline is also consistent with a phytohormonal model of the influence of mature fruits on new flower and fruit development. A decline in bud opening as fruits increase is a common phenomenon in flowering plants.

Rate of movement into the "open flower" stock depends on pollination. The rates at which flowers move out of the standing crop pool, either to become pods, or not, also depends on pollination because of the difference in longevity of tripped and untripped flowers. This phenomenon may be uncommon among flowering plants, but it has not often been studied.

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For further information:

Strickler, K. 1996 Seed and bee yields as a function of forager populations: alfalfa pollination as a model system. J. Kansas Entomol. Soc., 69(4) suppl.: 201-215.

Strickler, K. 1997. Flower production and pollination in Medicago sativa L. Grown for seed: model and monitoring studies. In, K.W. Richards, ed. Proc. Int’l Symp. on Pollination Acta Horticulturae 437, ISHS pp. 109-113.

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