ALKALI BEES

A, Bee tripping alfalfa blossom (about five times natural size). B. Typical weedy nesting site showing surface mounds and underground burrows and life stages': a, male bee; b. female; c, egg on pollen ball; d, young larva; e, prepupa; f. fully fed larva; g, light pupa; h, dark pupa; i, unfinished pollen ball. (All about natural size.)

ALKALI BEES

Alkali bees inhabit the salty valleys west of the Continental Divide. In places where the soil meets their requirements, they may form great aggregations of nest burrows that number a million nests and occupy an acre or more of ground. Even the smaller nesting sites generally contain thousands of nests. Such sites, housing populations of wild bees comparable to hives or whole apiaries of honey bees, are valuable pieces of real estate to the grower of legume seeds. Wherever alfalfa seed is grown close to good nesting sites of alkali bees, yields are exceptionally high if other factors in seed production are properly handled. Some districts in central Washington and central Utah, which are becoming famous for their consistently high yields of alfalfa seed, depend largely on these bees for pollination.

Alkali bees locate their nests in fine-grained soils with high moisture and low organic content. They avoid areas where water stands for extensive periods. They tolerate only short, sparse vegetation. Consequently most nesting sites are found on low hummocks and gentle slopes where soil moisture is held close to the surface and where a high evaporation rate has left salty conditions and scanty vegetation.

In recent years alkali bees have been increasing throughout most of their range, very likely because of expanding acreages of their favorite forage plants and favorable man-made changes in soil conditions. Some progressive farmers now are protecting the nests rather than plowing them up. In some places farmers have undertaken to create new nesting sites.

Alkali bees are highly gregarious but are classified as solitary bees in the sense that they have no caste system or division of labor. Each female constructs, provisions, and seals her own nest. After laying her eggs in separate cells, she has no further contact with her offspring. Adult males and females emerge from the soil in the summer. Males emerge first and divide their time between sipping nectar from nearby plants and zigzagging over the fields and nesting sites in search of females. Soon after emerging, the females mate and begin digging their nests. Before bringing back her first load of pollen from the field, a female bee must construct her main burrow, rough in a few cells, and polish one ready for occupancy. Three or four loads of pollen are formed into a rough ball which is then mixed with a load of nectar and troweled into a smooth, flattened spheroid. An egg is laid on the pollen ball before the cell is sealed and plugged. A completed nest usually contains from 8 to 15 cells.

Within a few weeks the larval bees consume their provisions. Some of them pupate and emerge as a partial second generation. The others and the progeny of the second generation overwinter as mature larvae, which do not pupate until a few weeks before emergence time the next summer.

Most nesting sites are active for about 2 months. The peak of activity, which lasts for about a month, usually falls in the latter part of July and early August but may be advanced or retarded by early or late development of high soil temperatures. To get maximum benefit from alkali bees, seed growers must properly time the blossoming period of their crop. On sites with vegetation it is possible to advance the emergence date of the bees by applying a weed killer in the spring.