Honey bees, Apis mellifera L. (Hymenoptera: Apidae), as pollinators of upland cotton, Gossypium hirsutum L. (Malvaceae), for hybrid seed production

Ultrasonic pollen removal followed by focused flow counting of the pollen grains with an electrical sensing zone particle counter provided a uniform approach to measure rapidly and with good precision pollination dynamics in cotton.;Cotton pollen collection by Apis took place only when colonies experienced a severe dearth of pollen, but pollen collectors were not effective for pollination of MS flowers since they seldom switched between lines. Higher relative humidity in the area from sprinkler irrigation resulted in increased cotton pollen collection. Honey bees were unable to harvest cotton pollen as efficiently as that from commonly foraged plant species and the length of the spines of cotton pollen were the main factor responsible for this reduced gathering ability by honey bees.;Fertilization efficiency varied significantly with the pollination situation and, at a given pollination intensity, the seed set per flower increased when pollination was low mainly as a result of greater boll retention. The average pollination intensity needed to reach maximum seed set was calculated to be around 130-140 pollen grains per MS stigma.;Pollen dispersal, measured by the MS seed yield, decreased as the inverse of the distance to the pollenizer row and it did so significantly up to 7 rows from the row of MF plants. Pollination efficiency and pollination effectiveness decreased as MS rows in a planting pattern increased and a 4MS:2MF row ratio gave the highest yield of hybrid seed per ha planted.;Honey bees were effective pollinators of hybrid cotton parental lines, though the efficiency of individual foragers was low. Pollen carryover of foragers on male-sterile (MS) flowers was only 50-150 cotton pollen grains with only a few grains deposited at each visit. Pollination effectiveness, measured by the seed cotton yield ratio, increased linearly with the stocking rate (colonies/ha), mainly as a result of larger MS bolls. The seasonal density of Apis foragers on male-fertile (MF) flowers increased linearly with the stocking rate, indicating increased foraging competition. Pollination effectiveness and the Log of MS pollination intensity both increased linearly with the Log of the forager density on MF flowers.