While lime trees have flowers with both male and female reproductive parts, pollination by bees, insects and even humans can increase the size and quality of fruit harvests. When lime tree cultivars are self-incompatible--meaning their reproductive parts do not work as planned--cross pollination is required for fruit to set. Honeybees are attracted to lime tree flower nectar, and they are the best and least labor-intensive means of pollination. When bees are missing due to pesticide poisoning, some hand pollination can be done on smaller single trees, but it is not practical on a large scale.
Encourage honeybee and insect activity around your lime trees by refraining from applying liquid or powder pesticides from early spring until mid to late summer after the flowers have all bloomed and dropped and foraging bee populations have moved on from the area.
Plant a pollinating partner tree for lime trees known to self-incompatible by their labeling or by their inability to produce fruit after reaching maturity. Choose a different cultivar of lime tree from the one you wish to pollinate to ensure compatible cross pollination. Plant the two trees within at least 100 feet of one another for best pollen transfer rates.
Hand-pollinate lime flowers when bees and other insects are not present and a tree fails to produce fruit. Pick up a few grains or more of the sticky pollen from the tips of the yellow anthers, and paint it onto the pale green stigma and stile that protrudes up in the center of the flower.