with 60–65% edible kernel per nut. Requires pollination from other almond varieties for good nut production. Tuono – originates in Italy. Has thicker, hairier shells with only 32% of edible kernel per nut. The thicker shell gives some protection from pests such as the navel orangeworm. Does not require pollination by other almond varieties. Mariana – used as a rootstock to result in smaller trees Breeding Breeding programmes have found the high shell-seal trait. Pollination The most widely planted varieties of almond are self-incompatible; hence these trees require pollen from a tree with different genetic characters to produce seeds. Almond orchards therefore must grow mixtures of almond varieties. In addition, the pollen is transferred from flower to flower by insects; therefore commercial growers must ensure there are enough insects to perform this task. The large scale of almond production in the U.S. creates a significant problem of providing enough pollinating insects. Additional pollinating insects are therefore brought to the trees. The pollination of California's almonds is the largest annual managed pollination event in the world, with 1.4 million hives (nearly half of all beehives in the US) being brought to the almond orchards each February. Much of the supply of bees is managed by pollination brokers, who contract with migratory beekeepers from at least 49 states for the event. This business was heavily affected by colony collapse disorder at the turn of the 21st century, causing a nationwide shortage of honey bees and increasing the price of insect pollination. To partially protect almond growers from these costs, researchers at the USA government Agricultural Research Service have developed self-pollinating almond trees that combine this character with quality characters such as a flavor and yield. Self-pollinating almond varieties exist, but they lack some commercial characters. However, through natural hybridisation between different almond varieties, a new variety that was self-pollinating with a high yield of commercial quality nuts was produced. Diseases Almond trees can be attacked by an array of damaging microbes, fungal pathogens, plant viruses, and bacteria. Pests Pavement ants (Tetramorium caespitum), southern fire ants (Solenopsis xyloni), and thief ants (Solenopsis molesta) are seed predators. Bryobia rubrioculus mites are most known for their damage to this crop. Sustainability Almond production in California is concentrated mainly in the Central Valley, where the mild climate, rich soil, abundant sunshine and water supply make for ideal growing conditions. Due to the persistent droughts in California