Pollen tube growth is toward eggs of the same species as the pollen. Pollen germination has three stages; hydration, activation and pollen tube emergence. Pollen apertures are any modification of the wall of the pollen grain. Pollen cones with 2-6 pairs of 2-4 pollen sacked sporophylls. Common allergens include pollen and certain foods. Adult Micropterigidae chew the pollen or spores of ferns. Adults feed on the pollen and nectar of flowering plants. Bees use poppies as a pollen source. Worker larva are fed bee bread which is a mixture of nectar and pollen. Megabats are mostly fruit, nectar and pollen eaters. Other researchers are trying to silence genes in ants, caterpillars and pollen beetles. Many animals pollinate flowers in exchange for food in the form of pollen or nectar. Adults feed mainly on nectar and pollen. Allergies to pollen or animal hair are also a common cause. The saguaro provides voluminous amounts of pollen, nectar, and fruits.