Mar. 14, 2006 If you build it, they will come. Native bees that is. And when native bees do come, they may be a hundred times more efficient as pollinators than are honeybees, said Jeff Brady, research assistant with the Texas Agricultural Experiment Station.
Brady, working with Dr. Forrest Mitchell, Experiment Station entomologist, is building trap nests, a way to encourage native bees to do the agriculturally vital role honeybees have been relied upon for so long: pollinating crops.
Honeybee populations, either because of fierce competition from Africanized honeybees or from species of mites they have no resistance to, are on the decline.
Native bees offer an alternative because they are resistant to both the varroa and tracheal mites. And because they do not live in hives, native bees are not at risk of being overcome by Africanized bees.
Native bees, also called solitary bees, do not live in collective hives as do honeybees. They build nests in tiny holes or tunnels that they find, typically in trees and shrubs. Unlike honeybees, who have workers with specialized tasks, with only a part of the hive collecting pollen, each native bee is "on her own," and each is a potential pollinator, Brady said.
Each native bee deposits her collected pollen as small balls inside the tunnel of a nest, then lays an egg, and seals it off with mud or circular pieces of leaves.
She'll then collect more pollen, deposit another pollen ball then lay another egg and so on. Depending upon the species of native bee and the depth of the nest, the female may lay as many as 15 to 20 eggs in a single nest, sealing each egg off in its own cell with its own pollen ball. She may make as many as 100 trips to and from flowers to gather pollen for each of these eggs.
And while honeybees hover around flowers taking pollen when and if they can, many native bees may have evolved so their actions on the flower actually trigger pollination.
"You can actually find a native bee that's been (evolutionarily) tailored to a specific crop," Brady said.
For example, some native bee species are particularly suited – having adapted their life cycles – to crops such as peaches, blackberries or watermelons. For example, one species is dormant or in developmental stages for 11 months of the year, and only emerges when crops such as melons are pollinating. Other species have adapted to row crops such as alfalfa may be active for most of the year.
There's a great deal of genetic variance, Brady said, with more than 500 native bee species in Texas alone. Each may be adapted to specific crops, and each may have a different preference for nesting sites.
For these reasons and others, for a specific crop at least, native bees, such as the alfalfa leafcutter bee, may be much more efficient pollinators than honeybees, Brady said. "Two hundred alfalfa leafcutters can to do the same amount of pollination that a 20,000 honeybee hive could."
Honeybees have other advantages however, most notably their honey production. Because humans have cultured them for centuries, Brady said, they offered some advantages to the agricultural producer who wished to ensure there were enough local pollinators for his crop. He or she could simply establish hives near the crop.
And though honeybees aren't as efficient pollinators as native bees, they make up for it in the sheer brute force of numbers. But these advantages have waned as both wild honeybees and cultured honeybees have fallen prey to parasitic mites and Africanized bees.
Living in hives, honeybees have strength in numbers, offering the collective protection from enemies. Native bees, because of their solitary nature, are often at the mercy of predators, such as woodpeckers and parasitic wasps.
"They are completely opportunistic when it comes to finding nests," Brady said. "They'll nest wherever they find the right size hole, in a dead tree, in a wind chime, even in the empty bolt holes of an abandoned tractor."
This "opportunistic" behavior offers researchers an opportunity of their own, he said. By learning to build the right size nests for native bees, he or she should be able to encourage them to nest near agricultural crops for pollination.
But it's not just a simple matter of one size fits all, he said. Not only are native bees adapted to specific crops, they are also adapted to different sizes and depths of holes. So the first stage of Brady's research is to take a bee census, finding what bees are attracted to what crops and what size holes they prefer.
Brady has been building dozens of different size"trap nests," blocks of wood with holes or collections of tubes designed to "capture and hold" the bees as eggs, larvae and/or pupae. He distributes the trap nests near crops in the spring, and when collected later in the year, they can give him a snapshot of what bees and how many frequent certain crops.
Brady can also get an idea of what size holes or tubes certain species prefer, he said.
Knowing the right nest for the right native bee species will eventually allow him to help build populations where they are needed.
Brady noted that many native bee species build their nests in the ground. Presently, the only species drawn to the trap nests are the ones that opportunistically hunt for already-made holes as nests.
But Brady cautions what he's actually doing is perfecting a technique for determining the best nests for native bees, not building a one-size-fits-all nest. That would be impossible.
"The interesting thing about them (native bees) is they vary so much from region to region, he said. "The biological and other dynamics vary quite a bit."
It is that variance, however, that makes them so well adapted – and the perfect choice as pollinators for many crops, he said.
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