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Study confirms complex web of life  RSS feed

 
Al Loria
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Location: New York
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Always good when science confirms natural systems being the balance that achieves what man tries to do with chemical compounds.


10-year study confirms complex organic web of life

By the University of Michigan news service

Proponents of organic farming often speak of nature's balance in ways that sound almost spiritual, prompting criticism that their views are unscientific and naïve. At the other end of the spectrum are those who see farms as battlefields where insect pests and plant diseases must be vanquished with the magic bullets of modern agriculture: pesticides, fungicides and the like.

Which view is more accurate? A 10-year study of an organic coffee farm in México suggests that, far from being romanticized hooey, the "balance and harmony" view is on the mark. Ecologists John Vandermeer and Ivette Perfecto of the University of Michigan and Stacy Philpott of the University of Toledo have uncovered a web of intricate interactions that buffers the farm against extreme outbreaks of pests and diseases, making magic bullets unnecessary. Their research is described in the July/August issue of the journal BioScience.

The major players in the system — several ant species, a handful of coffee pests, and the predators, parasites and diseases that affect the pests — not only interact directly, but some species also exert subtle, indirect effects on others, effects that might have gone unnoticed if the system had not been studied in detail. 

A key species in the complex web is the tree-nesting Azteca ant (Azteca instabilis). The ants aren't particular about the kind of tree they live in, but for some reason their nests are found in only about 3 percent of shade trees on the farm, and ant-inhabited trees aren't randomly distributed — they're found in clumps. 

The researchers believe the clumpiness results, at least in part, from the ants' vulnerability to a parasitic fly. Ant colonies expand by sending off queens and broods to nearby trees, but when all the trees in an area have ant nests, the flies can more easily find ants to parasitize. So high-density clusters are preferentially attacked and eventually disappear, either because the ants all die or because the ants move to other trees. 

The ants have a cozier relationship with the green coffee scale, a flat, featureless insect that is a serious coffee pest in some regions, but not on the farm where the study was done. Azteca protects the scale from predators and parasites in return for honeydew, a sweet, sticky liquid the scale secretes. One of those predators is the lady beetle (Azya orbigera), whose adult and larval forms both feed on scale. When an adult beetle tries to attack a scale insect, the ants chase it away. But beetle larvae, which are covered with waxy gunk that gums up the ants' mouthparts, are able to polish off plenty of scale. The ants even aid the murderous larvae, albeit inadvertently. In the course of shooing off parasitic wasps that attack scale, the ants also scare away bugs that parasitize beetle larvae. 

The beetles also seem to influence the ants' distribution patterns by preying on the scale, on which the ants depend for honeydew. The researchers explored the relationship using theoretical modeling and found that if ants take over the whole plantation, the beetle goes extinct because adult beetles can't get enough to eat. If the ants disappear from the farm, the beetles go extinct because the larvae starve. But if ants are confined to clusters, due to the influences of both beetles and parasitic flies, the beetles thrive and keep the scale insects under control.

"The interesting thing is that the beetles could not exist except for the highly patterned ant population, but it could be those very same beetles causing the pattern formation in the first place," said Vandermeer, a professor of biology. "The beetle creates the conditions for its own survival."

The white halo fungus, a disease of scale insects, also

A.M. Costa Rica file photo
Ladybug or lady beetle plays a role in the complex coffee farm web of life.

enters in. The disease occurs here and there throughout the farm but runs rampant only where large populations of scale are found, which is only where the ants are protecting the scale. By suppressing the scale, on which the ants depend for honeydew, the fungus indirectly affects the ants' survival. But that's not all: The fungus also attacks coffee rust, a notorious pest that virtually wiped out coffee production in Sri Lanka, Java and Sumatra in the mid-19th century and has since infiltrated Central and South America but has not caused serious problems in those areas. White halo fungus only works its magic against coffee rust, however, in the process of conducting major assaults on scale, and those assaults happen only where there's lots of scale — in other words, where the scale is under ants' protection.

In addition to Azteca, other ant species protect scale, and some of these ants are predators of the coffee berry borer and leaf miner, which are also coffee pests. The researchers are still working out the details of the relationships among the various ants and the other species with which they interact. 

As the research team continues to discover more species that are part of the web and more complex direct and indirect interactions among all the members, it's increasingly clear that the naïve view of nature working in harmony closely matches the scientific facts.

"There are many farmers in the tropics who have been on their land for a long time — sometimes many generations — and have seen these things happening and intuitively understand the connections," said Vandermeer. "The stories they tell about the balance of nature sound almost romantic and religious sometimes, but if you just change the words, they start sounding like what we're describing."

Though this study is being done within the confines of a 300-hectare (740 acre) farm in southern Mexico, the researchers believe their approach and findings are more broadly applicable.

"Our view is that interaction webs of this sort will prove common in agro-ecosystems in general," said Perfecto, professor of ecology and natural resources. "Although widely appreciated in natural systems, such webs haven't been seen in agro-ecosystems because the people studying them haven't looked at them in this way. They're looking for magic-bullet solutions. They want to find the thing that causes the problem and then fix it. Our approach is to understand systems that are working well, where there are no problems. By doing that, we can define systems that are more resilient and resistant to pest outbreaks."

Original article in a Costa Rican online news daily dated 8/26/10: http://www.amcostarica.com/morenews3.htm
 
Brenda Groth
pollinator
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Location: North Central Michigan
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i believe this is great that this article might open some people's eyes to the complex web of life all over the planet in all areas, and maybe people will stop jumping out ahead of nature and destroying things that are helpful.

i know myself in the past i have gotten overwhelmed with the  enormous amount of pests that can overrun when things get out of balance..ex. the 2009 tent worm infestation in Michigan..which was horrible..defoliating over 50 % of the trees in the state..

however..

this spring there was a huge outbreak of these big flies that looked like houseflies..they were feeding on the young tentworms that were coming out..

there were a LOT of tent worms, but not as many as there were the year before, but there were a LOT of flies..

now the flies are gone and the tent worms are gone for the season, it will be interesting to observe next May what kind of balance they have achieved
 
John Saltveit
gardener
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An excellent depiction of what goes on in our forests.  The diversity exists to prevent wholescale destruction because all of the little players are there.  If we wipe them out with pesticides and synthetic fertilizers, they won't be there to bring back balance.  Italian farmers have traditionally grown grapes on maple seedlings. They didn't know why. It just worked.  Recently we have found out that a tiny mite, living on the maple, will grow quickly to destroy insect pests if they are already there on the maple.  Otherwise, it's widespread destruction.
John S
PDX OR
 
                                    
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Location: Ishpeming, Michigan
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Brenda Groth wrote:
i believe this is great that this article might open some people's eyes to the complex web of life all over the planet in all areas, and maybe people will stop jumping out ahead of nature and destroying things that are helpful.

i know myself in the past i have gotten overwhelmed with the  enormous amount of pests that can overrun when things get out of balance..ex. the 2009 tent worm infestation in Michigan..which was horrible..defoliating over 50 % of the trees in the state..

however..

this spring there was a huge outbreak of these big flies that looked like houseflies..they were feeding on the young tentworms that were coming out..

there were a LOT of tent worms, but not as many as there were the year before, but there were a LOT of flies..

now the flies are gone and the tent worms are gone for the season, it will be interesting to observe next May what kind of balance they have achieved

In the past few years they were so bad here that parts of the road  were just covered with them...haven't even seen a web in a tree this year
 
Susanna de Villareal-Quintela
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This past spring, I had a neighbor come over to our property to see how things were growing on the "crazy-neighbor's farm."  On the way to my little orchard, he commented that I had a few ant hills to kill before they became a "real problem."  I told him I couldn't kill the hives or I'd be in "real trouble."  I guess he found that comment curious but he never asked what I meant (he might have feared a verbose tangent). 

What he did ask, when we got close enough, was what spray I was treating my peach and plum trees with to keep the insects at bay.  He couldn't believe it when I told him nothing!  I suggested he take a closer look at the trees.  After a few minutes, he realized there was a workforce of ants busily scouting every centimeter of each tree in search of a tasty tidbit.  The lightbulb came on and he said: "Ohhh... so, that's what you meant."  I think I might have become a little less "crazy" that morning.

The ants seem to patrol all of my fruiting bushes and trees.  I love them!  As an aside, I have never noticed the ants mining into fruit unless it has fallen to the ground (which is a rare event at my place!).  Has anyone had trouble with ants harvesting fruit on the tree?
 
Haru Yasumi
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While I appreciate the conclusion of the article and its points, I really don't think the word "naive" is appropriate when referring to people who see nature as a system that can achieve balance.  Just because people aren't being paid as scientists and trying to quantify everything so it will fit neatly into a paper doesn't mean their experiences and observations are invalid.  Sometimes I feel like if I fell and broke my arm then said, "Wow, this hurts," it would take scientists a decade to confirm that I really did perceive pain.

The house I live in has a vacant project home next door also owned by our landlords.  There are maybe 50 varieties of roses growing there from when a botanist used to live in this house.  Each year there are many aphids that move in for some easy feeding, since the roses are mostly uncared for other than an occasional watering and cutting back for winter.  I have very little interest in the roses myself, but cherish them for their aphids!  The aphids keep a huge population of ladybugs around and every year I appreciatively observe their larvae protect our grapes, apple tree, and my garden.  There's no more voodoo or magic to it than the fact that bees and other insects pollinate many plants - it's common sense food web stuff that modern agriculture ignores.

The scientific method is a great tool, but science itself is at the mercy of human perception and interpretation.  Daily I come across what I consider to be absurd claims and new "discoveries" such as the "discovery" that language really can influence the way people think.  I wouldn't be surprised if tomorrow I saw a news article up on google informing me that "double-knotting shoes really does work 92% of the time."
 
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