Robert Pore's Ag Blog

In a fascinating study appearing in the November issue of The American Naturalist, biologists investigated the response of small animals to climate change on a remote sub-Antarctic Island. From an evolutionary standpoint, acclimatizing to a change in circumstances seems to make evolutionary sense. However, Steven Chown and Jacques Deere (both of Stellenbosch University) found that terrestrial animals don't adapt. Why not?

"Acclimation only makes sense if tomorrow is likely to be similar to today," noted Chown, "and at Marion Island the sea is always cool, but from one day to the next it's never quite clear what the weather will bring on the land."

Animals have adapted this flexibility. Terrestrial animals facing highly unpredictable environments show no acclimation response at all, whereas the marine species reacted to life in a cold, predictable environment. This research found that unpredictability is a key to status in the face of change.

Marion Island is a great place to see the effects of global warming. On this island the average annual temperature has increased by more than 1° Celsius for the past fifty years. According to Jacques Deere, "This island and its animals provide a great research platform for assessing the taste of things to come."

URBANA -- Global warming strikes again. A University of Illinois researcher reports that a red-winged black bird population in Ontario, Canada has decreased by 50 percent since 1972. The decrease is related to a positive shift in the North Atlantic Oscillation which has resulted in warmer, wetter winters in the southeastern United States.

When Patrick Weatherhead put his 25-year data about the red-winged black bird alongside climate records, he found a direct correlation with the North Atlantic Oscillation. The NAO is a dominant cause of winter climate variability in the North Atlantic region ranging from central North America to Europe and much of Northern Asia. It has been on an upward trend for the past 30 years.

Weatherhead, an ecologist who specializes in the behavior of birds and snakes, says that although some people may be in denial, global warming exists. "There are long-term records that show melting glaciers and altered ecological patterns like earlier migration and earlier nesting of birds.

"When you first start out, you don't set out to get 25 years of data on a topic," he said. "But when you're in the field long enough like I have been, that's what you wind up with -- long-term ecological data which may have unintended uses."

The data was collected in Ontario, Canada at the Queen's University Biological Station from 1975 to 2000, with some additional data in 2005.

"We also found that although the breeding season started at the same time each year, it lasted longer," said Weatherhead. "The birds appear to be interpreting the longer season as the end of the season lasting longer, when more female eggs typically hatch, so that shift has affected the population sex ratio."

Over the years, Weatherhead's team has put bands on the legs of thousands of red-winged black birds in order to track their nesting habits. They winter in southeastern United States. In mid-July they become gregarious and switch from eating insects to eating corn and have caused millions of dollars of damage.

Red-winged black birds feed on corn borers, so that makes them well-liked by farmers, until they switch in the breeding season to eating corn. That's when the hero suddenly becomes the pest.

So, is the 50 percent decline in population a good thing for the environment?

Weatherhead says that what will happen in the future isn't clear, but if the climate trends continue, there are likely to be further changes in population size.

In 2005, Weatherhead returned to the marshy region of Canada where the other decades of data had been collected. The North Atlantic Oscillation had returned to neutral values. "We found that the harem size [the number of female birds per male] had rebounded to 2.06 which is less than expected, but it did go up. We are currently measuring the length of the breeding season to see if that has changed, affecting the sex ratio as well."

WEST LAFAYETTE, Ind. — Farmers could save $10-$12 per acre on insecticide treatments for soybean aphids by turning to a control method that money can't buy, said a Purdue University entomologist.

That control option, said Bob O'Neil, is the aphid's insect enemies.

Research by O'Neil, fellow Purdue entomologists and entomology colleagues at four other Midwest land-grant universities found that in most cases predators are able to consume enough aphids to keep aphid populations below crop-damaging levels. The multi-state research project has been ongoing since 2003.

"We did several studies in which we isolated soybean aphids away from their predators," O'Neil said. "We built small screen cages and put soybean aphids inside them. There were similar numbers of soybean aphids outside the cage on plants.

"What we found was that the population size of soybean aphids inside the cage increased four times, whereas outside the cage aphid numbers typically decreased.

"Outside the cage, the natural predators were reducing the aphid population. When we protected the soybean aphids, those populations grew. That told us that these natural predators were important and that farmers need to pay attention to them."

Aphids have been a problem for farmers since the pinhead-size yellow-green insects were first found in United States soybean fields in 2000. Major aphid infestations have occurred in odd-numbered years — a phenomenon that researchers don't fully understand.

Aphids damage soybeans by injecting their needlelike mouthpart into a plant's leaves and extracting sap, limiting the plant's ability to produce seeds. The insect's rapid reproduction — it can birth as many as 15 generations in a single crop season — makes the aphid a dangerous pest.

Yield losses of up to 30 percent have been reported in some areas. The aphid already has caused an estimated $500 million in crop damage in the United States, O'Neil said.

"We've estimated that Indiana farmers spent more than $7 million to control the soybean aphid in the 2003 outbreak," O'Neil said. "By far, the soybean aphid is the most damaging insect we've ever had in soybeans."

O'Neil and his research team examined aphid predators and their feeding patterns, and discovered that predators are present throughout the critical phases of soybean development.

"There's quite a few predators in soybeans, but when you take a look at who is out there, in what numbers and who is having a major impact, it comes down to a few species doing the heavy lifting," O'Neil said. "Early in the season there's a predatory bug called the insidious flower bug, also known as the minute pirate bug. That particular insect is important when there are relatively few numbers of soybean aphids in the field.

"Later in the season — in August and into September — when soybean aphid populations are higher, there's another set of predators that come in. These tend to be the predatory beetles. One of them is the Asian lady beetle and it does a great job. So between the minute pirate bug and the lady beetle, you've got a kind of one-two punch."

Pirate bugs eat up to eight aphids per day, O'Neil said. The lady beetles consume 30 to 40 a day, he said.

Between the two predators, aphid populations often stay below significant yield loss — or "economic threshold" — levels, O'Neil said.

"The economic threshold is 263 aphids per plant," he said. "We round that to 250 because it is a bit easier to work with.

"It's really important for farmers to know that bit of information. They also should know that just because you have soybean aphids in your field doesn't mean that you have a pest problem in your field. If you don't get to that threshold level the soybean aphids are just living out there — they're not doing any damage and it is not worth the cost of control."

Not only could farmers be spending money needlessly on insecticides but also reducing the predator population, O'Neil said.

"By spraying too early or at times when they shouldn't be spraying, farmers can be destroying these natural predators," he said. "It's sort of akin to taking the bank guard out of the bank. It's just not something that you want to do, unless you really have to treat that field."

Researchers next hope to determine how many predators per soybean plant are necessary to keep aphid populations from reaching the economic threshold. Until then, O'Neil encouraged soybean farmers to become familiar with the minute pirate bug and Asian lady beetle.

"They need to be able to identify their friends as well as their enemies in the soybean field," O'Neil said.