Plants' Defense Against Insects is a Boquet

Michigan State University By Joy Landis December 13, 2018

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Michigan State University scholar Andrea Glassmire and her colleagues have revealed how the mixture of chemical weapons deployed by plants keeps marauding insects off base better than a one-note defense. This insight goes beyond the ecological convention of studying a single chemical compound a plant is packing and offers new ways to approach agricultural pest management. The research was published in the latest Ecology Letters.

Glassmire, a post-doctoral scholar in MSU’s Department of Entomology and colleagues from the University of Nevada, Reno, found important relationships between plant defensive chemistry in the neotropical shrub, Piper kelleyi, and its associated insect pests.

Since plants cannot move, they defend against pests that eat them using a bouquet of chemical compounds. Ecology, however, has been biased towards studying effects of single compounds even though a feeding insect would encounter a blend of plant compounds. It turns out that the type of defense bouquet matters, whether bouquets have the same compounds or a blend of different compounds.

“If we can figure out the specific type of defense bouquet that is most effective at reducing insect feeding, then we can extrapolate these findings to agricultural systems to cut down on pesticide use,” said Glassmire.

Glassmire and colleagues manipulated plant chemical defenses in the Andes Mountains of Ecuador using a field experiment where plants were hung at different heights in the forest understory, exposing them to a range of light levels.

Their results suggest P. kelleyi plants consisting of defense bouquets having more kinds of defensive chemicals were more effective at reducing insect damage compared to defense bouquets having one kind of defensive chemical. The composition of defensive chemicals was dependent on the amount of light available. Subtle differences in light in the shaded forest understory induced changes in the defense bouquet. Remarkably, lower amounts of light increased the defense effectiveness of plants compared to higher amounts of light. Consequently, insect damage was reduced by up to 37% when P. kelleyi plants had bouquets of a blend of different compounds. Insects had difficulty consuming plants with different compound blends compared to plants with similar compound blends.

Understanding how plants’ chemical defenses vary across the geographic landscape could have important implications for agriculture. Glassmire and colleagues’ results suggest that feeding insects have difficulty adjusting to neighboring plants that are chemically different and that reduces damage. Agricultural systems comprised of a single crop monoculture lack differences in their defense bouquet because they are all the same.

“I’m excited to see how future applications of this knowledge could help farmers,” said Glassmire. “In the Wetzel lab, we are using a model crop system created by breeding commercial tomatoes with wild tomatoes to manipulate plant defense bouquets. This work will lead to new means of agricultural pest management in the future.”

The paper was co-authored by Casey Philbin, Lora Richards, Christopher Jeffrey and Lee Dyer of the University of Nevada, Reno, along with MSU’s Joshua Snook. The work was funded by the National Science Foundation, Earthwatch Institute, and a generous donation by the Hitchcock Fund for Chemical Ecology Research.

Here's the Buzz That Might Change How We Think

Bug Squad - Happenings in the Insect World   By Kathy Keatley Garvey    4/7/14

Talk about a good insurance policy.

Researchers at Michigan State University (MSU) just published an article in the Journal of Applied Ecology that indicates that blueberry growers who invest in nearby wildflower habitat to attract and support wild bees can increase their crop yields.  They're saying that the cost of planting a habitat for wild bees can pay for itself in four years or less.

"Other studies have demonstrated that creating flowering habitat will attract wild bees, and a few have shown that this can increase yields," MSU entomologist and co-author Rufus Isaacs said in a press release. "This is the first paper that demonstrates an economic advantage. This gives us a strong argument to present to farmers that this method works, and it puts money back in their pockets." 

"This is HUGE news," said pollination ecologist Neal Williams, associate professor of entomology at UC Davis, who was not involved in the study.  "This is the first study to quantify pollination benefit as a result of habitat planting adjacent crops.  It also works through the economics of the implementation of the the habitat and accrued economic and yield benefit over time.  Fantastic stuff."

This is right up Willilams' alley, er, hedge row. He and his colleagues are exploring the role of wild native bees, honey bees and other managed species as crop pollinators and the effects of landscape composition and local habitat quality on their persistence. His research on pollination spans the disciplines of conservation biology, behavioral ecology and evolution. One of his primary research foci is on sustainable pollination strategies for agriculture. This work is critical given ongoing pressures facing managed honey bees and reported declines in important native pollinators such as bumble bees. 

Williams' research has taken him from eastern Pennsylvania and New Jersey to California's Central Valley.  "A continuing goal is to provide practical information that can be used to improve the long-term stability of pollination for agriculture in California, as well as promote pollinator conservation and management," Williams says.  In addition to work in agriculture, he is also studying how habitat restoration affects pollinator communities and pollination.  

Earlier California studies, involving Clare Kremen of UC Berkeley, Neal Williams and other colleagues, showed that wild bees make honey bees better pollinators; that is, the presence of wild bees makes the honey bees work harder.

Regarding the MSU study, the research team planted surrounding bueberry fields with a mix of 15 native perennial wildflowers, hoping to increase the wild bee population and thus improve pollination in the blueberry fields. 

And yes, that's exactly what happened. 

"In the first two years as the plantings established, we found little to no increase in the number of wild bees," Isaacs related in the press release  "After that, though, the number of wild bees was twice as high as those found in our control fields that had no habitat improvements."

To quote from the press release: "Once the wild bees were more abundant, more flowers turned into blueberries, and the blueberries had more seeds and were larger. Based on the results, a two-acre field planted with wildflowers adjacent to a 10-acre field of blueberries boosted yields by 10-20 percent. This translated into more revenue from the field, which can recoup the money from planting wildflowers."

Isaacs was quick to point out that the researchers are not suggesting that growers cease using honey bees for pollination services.  But with 420 species of wild bees in Michigan alone, he says, it makes sense to attract the "free" wild bees. Indeed, it does.

This study could have major implications for not only research in California, but nationwide.

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Attracting Wild Bees to Farms is Good Insurance Policy

  Michigan State University     Contacts: Layne Cameron, Rufus Isaacs    4/3/14

Investing in habitat that attracts and supports wild bees in farms is not only an effective approach to helping enhance crop pollination, but it can also pay for itself in four years or less, according to Michigan State University research.

The paper, published in the current issue of the Journal of Applied Ecology, gives farmers of pollination-dependent crops tangible results to convert marginal acreage to fields of wildflowers, said Rufus Isaacs, MSU entomologist and co-author of the paper.

"Other studies have demonstrated that creating flowering habitat will attract wild bees, and a few have shown that this can increase yields," he said. "This is the first paper that demonstrates an economic advantage. This gives us a strong argument to present to farmers that this method works, and it puts money back in their pockets."

As part of the study, marginal lands surrounding productive blueberry fields were planted with a mix of 15 native perennial wildflowers. The fields were pollinated by honey bees...


Single Gene Separates Queen From Workers

Michigan State University    Contacts: Layne Cameron, Zachary Huang   1/29/14

Scientists have identified how a single gene in honey bees separates the queens from the workers.

A team of scientists from Michigan State University and Wayne State University unraveled the gene’s inner workings and published the results in the current issue of Biology Letters. The gene, which is responsible for leg and wing development, plays a crucial role in the evolution of bees’ ability to carry pollen.

“This gene is critical in making the hind legs of workers distinct so they have the physical features necessary to carry pollen,” said Zachary Huang, MSU entomologist. “Other studies have shed some light on this gene’s role in this realm, but our team examined in great detail how the modifications take place.”

The gene in question is Ultrabithorax, or Ubx. Specifically, the gene allows workers to develop a smooth spot on their hind legs that hosts their pollen baskets. On another part of their legs, the gene promotes the formation of 11 neatly spaced bristles, a section known as the “pollen comb.”

The gene also promotes the development of a pollen press, a protrusion also found on hind legs, that helps pack and transport pollen back to the hive.

While workers have these distinct features, queens do not. The research team was able to confirm this by isolating and silencing Ubx, the target gene. This made the pollen baskets, specialized leg features used to collect and transport pollen, completely disappear. It also inhibited the growth of pollen combs and reduced the size of pollen presses.

In bumble bees, which are in the same family as honey bees, queens have pollen baskets similar to workers. In this species, Ubx played a similar role in modifying hind legs because the gene is more highly expressed in hind legs compared to front and mid legs.

Besides honey bees, which aren’t native to North America, there are more than 300 species of other bees in Michigan alone. These include solitary leaf cutter bees, communal sweat bees and social bumble bees.

“The pollen baskets are much less elaborate or completely absent in bees that are less socially complex,” Huang said. “We conclude that the evolution of pollen baskets is a major innovation among social insects and is tied directly to more-complex social behaviors.”

Future research by Huang may pursue investigating how bees could be improved to become better pollinators. While this won’t provide a solution to bee colony collapse disorder, it could provide an option for improving the shrinking population of bees’ pollen-collecting capacity.

Huang’s research is supported in part by MSU AgBioResearch.

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 Source: Michigan State University