Fungus Kills Caterpillars to Feed Its Plant Host

An insect larva mummified by the Metarhizium fungus

Plants and fungi look like peaceful woodland scenery, but underneath the soil some plant-fungi pairs act as a deadly team mummifying insects and draining them of their nutrients, according to a new paper published  in Science.  The study by Canadian grad student Scott Behie and his research group, shows that the soil fungus Metarhizium can parasitize soil insects and deliver their nitrogen to it’s symbiotic plant partners.  While soil bacteria often break down dead insects, this is one of the first examples of a fungus specifically targeting living insects for their nutrients.

Plants and fungi have a long history of cooperation; plants need nitrogen, but only certain types of nitrogen-based molecules will do.  Plants often get around this problem by forming symbiotic relationships with fungi that can convert nitrogen into biologically useful forms, sometimes even allowing the fungi to live inside their root cells.   In return, fungi get some of the sugars that the plants produce through photosynthesis. However,  Metarhizium and it’s plant partners take things a step further:  in addition to converting nitrogen into plant friendly forms, Metarhizium is a also deadly insect pathogen.  When an insect is infected with Metarhizium the fungus quickly consumes the insect’s tissues from the inside out, mummifying it within a few days.  It now seems that Metarhizium is sharing it’s insect prey with it’s plant host.

Behie and his research team wanted to find out whether the fungus was specifically targeting insects to share with it’s host plant, or whether the insect infection was unrelated.  To test this, Behie injected waxmoth larvae with a special type of traceable nitrogen, called Nitrogen-15 .  He then infected some of the caterpillars with Metarhizium and left some healthy.  He then put some healthy and infected insects in pots with plants (common beans and switchgrass) that have symbiotic relationships with Metarhizium .  After a month, he tested the plant leaves for the Nitrogen-15 from the caterpillars. He found that in plants that had infected caterpillars had 40 to 50% more Nitrogen-15 than those with healthy caterpillars.  The Nitrogen-15 injected into the caterpillars had found it’s way into the leaves in just a few weeks.

However, it is possible that the Metarhiziuminfected caterpillars died more quickly than the healthy caterpillars, and simply released their Nitrogen-15 as they decomposed.  To confirm that the Metarhizium was actually transferring Nitrogen directly from the insects to the host plant, Behie did a second experiment with another insect pathogen (Aspergillus flavus) that did not have a symbiotic relationship to plants.  Plants with the non-symbiotic fungs had only tiny increases in Nitrogen-15 , no different from the increases found in plants without fungus at all.  Only plants that had Metarhizium were able to gain Nitrogen-15 from the insects.

The discovery that Metarhizium can both kill insects and aid plants is exciting to agricultural scientists.  Metarhizium is used as a natural pesticide to protect crops from insect pests.  However, it now seems like it might also be natural fertilizer too, converting once deadly pests into a useful source of nutrition for plants.   Since Metarhizium is an incredibly common fungus, found all over the world, it’s likely that there may be some underground mummifcation going on in your back yard.

SW. Behie, P. M. Zelisko, M. J. Bidochka1 (2012). Endophytic Insect-Parasitic Fungi
Translocate Nitrogen Directly
from Insects to Plants Science DOI: 10.1126/science.1222289


British Butterfly Thrives on Climate Change

Climate change is reviving   a once rare British butterfly, according to a new article in the journal Science.   The brown argus butterfly was once scarce, but has doubled the size of its range in the last 20 years.   The study, authored by biologists at the University of York, indicates that at warmer temperatures brown argus butterflies are able to feed on more common plant species, allowing them to expand into new territory.

Brown argus caterpillars normally feed on the rockrose plant, but they occasionally use plants in the geranium family during warm summers. The rockrose usually lives on sunny, south facing slopes and brown argus caterpillars depended on these warm microclimates for survival. However, for the last 20 years summer temperatures have been on the rise and the brown argus has been shifting it’s egg laying towards geraniums.

During cold summers, the brown argus butterfly uses the rockrose plant (left) but climate warming has allowed it to thrive on the wild geranium (right)

To test whether climate caused the shift in food choice, lead author Rachel Pateman and her colleagues used data collected from 200 sampling sites in southern England.  Butterfly sightings at the sampling locations were reported by volunteer naturalists, and some sites  been monitored since the 1900s.   Each sampling location had only rockrose or only geranium growing nearby.  The researchers used butterfly counts from the volunteer records and matched it to historical temperature data. They found that the butterfly populations grew faster at geranium-only sites during warm periods, and faster at rockrose sites in cool years.

The scientists also looked at  changes in brown argus populations in the last 20 years, when temperatures have been especially warm.  They found that the brown argus had become  5.3 time more plentiful at geraniums sites, but that

The brown argus has nearly doubled the size of its range in the last 20 years. Dark red and blue are locations where it was found prior to 1990, the light blue and pink circles indicate new territory gained in the past two decades. Most gains have been in areas where geraniums are found.

rockrose areas had not changed at all. The butterfly had also expanded it’s range north by 79 kilometers in just 20 years. Co-author Chris Thomas thinks that the common geranium plant may serve as a stepping stone, allowing the brown argus to branch out into new regions without having to fly long distances.  Says Thomas “Wild Geraniums are widespread in the landscape, the butterflies can now move from one patch of host plants to next and hence move rapidly through the landscape expanding their range generation after generation.”

While climate change has been an unexpected bonus for the brown argus, it’s unlikely to be such a boon for other species.  According to Stanford biologist Terry Root (who was not involved in the study), for every species that turns out to be a climate change “winner” there are expected to be three “loser” species that suffer population declines or go extinct.

Teen Lepidopterist Decodes the Secret to Butterfly Sense of Smell

Alexandra Sourakov working in the University of Florida Butterfly house

Alexandra Sourakov has logged hours of research at the University of Florida’s butterfly house.  She used a combination of behavioral experiments and electorantennography (measurements of electrical current in butterfly antennae) to determine how butterflies find food.  Her most recent paper on foraging in Blue Morpho butterflies appears in this month’s edition of Psyche – Journal of Entomology.  Alexandra Sourakov is also about to finish her sophomore year of high school.

Sourakov began her study as part of an eighth grade science project. She used the butterflies in the University of Florida Natural History museum’s butterfly house to see whether flower-feeding and fruit-feeding butterflies responded differently to color. Sourakov used different colored landing pads baited with food to see whether butterflies preferred brightly colored surfaces to black. She found that flower- feeding butterflies were attracted to bright hues, but that fruit-feeding butterflies were indifferent to color. Presumably, flower-feeding butterflies evolved to respond to color cues because they aid in finding brightly colored flowers, while fruit-feeding butterflies usually feed on fruit that has fallen to the dark forest floor, where visual cues would be of little use.

Blue morpho butterflies sense odors with their legs and mouth parts in addition to their antennae, according to a new study by high school student,Alexandra Sourakov

After winning the science fair, Sourakov decided to scale up her research program to investigate how the fruit feeding butterflies found their food. If they weren’t using color, how did they find fruit? Partnering with USDA researcher and science fair judge Adrian Duehl, she launched a multi-faceted approach to understanding butterfly foraging. Sourakov and Duehl used gas chromatography to determine what chemicals in rotting fruit might be attractive to butterflies. They applied these chemicals as volatiles to the antennae of Blue Morpho and Owl butterflies. These two fruit-feeding species did not show any preferences for color during the experiment. With the help of electrodes, they measured the electrical output when the butterfly was exposed to different chemicals. They found that several chemicals that give bananas their distinctive odor provoked a response in the butterfly antennae. Even more interesting, they found that it wasn’t only the antennae that registered a response of the chemical, the legs and proboscis (feeding tube) also responded to the scents. The labial palpi (mouth parts on a butterfly’s head below the antennae) reacted to a different set of chemicals, indicating that butterflies may use multiple organs to detect a variety of odors.

“I was surprised by the results from the body parts because I wasn’t even sure if any of them, except the antennae, would react to the volatile chemicals,” said Alexandra Sourakov in an interview to the University of Florida News. “This was interesting because it shows a joint message may be sent to the brain from these different organs. This expands our understanding of butterflies’ sense of smell.”

The researchers hope that their work will allow them to develop new types of bait designed to target specific species of insect, while leaving other species unaffected.  You can read Alexandra’s full article here:

Early spring meltdown a threat to butterflies and flowers

Spring has been coming early to the Rocky Mountains, and while warm weather may be good news for humans, it’s bad news for flowers and butterflies. A  long term study by Carol Boggs (Stanford University) and David Inouye (University of Maryland) shows that early snowmelt causes a decrease in flower populations, which in turn means reduced food for the mormon fritillary butterfly. In years where the snow pack melted early, spring frosts often damaged newly emerged plants, and the butterfly’s preferred flowers became scarce.   Caterpillars were also casualties of this early spring thaw; butterfly larvae emerged before the danger of frost had passed and were often victims of sudden freezes. The Rocky Mountains are warming faster than other parts of the country, so the effects of early snow melt are expected to worsen in coming years.

The Rocky Mountain Biological Laboratory in Gothic, CO

Mormon fritillary caterpillars have an unusual life cycle that makes them especially vulnerable to climate change: their eggs hatch in late summer before snow fall and caterpillars hibernate under the snow pack until spring.  Early snow melt can be  a  false alarm for caterpillars: if they come out of hibernation before the danger of frost has passed, they may perish in a sudden cold snap.  Adult butterflies are similarly affected by spring frosts.  Females depend on nectar to produce eggs, and early frosts can kill  newly sprouted flowers. In years where flowers are scarce and butterflies are abundant, females must compete for food and produce fewer eggs, resulting in smaller butterfly populations the next spring.

Boggs has been studying the mormon fritillary for 34 years at the Rocky Mountain Biological Laboratory (where Jessica and Heidi do their field work).  She and Inouye wanted to use this long term data set to  test whether early warming had an effect on butterfly populations.  The researchers combined  flower surveys with butterfly population counts from 1980 to 2005, and used this data to build a mathematical model to see whether the number of flowers and the snow melt date in a given year could predict how many butterflies emerged in the spring.  They found that the number of flowers per female was a good predictor of butterfly populations the next spring. However,  flowers alone didn’t explain the population declines: early snow melt also decreased butterfly populations in the following year through caterpillar mortality.  Together, these two factors explained 84% of the variation in butterfly populations.  The study showed that climate can affect a species in two ways, indirectly through it’s food chain and directly through temperature stress.

Boggs and Inoye were able to detect this pattern because their data set spans three decades. Long term studies like this one are the only way to accurately detect the effects of climate change. Becasue there can be substantial variation in temperature from year to year, it may take decades to understand how slow shifts in climate affect wildlife populations. The Rocky Mountains are a particularly important location for climate change research because they are a warming hot spot. The american west is warming 70% faster than the global average, and temperature data from Rocky Mountain Biological Laboratory shows that the average temperature has increases 0.72 degrees F per decade. While that sounds small to a human, it can mean big problems for butterflies and flowers.

If you want to follow the weather at the Rocky Mountain Biological Laboratory, you can find weekly updates  here

To read the full paper:

Boggs, C., & Inouye, D. (2012). A single climate driver has direct and indirect effects on insect population dynamics Ecology Letters DOI: 10.1111/j.1461-0248.2012.01766.x

Science Online 2012

This week Jess and I attended the Science Online 2012 conference in Raleigh.  This so -called  “un-conference” is designed to bring together scientists, science writers, educators, and bloggers of all stripes to learn about using the web for science communication.  The conference was an amazing experience, and I met so many people doing cool things.  Although pretty much every session or workshop was incredible, I narrowed my list down to my five favorite things about Science Online. Before I start the list,  I have to thank the National Evolutionary Synthesis Center, who gave me a scholarship so I could attend.  It was a real honor to be selected, and I’m really grateful that I got to go to this amazing conference.  Also, look for Grad Student Jess’s post soon about her favorite things from Science Online 2012!

Five Favorite Things About Science Online:

1.  The constant tweeting! Lots of conference goers chose to live-tweet the workshops and sessions at Science Online.  At first I found the constant tweeting a little overwhelimng, but pretty soon I was compulsively checking twitter with the rest of the crowd.  It was great to be able to see what was going on in other sessions, and it provided a fun record of everything that went on at the conference from insightful comments to the location of free ice cream.  Below a map of all the tweets at Science Online (Jessica and I are in there somewhere!)

Science Online 2012 Tweet Map

2. A special science themed story slam by The Monti! Some readers may be familar with The Moth, a live storytelling event in which people (often young, bespectacled Brooklyintes) share funny, sad or surprising stories with a live audience. It’s like stand up commedy, if standup commedy hit a nerve as well as tickled your funny bone. The Monti is a local version of the Moth, run by Jeff Polish a former scientist turned story teller.  Ben Lillie of Story Collider (another great story telling project) performed too! I’ll definitely be attending their other non-science shows around Chapel Hill and Durham.

3.  A stand up set from science comedian Brian Mallow

4.  Map making workshop taught by Tim De Chant, who writes the awesome blog Per Square Mile. Understanding how species move across the environment is such an important part of my work, and sometimes you just need a good map to make your point. We learned about some cool, open source map making  and spatial analysis tools, like QGIS .  Look forward to some cool maps and graphics on the blog!

5.  Sketchnote seminar taught by Perrin Ireland of Alpha Chimp Studios, a company that teaches visual brainstorming.   Sketch-noting is a style of visual note taking, and is a popular way to share ideas from meetings and conferences.  It also helps you remember information and pay attention too!  The famous TED talks lecture series uses visual note taking so attendees can learn about talks they’ve missed.  Here’s a quick overview of visual note taking from the pioneer of the field, Sunni Brown.

Coming soon: Jess’s take on Science Online.

Mother Monarch Butterflies Medicate Their Offspring

An infected monarch butterfly struggles to emerge from it's chrysalis

While humans may rely on mom’s chicken soup to fight off infection, mother monarch butterflies lay eggs on medicinal plants to protect their offspring from disease. According to a new study by Emory professor Jaap De Roode and his research team, female monarch butterflies that are infected with parasites lay eggs on anti-parasitic milkweed species to protect their newly hatched caterpillars  from infection.

Parasite spores on monarch wing scales, photographed under a microscope

Monarch butterflies often carry a protozoan parasite similar to malaria, which can have detrimental effects on butterfly development. Infected butterflies have difficulty emerging from their chrysalis, fly poorly, and die young. The parasite is transmitted between adults when mating, or from mother to offspring through the surface of  their eggs (caterpillars often eat their egg shells after hatching for extra nutrition). However, monarch caterpillars can fight infection by ingesting certain species of milkweeds that contain cardenolides, toxic steroids produced by plants.  The toxins prevent parasite spores from establishing in the caterpillar’s gut which can prevent infection, or at least reduce the number of parasites the caterpillar caries.  Cardenolides can cause side effects in healthy caterpillars, like a slightly shorter life span, but these risks are minor compared to the damage caused by infection.

DeRoode and his research team tested how monarchs use the plants to prevent infection both as caterpillars and as adults. They found that caterpillars were unable to detect the presence of parasites and could not distinguiqh between medicinal and ordinary species of milkweed. However, mother monarchs could tell the difference. Infected mothers laid the majority of their eggs on medicinal plants, while unifected mothers showed no preference.

Caterpillars of other species can self medicate, so why haven’t monarch caterpillars caught up with the trend? DeRoode thinks this is partly because the medicinal plants only prevent infection, but can’t cure the parasites once the caterpillar has caught them.  By the time a caterpillar is a few days old, it’s fate is already sealed.  It makes more sense for female butterflies to start caterpillars on a protective diet from the moment they hatch, even if there are some costs to early medication.  Also monarchs aren’t as mobile as some other caterpillar species and don’t stray far from the plant that they hatched on. Even if infected caterpillars could benefit from medicinal plants , it’s unlikely that they would venture off in search of treatment.  Species of caterpillars that successfully self-medicate are those that frequently switch plants and are infected by curable parasites.

If  you’d like to read the original paper, see the link below.  If you’re interested in learning more about monarchs and their diseases, or you want to get involved in monarch research, the Monarch Health project  is looking for volunteers to help track monarch pathogens.

Behavioural resistance against a protozoan parasite in the monarch butterfly
Lefèvre T, Chiang A, Kelavkar M, Li H, Li J, de Castillejo CL, Oliver L, Potini Y, Hunter MD, & de Roode JC (2012). Behavioural resistance against a protozoan parasite in the monarch butterfly. The Journal of animal ecology, 81 (1), 70-9 PMID: 21939438

Prehistoric Moths Show Their True Colors

Happy 2012 butterfly fans!  In order to better celebrate the future, we’re taking a  look back into the past: the ancient past.  The earliest known butterflies and moths evolved about 50 million years ago (although there is some evidence that they might be even older and have coexisted with the dinosaurs).  However since fossils are pretty drab, nobody really knew what the ancient butterflies looked like until recently.

Butterfly scales reflect light to produce colorful patterns

Now scientists at Yale  have used fossilized moth scales to figure out what color ancient moths and butterflies were.  Butterfly wings get their vibrant hues from  scales that reflect light to produce colors and patterns.   These so called “strucutral colors” are produced by layers within the scales that reflect light like a prism.   The research group, led by Professor Maria MacNamara, analyzed the structure of the fossilized moth scales to determine how they would have reflected light, and therefore what color the moths would have appeared.

MacNamara's reconstruction of the fossil moth. The bright colors likely served as a warning to predators

The moths turned out to be bright green with blue wing tips, which means they would have been conspicuous as they fed on flowers in ancient forests.  However, the closest living relative to the fossil moths, the forester moth, also uses bright colors to warn predators that it is toxic.  MacNamara and her group think that ancient moths may also have been able to store toxins to ward off predators and used their colorful wings to deter attacks.    These results are exciting to biologists as well as paleontologists because they show that predator-prey interactions were as important in the ancient past as they are today.

McNamara ME, Briggs DE, Orr PJ, Wedmann S, Noh H, & Cao H (2011). Fossilized biophotonic nanostructures reveal the original colors of 47-million-year-old moths. PLoS biology, 9 (11) PMID: 22110404