Zombie Caterpillars Lurch Through Forest Canopy, Infecting Their Brethren

gypsy moth caterpillar "face"

The zombie caterpillar apocalypse has begun!   A recent study published in Science by Dr. Kelli Hoover and her research group at Penn State showed that a virus infecting gypsy moth caterpillars  causes them to become like the living dead.  Infected caterpillars crawl to the treetops where they die and their putrefying corpses shower virus particles over the terrified survivors.

An infected caterpillar hangs decomposing from a branch

Gypsy moth caterpillars are normally nocturnal and only forage in the the tree tops at night when they can avoid predators.   During the day they return to their hiding places  in the forest understory.  However, caterpillars infected with the virus climb to the top of the tree during the day and feed continuously.  They also stop normal development toward adulthood but become ravenously hungry,  growing larger and larger and providing the virus with more flesh to feed on.  Eventually, they die and their corpses liquefy and drip infectious material over the remaining caterpillars.

The coolest part?  The behavior is caused by a single gene in the virus.    This baculovirus has a gene that codes for an enzyme called  EGT, which  inactivates caterpillar molting hormone.  Caterpillars have to molt to grow and develop, so when they become  infected,  caterpillars are stuck in perpetual childhood, eating, growing bigger but never developing to adulthood.  The EGT enzyme also causes the climbing behavior, because without the urge to molt, caterpillars are driven to eat without stopping, and so they feed continuously day and night without ever coming down to rest.

Dr. Hoover and her team showed that EGT was causing the climbing behavior with a simple experiment.  They took some natural  strains of the virus with the EGT gene and two strains where they had artificially  inactivated the EGT gene.  Then they took Gypsy moth caterpillars, infected some with each virus  and placed them in soda bottles with holes.    The caterpillars with the natural virus climbed to the top of the soda bottle and died, just like they did in the wild.  Those that received the virus with the disabled gene died on the bottom of their cages.  In the wild, caterpillars that die in the understory or forest floor wouldn’t be able to infect many others, so the EGT gene is very beneficial for the virus becaus it allows it to spread rapidly.  Lots of parasites use this kind of mind control to force their hosts to spread them , but this is an exciting result, because it’s one of the first times science has shown that a single gene in a parasite can alter host behavior.

Of course, no zombie story is complete without some heavy-handed social commentary.  The gypsy moth is an invasive species introduced to North America in the 1860s and it spread quickly through America’s hardwood forests.   It’s since become a huge pest, and it’s boom and bust population growth cycles can cause massive defoliation in forests.  Scientists are actually using simlar viruses to control gyspy moth populations in areas that are too sensitive to use pesticides.  So the virus may actually provide forestry researchers with a new tool to control the gypsy moth menace.   As always, it’s human nature not the zombie hoard we should truly fear.

There’s a new butterfly in town

From time to time here at Butterflies and Science we’ll pick out a fun scientific paper about butterflies and highlight why we think it’s cool and important. This week has been a good one for butterflies with two cool news stories about them! The first one is about new species being formed as a hybrid of two others!

Move over Eastern tiger and Canadian tiger swallowtail there is a fancy new hybrid butterfly in town, the Appalachian tiger swallowtail!

One of my new favorite hybrids: A male Appalachian Tiger Swallowtail

Scientists at the University of Texas-Austin and Harvard University have discovered this new species of swallowtail living in the Appalachian Mountains. The Appalachian tiger swallowtail has evolved as a hybrid of the Eastern tiger and Canadian tiger swallowtail. The Canadian tiger swallowtail is found in the northern US and is more adapted to colder climates than the Eastern tiger swallowtail which is found well, in the Eastern US. The Eastern tiger swallowtail is unique in the ability to have two forms (colorations). One of these forms is the usual yellow wings with black stripes, but the other is an all black form that mimics the more poisonous Pipevine swallowtail.

The yellow striped form of the Eastern tiger swallowtail
The black form of the Eastern tiger swallowtail

What’s so cool about this hybridization is that the Appalachian tiger swallowtail inherited some of its cold tolerant genes from the Canadian tiger swallowtail and the genes to have the mimic form from the Eastern tiger swallowtail. It is a true hybrid of its parents both inside and out! Now the Appalachian tiger swallowtail is its own species that rarely mates with either the Canadian or Eastern tiger swallowtail.

So how do these sorts of hybrids arise? Glad you asked!

Generally when we think of new species arising it happens when one species splits into two and becomes isolated over time. In the rare case of hybrids two different, yet related species are able to mate with each other to create viable and fertile offspring. This happens a lot in plants, but is pretty rare in animals. The key is that the Eastern tiger and the Canadian swallowtail have only been unique species for about 600,000 years, before that they were the same. That may seem like a long time, but in evolutionary time that’s barely a blip! Because they were so closely related they were still able to mate with each other and have healthy, fertile offspring. Those offspring then diverged from both parents and have now become their own unique species. That is what makes this study so unique and exciting! It’s not often that conditions for this kind of speciation are right.

If you want to read more about this you can check out the scientific paper in PLoS Genetics here or you can read a less technical and shorter version here from ScienceDaily.

Butterflies and Social Science

Mother and Child Feeding Silkworms in Laos


One of the really fun things about my fellowship  in Japan was meeting other students from different  fields.  One person who does especially cool work is my friend Annabel Vallard, who is a postdoctoral fellow at the Center for South East Asian Studies  in Paris.  Annabel is an anthropologist who studies the silk production in Japan, Thailand, and Laos.  As I mentioned before, Silk worms are not technically butterflies.  However, they are in the same order (Lepidoptera), and I didn’t want to pass up the chance to interview a butterfly social scientist because of a technicality.

Silkworm farmer in Laos posing with a tray of silkworms

Annabel got interested in silkworms when she was studying textile industry in Laos and Thailand for her thesis. Since silk weaving is an important craft in the area, she started talking with rural silk producers about how they raise silk worms.  One thing she found out was that the Japanese government had started a collaboration in Thailand as early as the first decade of 1900’s and in Laos during the late 1950s in order to improve silk quality and to help impoverished Laotian and Thai silk farmers. Japan as a nation is very committed to international development and aid, and often sends its scientists abroad to do research or teach in developing countries.  Annabel’s work in Thailand and Laos focused on interviewing the silk farmers and the Thai and Laotian staff at the research station about how they raised silk worms as well as how they interpreted the scientific research and protocols for silk worm care.  Although scientists try to accurately follow standard protocols for their research, every person will perceive these instructions differently, and each culture has its own way of interpreting the same directions.  She’s now starting a new phase of the project here in Japan, trying to find the Japanese scientists who worked on the silkworm development programs in Thailand and Laos and to find out not only what they did in the project but what their current relationship to silkworms is.

Development programs and Silk

Even though the Japanese government started the program with the best intentions, silk

Postage Stamp Promoting Silkworm Production in Laos

production in Laos and Thailand was (and still is) a pretty different process from silk production in Japan.  In the previous blog post, I explained how the Meji emperor was influential in developing the science of silkworm breeding and rearing.  By the 1950s, silk production was a highly industrialized process in Japan, and silkworms were raised in sterile laboratories on artificial diet. However, Thailand and Laos were still using traditional methods of silk production.  Silk is still produced by individual households, where silkworms are raised in bamboo trays behind the kitchen and are fed mulberry leaves from the garden around the house.  At first, Japanese researchers tried to introduce the Japanese species of silk worms. However, the laboratory bred silkworms had evolved in sterile conditions and at cooler temperatures.  When they were crammed together in bamboo trays in the humid atmosphere of Laotian and Thai homes, they would get sick and die.  Eventually Japanese researchers hybridized the Japanese lab silk worms with Laotian and Thai native silkworms, and they produced a strain that could survive in the tropical heat in people’s homes. Today in Laos the Japanese government ships the research stations these special eggs produced in laboratories, the research station staff raises them, breeds the adult silkworms and supervises their reproduction. Then, they sell the new generations of eggs to local silk farmers that will raise them to maturity. More than half a century later, the Lao-Japanese program is still going, and every few years the Japanese government sends a diverse team of scientists to the field station to continue the research efforts.  The research team usually includes entomologists, soil experts, silk machinery engineers and silk worm disease experts.  Annabel’s new project is to find researchers who have participated in the project and to explore the manufacture of these biotechnological materials altogether in human imaginary and in practice. Annabel is interested in more than just silk worm raising technique though.  Just like Jess and I are interested in using butterflies to understand big questions about how insects can evolve in a changing climate, Annabel is interested in studying how two cultures can go about the same process in different ways, and what happens when people from those cultures try to work together.


A Day in the Life of a Butterfly Social Scientist

research station staff washing silkworm trays

Jess and I have talked a lot on the blog about what the daily life of a butterfly biologist is like.  Annabel’s work schedule is really different from that of a biologist.  Modern anthropologists use a method of data collection called “participant observation” where they try to become a part of daily life in the community they study.  They go about mundane tasks with the people while trying to observe and record what they are actually doing.   Since Annabel is just beginning her research here in Japan, her work right now consists of meeting with scientists and trying to track down the researchers who worked on the Laotian and Thai development projects.  In Thailand and Laos, however, her work day takes her to the silk research stations where she works alongside the staff to see what they’re doing.   If they’re breeding silkworms, cleaning cages, or answering questions from silk farmers, she’s right there watching how they work and sometimes working with them.  When they stop for a tea break or go out for a beer after work, she goes too.

While Jess and I use a lot of lab equipment, Annabel just uses a list of questions and a tape recorder or video camera to watch how people work.  She says recording is really important because it’s easy to miss something while you’re thinking of your next question.  However, it’s not just a simple interview process and you have to be a strong observer to catch and remember the smallest details.  Annabel says that you have sometimes to let your research subjects lead the conversation, and be flexible when they surprise you with a new topic or idea.  “In anthropology you have to be open to what will happen next”, she says.


Ethnoentomology: The Social Science of Insects

When I asked Annabel what surprised her the most when she started the silk worm project, she said “the fact that people can have such strong relationships with insects.”  Annabel says that there is a growing field related to anthropology called Ethnoentomology.  You may have heard of Ethnobotany, the study of how communities use plants, and Ethnoentomology is basically the same thing but for insects.   In the past, anthropologists usually studied human-insect interactions when insects were part of food, myths or ceremonies.  Now anthropologists are becoming interested in how people organize economic and social institutions around insects.  Most ethnoentomologists do this by studying a small scale example in detail.  For example one of Annabel’s colleagues, Nicolas Césard, studies urban bee keeping  in  France while another, Stéphane Rennesson, studies beetle fighting rings in Thailand.  Of course, biologists like Jessica and I are part of a community with our own beliefs, hierarchy and rituals surrounding insects.   Biological scientists are now becoming the subjects of research themselves, as anthropologists try to understand how the scientific community works .  While it can feel a little strange to be under observation yourself, I think it’s great that we have social scientists to help biological scientists understand the way we do our job.