Hello! I'm Veronica. I'll Be Your Nectar Guide Today

The plant below is called Veronica.  That's its scientific name and its common name.  In our outdoor classroom, it's located on the rocks behind the pond, and it's blooming like crazy right now.  Veronica flowers have something really neat called nectar guides. 

Nectar Guides on Veronica Flowers

Nectar guides help bees find flowers.  They point to the part of the flower that contains the nectar, which is what bees are looking for.  Nectar is sugary plant sap found in the base of many flowers, and it is perfect bee food.  I like to think of nectar guides working a lot like the stripes and lights on airport runways telling airplane pilots where to land their planes.

Why would flowers advertise where their nectar is?  It turns out flowers are offering the nectar in a bargain.  Do you see those tiny white structures poking out of the flowers in the picture above?  Those are anthers, and they contain a dust called pollen.  Flowers must have pollen moved from one flower to another in order to be able to grow seeds to grow a new generation.  While a bee sips the nectar in a flower, those anthers are in the perfect place to dab some powdery pollen onto the bee.  Then the bee rubs off the pollen at the next flower it goes to.  The flowers are giving the bees a meal in return for moving their pollen from one place to another.  (Do you remember the name for a close relationship between two organisms where both organisms benefit?  The answer is at the bottom of this page.)

Bee-pollinated flowers usually have nectar guides.  Flowers that are small, fragrant and with a shallow cup for nectar are usually bee-pollinated, and we have lots of bee-pollinated plants at our outdoor classroom to discover.  You may not always notice nectar guides on bee flowers because sometimes the guides are invisible to human eyes.  Strangely enough, there are more colors of light than humans can see.  Rainbows actually have more stripes than humans see, in colors we haven't imagined.  Bees can probably see one more stripe on the rainbow than we can.  We call this color ultraviolet, and know it exists because we can detect ultraviolet with machines.  But how do we know bees can see ultraviolet?  Because scientists have given bees eye tests!  Scientists tested bees' eyesight by making fake flowers.  On some flowers, they painted nectar guides with an ultraviolet dye.  When you offer fake flowers to bees, the bees are way more curious about the ones with the ultraviolet nectar guides than the ones without nectar guides.  Scientists have detected ultraviolet nectar guides on real flowers (sunflowers have ultraviolet nectar guides).

Go back to the picture above and see if you can find the nectar thief.  A nectar thief is something that steals nectar without moving pollen - a parasite!  The nectar thief on our Veronica flowers is an ant toward the left of the picture.  As we learned last week, ants eat sugar, so it's no surprise that they would like flower nectar.  The ants are too small for the anthers to dust them with pollen, so they slip in, drink the nectar and slip out again without helping the plant.  Ants mostly use smell and taste to find their way in the world, so they probably don't even notice the nectar guides.  If you are jealous of bees for seeing one more color than we do, then you're really going to be mad at ants.  Scientists think ants can smell and taste an enormous number of things humans can't, with much more precision.  If you don't believe me, try closing your eyes and finding your way around using just your nose and tongue, and you will appreciate just how much better ants' senses are.

Answer: Mutualism

Down on the Aphid Ranch

Originally this post was just going to be about vines.  There are four basic plant forms: trees, shrubs (small, branched trees), herbs (non-woody, soft plants), and vines.  Vines are woody but not strong, and they grow as tall as trees by climbing up other structures, often trees, and they usually have roots that are good for holding on, like this:

English ivy with roots that are good for holding on to buildings or trees.

 Some vines are evergreen like the English ivy on the back wall of our classroom:

English ivy doesn't lose its leaves in winter.

And some are deciduous like the milkweed vine on the lamppost by the playground:

Milkweed vines lose their leaves in winter.

Like I said, I was originally going to post about vines.  BUT when I was looking through my vine pictures, I noticed a very lucky but accidental detail on this picture of the English ivy:

New growth on the English ivy with some curious dots on the stem.

Look very closely at the stem, and you will notice there are ants walking on that stem:

Ants going up and down the ivy stem.

I started to wonder what ants were doing walking on an ivy stem, since there is not likely to be much ant food at the top of an ivy vine.  Then I looked even closer and I saw this:

An farmer ant and her aphids.

Now we have a story!!!  The picture is a little blurry, which means you're going to have to go out to the outdoor classroom and see this for yourselves.  The dark spots are insects called aphids (which can also be whitish or greenish), and the reddish brown spot is an ant.  What the ant is doing is called aphid farming.  It's a bit gross, but it's so amazing that it's completely worth learning about.

To explain aphid farming, we have to go back to plant sap.  Remember plants do photosynthesis and make sugars, which are dissolved in plant sap, making plant sap slightly sweet?  Aphids have pointy, needle-shaped mouthparts they poke into soft plant tissues, and they suck the plant sap out of plants for their own food - much like the psyllids we learned about back in the fall.  Since aphids live closely with plants, they are said to be in a relationship called a symbiosis.  In this relationship, the aphids are harmful to the plants because they 'sap' their energy.  The aphids benefit by getting food.  A symbiosis where one organism benefits and the other is harmed is called parasitism. 

Here's where it gets slightly gross.  Aphids drink a lot of plant sap, and they digest most of the sugar in it, but not all.  The leftover sap with a tiny bit of sugar in it goes on through and out the other end of the aphids' digestive system.  In all other organisms, this substance would be called feces or poo, but in aphids, the substance is a clear and sugary liquid, so it's called honeydew.  (Do NOT confuse this kind of honeydew with the delicious green melon you find in the produce section.)  If you have ever noticed sticky, clear spots on the hood and windshield of your car if you park it under a tree in summer, you have seen the results of the mist of honeydew that rains from the aphids in the tree.  Take a deep breath...it's really only plant sap run through an aphid!

OK, here's where it gets really gross, but also really, amazingly neat.  The sugars in the honeydew are technically a food source (like any other sugar), and ants eat sugar.  Put those two facts together, and you know what that ant is doing with the aphids on the leaf in the picture above.  Yes, some ants eat honeydew.  The ants know a good food source when they find it, so they protect the aphids and fight off aphid predators.  They even move the aphids around to better sap sources if their honeydew production slows down.  Some ants even keep aphid eggs in their ant nests in the ground during winter and place them on new plant growth in the spring so the aphid eggs have food when they hatch.  The ants are said to farm the aphids - just like humans farm cattle!  Dairy cattle ranchers protect the cows and move them around to new pastures with more food.  Cattle farmers also protect calves and raise them to adults.  And cattle are farmed to provide a liquid food source: milk! 

It's amazing to me that humans are not the only type of organism that does farming.  Ants live in groups and have very complex behaviors, as exhibited by the aphid farming.  Their behaviors often mimic human behaviors: they have 'jobs', fight battles, farm aphids (and fungi - neat story for another time), build large complicated structures and much more.

Ants and aphids are in a symbiosis - they live very closely together.  Their symbiosis involves both organisms benefiting from each other.  The aphids get protection, and the ants get food.  A symbiosis where both organisms benefit is called a mutualism.  Humans and cattle are in a similar mutualism.

The new growth on our ivy is very likely to have a constant supply of aphids and ants, so you should be able to find them any time!

Meet the Juniper (AKA Eastern Red Cedar)

Middle Tennessee is known for its cedar trees.  We even have a state park called Cedars of Lebanon.  The trouble is, the trees we call cedars are actually a type of tree called a juniper.  Our cedars have all the plant parts and structures of junipers, yet we call them Eastern Red Cedars.  Names are difficult to change once we get used to them, but I'm going to call our cedars junipers in this post.  The scientific name of our Middle Tennessee junipers is Juniperus virginiana, meaning juniper of the Virginia region.

Meet one of the junipers at our outdoor classroom.

Junipers have a million interesting characteristics.  My favorite thing about them is the difference in their immature and mature foliage (leaves).  Their mature leaves are smooth, rounded overlapping scales like you see in the picture below.  Junipers' immature foliage is sharp and spiky.  The easiest way to tell if foliage on a juniper is young or older is to close your eyes and feel the difference.  Fortunately, junipers are evergreen trees, so this is a great time of year to investigate their foliage.

Mature growth on a juniper.

Below is a juniper tree whole foliage is almost entirely immature.  It is about as big as the juniper in the picture above, so it must be about as old.  Spiky immature foliage protects young junipers from being eaten by deer or other animals.  I noticed the tree below was damaged and had its main stem cut.  Perhaps the tree is maintaining spiky, defensive foliage in response to what must have felt like a big bite to the tree (if trees could feel).

Spiky immature growth on a juniper.

On the branch below, you can see both mature foliage on older growth and immature foliage on new growth.  You can also see the cutest, tiniest cones you ever saw on an evergreen tree.  Juniper trees have two varieties: just like humans, they come in male and female forms.  Males trees produce cones like the ones you see below.  Female trees produce slightly larger purple cone-structures we call berries (because they look like berries).  Female trees must be larger before they can produce berries, so I didn't see any berries on our juniper trees, but we should have some in a few years.  We'll have to wait a few years to find out if any of our junipers are females.  Juniper berries are technically somewhat edible, but they have such a strong flavor that they are used mostly as a spice or flavoring.

Male cones, mature growth and immature growth on a juniper.

Below is the real prize.  I found one of these at the outdoor classroom, and I'm not telling where - you're going to have to find it!  No, it is not a piece of gum that someone stuck in the tree.  It is a fungus called cedar apple rust.  It grows on junipers (ok, cedars) for half its life, and it grows on apple trees for the other half of its life.  On junipers, it forms brown hard globs for most of the year.  After a warm spring rain, each of the dimples in the brown glob will sprout a bright orange spaghetti-shaped strand (I'm not making this up!).  The orange things produce spores that float away on the wind, land on a growing apple, and make the surface of the apple look splotchy.  The apple-stage of the fungus then makes spores that float and land on a juniper.  And you thought human life was complicated!

Juniper with cedar apple rust.

A Visit From the Psyllid Fairy

What happens when you lose a tooth?  You get a visit from the tooth fairy.  What happens when you write a blog post about hackberry leaf gall psyllids?  You get a visit from the psyllid fairy!!!

Envelope of psyllids and leaf galls - what a great surprise!

A parent of a lower school student, and an accomplished naturalist, learned about hackberry leaf gall psyllids after bajillions of them emerged from the leaf galls of the hackberries around her house.  She had saved some psyllids to identify them and brought some to my mailbox in an envelope after she saw last week's post.  Here's what was in the envelope:

Two hackberry leaves with galls and five hackberry leaf gall psyllids.

Those tiny dots in the picture above are hackberry leaf gall psyllids.  The large brown things are hackberry leaves.  I decided to have a microscope photoshoot with the psyllids, so I used a camera with a narrow lens and held it up to the eyepiece of a microscope to take the following picture:

Adult hackberry leaf gall psyllid at 20x magnification.

The psyllid in the picture above is long dead and a bit dried out, but it still looks pretty good for a dead bug.  Psyllids are true bugs, and true bugs are insects in the group called Hemiptera.  Hemipterans have mouthparts that are good for sucking plant sap, which is what psyllids are up to when they are living inside leaf galls.  You can see the mouthpart of the psyilld pointing down from the head, which is on the left side of the insect.  You can also see one of its antennae pointing to the left of the head. 

Two dried hackberry leaves, each with a leaf gall.

This time of year, the above leaves are all the evidence you'll see of hackberry psyllids.  The adult bugs have hidden away in bark or in cracks around the outside of your house.

Many thanks to the psyllid fairy for the fabulous psyllids!

Help! I've Got Hackberry Leaf Galls!

Last week students in our outdoor classroom sent the picture below, wondering what it was.  It's a very logical question, since those...things are growing out of what is obviously a leaf, but no normal leaf has weird miniature mushroom-shapes growing out of it.

Hackberry Leaf Galls (photo: M. Sherman)

The leaf above comes from a hackberry tree, whose bark I think is fantastic, and which we will explore later in the winter.  We have a gigantic hackberry tree in the outdoor classroom, and it's at the end of the row of parking spaces near the road.  Here's our hackberry:

Hackberry tree with most leaves already gone for the winter.

If you search through the fallen leaves around the classroom, you can find lots of hackberry leaves right now.  They have toothed edges (lots of tiny points), and they narrow to a tip.  Also, the wider end of the leaf usually is lopsided with one side larger than the other.  Most of the hackberry leaves have one or more of those big lumps on the lower side of the leaf.  The lumps are called leaf galls, and they are scar tissue the tree has grown in self defense against a parasite.

Three hackberry leaves, two with galls, one without.

So, what exactly is a parasite, you ask?  A parasite is a small organism that lives on a larger organism and often uses the larger organism for food, harming the larger organism in the process.  The larger organism is called the host.  There are lots interesting types of parasites in this world.  Dogs and cats sometimes have fleas for parasites.  Deer often have ticks.  Humans can sometimes have lice.  And plants can have parasites too.  The parasite on our hackberry leaves can only live on hackberries, not humans.  It is a type of insect called a psyllid (SIL'-id).  Psyllids look just like tiny cicadas - smaller than a grain of rice.

I broke open this gall, but it was empty.  The adult has already emerged from it.

Hackberry leaf psyllids lay their eggs on the underside of hackberry leaves in the spring.  The eggs grow into immature psyllids that look like this.  The psyllids damage the leaves, which causes the leaves to grow a lump of scar tissue (a gall).  The psyllids eat hackberry sap and live inside the gall as they grow larger through the summer.  In the fall, the psyllids grow into adults and drill out of the gall.  They fly or crawl to find crevices in bark or buildings to overwinter safely.  When the weather warms up in the spring, they lay eggs and start the cycle again. 

Hackberries grow well in Middle Tennessee, yet they almost always have hackberry leaf galls damaging their leaves.  The trees don't seem overly harmed by the gall psyllids' damage.  This is normal parasite behavior.  Most parasites don't cause extensive harm to their hosts.  They take just a little food from them but not enough to kill them.  If a parasite ate too much of its host and killed it, the parasite would be out of food and would die too.  Parasites use their hosts in a sustainable manner so that their food source will be available in the future.

American Chestnut Trees

Here's something you don't see every day...

American chestnut (Castanea dentata) leaves.

 ....an American Chestnut tree!  My parents are growing American Chestnuts (Castanea dentata) on their property to help bring this great American tree species back to prominence.  Mom learned about the American Chestnut and wanted to get involved, and Dad was game to help Mom put in the work needed to plant and protect these trees as they try to survive.  They are both pleased with their American Chestnuts.

Dad with an American Chestnut on Father's Day.

Eastern forests in the United States were once dominated by this tree species.   If you think about how prevalent oak trees are in the Eastern forests of this country, it gives you a sense of the size of the American Chestnut's niche.  Its nuts provided great quantities of seriously delicious food for people, deer, bears, squirrels and many other animals.  It is a fast-growing member of the oak plant family (Fagaceae), and its wood is strong and particularly resistant to decay, so it was an extremely useful lumber-producing tree.

Why am I speaking in the past tense?  Because this tree species is now mostly gone due to the chestnut blight.  Chestnut blight (Cryphonectria parasitica) is a fungal disease that evolved in Asia and was accidentally brought to the U. S. in the late 1800's, probably on furniture, lumber or nuts.  Chinese Chestnut trees evolved with the disease, so they are resistant to it, but our trees were not resistant, and they succumbed to the disease as quickly as Native Americans died from European diseases introduced by the first European settlers of this land.  The disease was discovered in 1904, and by 1950, almost all the American chestnut trees were dead, with only small shrubby root sprouts left surviving.

Chestnut catkins (flowers).  The narrow ones have only male flowers, the upper one has some pollinated female flowers, which will produce nuts.

Several organizations, including the American Chestnut Foundation, are trying to breed blight-resistant chestnuts and repopulate our forests with this missing foundation species.  Chestnut-lovers are using existing trees to search for blight resistance.  They are also breeding Chinese Chestnut trees with American chestnut trees, eliminating those that don't survive the blight, and crossing the offspring back with American Chestnuts to result in trees that are mostly American but with the Chinese blight-resistance genes.  Right now, there exist trees that are 98% American with 2% Chinese genes.  These mostly American Chestnuts are responding well to blight exposure.  Nothing against Chinese Chestnut trees - they are great, but they're adapted to Chinese ecosystems.  Chestnut-lovers and ecologists want to maintain both species - with the American Chestnut trees back in the ecosystems here.  In the mean time, many people have planted Chinese or European Chestnuts in their yards in order to have some chestnuts to eat in the fall. 

Chestnut catkins with pollinated female flowers that have become burs, and male flowers above them.

Chestnuts have either all male flowers or male and female flowers.  Mom and Dad obtained dozens of chestnuts from the American Chestnut Foundation so they would have many trees and guarantee that they could have cross-pollination between the trees.  Chestnuts cannot self-pollinate.  This time of year,  pollinated female flowers are enlarging into burs.  Burs are spiky fruits that contain chestnut seeds.  In the fall, the seeds will be mature, the fruits will crack open, and the whole bur will fall to the ground.  As soon as the burs crack open, the seeds are mature and ready to overwinter and grow into new trees or to be eaten.

There are a few remaining adult American Chestnuts in North America.  Many of the surviving ones are outside the former range for American Chestnut trees, so the blight hasn't spread easily to them.  Also, there are different climactic conditions outside our chestnut's normal range, which cause the blight fungus to be weaker, or hypovirulent.  Mom and Dad's chestnut trees are outside the normal range, so they may survive longer than other American Chestnuts.  Of the original seeds they planted, about half remain.  Their trees probably didn't die due to blight, but to non-ideal climactic conditions.  Blight tends to affect teenage trees, and these trees are younger.  It is likely that all my parents' trees will eventually die, unfortunately.  Still, they may have a resistant tree, and their trees help maintain living tissue, help educate people about the trees, and help scientists learn more about what these trees need to survive.  With so many people working to solve this ecological tragedy, it appears likely that American Chestnuts will eventually recover.  I'm so proud of my parents for helping the American Chestnut!

Zombie Worms From Planet Sphinx

This time of year, when you're harvesting tomatoes, you often notice part of the plant where the leaves seem to be missing and all that's left are stubby stems.  This is not a deformed tomato plant.  Look closely and you will see a stem that seems to be especially thick and stubby like so: 

Tobacco Horn Worm (Source)

The gigantic worm above is a tobacco horn worm.  It is a positively ravenous caterpillar that literally stuffs itself with tomato or tobacco leaves.  If you touch one, it seems to be so full that its skin feels like a grape leaf around a dolma.  It eats so much of the tomato plant that it can reduce tomato productivity dramatically.  Farmers dislike these caterpillars, but I bet most of them also admire the strangeness of these creatures. 

Tobacco horn worms grow from tiny eggs deposited on tomato plants by the Carolina sphinx moth, a gorgeous night creature that moves and hovers like a hummingbird.  It has a coiled proboscis that it uses to probe nectar from night-blooming flowers trumpet-shaped flowers.  Here is a sphinx moth feeding on an azalea:

Sphinx moth feeding.  (Source)

 Sometimes when you see a tobacco horn worm, it will appear to be covered with dozens of white, ovoid bead-like objects.  When you see this, you know the horn worm is one of the walking dead.  The white things are the pupal cases of a type of braconid wasp, which lays its eggs under the skin of the horn worm.  The eggs hatch inside the horn worm and eat the worm from the inside out.  The larvae begin to burst out of their horn worm and weave little white cases with lids around themselves.  In a few days, they will emerge as adult wasps, and the horn worm will expire as a shrunken husk of itself.  The adult wasps will go on to infect and kill other horn worms.  Braconid wasps are friends of the farmer because they help do the work of dispensing with horn worms.  Anytime a farmer sees an infected horn worm, she lets it be so that more wasps will hatch.  Farmers can even order braconid wasps in the mail to release on their farms.  Here is an infected horn worm:

I know it's hard to see, but there is a parasitised tobacco horn worm in the middle of the picture.  I'll bring a better camera to work tomorrow.

 Here are some better pictures I didn't take from this website:

A good picture of an infected hornworm.

An adult braconid wasp spreading its wings for the first time.

Giant Hornets of Death: Cicada Killer Wasps

For some reason in my Entomology class, my professor really liked to talk about giant ground hornets and how territorial and mad they were.  He told us they would be a trophy to add to our insect collections, but that they were dangerous to catch because their sting was so painful.   Unfortunately, I was afraid of them for years until the owner of the farm on which I work told me that the insect I knew as a giant ground hornet was the same as the cicada killer wasp, which her 9-year-old son loves to follow because of their unique behaviors.

Cicada Killer Wasp, picture source

Well, I had to do some research, and she is absolutely right - they are the same, and cicada killer wasps are generally docile and always awesome.  I actually got to know cicada killer wasps a few years ago because there were dozens of them living in an ivy patch outside the school where I used to work.  We science teachers had to research them to see if they were a danger to the students, and we decided that they were so easy-going that we'd just keep kids from walking through the ivy and that the third graders would study them as part of their Biology unit.  They loved it and no one got stung.  I wish I had connected the dots at that time between cicada killers and giant ground hornets, because I had a close encounter with a giant ground hornet on the farm last week and had a very unnecessary scare.  It would be less confusing if we all just used the scientific name, Sphecius speciosus.

Cicada killer wasps/giant ground hornets are gigantic, up to two inches long.  They are yellow/orangeish and black and variously patterned with usually black abdomens.  They are charismatic animals, and they live large on the landscape.  When they are present, you will see them, but don't be afraid.  The females are technically capable of stinging, but they won't unless they are actually handled.  I'm assuming the ones in the picture below are deceased, either that or they are in the process of stinging.

They're gigantic!  Source

Cicada killer wasps emerge from the ground in early summer.  They feed on flower nectar and search for mates.  After they mate, the females dig a burrow 1-4 feet into the ground, piling up dirt at the entrance to the ground.  The burrows are quite visible in lawns, and many lawn-farmers usually don't appreciate the mini-mole-hills.  They wasps actually prefer bare soil, since it's easier to dig through.  Males cruise around the entrance to the burrow, protecting the burrow from enemies and other males.  Their buzz is definitely bigger than their bite because males can't sting.  Still, they can and do fight fiercely in mid-air, careening around in wrestling-holds with their competitors.

After digging a burrow, the females go on the hunt.  They search for cicadas - but not to eat.  When a female finds a cicada, she stings her prey, paralyzing it but not killing it.  Then the female begins the gargantuan task of hauling the cicada, which can be three times her weight, back into her burrow where she will lay an egg on it and seal it into a chamber.  The egg hatches into a larva which then slowly eats the cicada until the cicada is a shrunken shell and the larva is huge.  Females will make several chambers in each burrow - each of her children gets its own room.  The kiddies overwinter as larvae to emerge next year.

The Wasp Finds a Victim, Source

It seems the female can tell the sex of the eggs she lays.  Her female offspring get two or three cicadas to eat, and her male offspring get just one.  Females grow much larger than males, so they need more food.

Cicada killer wasps have their own parasites that lay their eggs on the cicada killer larvae.  Velvet ants, which are wingless wasps, are parasites on parasites.  If you must fear an insect, you could choose velvet ants (also know as cow-killer ants, though they don't actually kill cows).  Velvet ants have a MAJOR sting, which I can attest to from personal experience.  If you see one, don't bother it!

Velvet Ant Source

The Ladybug's Obnoxious Cousin

Everyone loved ladybugs as a child.  We picked them up; we counted their spots, and we may have even brought them inside.  The cute, round bugs are ubiquitous on children's books and clothes.  Ladybugs are some of our earliest friends, so it's surprising to find a pest dressed up like our little pals.

The Mexican bean beetle looks like a ladybug that has rolled in the dust.  It's coppery-brown but still covered in spots and half-dome-shaped.  These beetles are true ladybugs, and they are classified in the ladybug family, the Coccinellidae, which is a subset of the beetle order, the Coleoptera.  All my entomologist readers just cringed a bit after reading that last sentence (sorry!), since ladybugs are not actually bugs.  Entolomogists call them ladybird beetles.  I still use the term ladybug, because that's what I learned when I was 4 years old.  True bugs are in a different group of insects, Order Hemiptera, that includes stink bugs, aphids, leafhoppers and cicadas, but definitely not beetles.

Unlike almost all the other types of ladybugs, Mexican bean beetles are damaging to crops.  Ladybugs are generally famous for their ability to eat vast quantities of aphids and other pest insects.  But Mexican bean beetles are infamous for their herbivorous appetites.  The adult beetles are only moderate consumers of bean leaves, but after they lay their eggs, the larvae which emerge are voracious and insatiable.  Right now the larvae are out in full force.  Their little spiky orange bodies look like tiny Pokemon characters covering the bottoms of the leaves.  Every few days, as they grow, they slip out of their skin and leave it behind to grow a new one.  After a few weeks, they shed their skin and emerge as adult beetles.  Here is a spiky Mexican beetle larva along with some major leaf damage:

The Mexican bean beetle is currently helping itself to the snap beans on the farm, and it seems to show a slight preference for one of the two varieties we have.  They technically will eat any kind of bean plant, but snap beans and lima beans are their favorites.  Many of this season's bean plants have been reduced to lacy brown ghosts of themselves.  The plants are still are squeezing out a few green beans, but these poor plants are stressed to the max by their little inhabitants.

There are many strategies to dealing with Mexican bean beetles on an organic farm.  One strategy is to time the bean crops to minimize damage.  The beetles emerge every year around mid June.  They have overwintered as adults, hiding in warmer places or under debris, and the first adults to emerge are especially drawn to bean plants to lay eggs.  If you plant your bean crop early, you can harvest beans before the scourge begins.  Also, you can wait until the first round of adults emerges and flies somewhere else to look for beans and then plant your crop.  It is thought that eliminating probable overwintering locations can be helpful.  Beans in infested areas should be harvested quickly before the beetles can damage them. In addition, the larvae are susceptible to insecticidal soaps, which disrupts their cuticles and they desiccate. 

The farmer I work for is using a neat but gruesome approach to eliminating the Mexican bean beetles.  She and her son ordered wasps through the mail and released them into the bean field.  These wasps lay their eggs on Mexican bean beetle larvae.  The wasp eggs grow inside the larvae, eating its flesh, and then they emerge from the larvae as adult wasps that go on to lay their eggs on other unsuspecting beetle larvae.  As you might suspect, the larvae do not survive this process!  The parasitized larvae enlarge and turn orange-ish.  At this stage, they are referred to as mummies.  Here is a picture of a bean leaf with both yellow larvae and orange mummies:

The wasps' life cycles repeat in quick succession, and soon the larvae should be mostly mummified.  The bean plants will hopefully recover - even now, their newer growth looks healthy and robust.  Soon I'll be able to stop looking at every ladybug with a suspicious eye.

Here is your reward for making it to the end of this post:  All members of the ladybug family can secrete a noxious compound from their knee joints when they are irritated.  The compound is subtle to our noses, but you can smell it if you bother a ladybug and sniff its knees.  The scent from Mexican bean beetles is a little stronger.  This secretion is a deterrent to predators, who find it distasteful.

Japanese Beetles Put their Thumbs on the Scales

The stability of any ecosystem depends on having a multitude of species playing different roles in that ecosystem.  Some are producers, some are decomposers, some are predators, and no one gets out of hand.  The predators don't take over because there are bigger predators, disease organisms, and competitors for food and other limiting factors. 

Invasive species are the newcomer species that upset the fine balance, altering ecosystems and even causing extinctions.  For example, entire food chains have collapsed in the Great Lakes due to the invasion and overgrowth of the zebra mussel.  The zebra mussel eats all available algae, and other species starve.

Invasive species arrive in many ways - sometimes by expanding their range but usually because they have been carried from one place to another by humans.  Our species of the day, the Japanese beetle (Popilla japonica) (picture), was accidentally brought into the United States from Japan as grubs in soil of ornamental plants.  The new species was detected in New Jersey in 1917 and quickly traced to a plant nursery in the area.

Because invasive species are new to an ecosystem, they are neighbors with other species to which they have not evolved.  That means their neighbors have not had a chance to adapt to eating the invasive species, or competing with it or infecting it.  That's how you end up with entire mountains covered in kudzu.  Or the entire eastern United States covered in Japanese beetles (range map), despite massive federal, state and private efforts to destroy this aggressive farm pest.

But even invasive species are fascinating.  Japanese beetles are beautiful, metallic beetles.  Also, they might just be the only insect capable of growing one body part at a time, according to Dr. Hans-Willi Honegger, an entomologist who also works on the farm.  Dr. H thinks they might be able to grow their jaws, which would make sense since they are such voracious feeders.  Japanese beetles' life cycles are also very interesting.  They emerge in late spring, feed like crazy on leaves of their favorite plants, mate and lay their eggs in the soil.  Most of the adults die off by late August, but the larvae are just starting to get busy.  They burrow in the upper layers of soil throughout the fall, eating roots and organic matter in the soil.  When the temperatures start to drop, the beetles burrow deeper and deeper to stay warm only to come back up when the spring thaw comes again.

On the farm, the beetles are just starting to emerge.  According to the farm owner, the beetles have gotten a little worse over the past few years as their range has expanded.  Now that they are here, they are probably already laying eggs here for next year, and their numbers may increase.  Once beetles establish themselves, they are really impossible to get rid of, but several strategies can help.  A soil drought during early larval stages can kill many larvae; parasitic wasps, worms or bacteria can be released into the area to help kill beetles; traps do attract beetles, but they don't seem to help the overall problem; and insecticides are of course used on non-organic farms.  A surefire way to control Japanese beetles would be to simply wait around long enough for evolution to take its course.  All those Japanese beetles are a great food source for any animal that could evolve to eat them.  Given the rate of evolution, we might only have to wait about 20,000 years for Japanese beetles to become a part of our balanced ecosystem.

Vegetarian Vampires

There is a particularly interesting killer on the farm. It creeps silently toward its prey, searching victims by their shadows and their smell. It kills its victims gradually, sometimes over months, slowly drinking their fluids until there are none left and the dessicated victims expire from exhaustion.

Terrified? Don’t be. These predators are vegetarians – vegans even. They are actually parasitic plants called dodder, in the genus Cuscuta. picture They are the ghostly bleached cousins of morning glories. Dodders comprise approximately 150 closely-related species of flowering vines with no green chlorophyll. Their appearance reminds me of a childhood poem I once loved about spaghetti trees, because they drape over their victims with vast quantities of whitish-yellow strands.

Dodder produces flowers, fruits and seeds like any normal plant. Their flowers are small white clusters that develop in to fruits with multiple seeds. The seeds drop in groups onto the soil to germinate up to 5 years later. Even as the seeds germinate, the plant seems normal. The seedlings grow using the energy stored inside the seed by the mother plant. Since seedlings of most plant species grow from stored energy, it is common for seedlings to be white or yellow like those of dodder. Most plants quickly grow leaves that fill up with chlorophyll, and they start making their own food before they run out of what’s stored in the seed. But here is where dodder is unique.

If dodder seedlings don’t find a victim within 10 days of germination, they will starve. They are somewhat picky eaters, as dodder won’t parasitize grasses or corn. Fortunately, they have evolved the ability to find their preferred foods. The seeds germinate faster when a preferred host is near. They grow toward host stems by growing toward shade (most plants grow toward light), and by curling when they touch something. The most amazing feature of dodder is that it can find its hosts by smell. Dodder can detect and grow toward the volatile compounds produced by its food. Ever smell a tomato plant? Dodder has too!

When dodder finds a host, it punctures the stem and grows into the food veins, or phloem, of the plant. It absorbs water, sugar, minerals and everything else it needs straight from the plant. It discards its own stem and root connecting it to the ground and goes completely airborne as it quickly covers its host plant with spaghetti stems.

Dodders are annuals, meaning they die back each year and regrow from seeds. Some, however, have figured out another way to survive the winter. If they colonize a host plant that survives the winter, the dodder growing inside the host stem can survive and resprout the next spring.

The best parasites don’t usually kill their hosts, because then they would be out of a food source. This is usually true with dodder too. It may kill some of the plants it is in contact with, but it usually maintains at least one live host. It certainly reduces host plant size, which is a problem for farmers when the host plant is a crop plant. Farmers don’t like dodder, and they often have to work hard to get rid of it. On the farm where I work, we hand-pull the dodder and throw it onto mowed grass, where it can’t regrow. Desperate farms can switch to non-host plants for a few years in particularly infested fields.

As much as I know I should hate the plant, I can’t quite. It’s just so darn strange. There are very few truly parasitic plants, and this is one. People always think Venus Fly Traps are the consumers of the plant world, since their little traps look so much like mouths, and they move (!), but sadly, they are not consumers. They are green, indicating chlorophyll, and they get all their energy from the sunlight. They do, however, absorb nitrogen, which is like a plant vitamin, from the flies they trap. Dodder, though, has discarded its ability to photosynthesize. The loss of a trait is fascinating from an evolutionary perspective. Organisms evolve new traits all the time, but they don’t usually lose them. Of course, dodder probably still has most of the genes necessary for photosynthesis, because it is so closely related to and descended from photosynthesizing plants. But there is really no need to spend the energy to maintain those genes. The dodder plants that spent more energy parasitizing host plants and less energy maintaining their ability to photosynthesize found the successful strategy.

Are their any plants that are parasitic on animals? No. But the laws of natural selection say that will be is variation. Doubtless there is some dodder plant out there that might just maybe be able to puncture human flesh and collect its energy from me. So you’ll find me moving just a little bit faster past the dodder plants!