Sunday, March 05, 2017

Introduced Species Develop Unexpected Relationships

Ailanthus webworm moth (Atteva aurea)
© Beatriz Moisset
Somebody I know lamented that the pretty ailanthus webworm moth (Atteva aurea), despite being native, got the name of the tree of heaven (Ailanthus altissima), a Chinese tree that, after being introduced as an ornamental, has become dreadfully invasive. The explanation of this state of affairs makes perfect sense.

The ailanthus webworm moth's original geographic range extended from Central America to southern Florida where its larvae used to feed on several trees, related to the tree of heaven. Probably it was known only by Lepidopterists, those who study moths and butterflies, and not by the general public. When the tree of heaven was introduced as an ornamental, the moth took a liking to it and found it quite digestible. Now it was free to move to other places, following this new host plant. With time it became far more abundant and widespread than originally.

Nowadays it is found throughout eastern and central United States and Canada, wherever the tree of heaven is grown. In fact, it cannot be regarded as a native species in such areas, but an introduced one. Political boundaries are irrelevant. What matters is the ecological distribution.

Even more complex is the story of theColorado potato beetle (Leptinotarsa decemlineata) which is neither from Colorado, nor a potato beetle. Originally this beetle lived on Mexico and southern United States and fed on local plants related to the potato.

Colorado potato beetle (Leptinotarsa decemlineata)
larva and adult
© Beatriz Moisset
The adult beetle is roundish with ten stripes along its body. This is what decemlineata refers to. The larva is also almost round, orange with black spots. The larvae feed on buffalo bur, so called because its fruits are burs that cling to the fur of animals. The plant uses this means of transportation to spread to other places. It turns out that the beetle larvae can catch a free ride and also expand its territory by this means. Buffalo bur is related to potatoes. They are both members of the same genus, Solanum.

Buffalo bur (Solanum rostratum)
The potato beetle started getting longer rides when cattle drives became common. This is how it eventually arrived in Colorado and Nebraska. Buffalo bur and a few other members of the Solanum genus were present there, so the beetle found enough food to make a living. And then, one day, oh joy! Potato agriculture started in the United States. Potatoes turned out to be a great food for these beetles, and they were available in abundance. What a bonanza!

Flowers of potato plant (Solanum tuberosum)
© Beatriz Moisset
This is how a beetle that had been hardly noticed until then became the exasperation of potato growers and this is how it earned its common name. It never had one before. Nowadays it has spread to most of North America and, not content with that, it has managed to go to other continents wherever potatoes are grown.

"The presence of aurea in the eastern United States and Canada and its association with Ailanthus altissima (Mill.) (Simaroubaceae) is an interesting subject to be investigated. This plant is an ornamental introduced from Asia and now considered one of the most serious weeds in the United States. It was first planted near the University of Pennsylvania, Philadelphia, in 1784 (W. Thomas, pers. comm.) and from there it spread over the entire country. Once it reached southern Texas, where presumably aurea was already present, the moth started to move north. By 1856 it had reached Georgia, as indicated by the material described by Fitch (1856: 486). Riley (1869: 151) found it common in Missouri, feeding on ailanthus. These records indicate that this showy and common moth was absent in the region before the introduction of ailanthus, and the approximately 70-year gap between the introduction of the host, to the first record of the moth by Fitch, is the time it took the plant to move south and the moth to move north." 

Monday, February 06, 2017

Funny Larvae

Firefly larva © Corey Kallstrom
Who would think that insect larvae can be interesting? They don't have much to offer when compared to their adult counterparts. We can't help but notice adult insects. They fly, they buzz; in fact they can make quite a racket during hot summer nights. Some blink their little green lights over the meadows. Others wear flamboyant colors that seem like works of art.

Glowworm (Phengodes sp.) © Ashley Bradford
Larvae, on the other hand, at least most of them, lead obscure, secluded lives, hiding in secret places. They are rather colorless and shapeless worm-like things, with stubby little legs or no legs at all, with tiny eyes or no eyes at all. None of this is surprising. Larvae have only one function in life, eating and growing bigger. They have nothing to do with the more exciting things like sex. That is left for the adults. Well, larvae actually have two functions. They possess strategies for fighting or evading enemies. Despite such dull lives some insect larvae manage to be quite interesting.

Lightning bug larvae have green lights along their bodies. They look like little trains, and that is what we call them in Argentina, trencitos. One wonders about the purpose of these lights. Adults use theirs to attract members of the opposite sex, but larvae have nothing to do with that. These lights must serve another purpose. It turns out that lightning bugs are highly toxic and bad tasting, so the lights are telling predators to stay away and avoid the unpleasantness.

Monarch caterpillar
© Beatriz Moisset
Some caterpillars use the same strategy. The monarch butterfly caterpillar wears bright black, yellow and white colors arranged in a bold pattern to advertise its toxicity obtained from feeding on milkweeds. Other caterpillars have a variant of this method. The eastern swallowtail butterfly is large and colorful with a pattern of black and yellow. The larvae change their appearance dramatically as they age. The nearly fully grown caterpillar is bright greenish yellow with two large eyes on its head, except that these are not real eyes but just look like them. It is thought that this feature serves to deter predators that erroneously assume that they are dealing with a larger and more powerful creature at the sight of these large eyes. They have another feature for defense against enemies. When threatened, they pop up two bright antenna-like threads. These appendages emit a nasty smell that seems to be effective in keeping other creatures away.

Eastern swallowtail butterfly caterpillar.
Showing its osmateria when threatened
© Beatriz Moisset
Some larvae feed on extremely poor food, such as leaves or wood. It is rather remarkable that they manage to extract nutrients out of them, especially the ones that feed on wood. Most of what they eat goes through their digestive system and comes out of the other end with little modification. A partially rotten log may contain long tunnels filled with what looks like sawdust. They are the holes made by beetle larvae as they grow and advance in search of more food. The sawdust is their poop, which takes the name of frass. Some caterpillars live inside a bunch of leaves which they tie together and curl up so they can hide from predators while they munch away. If you open one of these bundles you find a large amount of frass surrounding the caterpillar.

Caterpillar and some of its refuse or frass
© Beatriz Moisset

Larval tunnels on wood (possibly a beetle)
filled with frass
© Beatriz Moisset
At the other end of the spectrum, there are larvae whose mothers have provided with a rich, highly nutritious food. Many wasps and bees do that. In the case of wasps, the food is insects or spiders; bees, on the other hand, collect pollen and nectar for their brood. These larvae live in splendid isolation inside small compartments, called cells, built by their mothers. The amount of food supplied is slightly larger than the future adult bee or wasp. Almost all of it is converted into flesh and nothing is wasted. At the end of the larval stage, only a small pellet of fecal matter is produced. It gets the name of meconium, comparable to the first bowel movement of a newborn baby. The baby's meconium is the accumulated waste of a few months; so the similarity is strong.

Cell of Crabronid wasp larva (Trypoxylon collinum)
Opened cell reveals the fully grown larva and the pellet of meconium (left)
No remains of the spiders that fed this larva
© Beatriz Moisset
A lot more can be said about larval poop. A number of larvae use their own fecal matter to keep enemies away. Some carry their own feces as an umbrella, others build a little case. They hide inside it the way a snail hides inside its shell. Some insect larvae don't use real poop, but it looks like it. A whole group of caterpillars is called bird-dropping caterpillars. Still others fling their waste as far away as possible so as not to give away their position to possible enemies. I don't need to repeat these stories as I have written about them in two articles that you may find interesting: "The Poop Bug and the Golden Beetle," 2009 and "Poop Flinging and Other Poop Strategies," 2012.

Golden tortoise beetle larva carrying its feces
© Beatriz Moisset

Neochlamisus beetle larva and its fecal case
© Beatriz Moisset

List of articles
Beginners Guide to Pollinators and Other Flower Visitors

© Beatriz Moisset. 2017

Tuesday, July 12, 2016

Pollinator Gardens do Double Duty

Syrphid flies. Pollinators and biological controls. Their larvae feed on aphids
© Beatriz Moisset

More gardeners are learning about pollinators and creating habitat for them. It warms my heart when I see them selecting plants beneficial to pollinators, converting portions of the lawn into flower plots, cutting down on pesticides, and creating the right conditions for pollinators’ nests. Many gardeners are learning to be grateful to pollinators for their services. Some are familiarizing themselves with the most common ones. This is a healthy trend.

Syrphid fly larva devouring aphids
© Beatriz Moisset
An additional advantage of pollinator gardens is that they serve another useful function. Many other beneficial insects depend on pollinator gardens and, in turn, gardens and farms profit from their presence. I am referring to predators and parasites of plant-eating insects. Such beneficial insects have earned the name of biological controls, or biocontrols for short. Many biocontrols need nectar, or nectar and pollen, during part of their life cycle. Some of them prefer to eat insects but can survive on nectar and pollen in the absence of their prey. Thus they are ready to spring to action when the unwanted pest arrives. Gardens lacking on floral resources are not as well protected against pests.

Tachinid fly, Trichopoda pennipes. Its larvae feed on insects
© Beatriz Moisset
The extra bonus of growing a pollinator garden became apparent in studies done by Cornell University. Apple growers could cut down pesticide treatments from ten to two or three a year when they started growing plants for pollinators.

Robber fly, Laphria thoracica, a formidable hunter of insects
© Beatriz Moisset
It is a great thing that the needs of pollinators and those of many biocontrols overlap. Syrphid flies illustrate this point. The adults are bee-like and hover over flowers, earning them their common names, flower flies or hover flies. They feed on nectar and pollen and manage to do some pollination. Their larvae are little green maggots that feed voraciously on aphids. They frequently escape notice. I have learned to check aphid colonies and frequently I find some of these maggots doing what they do best, getting rid of aphids.

An ichneumonid parasitic wasp
Its impressive appendix is an ovipositor (egg laying organ), not a stinger
So there is nothing to fear from this wasp
© Beatriz Moisset
One of the solitary predatory wasps, potter wasp (Eumeninae)
hunting a caterpillar hiding on the flower head
© Beatriz Moisset
Here are a few other examples of biocontrols that prosper in pollinator gardens: Tachinid flies, some of which are hairy, robust and rather ugly, while others are elegant and colorful. All lay their eggs on or in other insects and help control many pests, even gypsy moths and Japanese beetles. Robber flies are fast fliers and skillful at pouncing on unsuspecting victims. Wasps are great garden helpers, both the parasitic ones, which lay eggs on other insects, and the predatory ones, which catch prey to feed their babies. The adults feed primarily on nectar and pollen. It is good to remember that parasitic wasps don’t sting and that most predatory ones are not inclined to do so. In most cases there is no need to fear these wonderful biocontrols. Assassin bugs have front legs that resemble those of praying mantises and, like them, use them to grasp their prey with a swift movement. Not all stink bugs are plant pests; the predatory ones feed on the pests themselves. The merits of lady beetles as eaters of aphids and other soft bodied insects hardly need mentioning. Both larvae and adults feed on these pests. The adults are also fond of nectar and pollen. Other beetles worth mentioning are the soldier beetles, so called because their colors and pattern resemble those of old army uniforms. They are frequently seen visiting goldenrods.

Assassin bug, Zelus luridus
© Beatriz Moisset
Among the plants that feed both pollinators and biocontrols are many Asteraceae, such as coneflowers, coreopsis, yarrow, and goldenrods. Other families include Apiaceae, the carrot family, Lamiaceae, the mint family, Euphorbiaceae, the spurge family, and Fabaceae, the pea family. The best information on planting for pollinators by region is provided by the Pollinator Partnership. You can also find some information in Attracting Beneficial Insects with Native Plants.

Soldier beetles, Chauliognathus
© Beatriz Moisset
In summary, your pollinator garden does double duty, helping pollinators and also biological controls. Perhaps we could say that it does triple duty, as many of the flowers are beautiful and we get to enjoy them too. Happy plantings!

Polished lady beetle, Cycloneda munda
© Beatriz Moisset

© 2015, Beatriz Moisset. First published in Native Plants and Wildlife Gardens. 4/7/15

Friday, July 01, 2016

The Twin Brooks of Yesteryear

Two small streams traverse our condominium and they give it its name, Twin Brooks. They escape notice by most visitors because they are no more than tiny rivulets that a young person, not me, could cross in a single jump. Moreover, all the landscaping has done much to hide them out of sight. Probably a good part of the water runs through underground pipes. But Nature persists as best it can and a good observer perhaps could imagine what the land looked like before all the earth moving, paving and construction that could place in recent times.

Where the two brooks meet, a small pond is present. Ducks and geese raise their families there some years. An occasional blue heron visits the pond and manages to make a meal of some little fish. Also, a muskrat hangs around the edge of the water.

I wonder what the land was like a few thousand years ago before Europeans arrived and populations grew and grew to what they are nowadays. There were Native Americans then, tribes distributed across the land. The ones living here were the Lenape (or Lenni-Lenapi). Were some of them camped in the Twin Brooks site either temporarily or generation after generation? Do I walk on their steps sometimes?

I search for information on the original residents of this land and learn that the Lenape tribe covered part of Delaware, eastern Pennsylvania, all of New Jersey and a southeastern part of New York state. The region was known to them as “Lenapehoking,” which meant land of the Lenape. These Native Americans had a matrilineal system, that is children belonged to their mother's clan, from which they gained their social status and identity. Male leadership was passed through the maternal line and elder women could remove leaders they didn't approve of. Not exactly equal rights but far better than the condition of European women of those days.

So, I try to imagine the Twin Brooks family or families that occupied this area long before our condominium was built and long before I moved here. Perhaps they built their wigwam at the spot where the two streamlets met. Did they grow the Three Sisters –corn, beans and squash– where we have a parking lot? Are there some broken clay shards buried somewhere? Perhaps a little girl lost her doll exactly under my bedroom, the doll her grandmother lovingly made using corn husks and strings. I have no doubt they hunted deer and turkey nearby. Rarely a lost deer wanders into our property, desperately looking for better cover and finding only pavement, traffic and frightening noises.

They must have gathered berries. Still some berry shrubs grow here and there. Chestnuts must have been an important part of their winter food. It is sad to think that practically no chestnut trees are left because of a terrible blight accidentally introduced from overseas.

European colonists coveted the land when their population kept growing, so they relocated the Lenape Indians a couple of centuries ago. “Relocated” is just a wishy-washy way to say that the original residents of the land were robbed of their rights, uprooted and sent to an uncertain fate to the Indian Territory in Oklahoma. There, they had to survive as best they could, making do with limited resources and competing with other tribes already present in the area.

I wonder what we mean when we sing: “This land is my land.”

Thursday, March 12, 2015

Follow the Monarchs

Monarch Butterfly Migration Map

Follow the migration of the monarch butterfly with the help of these maps provided by Journey North. Bear in mind that the subspecies of monarch, Danaus plexippus plexippus, is the migratory one, the one we are familiar with in the United States and Canada. There are 5 non-migratory subspecies in the neotropical region - portoricensis in Puerto Rico; leucogyne on the Virgin Islands; megalippe in Cuba, the Bahamas and the Caymans; tobagi on Tobago, and nigrippus in the Andes. We know next to nothing about these subspecies and their conservation status. Some may be more endangered than “our” monarch. We just don’t know. Some consider all the non-migratory monarchs as members of a single subspecies, megalippe. Still others think that there are 8 subspecies.

The southern monarch, Danaus erippus, of southern South America is closely related and similar looking. It was considered a subspecies of Danaus plexippus, but now it is regarded as a separate species. It is also migratory to some extent. Very little is known about its migration.

Learn more about the present status of the migratory monarch subspecies, Danaus plexippus plexippus:
Conservation Status and Ecology of the Monarch Butterfly in the United States

Sunday, November 23, 2014

Food Chain in the Milkweed Patch

Common milkweed. © Beatriz Moisset
The common milkweed teems with life. Numerous insects feed on leaves, stems, and roots or sip nectar from their flowers. It is ironic that a plant so well protected by powerful toxins and sticky sap behaves like a magnet for a large assortment of creatures. The best known dependent of the common milkweed is the monarch butterfly, but there are many others that deserve our interest. Many species have found ways to overcome the defenses of this plant. They have developed resistance against the toxic cardenolides and methods to avoid the milky sap.

The herbivores are in turn eaten by other insects or spiders, which may fall prey to still other carnivores. It is worthwhile to examine one of these so called food chains or food webs.

Oleander aphids on common milkweed. © Beatriz Moisset
One milkweed feeder, the oleander aphid, has become incredibly common in recent years. This bright yellow-orange aphid was accidentally introduced in this country with oleander plants, widely used in ornamental gardening. It established itself successfully and became adapted to milkweeds. It multiplies in huge numbers near the end of the season. It can do so because females reproduce parthenogenetically, that is without help from males.

Parasitized or mummified aphids. One wasp left the corpse through a round hole. © Beatriz Moisset
This aphid has few enemies. One of them is a tiny parasitic wasp. The mother wasp lays one egg inside a growing aphid and the larva completes its entire life cycle inside the unfortunate host. By the end of the aphid's life, it becomes dark, rounded and dried up. We call that a mummy. The fully grown wasp cuts out a round hole and emerges ready to start parasitizing other members of the aphid colony. It isn't easy to see the wasps, but almost every aphid colony has some of these mummified bodies. So you know that the parasitic wasps have been around.

Parasitic wasp. © Beatriz Moisset

Lacewings, lady beetles and syrphid flies also feed on aphids. Their stories are worth telling but we'll let them be for now.

The food web does not end there. Not surprisingly, many predators visit the milkweed patch in search of animal food. Parasitic wasps seem to be a delicacy among some flies. I have found members of two different families of predatory flies dining on the wasps.

Robber fly (Taracticus octopunctatus) feeding on a parasitic wasp. © Beatriz Moisset
One is a member of the family of robber flies, Asilidae. The name describes the members of this family well. They are seen pouncing mercilessly on their prey. One of them is Taracticus octopunctatus (no common name), a slender, hunchbacked fly with large eyes.
Long-legged fly feeding on a parasitic wasp. © Beatriz Moisset
Another one is a longlegged fly, Condylostylus, a shiny metallic green fellow, with long skinny legs. Parasitic wasps are part of its menu.

I marvel about this food preference. Evidently, these flies look down on the most abundant food nearby, the aphids, and go for the far less common parasites. Perhaps, the latter have less cardenolides than the aphids and this is why the predatory flies prefer them as food.

Longlegged fly caught by a spider. © Beatriz Moisset
A second layer of predation is added to the one just described. A spider feeds on a longlegged fly. We can summarize this food chain this way:
Milkweedaphidparasitic wasppredatory flyspider

Will a bird sweep by and eat the spider? Will it in turn fall prey to a hawk or a snake? How many steps can be added to this food chain? Common milkweed feeds many members of the wild life directly and indirectly. The links of this food chain are numerous.

More on milkweed dependents and visitors