It Takes a Village ….A Milkweed Village

monarch-2

As the obligate host plants for monarch caterpillars, milkweeds are a staple in any butterfly habitat garden. However, milkweed is not just for monarchs! Many other insects call the genus Asclepias home, giving rise to the concept of a “milkweed village.”

Milkweed plants produce bitter tasting toxins called cardiac glycocides, and insects that eat milkweeds have evolved to use these to their advantage, sequestering the toxins in their bodies to protect themselves from predators. Most, if not all milkweed-eating insects have markings of black and orange or yellow, a type of aposomatic coloration that warns predators of their horrible flavor. If a predator such as a bird, lizard, or spider were to eat one of these insects, it would spit it out. The next such insect would be avoided, as its coloration would remind the predator of its foul flavor.

Most butterfly gardeners have encountered the bright yellow oleander aphid, Aphis nerii, which congregates on the new growth, flowers, and developing seed pods of milkweed plants. Aphids are phloem feeders, meaning that they suck the sap, along with the toxins, out of the plant’s vascular tissue.

Ladybug larva

Ladybug larva

The presence of these aphids on milkweed attracts a number of predatory insects. Ladybug larvae and adults (Hippodamia spp. and others) are important predators of milkweed aphids. Other small beetles such as mealybug destroyers, Cryptolaemus montrouzieri, and scale destroyers, Lindorus lopanthae, eat aphids along with other small sap-feeding insects. These beetles are interesting creatures in that their larval stage looks just like their namesake (i.e., mealybugs and scale, respectively).

scale destroyer larva2

Scale destroyer larvae

The maggot-like larvae of syrphid flies also eat aphids, sucking their bodies dry. Syrphid pupae look like little brown or tan teardrops. If you notice these on your milkweed plants, leave them in place to ensure another generation of these beneficial flies.

Syphid fly pupa

Syrphid fly larva

Tiny parasitic wasps such as braconids lay their eggs in aphids’ bodies. The wasp larvae feed on the inside of the aphid until they pupate, then exit as an adult wasp through a tiny hole in the aphid’s exoskeleton. The leftover brown “shell” is called an aphid mummy. These mummies are a good sign that your aphids are being parasitized. Don’t worry, these wasps don’t harm monarch caterpillars.

aphid mummy

Aphid mummies

With all of these great beneficial insects around, I hardly had to spray our milkweed crop at the museum with any insecticidal soap this year. However, if the aphid population on your milkweeds gets to be overwhelming, the best way to knock them back is to spray them off the plants with a sharp stream of water. Try to avoid damaging or knocking off any beneficial insects in the process.

Other “pests” of milkweed plants include the milkweed leaf beetle, Labidomera clivicollis. These chunky, orange and black beetles and their larvae feed on milkweed leaves.

Milkweed Beetle (Wikipedia)

Milkweed Beetle (Wikipedia)

Large milkweed bugs, Oncopeltus fasciatus, are also common in the southern United States. These oblong-shaped, sap-sucking true bugs are orange and black and mostly feed on the developing seeds, flowers and nectar of milkweed plants. They don’t usually cause much damage.

Now we come to the most familiar milkweed inhabitant – the monarch butterfly, Danaus plexippus. As we all know, monarch caterpillars eat voluminous quantities of milkweed leaves, and display the textbook aposomatic coloration of white, black and yellow stripes. Their chrysalids, or pupae, are a gorgeous jade green with gold lines and spots.

monarch

Here in Houston we sometimes encounter another milkweed visitor – the queen butterfly, Danaus gilippus. Queen caterpillars look very similar to the monarch, but they have three pairs of tentacles instead of the monarch’s two. Their chrysalids are also similar, but are a bit smaller and may sometimes be a pale pink rather than green.

Like everything else, monarchs are part of the food chain, and are preyed upon or parasitized by a number of different organisms. One of their most prevalent parasites is a tachinid fly, a gray, hairy species about the size of a house fly. An adult fly female will lay her eggs on a monarch caterpillar and when they hatch, the maggots burrow inside. The maggots live inside the caterpillar, eating its tissues, until they are ready to pupate. At that point they crawl out of the caterpillar and fall to the ground, where they pupate in the soil The maggots often leave the caterpillar after it has pupated, leaving a trail of slime that dries up and looks like white strings hanging from the chrysalis. These strings are tell-tale signs of a tachinid fly infestation.

Tachinid fly larva emerging from monarch caterpillar.

Tachinid fly larva emerging from monarch caterpillar.

Assassin bugs, Zelus sp., are frequent visitors to milkweed plants. This true bug will stab monarch caterpillars with its rostrum or beak, paralyzing the victim and liquefying its insides, making it easier to consume.

Vespid wasps are another important predator of monarchs. The familiar large red wasps, Polistes carolinus, and the smaller yellow and black European paper wasp, Polistes dominulus, both hunt caterpillars as food for their own hungry larvae. Once a wasp finds a host plant with caterpillars, she will come back regularly to check for more, especially in the summer months when wasps are the most active. This can be upsetting to butterfly gardeners. To protect your caterpillars from these all-too-efficient predators, place a screen such as a pop up or mesh laundry hamper between them and the wasps.

Polistes carolina  Photo by Val Bugh

Polistes carolina Photo by Val Bugh

 

Polistes dominulus

Polistes dominulus

Finally, a parasite of notable concern that specifically affects monarchs (and also queens) has emerged on the scene of butterfly gardening. This protozoan parasite, Ophryocystis elektroscirrha, commonly known as Oe, begins with a dormant spore, usually deposited by an infected female monarch as she lays her eggs on a milkweed. When the caterpillars hatch and begin to eat, they consume the Oe spores along with the leaf. Once inside a caterpillar’s gut, the spores become active and reproduce several times. When the butterfly emerges from its pupa, it is covered in dormant Oe. spores, giving rise to the next generation of infected monarchs. Mildly infected butterflies may show no sign of infection but as Oe levels build up, they eventually cause problems such as weakness, deformity, and even death.

OE Life Cycle (Monarchparasites.org)

OE Life Cycle (Monarchparasites.org)

The annual migration to Mexico each fall helps to weed out infected butterflies, which are usually too weak to make the long trip and die along the way. However, some monarchs don’t migrate and may stay in the Houston area all winter long. In the south, butterfly gardeners primarily grow tropical milkweed, Asclepias curassavica, which unlike the native milkweeds does not die back to the root in the fall. Oe spores can remain viable on the leaves of this perennial species for some time, infecting the next generation of caterpillars that eats them. As this situation repeats, it can cause populations of severely infested monarchs. We therefore encourage butterfly gardeners to cut back their tropical milkweed every spring after the first generation of monarchs arrive and eat the milkweed down, and then again in the fall before or during the migration, so that the butterflies will be encouraged to migrate and not overwinter here.

Spiny soldier bug nymph eating a monarch caterpillar. (Photo by Dan McBride)

Spiny soldier bug nymph eating a monarch caterpillar. (Photo by Dan McBride)

With all of these challenges, it’s no wonder that only five to ten percent of monarch eggs make it to adulthood. Keep in mind however, that monarchs are an important part of the food chain and without their survival and natural demise, our native ecosystem would not be as diverse as it is. In any case, human interactions with the environment have caused the most damage to monarch populations – huge amounts of monarch habitat has been lost due to the expansion of agricultural land and use of Roundup Ready crops. Planting butterfly-friendly gardens, especially if they include milkweed, can help mitigate this loss of habitat.

You can do your part by attending our fall plant sale at the Houston Museum of Natural Science. Stock up on the nectar plants that monarchs need to fuel their migration as well as host plants for native butterflies.

The sale will be held on Saturday, October 11th from 9:00 a.m. until noon (or until plants are gone), and will take place on the 7th level of the museum parking garage. Remember, the early bird gets the larva, so to speak, and don’t forget your wagon!

Beetle-mania!

Think it’s good luck when a ladybug lands on your hand? Do you delight in dancing fireflies lighting up the night? Are you gaga for grub worms? Then, my friend, you’ve caught it…Beetle-mania! I know what you’re thinking; ladybugs and fireflies are beetles? Isn’t a grub a worm!  Don’t fret if you can’t name them all. Coleopterans (members of the beetle family) are a widely diverse group of organisms that make up a quarter of all animal species known to science.

scarab beetle
Creative Commons License photo credit: llisa

Beetles, like all insects, have an exoskeleton made of chitin. (Side note: THIS is the reason they crunch if you accidentally step on them!) They have six legs and can come in all the colors of the rainbow. Scarabs, in particular, are sought after by collectors for their brilliantly hued, glossy forewings. Think you’d need to visit an ancient Egyptian tomb to see a scarab? Think again! Just turn on your porch light and open your door around the sixth month of the year and try to keep the June bugs out.

Lady Beetles (Coccinellidae)
Creative Commons License photo credit: jpockele

Beetles are not just fun to look at (though they really, really are); they provide invaluable services to many human professions. Gardeners, landscapers, and farmers use beetles to help in pest management. For example, some species of lady beetles, commonly known as ladybugs or ladybird beetles, are aphidophagous, meaning they eat aphids. Other beetles prey on parasites, such as caterpillars, and even eat fly eggs.

Forensic entomologists can use beetles to identify a post mortem interval. Insects like beetles and flies are among the first to discover a corpse. Members of the Scarab, Carrion, and Carcass beetle families arrive at the scene to help break down the carrion and to eat the larvae of the flies that got there first. (Side note 2: Look up some info on blow flies to learn more, especially Chrysomya rufifacies, the hairy maggot blow fly! My favorite.) Dermestids, or Skin/Hide beetles, are among the last wave to arrive. Because of the very predictable development times of these beetles, forensic entomologists are able to count backwards to estimate the postmortem interval, and can sometimes do so to within a few hours.

Now that your brain is full of beneficial beetle facts, go look under a rock and see what you find! Don’t be surprised if you like it. If you want more, come to the Entomology Hall in the Cockrell Butterfly Center and discover the world beneath your feet!!!

Photo from US: Insect Identification

cicada

Yes! This week, the title “Insect Identification” is really an accurate title. One of our own, Chris Flis, took this awesome photo out at the HMNS paleological dig site in Seymour, Texas, where our team is working hard to uncover new bones and fossils. This is our first insect submittal and I’m very excited because this is one incredible insect.
This is an insect that you rarely see, but find traces of them everywhere. During the warm months of the year, people all over the country come accross peculiar shells which look like bugs, but appear to be empty. As a kid, I would find these all over my grandparents heavily wooded backyard and I loved to scare my brother and sister with them. I would call them, along with about 99.9% of the population, locust shells. It was not until I studied insects in college that I discovered that locusts are a kind of grasshopper, and these shells I was seeing everywhere belonged to a bizarre little bug called a cicada. In this photograph, you can see the actual adult cicada clinging to its old shell, or exoskeleton. It is probably waiting for it’s new skin to completely harden so it can roam the forest in search of a mate.

Cicadas are insects belonging to the order Homoptera, an order containing mostly plant pests such as aphids, scale insects, mealybugs, and whiteflies. Cicadas themselves do very little damage to plants and are not considered pests. They have simple or gradual metamorphosis, meaning they have only three different life stages: egg, nymph, adult. The nymphs spend their time underground sucking fluids from roots of trees. When it is time for them to become an adult, they tunnel their way out of the earth, attach themselves to the bark or branch of a tree, and molt for the final time. The adult that emerges looks almost identical to the nymph, only larger with big beautiful wings. This always happens at night, so we don’t see the adult, just the skin they leave behind which is perfectly preserved and very crunchy. The adult males are capable of producing sound from their abdomen which they use to track down a mate. Cicadas are active during the daytime, so that VERY loud hissing sound you hear during the hottest hours of the day are lonely male cicadas. At night, we are serenaded by nocturnal crickets, katydids, and of course, frogs. There are around 3000 species of cicada, each producing a unique sound. You can click here to listen to some different cicada songs as well as some katydids and crickets. Most cicadas have a pretty long lifespan, remaining underground as a nymph anywhere from one to three years. These are known as annual cicadas and can be seen every year. This one in Chris’s picture is an annual cicada.

Now why do I say these are such incredible insects? You may have heard of a periodical cicada. These cicadas belong to the genus Magicicada which contains only seven species. There are two types of periodical cicadas; 13 year and 17 year cicadas. This means that these guys spend either 13 or 17 years as a nymph, underground sucking on roots, which is incredible. Not only do they live for an unbelieveble amount of time, their emergences are synchronized, creating one of natures greatest phenomenons. When an emergence takes place, millions of cicadas come out of the ground for several weeks providing food for hundreds of species of birds, mammals, reptiles, and other arthropods. These animals feast on cicadas until their bellies are about to pop, but they don’t even put a dent in the cicada population. So many of them die that the forest floor is covered by several inches of decomposing cicada bodies, giving the trees a tremendous dose of fertilizer that can only come from such an incredible event. This spectacle of nature can be seen in my favorite program ever, the Planet Earth series (the Seasonal Forests episode). These periodical cicadas look much different from the usual annual cicadas. They have a black body, red eyes, and orange veins in their wings. This website has a lot of great information about periodical cicadas, including an emergence chart which shows when certain broods will emerge next.

Thanks so much for sending in this picture Chris, it spurred such an interesting topic. I hope I’ve cleared up ya’lls misconceptions about cicadas and I hope you find them as amazing as I do.

Adult Cicada

Creative Commons License photo credit: trekkyandy
A Periodical Cicada