Bug of the Week – European Elm Bark Beetle

Salutations, BugFans,

 

The BugLady loves finding these runes, inscribed by long-departed insects (they are also reminiscent of a diagram of meiosis from the BugLady’s past).  The tale that they tell is one of lust and fertility and survival (OK – a little florid, but it’s snowing.  Again).  Turns out that there was much more to the story of the European elm bark borer than first meets the eye.  Put your feet up – it’s an epic tale.

 

There are a number of beetle families whose larvae burrow beneath the bark.  The offspring of the prominent and showy Buprestids (metallic wood borers like the infamous Emerald ash borer) and Cerambycids (Long-horned beetles) are borers.  Bark beetles, in the weevil family Curculionidae, are small and seldom noticed, and they tunnel as both adults and larvae.

 

Older books and internet sites list them in their own family, Scolytidae, but with the constant review and reshuffling that is scientific taxonomy, they are now grouped with the weevils.  Their subfamily, Scolytinae, gives a nod to their former classification.  There are about 6,000 species of Scolytini worldwide; 525 in North America.  They look a lot alike, and one way to narrow down the species is by noting the type of tree, the location of larval feeding, and the shape of the larval galleries (tunnels) (Scolytinae also includes a group called the Ambrosia beetles, who plant fungal spores in their tunnels and then eat the plant tissue that is softened by the growing fungi.  The larvae of European elm bark beetles tunnel, but they do not farm).

 

There are a number of serious pests, both native and introduced, within the Scolytinae, like the several species of extremely worrisome pine beetles that are impacting trees in western and southeastern North America.  The European elm bark borer (Scolytus multistriatus), a.k.a the Dutch elm weevil, a.k.a. the Smaller European elm bark beetle, is an alien that was first observed in the US in 1909, though it undoubtedly arrived earlier.  Surveys in 1933 found the beetles clustered around the seaports of Boston, New York City, and Philadelphia.  Look for them today across the US, north into Canada and south into Central America, wherever elms grow.  Look sharp, because they’re tiny – only 2 or 3 mm long (1/8 inch) long http://www.eakringbirds.com/eakringbirds5/insectinfocusscolytusmultistriatus.htm.

 

For EEBBs, feeding and breeding are interwoven.  Long story short – newly-emerged adults seek food, preferring to feed in the top half of healthy elms in a twig crotch, at the twig-leaf connection (axil), and sometimes on the buds.  When they are sated (or when, as one source implied, they have seen enough of the sun), they look for a cut, diseased or compromised elm.  The female EEBB burrows under the bark and creates a long (up to four inches), straight tunnel parallel to the grain of the wood (in one of the BugLady’s pictures, Mom’s tunnel curved when she encountered the tough wood of a knot).  A widened cup at one end serves as a mating chamber.

 

At intervals along the sides of her tunnel she carves little alcoves, each a repository for an egg, and when she is finished ovipositing, she remains in the tunnel to protect her young and keep the tunnel clean (her offspring aren’t as tidy, and their tunnels are packed with frass (bug poop)).  When the eggs hatch, the larvae chew outwards “with the grain,” at right angles to the maternal gallery, eating their way through the living vascular tissue (cambium and phloem) under the bark.  Unless population densities are high, larval tunnels don’t intersect, and as a larva fattens, so does the circumference of its tunnel.  It will pupate in the outer bark at the far end of its excavation.  There may be several generations in a summer, and the fall larvae overwinter under the bark as larvae, to metamorphose when elm leaves appear in spring.  When a cohort of adult EEBBs emerge, they leave the bark with a “birdshot” appearance.

 

Ah, but the devil’s in the details, and the escapades of the adults are a testament to Better Living through Chemistry [av_side note – check out the etymology/origins of the saying “the devil’s in the details” in Wikipedia].  Hungry adults may locate healthy elms via the elm’s airborne scent, or they may have to land on the tree to “scratch and sniff.”  Receptors on their antennae allow them to “smell.”  These tree odors act as feeding stimulants, and as the beetle chews on the twig, more elm “volatiles” are released and more beetles come.

 

The EEBB locates its brood tree in the same way.  Damaged elms give off a number of chemicals, one of which is similar to vanilla and another that smells like “sweet and spicy apples.”  As they excavate their brood tunnels, virgin female EEBBs release “aggregation pheromones” (airborne chemical attractants) at the entrance to the breeding chamber that invite both sexes to the party (even her frass is scented).  The brood tree ends up as a beetle mecca (EEBBS prefer trees that have other EEBBS in them), which results in more egg-laying (a “breeding attack”), which wears down the tree’s defenses.  There’s a tiny, parasitic wasp that follows its nose to the EEBBs, too.  Pheromone traps offer a way to control EEBBs.

 

This tunneling by EEBBs damages their (already ailing) host trees mechanically because the centipede-shaped galleries of the larvae interrupt the transport of nutrients throughout the tree, but EEBBs pack a one-two punch.  The first recorded case of Dutch Elm Disease (DED) in the United States was recorded in 1928, and in 1937, a report from the Massachusetts Agricultural Experiment Station states that the EEBB is “now considered to be the most important insect carrier concerned in the spread of the causal fungus [av_for Dutch elm disease] in the United States.”  DED first appeared in Europe (in a significantly milder form) in 1910, and having made landfall here in the late 1920’s, it arrived in Chicago and St. Paul by 1960 and California by 1973.

 

Dutch elm disease in the US is caused by two fungi, Ophiostoma ulmi and Ophiostoma novo-ulmi, and it’s transmitted by the EEBB, by a native elm bark beetle and by the alien Asian/Banded BB, a 2003 arrival that’s in the same genus as the EEBB.  If the dead or dying tree chosen by Mom for the natal chamber was infected with the Dutch Elm Disease (DED) fungus, the new adults will be coated with spores when they emerge and may also have spores in their guts.  They will inoculate both the healthy trees they feed on and the trees they lay eggs in.  Because of differences in the phloem tubes over the growing season, elms are more susceptible to DED at the beginning of summer, when the first brood of EEBBs appears.  Ironically, damage from DED occurs when the tree plugs its own xylem/water-transport tubes in an effort to isolate the fungus.

 

The BugLady found a study in which Webber, et al demonstrated that in the early stages of their lives, EEBB larvae can’t tolerate the DED fungus (and possibly other kinds of fungi, either); if they are surrounded by fungus-infested tissue, they don’t make galleries.  Older larvae can eat fungi with impunity.  There is, apparently, a window on the usefulness of a declining elm.

 

Are trees helpless against the beetles?  Plants often mount a defense against their attackers by producing insecticidal/fungicidal/nasty-tasting/toxic substances, thorns, or sticky sap.  When it comes to EEBBs, not all elms are created equal.  The BugLady read one account of a Chinese elm that thwarted the beetles with its gluey sap.  The fungus transmitted by beetles may be their counterattack against the trees’ defenses, and more distressed an elm becomes, the more nursery trees are produced.

 

And then there’s the phoresy.  The BugLady is always blown away when she comes across examples of phoresy (benevolent hitchhiking), a stunning indication of how profoundly complicated things are in Nature.  In a European study, both mites and nematodes (roundworms) were discovered in EEBB galleries (nematodes are found everywhere in Nature), and mite associations have also been observed with American EEBBs, as early as the 1930’s.

Although their ecological roles are unknown, scientists hypothesize that the mites move with the adult EEBBs from their natal tree to the tree where eggs will be laid.  When they hop off of their transport, mites spread fungal spores in their new location.

 

The BugLady recommends A Guide to Nature in Winter by Donald W. Stokes, and Tracks and Signs of Insects and other Invertebrates by Eiseman and Charney.  Both will help BugFans make sense of the clues that insects leave behind.

 

FYI, the internet rhyming site was stumped when it came to a rhyme for Scolytus multistriatus.  Go figure!  Hiatus?

 

The BugLady

Bug of the Week – Chickweed Geometer Moth

Salutations, BugFans,

 

This lovely little Chickweed geometer moth appeared on the BugLady’s tomatoes (the male, note the fuzzy antennae) and her front porch (the female – note the plain antennae).  She blames her lamentable inattention to small moths for not noticing them before, because they are allegedly pretty common.

 

Chickweed geometers are members of the family Geometridae.  As BugFans will recall, geometer caterpillars are called inchworms – they are missing several sets of prolegs in their midsection and that causes them to “inch” (hike their rear end toward their front) rather than “undulate.”

 

Proceeding on the assumption that scientific names are not just meaningless tongue twisters, the BugLady loves to find out the etymology of insect names.  Geometer means “earth measurer.”  Bugguide.net says that the genus part of a Chickweed geometer’s scientific name (Haematopsis grataria) comes from the Greek “haima” or “haimatinos,” meaning “blood/of blood,” probably refering to the pink markings on the wings, which can approach blood red in some individuals.  On-line dictionaries attribute the species name, “grataria,” to a Catalonian word (Catalonia is a region of Spain) meaning “to scrape, itch, squawk or scratch.”  The BugLady is going to have to chew on that one for a while.  According to Donald Borror’s Dictionary of Word Roots and Combining Forms, the prefix “grat,” from the Latin, means “pleasing” or “favor.”  A choice between grace and irritation.

 

Except for the far east and west coasts, CGs are found from the Rio Grande well north into Canada, especially in the eastern half of the US.  Because their larvae eat the leaves of chickweed (and clover and smartweed and other low plants) and because lawns may be hotbeds of chickweed and clover, CGs are often found in manicured situations, where their presence is welcomed.  Adults may sit on flowers, and they may pollinate flowers, but they probably do not eat.  They are eaten by predators, but Sogaard, in Moths and Caterpillars of the North Woods, wonders if their cheery colors signal that they are distasteful.

 

CGs are another “not much else looks like this” species.  Males and females are similar, with wingspreads just under an inch.  Because they are colorful and diurnal (day-flying), and they perch with their wings spread flat, they are often mistaken for butterflies.  Geometridae is a huge family, but Haematopsis is a tiny genus, with only this species in it.

 

CGs are seen throughout late spring and summer, until the first frosts.  The larvae develop quickly (a month as larvae; two weeks as pupae), there are several broods throughout its range.  The caterpillars from the first brood pupate briefly in a cocoon that they spin.  Larvae of the final brood overwinter as pupae.

 

The BugLady

Bug of the Week

Howdy, BugFans,

 

Here are two pretty beetles to remind us of summertime.

 

SHINING FLOWER BEETLES appeared in the first half of August, covering goldenrods and a few other members of the Aster/Composite family as though scattered from a cosmic pepper grinder.  Tiny, shiny, round, black dots that were, just as suddenly, gone.

 

SFBs in the genus Olibrus are in the Shining flower beetle family Phalacridae (from the Greek for “shining” and “circle”), and, first off, they’re misnamed (more about that shortly).  The SFBs are a small family, with about 125 species in North America and fewer than 650 species worldwide.  Olibrus is the largest of the 50 or so genera in the family.  Since they’re in the one to three millimeter size range, keying them to species requires scrutinizing their hind feet, antennae or, as Monty Python would say, their “naughty-bits” under good magnification.

 

Most members of the extended SFB family dine on fungus spores or hyphae (the threadlike filaments that make up the fungus’ support system).  As adults and as larvae, Olibrus SFBs are found on flowers.  Olibrus adults feed on pollen (one author wondered how, with SFBs so numerous, the goldenrods had enough pollen left to reproduce), and the larvae, buried deep in the flowers, drink only sap (they chew through flower buds and seeds to get the plant juices flowing, but apparently they spit the solids out and start sipping).  Because Olibrus SFBs are so conspicuous and easily collected, they have become the poster-beetles for the whole family, so while some sources refer to the family as Shining Mold beetles, most call this group of fungus-eaters the Shining Flower beetles.

 

Olibrus SFBs produce a single generation a year, timed to coincide with the flowering of their favorite composite.  In fall, the larva falls from the plant and tunnels into the soil, where it spends the winter as a pre-pupa; it will pupate the following spring or summer.  The beetles’ domed shape allows them to practice the stop-and-drop response when alarmed.

 

When the BugLady encountered these lovely black beetles with red epaulettes and derrieres, they were helping to control the sumac population.  With no common name in sight, the BugLady hereby dubs them the BLACK AND RED SUMAC LEAF BEETLE (Cryptocephalus quadruplex) (probably), though they are polyphagous (which means that they eat a bunch of different plants including sumac).  According to reports from the late 1800’s and early 1900’s, their taste for raspberry and blackberry leaves, got them blacklisted as pests.

 

Their genus name, Cryptocehpalus (“hidden head”) refers to the fact that the beetle’s head is recessed or tucked/tipped down into its thorax (quadruplex sounds like a movie theater with four screens, but according to bugguide.net, it is from the Latin for interwoven or network. The BugLady doesn’t get it, either.).  BaRSBs are one of about 80 species in the “case-bearing” leaf beetle bunch, beetles whose larvae travel about in cases made from their own fecal material.  Females oviposit in the leaf litter, the larvae eat dead leaves and grow there, and the almost-grown larvae spend the winter deep under the insulating leaves and are ready to emerge as adults by the end of May.  At 4 mm in length, they are giants next to Olibrus SFBs.

 

Other than their presence on the lists of many state museums and nature areas, these are small, pretty, “unsung” leaf beetles in the huge family Chrysomelidae.  BaRSLBs live within a giant area running from Maine to Georgia to New Mexico to Montana, spilling over into Canada.

 

The BugLady

Discovering Snowflakes

Our featured finding this month is….snow!  With all the snow in our area this year, its a great time to get outside and explore.  Our education staff put together a fun activity for members of any age.

Make Your Own Snowflake ID Book

Have you ever looked at snowflakes up close?  Are there really no two alike?  Create a snowflake ID key and find out more about the snow all around you.  This is a great activity for everyone in the family.

There are seven common snowflake shapes: Hexagonal Plates, Stellar Crystals, Hexagonal Columns, Needles, Spatial Dendrites, Capped Columns and Irregular Crystals.  You can use the chart below or do some research on the internet to easily create your own key.  You’ll find different snowflake shapes as the temperature and humidity levels change – so go outside with each snowfall to see if you can eventually find all seven shapes!

After you have created  your key, attach black felt to the left side of the paper with glue.  This will allow you to “catch” your snowflakes right next to your key for easy identification.  Make sure to put your key outside or in the freezer before catching snowflakes – that way they won’t melt right away!  How many different snowflakes can you catch?

snowflake chart

Bug of the Week

Howdy, BugFans,

This is a rerun (with a little tweaking) from the Christmas season of 2009.

Ah, the surprising American Pelecinid wasp!

Surprising because it is an impressive insect to see flying through the air; because despite similarities in size and shape, it is not a damselfly; because it appears to have a fierce stinger but appearances can be deceiving; because it is the lone remaining genus in its family; and because it’s got that parthenogenesis thing going.

The BugLady is always happy to see this startling wasp, and she saw more of them than usual in the summer of 2013. American Pelecinid wasps (Pelecinus polyturator) belong in the family Pelecinidae, and they are a New World wasp (with distant, fossilized/amber-ized relations from the Old World). APWs are relatively common in woodlands, grasslands and gardens from Argentina through Canada, where they are seen from mid-summer to early fall. Two other PW species occur exclusively south of the border. APWs are whip-thin, shiny, and black, with extra-long antennae and a long, curved abdomen. A female may measure almost 2 ½ inches long (five-sixths of her length is abdomen), but males are only about an inch long. Pelecinids have short wings for their length and are slow flyers as a result (except when you’re stalking them with a camera).

The diet of adult APWs is nectar, perhaps supplemented by some pollen and water. APW larvae follow the parasitoid path. Mom reaches down into the soil with that wonderful, jointed, flexible abdomen and determines the presence there of a May/June beetle larva (grub). She deposits her egg directly into/onto the beetle grub and goes her merry way, and when her larva hatches, it dives into the grub. Its feeding kills the grub, and the APW larva continues to feed/scavenge on grub’s tissue until the immature wasp is ready to pupate, right there in the soil. Biologists who gather June bug larvae to rear for experiments often find themselves with wasp collections instead.

A further word about parasitoid(ism). Parasites find it counterproductive to kill their hosts; parasitoids live to kill their hosts/kill their hosts to live. The only question is – how fast. Some parasitoids prefer live food and eat around their host’s vital organs until it’s time for the End Game. APWs do the deed quickly because they don’t mind eating dead tissue. The term necrotroph (from the Greek nekros- “dead body” – and trophe – “nourishment”) applies. According to Frost, in Insect Life and Natural History, parasitoids are plunked down on the continuum between parasites and predators. Their habit is considered highly evolved, and they’ve often co-evolved with their hosts. Only insects with complete metamorphosis (egg-to-larva-pupa-to-adult) need apply for the parasitoid lifestyle, and only the larvae have the ability to do it, though their victims may come from any stage of life. Some parasitoids specialize on a single host species and others are less picky. Along with the label parasitoid, APW larvae are also classed as endoparasites (endo meaning that the larva is feeding from the inside).

With a nod to their long, curved abdomens, these beauties are sometimes called scorpionflies. Common names rarely reflect an organism’s actual biological family tree, and APWs are not related to the family Mecoptera, the home of the true scorpion fly. Is that long, pointy abdomen as dangerous as a scorpion’s? It does culminate with a stinger, which Ms. APW will use to probe the fingers of anyone handling her, and there are reports of “pin prick” stings being administered. As wasps go, these are docile and harmless

Their parthenogenesis (from the Greek parthenos, meaning “virgin” and the Latin genesis, meaning “genesis”) results from the fact that north of the Rio Grande, males are so rare that females have developed the ability to reproduce without them. Or is it the other way around? Parthenogenic females tend to produce more females. Male APWs may be absent from our landscapes, but they are present in the more torrid climes. South of the border, it does take Two to Tango. Not just parthenogenesis, but “geographic parthenogenesis.”

The BugLady

 

riveredge in winter

Winter is a Great Time to Explore Riveredge

Winter has come to Wisconsin in a glorious way.  There are many ways to have fun at Riveredge in the winter:

  • Snowshoeing is an easy way to have fun outside.  Riveredge has snowshoes for use during our regular building hours.  All Access members have free, unlimited use throughout the winter.  Trail pass members may rent them for $5 per hour and non-members are invited to rent them for $10 per hour.
  • Youth & Family outdoor program don’t slow down in winter!  Every Saturday at 10 am come explore the winter environment with our naturalists!
  • Special events take on a special type of fun in winter.  Come play with us during our Celebrate Winter family event on Saturday, January 25th from 12:30 – 3:30 pm or join us in our inaugural “Sugar Dragon Snowshoe 5K” event in partnership with the Feith Family YMCA on Sunday, February 9th.

Before you know it, winter will be gone and Maple Sugarin’ season will be here.  Enjoy the snow before its gone!