Eastern North America is the Asian Lady Beetle’s Bridge to the World

Harmonia axyridis, the Asian Multicolored Lady Beetle

If I had to pick the most annoying insect in Illinois it’d be Harmonia axyridis. This lady beetle was introduced to our continent as a control agent for aphids but became a pest in its own right. It consumes not just aphids but all manner of other insects, including beneficials like native lady beetles. Swarms of them descend into our houses in the fall. They get just about everywhere. They have a noxious odor. And they bite.

A study out in PLoS One byLombaert et al has determined that our local beetles here in eastern North America are the culprit behind a spate of recent invasions elsewhere in the world. The researchers extracted DNA from 18 loci across the various populations, modeled several different introduction scenarios, and concluded that one story makes the observed genetic data the most likely.  It’s this one:

Figure 1 from Lombaert et al 2010 showing the most likely path of introductions of H. axyridis.

The authors call this result “surprising”, but I disagree. If a pest builds to enormous numbers in a region that sees a lot of commerce, exports of that pest may become much more likely than exports from the native range. Especially if native populations are kept down by predators and competition.

We see this in ants all the time.  The invasive Argentine ants in California arrived from an earlier invasion to the eastern U.S., not as a separate colonization from Argentina.  Fire ants in Australia appear to be from the United States, not South America.

In any case, it’s an interesting and timely study. Now, if they could just figure out where I can send the beetles in my house so they don’t come back, that’d be really valuable.

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source: Lombaert E, Guillemaud T, Cornuet J-M, Malausa T, Facon B, et al. 2010 Bridgehead Effect in the Worldwide Invasion of the Biocontrol Harlequin Ladybird. PLoS ONE 5(3): e9743. doi:10.1371/journal.pone.0009743

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The eggs that weren’t

I did not expect everyone to nearly instantaneously solve yesterday’s termite ball mystery.  I’m either going to have to post more difficult challenges (from now on, nothing will be in focus!) or attract a slower class of reader.

Cuckoo fungus grows in a termite nest.

As you surmised, those little orange balls are an egg-mimicking fungus. It is related to free-living soil fungi, but this one has adopted a novel growth form that is similar in diameter, texture, and surface chemistry to the eggs of Reticulitermes termites. These hardened sclerotia are carried about the termite nest as if they were the termite’s own offspring, earning them the title “Cuckoo fungus”. Since termites are blind there is no advantage to the fungus in visually looking like an egg, though, so we sighted creatures can tell the difference at a glance.

For more about the Cuckoo fungus, check out the publications of Kenji Matsuura. Matsuura first identified the balls as a fungus ten years ago, as a graduate student, and has been working on them ever since.

Termites can't tell the difference between their own eggs (white) and the fungal sclerotia (orange).

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Ant Ecology now available

Surfing around the bookstores this morning I see that the much-anticipated Ant Ecology book is out. At $129.00 it’s not something the casual reader is liable to pick up. Nonetheless, Ant Ecology is a beautiful volume reviewing the state of the field, and scientists who work on ants should probably own a copy. Or at least get one on time-share.

The book is a collection of 16 chapters edited by Lori Lach, Kate Parr, and Kirsti Abbott. There’s a mellifluous forward by Ed Wilson, but then, most ant books have a mellifluous forward by Ed Wilson. Ant Ecology‘s real strength is that each chapter is written by researchers actively working on their chosen topics. Thus, the full volume is a collaboration across the leading edge of myrmecology, and the perspectives they offer are a glimpse into the burning scientific questions of the day from the mouths of the very people working hard at answering them. Among others, Brian Fisher covers ant biogeography, Christian Peeters does ant life history, and Anna Dornhaus & Scott Powell write about ant foraging strategies. As a teaser, Amazon previews part of Phil Ward’s chapter on systematics here.

I’m still only a couple chapters in, so that’s all the detail you get for now.

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disclaimer: You probably shouldn’t trust me for an unbiased review. I provided most of the book’s images, and many of the authors are friends of mine. Plus the editors- bless them- sent along some simply lovely ant attire as thanks for the images (I’ll post photos shortly…)

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The other ant-fungi

If I were to mention an ant-fungus mutualism- that is, an ecological partnership between an ant and a fungus that benefits both- most biologically literate people might think of the famed leafcutter ants and the edible mycelia they cultivate.  But that is just one example.

Several other fungi have entered into productive relationships with ants, assisting especially in ant architecture.  Consider:

Lasius umbratus walking in the galleries of an underground carton nest (Illinois)

A larger view of the same nest. The intricate galleries are made from fungal mycelia growing through a matrix of ant-chewed wood pulp.

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An Ant Lion in Action

An ant, climbing from the pit of a predatory ant lion.

The predator, buried in sand at the base of the pit, hurls a volley of debris towards its target.

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Images of the Archbold Biological Station

dawn in the scrub

I spent last week in central Florida at the Archbold Biological Station.

Archbold preserves 5,000 hectares of Florida sand scrub, some of the last remaining patches of an ecosystem now largely lost to agriculture and strip malls.  The sand scrub is an odd place, a fossil beach from when sea levels were high enough to restrict peninsular Florida to a narrow sandbar.  Water runs right through the coarse sand, leaving the scrub looking much like a desert in spite of regular afternoon rains.  Cacti thrive.  It is a paradoxical place.

The scrub is also remarkable for receiving more lightning strikes than anywhere else on the continent: about 50 strikes per square mile per year.  So the scrub burns all the time, and has come to depend on frequent fire to maintain the structure of the forest.  This unique system has birthed dozens of sand- and fire-adapted plant and animal species that are found nowhere else.

The trip was a spur of the moment decision for me.  Budding myrmecologist Fred Larabee, a student here at the University of Illinois studying the evolutionary ecology of Odontomachus trap-jaw ants, was driving down to collect Archbold’s three resident species.  I hitched a ride.

Below are a few photos from the week.

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Predator vs Harvester

A recent study by Gabriela Pirk in Insectes Sociaux provides me with an excuse to share this photo:

Minor workers of the seed harvester Pheidole spininodis (left) and the predatory Pheidole bergi lock jaws in combat. Jujuy, Argentina.

Pirk et al examined the diet of both Pheidole species in the Monte desert of Northern Argentina.  Why would someone spend time doing this?   Ants are important dispersers of seeds, and these Pheidole are two of the most abundant seed-eating ants of the region.  What they do with the seeds, which ones they choose to take, and how far they take them has implications for the ecology of the desert.

The interesting bit in my opinion is that the two ant species are rather different, both ecologically and biomechanically.  Pheidole spininodis is a dedicated seed harvester.  Their majors have enormous blocky heads with blunt mandibles for milling seeds:

Pheidole spininodis, major worker

In contrast, Pheidole bergi is primarily predatory, taking seeds only opportunistically.  Their majors are slender, fast, and with relatively small heads and sharper mandibles better for slicing up the insects that they most commonly feed on:

Pheidole bergi, major & minor workers

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Ants as seed dispersers – part I

Aphaenogaster workers tasting the elaiosome of a bloodroot seed. Illinois.

Some plants have come to rely so heavily on ants to spread their seeds about that they offer the insects a tasty treat in exchange for the dispersal service.  Seeds of these species bear a lipid-filled structure called an elaiosome, whose sole function appears to be the attraction of ants.  A recent study suggests that plant lineages dependent on ants in this way speciate more rapidly than related ant-free lineages.

photo details (both photos): Canon MP-E 65mm 1-5x macro lens on a Canon EOS 50D
ISO 100, 1/160 sec, f13, indirect strobe in a white box

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Native ants on introduced nectaries

I took my shiny new Canon 50D out for a spin this weekend, and along the railroad tracks I found a worthy myrmecological subject: Crematogaster feeding at the swollen nectaries of an Ailanthus Tree of Heaven.  Ailanthus is an introduced Asian tree that’s gone weedy across much of North America.  Our local ants don’t seem to mind, though, it’s extra snack food for them.

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Are there more ants in the Southern Hemisphere?

A bold paper by Rob Dunn et al in Ecology Letters is making news this month.   Dunn and an impressive list of coauthors pool observations of ant species richness from more than 1000 sites worldwide, finding that southern hemisphere habitats consistently support more species than their equivalents in the northern hemisphere.  The pattern appears to be predicted primarily, but not entirely, by climate.

These results strike me as intuitively correct, and I suspect anyone who has collected ants in both hemispheres will agree.  Brazil’s fauna is spectacularly rich.  That of Oklahoma, less so.

But intuition is a self-reinforcing trap, so we’ll want to evaluate the study based on more objective criteria.  And there are a couple things here that make me uncomfortable.  Not with this study per se, but with macroecological studies in general that rely on aggregated data from different sources.

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