The Bug Geek

Insects. Doing Science. Other awesome, geeky stuff.

Category Archives: Flora

A fungus ate this moth’s head

It’s been far too long since we’ve had a good gross-out parasite post, so let’s rectify the situation, shall we?

I captured this gruesome scene at the end of June, in the park where I was camping.

This poor unidentifiable moth met a horrifying end in the grips of an entomophathogenic fungus, which, though technically not a parasite, is nevertheless growing gangbusters out of the moth’s head.

While non-pathogenic fungi use less gory approaches to dispersal and propogation, relying on things like wind and water, entomopathogenic (EP) (entomo=insect; pathogenic=disease-causing) fungi use insects and other arthropods as their food source and means of spore transmission.

EP fungi produce spores that attach to, sprout on, and penetrate the outer shell (or cuticle) of their host.  Once they’ve breached the outer barrier, they feed on the nutrients available inside the host, ultimately killing them. What you see in the photo above is the final stage – the host has been killed, and the fungus has produced mature fruiting bodies from which more spores will be produced.

One of the most fascinating aspects of these fungi is their ability to alter their hosts’ behaviours – sometimes in ways that maximize the likelihood of spore dispersal, and sometimes in ways that actually harm the fungus and help the host fight off the infection – there seems to be a finely tuned evolutionary tradeoff at play in these systems that permits both the fungus and the host to persist and thrive despite the unpleasantness of the interaction between them.

For example, a fungal infection may lead a host to seek out sunlight or other sources of heat; by raising their body temperature (a so-called “behavioural fever”), the host can sometimes make its body inhospitably warm for the invader. Other EP fungal infections, such as those seen in pea aphids, can cause an infected aphid to move to unusual, more exposed parts of the plant to feed. This could be the fungus’ way of ensuring better spore dispersal, or might be the aphid’s way of preventing the fungus from spreading to the rest of its colony. Some fungi seem to make female hosts more attractive to males (presumably to aid in spore transmission), while others cause hosts to seek out elevated sites before their deaths (as was most likely what happened to this moth).

This is all terribly reminiscent of the mind-controlling hairworm I posted about last year, and behavioural changes have also been shown to be induced by insect parasitoids; it’s clear that behaviour modification is a useful strategy for many organisms that rely on a host to complete their life cycle!
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ResearchBlogging.org

Roy HE, Steinkraus DC, Eilenberg J, Hajek AE, & Pell JK (2006). Bizarre interactions and endgames: entomopathogenic fungi and their arthropod hosts. Annual review of entomology, 51, 331-57 PMID: 16332215

Grosman AH, Janssen A, de Brito EF, Cordeiro EG, Colares F, Fonseca JO, Lima ER, Pallini A, & Sabelis MW (2008). Parasitoid increases survival of its pupae by inducing hosts to fight predators. PloS one, 3 (6) PMID: 18523578

Arctic beetle trophic structure and shiny new research direction!

I am pretty excited by the next step I’m taking with one of my projects.

I’ve spent the past few months looking at a season’s worth of subarctic beetles from my summer in Kug, back in 2010. In my mid-field-season post that year, I mentioned that the community of beetles seemed pretty darned weird, at least to the naked eye: my traps were full of predatory beetles, but I was hard-pressed to find many herbivores, either in my traps or just by looking around on plants.

Now that I’ve actually gone through all of the samples, it’s clear that what I thought I saw was actually pretty much the case. Out of exactly 2638 adult beetles, 88.3% of them are carnivores. Only 11.2% are plant-feeders of some kind, and less than 1% are scavengers. I see almost identical figures if I consider the animals in terms of their mass and not just their numbers: about 87% of the “bulk” of all beetle bodies is carnivorous.

So why is this so weird?

Usually, when we think about how animals feed on each other, we tend to think of something rather pyramid-shaped, like this:

This is the “trophic structure” of a typical community of organisms. Each level in the pyramid is called a trophic level.

Most places on earth have a lot of plants. There are enough plants to feed, and provide energy to, all of the herbivores. Those herbivores are eaten by, and provide energy to, predators, which are fewer in number. Some trophic structures may have an additional level of “top” predators, that feed on just about everything, including other carnivores.

You can see how each trophic level in the pyramid gets smaller; it’s what keeps the community stable. For example, if there were more herbivores than plants, the herbivores would eat all of the plants (obliterating that level) and then they would in turn die off because there was nothing left for them to eat.

What I have found with my beetles from Kug is a trophic structure shaped something like this:

There are still quite a lot of plants, though not as many as you’d normally find in, say, an old open field in rural Ontario (this is the Arctic, after all). But the rest of the pyramid has essentially inverted: there are few herbivores and lots of predators.  The usual upward flow of energy seems to be disrupted.  Where are all these predators getting their energy?

My answer at this point is: I have no idea.

But I have two guesses:

1. Maybe I’m not seeing the whole picture – the predators might be eating other things!

Beetles don’t necessarily feed on other beetles. Maybe, if I added in other groups of animals, the trophic structure might look a little more “normal”. I don’t actually think this will be the case. I have started to look at the other critters I collected in my traps, and MOST of them are large, heavy-bodied, predatory spiders. There are a smattering of plant-eating bugs, grasshoppers, caterpillars and springtails, but I am almost certain there are not enough to provide energy to all the “bulk” of beetles and spiders.

2.  Who needs herbivores – why not just eat other carnivores?

I think these beetles (and the spiders, too) are actually feeding on each other  – this is a type of cannibalism, called intratrophic predation. In this kind of arrangement, predators get their energy by feeding on other high-energy predators. This is not unheard of; it’s been seen in desert communities, for example, but these kinds of trophic structures are not terribly common.

Anyways, I’d like to figure out exactly what’s going on in this system, and particularly if my second guess is correct. Since I wasn’t able to directly observe what all these beetles were eating while I was up north, I have to rely on some fancy-schmancy and new-to-me lab techniques

(*Gasp!*  TGIQ doing lab stuff??!?  I know, right?  This is all in the name of trying out new binoculars, friends).

The technique I’m going to start working on soon is called stable isotope analysis.

I’ll save the inner workings of this method for another post (not just a little bit because I’m still sorting out all the details myself!), but I’m pretty excited about trying it out. My job will be to carefully prepare beetle specimens by drying, crushing, and weighing tiny samples of their bodies into special teensy little tin cups. Then I’ll send them out to a lab that has a couple of specialized bits of equipment (which, last time I checked, I did not have sitting on my lab bench) that will measure the amount of nitrogen and carbon in each sample.

In a nutshell, this technique should let me figure out the trophic levels of all my predators (i.e., where exactly on the pyramid they sit), mainly by the amount of nitrogen in their bodies.  If they’re eating only herbivores, they’ll have less nitrogen, and will be on a lower trophic level. If they’re eating only other predators, they’ll have lots of nitrogen, and will show up at the highest level. Beetles eating a mix of herbivores and other predators will show up somewhere in the middle, with an in-between amount of nitrogen.

If I see mostly herbivore-feeders, and not predator-feeders, then I’ll know that my guess #2 is incorrect, and that I’m missing a piece of this little trophic puzzle.

Stay tuned for updates in the new year on this project!

I’m not mad, I’m concentrating…

BugShot 2011 participant Pat Porter just sent me this candid photo of yours truly…

Photo credit: Pat Porter

My first thought was, “why am I so ANGRY?” I stared at the image for a while and then remembered the circumstances under which this shot was taken (apparently by a very stealthy photo-ninja). I had spied a tiny but lovely moth (the Ailanthus webworm moth, Atteva aurea) who was slightly obscured by several petals of the yellow flower on which it was perching. Although I usually don’t pick too much at the nature surrounding my photographic subjects, I made an exception this time because I’d never seen one of these in the flesh before.  I had to remove three petals without disturbing the critter…hence the frowny-face.

Here is the shot I ultimately got…I was using one of Alex’s off-camera remote flash units, which accounts for the black background (it was my first time trying this kind of gear out in the field – with VERY mixed results. Actually, not so mixed: mostly crappy, but hey, it’s a learning curve).

Ailanthus webworm moth, Atteva aurea

Sneak Attack! (Goldenrod crab spider, Misumena vatia)

Our gardens provide an excellent close-by space for bug hunting.  Most days I do a “tour of the grounds”, inspecting flowers and leaves for interesting critters.  So the other day I was poking around a patch of purple coneflowers, when I saw this:

A bee head...upsidedown?

A little bit of bee peeking out from behind the pink petals.  Something was all wrong, though.  First, it wasn’t moving, and secondly, it was peeking out head-first.  Very odd.  Crouching down to get a better look beneath, the problem quickly became apparent:

Goldenrod crab spider with prey

A well-hidden goldenrod crab spider (Misumena vatia: Thomisidae) had snatched up the unsuspecting foraging bee and was now enjoying a well-deserved snack.

As I photographed the scene, I noticed a pair of very small flies circling nearby.  They occasionally landed on the bee.

Little...Muscids? Doing...something?

I’m really not sure (little help, fly guy or other fly guy?) but I think they’re little Muscids of some kind.  If I had to guess, I would say that they were feeding on the pollen grains clinging to the bee’s hairs…I can’t think of what else they’d be doing…does anyone else care to venture a guess?  (Ooh, I’d take guesses on the ID of the prey, too!!!)

***Edited to add: read the comments (Dooooooo it.  Do it now). Morgan from Biodiversity In Focus (aka “Fly Guy #1) has some great insights here!

***Edited to add #2: Micheal has offered another really interesting suggestion, and a nice pic to boot (in other words, if you haven’t read the comments already, you really should now).

Break Time

So much work, so little time.  My desk chair has been permanently stamped with the imprint of my rear. 

Either that, or my rear has assumed the shape of my desk chair.  Not very flattering either way if you ask me.

My wife called me today from work and suggested I take a break and play outside. It was a balmy -12C today (yes, that’s quite balmy after the near -40C we’ve had for the past two days), the dogs were short-circuitng from lack of exercise, and my wife is usually right about stuff anyways (don’t tell her I said that), so I went and played outside.

Although it was dark and grey, fresh snow was on the ground, and I got to try out my new toys:

That’s an old, shrubbed-over agricultural field.  There are squat stonerows  running along either side of the open area, and lots of early ii trees around the edges (birch especially) along with thick tangles of invasive buckthorn  native hawthorn (thanks for the clarification, Seabrooke!)

Evil Hawthorn...thorns.

Speaking of trees, and of bucks (aw nuts, now my nice little segue doesn’t work as well *harumph*),  I found a pretty recent deer rub on a young tree.  Bucks will rub their antlers on trees for a few reasons: in the early summer/late fall, they do it to slough off any velvet remaining on the rack; during rut, they rub to mark their territory.  If done aggressively enough, this action can kill the tree by cutting the flow of water and nutrients.

The small mugsly dog found something too:

C'mere, you wascally wabbit...

The occupant had left tracks nearby, but wisely stayed out of sight…

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