Little things that run the world: Parasitic Wasps

The parasitoid wasp Telenomus podisi emerging from Euschistus servus stink bug eggs.  The wasp is about 2 mm in length. As she developed, she consumed the bug inside the egg.  Both the wasp and the host stink bug egg are native to the Eastern U.S.

Parasitoids differ from other parasitic organisms in that they kill their hosts as a normal part of their life cycle.  Because many are quite small they often go unnoticed, however, their degree of importance in ecosystems far outweighs their diminutive size.  Parasitoids can be important for controlling populations of their hosts, and as such they can be great drivers of evolution of defensive behaviors and forms:

Defensive behavior: A Costa Rican stink bug in the genus Loxa defends her eggs by standing over them.  She will use her hind legs to deliver a sharp kick to any intruders; enough to startle a human or send a small parasitoid careening through the air.

Defensive form? All stink bug eggs have micropylar processes - a ring of tubes that allow sperm and oxygen to enter the egg.  Those of Podisus maculiventris are very long, forming a spiky crown around each egg.  I wonder if they serve an additional purpose in interfering with the movement of small parasitic wasps among the eggs.

Because parasitoid wasps are so effective at reducing populations of their hosts, they can be very useful for providing control of pest species.  When one organism is used to control another, this is termed biological control.  Current research is investigating certain parasitoid wasps as potential biological control control agents for the brown marmorated stink bug.

The brown marmorated stink bug is a familiar pest because of its annoying habit of hiding out in houses during the winter months.  Unknown to many, it causes huge losses in agricultural systems and negatively affects the environment; farmers must spray more pesticides to control stink bugs.  Researchers hope parasitoid wasps in the genus Trissolcus (a relative of the Telenomus wasp pictured above) will be able to provide control of the brown marmorated stink bug, without being a hazard for native stink bugs and ecosystem function.  Because of the close relationship that many parasitoids share with their hosts, many will not attack other species.

Halyomorpha halys, the brown marmorated stink bug.  Originally from Asia, this insect is a serious agricultural pest and a nuisance pest in buildings.  It is broadly distributed and has a growing range in the U.S. and worldwide.

When insect photography goes bad

The beautiful tachinid fly Trichopoda pennipes, cooked medium-rare a la torchiere

 Trichopoda pennipes is a parasitic fly that attacks true bugs, and is the particular dipteran responsible for 'death by maggot'.  In addition to devouring leaf-footed bugs from the inside, this Halloween-colored insect also attacks stink bugs, and has been used as a biological control agent for some species in Europe.  For some time now I've been wanting to get a picture of these 'feather-legged flies' laying eggs on stink bugs, and so was delighted to catch a mating pair this afternoon.

Unfortunately, Trichopoda like many insects exhibits a behavior that entomologists call "positive phototaxis."  This is the same behavior that draws a moth to a flame, or as it were, a pair of flies to a 300-watt halogen floor lamp.  As soon as I opened the container both flies spiraled upward with Icarus-like disregard, achieving results comparable to the myth.  Alas, rather than the oviposition action shot I had hoped for, we are left with this photo of another upside-down insect.

Her mate, I am afraid, fared even worse and could not be salvaged at all.  Consequently, it smells of charbroiled death in here, and I am inspired to retire for the evening.

NMW: Moth Fashion!

Who knew fur leg warmers could be so fashionable in the tropics?

National Moth Week continues with some bold fashion accessories demonstrating the amazing diversity of this group.

  The moth above is from Costa Rica.  I can only guess why it has evolved leg warmers - except that I severely doubt they are for warming legs.  Maybe they are for brushing away would be attackers, or dampening bat sonar?  They could be for putting the moves on a female, or they might work great for blending in on my dog (again very unlikely).  It's a mystery for now.  Any ideas?

Sphingidae, Costa Rica

Sphinx moths are pretty speedy on the wing - but this one looks fast just sitting still.  With the swept wings and the tail fin - it's hard to look at it without the 'Top Gun' theme song popping into your head.

Adult moths aren't the only ones with intense ornamentation, caterpillars are often just as striking as their adult counterparts.  The Costa Rican Saturniid below is covered in spines that may make it difficult for a parasitoid fly or wasp to land and lay an egg.  At the same time bright colors advertise to larger predators that the spines are capable of delivering a painful sting.

The Delaware native paddle caterpillar below also employs it's adornments for defense against parasitoids.  When touched, the caterpillar thrashes its head from side to side, sending the 'paddles' flailing wildly - a formidable challenge for a small wasp.  Instead of stinging, the caterpillar (larva of the funerary dagger moth) hides out during the day doing its best impression of bird poop.

Acronicta funeralis

Our last fashion victim is horned spanworm or filament bearer.  The tentacles may help disguise the caterpillar as a dead leaf, but then bothered, they expend to twice their normal length.  It is one of the most bizarre caterpillars I have yet to encounter:

Nematocampa resistaria, Delaware

Death By Maggot

This leaf-footed bug (family Coreidae) has succumbed to a attack by a parasitic fly.  A fly in the family Tachinidae laid an egg on the bug's head (it is visible near the eye).  The larval fly tunneled out of the bottom of the egg and into the body of its host, where it consumed it from the inside out.  Finally, the maggot chewed out of the coreid and formed the puparium pictured, where it will undergo metamorphosis and emerge as an adult fly.  Tachinid flies are 'parasitoids' because they are parasites that eventually kill their host.

Leafcutter ant 'hitchhiking'

A minor worker rides on a cut leaf

 When watching a foraging trail of Atta cephalodes leafcutter ants, you will likely notice that occasionally a smaller ant will be 'hitchhiking' on a leaf fragment that a larger ant is carrying.  At first look, these ants appear lazy but they are actually providing a critical service to their colony.

In many habitats, these ants are attacked by flies in the family Phoridae.  Female flies alight on leaves in transport, crawl towards the carrier, and lay eggs on the unwitting ant.  When the eggs hatch, they enter the ants body and consume it from the inside out, eventually killing it.  Hence the reason for the seemingly lackadaisical passengers.  A fly is much less likely to land on a leaf with a rider, and if it does it will quickly be chased off.  The minor workers are defending their sisters from aerial parasitoid attacks.

If you are worried about flying parasitoids, for a small fee I will ride around on your shoulders for a day, defending you from various forms of death from above.

Ants and Fungus

Fungi can be found nearly anywhere on earth, and species have developed complex interactions with many other organisms.  Ants are also nearly ubiquitous, and the intersection of myrmecology  and mycology is fascinating.

Atta cephalotes workers carry leaves to their nest

Leafcutter ants are easy to find in Costa Rica.  They keep their foraging trails clear of debris; the busy highways really stand out among the leaf litter of the jungle floor.  The zampopas as the locals call them do not eat the leaves they collect, but use them to farm fungus that is fed to developing ants.  The ants grow only one type of fungus, and are able to prevent other types of fungus from growing in their farms.  The leafcutters and fungus have evolved a 'mutualism' where both the ants and the fungus benefit from the interaction, however, this happy arrangement is not the case for all ant-fungus interactions:

Fruiting bodies of Cordyceps grow from the corpse of an ant that the fungus has killed.

Fungi in the genus Cordyceps are parasitoids (a parasite that eventually kills its host).  Most cordyceps  attack insects, and are very specific as to the species they can develop on.  As the fungus infects, it also alters its host's behavior to increase the chances of spores infecting another host, as seen in this BBC clip:

Host behavior modification by parasites is more common than you might want to imagine, but there is no need to worry in this case; there is no Cordyceps that specializes on humans.  I have been told however that there is a video game in development that features just that scenario in the storyline.