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.

New Zealand: Land of the long...

A New Zealand Stick Insect, probably in the genus Acanthoxyla.  All species in this genus are entirely parthenogenetic; populations consist only of females that reproduce asexually.

Moving to a new part of the world is a big adjustment, and perhaps particularly so for a biologist.  Getting used to the New Zealand culture has been a minor adjustment, but finding myself surrounded with species and ecosystems that are mostly unfamiliar to me has been a much bigger change.

For me, a walk through the woods, or 'bush' in New Zealand is a bit like reading poetry in French (Je ne parle pas français).  I know that it is beautiful, and recognize things here and there, but still have a lot of learning to do to fully understand what I am seeing.

Despite the learning curve, I have been doing some exploring and photography.  I don't have enough images yet to tie together a biologically relevant theme - but I have noticed one trend in my photos: animals of unusual size.  The Māori name for this land is Aotearoa, "the land of the long white cloud," but judging from my photo library, this is also "the land of the long invertebrates."  Here are a few of the lengthy critters I have come across thus far:

A male sheetweb spider in the family Stiphidiidae.  These can be quite large spiders, the leg span on this one was at least 6 cm, and... wow!  Hey there, mandibles!
 New Zealand has a number of amazing spiders (more of those on the way!)  Some of the most impressive are the sheetweb spiders.  They are quite common in bush fragments with native plants.  Their complex webs are often seen at the bases of large trees, with the spiders hiding out nearby during the day.  This large sheetweb was found high up a tree by a researcher climbing in the canopy.  They can be a bit startling at first, but of course, I find them quite beautiful!

Many of the caterpillars I've been finding in New Zealand are long, twig-mimicking geometrids, or 'inchworms'
As we've discussed previously, many caterpillars are 'masters of disguise,' hiding themselves from hungry birds and other animals that would like to find a high-protein snack.  The moth family Geometridae are the best of the best when it comes to hiding in plain sight, and a number of the new Zealand fauna are excellent when it comes to pretending to be a stick (although the stick insect at the top of this post may give them a run for their money).

Not all animals take the hiding approach.  This lovely yellow terrestrial flatworm isn't hiding from anybody - and I suspect that the bright color would be followed by a nasty taste, although I didn't have a bite to find out.
A bright yellow terrestrial flatworm, around 15 cm long.  Terrestrial flatworms are predators;  they eat other invertebrates including slugs and earthworms.  I haven't been able to find out much about this species, but it may be an introduced species from Australia.

One of the New Zealand insects that I was most looking forward to seeing was the New Zealand Giraffe Weevil.  There was no mistaking it:

The New Zealand Giraffe Weevil Lasiorynchus barbicornis (Brentidae) is worthy of attention.  They can be over 8 cm (3 inches) long!
 These beetles have extreme sexual dimorphism; the males are  much larger than the females.  These males fight each other for opportunities to mate with females, with the largest males usually having the upper hand.  However, there is a notable exception to the rule: the male pictured here is relatively small: closer to the size of a female than to a large male.  Rather than being a fighter, this male is probably a 'sneaker' who will mate with females without being noticed by large males, even if they are mating right under their (long) noses.

This method of circumventing that seem to be the normal rules of engagement is what biologists call an 'alternative mating strategy,' and similar sneaking behaviors have been recorded in many animals from insects, to fish, to orangutans.  It would be really cool to know if the smaller males have similar success rates to larger males when it comes to fertilizing eggs; for many insects, the act of copulation is only half the battle when it comes to passing genes along.
My, what a long nose you have, Lasiorynchus barbicornis
More adventures in Aotearoa to follow!
newer post older post