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.

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.

Food webs in the garden: ladybug beetles

Name that state insect?

The goldenglow aphids in our garden are under attack!  One of the predators that are most easily spotted are these seven-spot ladybird beetles Cocinella septempunctata.  These familiar insects are attracted not by the aphids themselves, but by chemicals that the plants release only when aphids have been feeding on them.  Both the adult and larval beetles are very efficient aphid predators, plucking them off the plant and chewing up their soft bodies with strong jaws.

Probably Coccinella septempunctata eggs

 Adult beetles lay clusters of eggs on leaves that look like clumps of yellow rice.  If you've ever been bitten by a ladybug larva, you know their jaws can deliver a strong pinch!

nom nom nom

 Cocinella septempunctata is not native to the Americas, but was introduced from Europe and by 1973 was established as part of a biological control program for pest aphid species.  This familiar insect was selected as the state insect of 6 states, including Delaware (I probably would have selected an insect more indicative of the region).  Another introduced coccinellid that I commonly find in our garden is the striking twice-stabbed ladybird beetle Chilocorus kuwanae.  There are native Chilocerus that look very similar but I have not yet seen one here.

Next up: fearsome flower flies!