Friday, January 10, 2014

D. irritator is Boring

D. irritator- Sheila Watson
Our neighbor Sheila sent me this picture of an insect she found out flying on a warm day in early November.  I was impressed she would hold an insect with such a formidable appearing ovipositor attached behind its abdomen, a finding that would send many people running.  There are several families of wasp-like insects to thumb through so I sent the picture to  Within several hours I had an answer.  This is Dolichomitus irritator, a member of the Ichneumonidae family, frequently referred to as ichneumon wasps (ick-new-man).

While we tend to think of all wasps as stinging menaces, only females of some species have defensive stingers.  This dangerous female tendency might have broader implications among humans but I won't go there.  The ichneumon wasps do not sting in defense but instead pass their eggs through their modified stinger, sometimes with some venom to paralyze their prey.  They are parasitoids, their larvae developing on the larvae of beetles, lepidoptera (butterflies and moths) and other wasp species.

D. irritator female  Tom Murray
The most distinctive feature of this family are the long antennae on a wasp-like body and the extremely long ovipositors of the females, usually longer than their body.  Although they lack stingers, they are quite "boring," able to penetrate deeply into a tree where they sense a beetle larva is living.

Their reproduction strategy is a story of persistence.  Their larvae require a woodboring insect larval host to feed upon.  First the female wasp crawls along the log, tapping its antennae on the bark in search for the scent of an underlying larva appropriate for her young.  Interestingly, the male also does this, but it is hunting for newly emerging females to mate with.

D. irritator male  Tom Murray
Once the female Dolichomitus irritator detects its prey, it has to deliver its egg to the larval body deep in the wood.  The wasp is less than an inch long and this is where the long ovipositor comes in.  She will patiently drill into the wood, sometimes for hours until reaching the host larva and injecting her egg.  The explanation of how this is accomplished is the subject of a later blog but the photographs of the process are here.

Wow, take a look at her ovipositor!
While ichneumon wasp larvae are the bane of the "butterfly wranglers" who raise caterpillars for our butterfly house, they have an important place in nature.  Spring tiphia wasps, Tiphia vernalis, have been introduced as a possible biologic control for Japanese beetles.  Spathius agrili is a parasitoid wasp from Northern Asia which is being studied as a biologic agent against Emerald ash borer.  Since parasitoid damage occurs out of sight, it is difficult to measure their effectiveness as well as the potential damage they could cause to native species.

Until recently, all known larval parasitized hosts were bark beetle larvae.  A recent paper  describes finding D. irritator parasitizing Dectes texanus, a pest infesting soybeans. If this turns out to be a widespread finding, this little wasp may become the farmer's new best friend.

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