Wood Wasps, Vol. 8, No. 30
“This thing looks like a hornet on steroids!”
Wood wasps are not as fearsome as they look. That long spike at the end of this female’s abdomen is her ovipositor. She can drill into a pine tree with it, but she cannot sting. The shorter spine is present on both males and females. This is not a stinger either, but it is the reason wood wasps are also called horntail wasps.
Although these are big, impressive insects, about 1.5 inches, wood wasps are not often seen. Females are active in the fall when they emerge from infested trees to mate and go find host trees for their young. They use their ovipositor to drill into the tree and deposit eggs. While ovipositing, they also inoculate the tree with fungal spores they carry in special pockets, called mycangia, at the base of their ovipositor. The larvae, which also have a spine on their rear, live as wood borers. Most wood wasps only complete one generation per year.
There are several species of wood wasps, and all are strikingly colored to mimic wasps that can sting. Wood wasps can’t sting, but they can bluff. They can also bite and occasionally do so if carelessly handled. Let’s briefly look at three species of wood wasps that occur in the state, and one non-native species that we do not want.
The wasp in the photo is Sirex nigricornis, a native species that only attacks dead or dying pines. This species poses no threat to southern forests, but Sirex noctilio does.
European wood wasp, S. noctilio is a non-native species first detected in the northeastern US in 2004. So far, S. noctilio has remained confined to the Northeast, with heaviest infestations in New York and Pennsylvania. This wood wasp can attack and kill live, healthy pines, including southern pines: loblolly, slash, and shortleaf. Ovipositing females inject a toxic mucus, along with a fungal disease that can kill trees. Trees growing in stressed, overcrowded conditions are most susceptible.
We already have examples of what happens when S. noctilio invades plantations of southern pines. Southern pines are grown in plantations in many Southern Hemisphere countries and some of these have been invaded by S. noctilio, where it is also non-native. Timber losses in these countries have been devastating—estimated in the tens of millions of dollars per year. Much research is being focused on keeping this pest out of the rest of the US, including Southeastern forests, and on developing effective cultural and biological controls.
The Asian horntail, Eriotremex formosanus, is a non-native wood wasp that now occurs throughout the Southeast. Fortunately, they only breed in dead or dying hardwoods and are not a threat to southern forests. These large wasps are black with bright yellow bands and markings and sometimes emerge from firewood that has been brought indoors. This was the “hornet on steroids” a client who found one of these in their den described in their phone call.
The pigeon tremex, Tremex columba, is a native wood wasp, that only attacks dead or dying hardwoods. They are marked much like Asian horntails, dark red to black with striking yellow bands around the abdomen. The larvae spend their life boring galleries deep inside hardwood logs, where you might think they would be safe from outside dangers. But the black giant ichneumon wasp has a four inch ovipositor that it uses to drill into pigeon tremex galleries and parasitize them.
Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service.
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