Tremex

Taxonomy

Order: Hymenoptera
Family: Siricidae
Subfamily: Tremecinae
Genus: Tremex Jurine 1807
Common names: horntails, woodwasps, tremex wasp

Background

The genus Tremex in the family Siricidae occurs in North America and Eurasia. This is a small genus with 33 species. Tremex columba (Fabricius) is the only species native to North America. However, Tremex fuscicornis (Fabricius), native to Eurasia, was unintentionally introduced to Canada, Australia, and Chile. Tremex larvae are wood-boring in hardwoods (Baldini 2002).

How to separate from Asian giant hornet

  • Horntails can be as long or longer than Asian giant hornets
  • Horntails have a long parallel-sided abdomen without a wasp waist

Distribution

Tremex is found throughout the Holarctic region. There are 33 known species; only two occur in North America, one native species, T. columba, and the introduced species T. fuscicornis (Taeger and Blank 2011).

Distribution map of Tremex sp. by GBIF: https://www.gbif.org/species/1358460

Diagnostic characteristics

  • The abdomen long and cylindrical without a wasp waist
  • The abdomen with an apical prong or horn (cornus) in both sexes
  • Antennal sockets far apart
  • Cell 2R1 about as long as or longer than cell 3R1
  • Fewer than 15 flagellomeres
  • Body with long setae
  • Females with the cornus in lateral view angular along the lower margin near its base
  • Males have hindtarsomere 5 as long as the length of hindtarsomeres 2+3

Diversity

Variations in abdominal coloration led to Tremex columba being divided into multiple species. However, using both DNA and morphology, Schiff et al. (2012) found that the three-color forms were all the same species. The reddish-brown form is found from southern New York and Illinois into the southeast. The darkest form with black and yellow marking is widespread in eastern North America from Saskatchewan to the Atlantic coast and south to Georgia. A form with a pale reddish-brown abdomen, black transverse bands, and yellow-tinted wings, occurs in the middle of North America from Canada, east of the Rocky Mountains across the Great Plains and south into northern Mexico. Wing color also varies geographically, with dark-winged forms to the south and amber-colored wings to the north.

Host/prey associations

Female Tremex oviposit in dead or weakened limbs of deciduous trees, particularly hickories, maples, and elms (Schiff et al. 2012). The larvae are wood-boring. In Chile, Tremex fuscicornis damages poplar (Populus nigra), as well as Robinia pseudoacacia and Acer negundo (Parra 2007).

Nesting and general behavior

Females begin laying eggs in mid-August and continue until late September. They lay 2–7 eggs in each oviposition hole. Eggs either hatch within 15–30 days, or overwinter and hatch the following spring. Larval development lasts two or more years in cold temperate regions. Larvae cannot develop without the presence of a wood fungus (Schiff et al. 2012). In Canada, new adults start to emerge in mid-August, peak in early September, and end in early October. Males emerge about one week before the females.

Megarhyssa macrurus, the giant ichneumon wasp, parasitizes Tremex columba. It searches for Tremex larvae in their tunnels and when it locates one it lays an egg next to it, and then stings the larva to paralyze it.

Known invasives

Tremex fuscicornis, a species native to Eurasia was accidentally introduced into central Chile (Baldini 2002) and is now found in Canada and Australia as well.

<p><em>Tremex</em> sp; photo by Joshua Allen, Flickr</p>
<p><em>Tremex columba</em>; photo by pverdonk, Flickr</p>
<p><em>Tremex</em> sp.; photo by Ryszard, Flickr</p>
<p><em>Tremex columba</em>; photo by Thomas Shahan, Flickr</p>
<p><em>Tremex columba</em>, dorsal view; photo by Hanna Royals, USDA APHIS PPQ ITP</p>
<p><em>Tremex columba</em>, dorsal view; photo by Hanna Royals, USDA APHIS PPQ ITP</p>
<p><em>Tremex columba</em>, lateral view; photo by Todd Gilligan, USDA APHIS PPQ ITP</p>
<p><em>Tremex columba</em> (left) compared to <em>Vespa mandarinia</em> (right), dorsal view; photos by Hanna Royals and Todd Gilligan, USDA APHIS PPQ ITP</p>