Sirex rufiabdominis (Xiao & Wu) - Red-bodied horntail

Hymenoptera: Siricidae

IDENTIFICATION

Adult females are 18 to 34 mm long with black, 19 to 22 segmented antennae.⁶³ The wings are transparent on the basal half and smoky-brown on the apical half.⁶³ The body is covered with yellowish-gray hairs that are particularly abundant on the head and thorax.⁶³ Adult males are 14 to 22 mm long and their bodies are similar in colour to females but have more hairs.⁶³ Wings are pale yellow.⁶³

HOST TREES

Pinus.⁶³

LOCATION OF INFESTATION WITHIN THE TREE

Larvae feed on the sapwood and heartwood along the stem between the base of the tree and the main branches.⁶³ They are primarily found 2 m above ground level.⁶³

HOST CONDITION

Weakened, stressed, or dying trees.⁶³ This insect prefers host trees growing in poorly sanitized or thinned forests or trees growing along the forest edge or on sunny slopes.⁶³

DISTRIBUTION

China.^{63, 119}

SIGNS AND SYMPTOMS

Females use their saw-like ovipositor to cut holes 1 mm into the sapwood.⁶³ At the time of oviposition, females first secrete a phytotoxic mucus (a colourless gel) that reduces the tree's ability to enclose the eggs.⁶³ One to seven eggs are laid per oviposition hole.⁶³ The browning and necrosis of the cambium that occurs around the phytotoxic mucus leads to wilting and tree mortality.⁶³

Larvae initially bore 10 to 20 mm into the sapwood and create vertical galleries.⁶³ Late instar larvae then bore into the heartwood and may even reach the pith.⁶³ Galleries are winding (15 to 20 cm long) and filled with sawdust and small, hard frass pellets.⁶³ Most larvae return to the sapwood to pupate. Circular exit holes are 5 to 8 mm in diameter.⁶³

A - Adult S. rufiabdominis (18-34 mm long).

B - Frass-filled S. rufiabdominis larval galleries.

Photo credits

• A Klaus Bolte, Natural Resources Canada, Canadian Forest Service
• B Dave Holden, Canadian Food Inspection Agency