Trachelus tabidus (Fabricius)
Common name: Black grain stem sawfly.
Taxonomic placing: Insecta, Holometabola, Hymenoptera, Symphyta, Cephidae.
Geographic distribution: North Africa, Southern, Middle and Western Europe, Middle East, and North America.
Morphology: Adult body length about 7-10 mm, shiny black with many yellow spots on the abdomen. Body of larva, yellow-white, about 12 mm long, curved, with a brown-red head and short, clavate antennae, and 3 pairs of underdeveloped thoracic legs, no prolegs.
Life history: The univoltine females lay 30-50 eggs each inside small cuts in the stalks of cereals in early spring. The larvae develop inside the stalk walls, gnawing and moving gradually downwards, into the soil. They then enter diapause which lasts throughout summer and winter, pupating next spring after which the adults emerge.
Economic importance: This is a serious pest of various Poaceae (Gramineae), especially wheat and barley, as well as oats, also attacking other fodder and wild-growing cereals. Reductions in grain weight can exceed 50% and its quality may deteriorate.
Management
Monitoring: Yellow watertraps are placed in the field to monitor adult emergence.
Horticultural methods: Deep autumn plowing to kill the diapausing larvae, early sowing of spring cereals and their early harvesting.
Plant resistance: Resistant wheat cultivars with solid stems are available.
Biological control: The ichneumonidendoparasitoid Collyria coxator (Villers) kills 30-70% of the larvae in Russia. In Israel parasitisation by a Tetrastichus sp. Eulophidae came to about 12%.
References
Gol’berg, A.M. 1986. Biology of the stem sawflies Trachelus tabidus and Cephus pygmaeus) in the Negev of southern Israel. Entomologia Experimentalis et Applicata 40: 117-121.
Shanower, T.G. and Hoelmer, K.A. 2004. Biological control of wheat stem sawflies: past and future. Journal of Agricultural and Urban Entomology 21: 197-221.