Symptoms, description and lifecycle

The Hessian fly is a serious pest of wheat and barley, resulting in stunted growth and reductions in grain yield and quality.

Feeding damage on cereal plants can cause leaf discolouration, from a darker green to bluish green or yellowing of new growth in seedlings. Plants are often stunted and tillers may be prevented from heading, or if they do, they can become weakened causing plants to lodge. The dark pupae imbedded into the cereal stems, particularly on wheat, is the most detectable stage of Hessian fly development.

Eggs are 0.5 mm long, elongated with rounded ends and glossy red becoming darker with age. They are laid on the upper surface of wheat leaves parallel with the veins. Larvae are maggots (legless) and undergo three instars growing up to three to four millimetres in length. The second instar becomes a puparium within which the third instar, pupa and adult will develop. Puparia are two to six millimetres long, dark brown and tapered. Adults are small, mosquito like flies two to four millimetres long, with an elongate cylindrical body tapered at one end. They have one set of wings with a few weak veins and beaded elongated antennae (Image 27).

Organism

Mayetiola destructor

Conditions favouring pest

Humid, moderately warm periods are prefered by adult Hessian flies. Evidence internationally indicates that grain growing regions averaging 450 mm annum rainfall are of greatest risk.

Host range

Primary host is wheat (Triticum sp.). Secondary hosts include wheat grass (Agropyron), barley (Hordeum vulgare) and rye (Secale cereale).

Method of spread

Adults spread by actively flying throughout the crop or can be dispersed by wind currents. Long distance dispersal also occurs by ‘hitchhiking’ on machinery, clothes or straw and other plant material.

Confused with?

This species is very similar and closely related to the Barley stem gall midge (Mayetiola hordei). It has been confused with this species in Africa.

Identification of the two species involves microscopic morphological differences and is best undertaken by an expert taxonomist.

Where?

Hessian fly is widespread in North America and Europe. It is also found in New Zealand, Africa and the parts of the Middle East.

Image 27. Female Hessian fly which are typically a bit bigger than the males.
Source: Scott Bauer, ARS/USDA.