Hessian fly a high-priority grains risk

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Image of a Hessian Fly

Exotic to Australia, the hessian fly is a high-risk pest.

PHOTO: Scott Bauer, USDA Agricultural Research Service

A recent review of 600 exotic pest threats to the Australian grains industry identified 54 high-priority threats, including hessian fly (Mayetiola destructor), which has caused extensive crop damage internationally, including in neighbouring New Zealand.

High-priority pests are those that are likely establish to here, and would cause significant losses if they were to do so, through reduced grain production, storage losses, control costs and lost market access.

Hessian fly is a significant pest of wheat and other winter cereals around the world. In addition to parts of the US and Canada, it is widespread in Europe and is prevalent through Tunisia, Algeria and Morocco as well as Cyprus, Iraq, Israel, Kazakhstan, Syria and Turkey. 

It is thought to have spread from Asia into Europe, arriving in North America in the straw bedding of Hessian (German) troops recruited to fight by the British during the American Revolution (1765–83). The hessian fly is now well established on both the North and South Islands of New Zealand.

Up to 40 per cent yield losses have been recorded in severe infestations in some of these countries. Estimated yield losses if it were to establish in Australia are five to 15 per cent. Australian hay exports to Japan and grain exports to other countries that are free of the pest, such as Iran and South Korea, would also be jeopardised. Border and pre-border restrictions are designed to keep hessian fly out, but surveillance by growers is also crucial to early detection and eradication.

What to look for

Host crops for hessian fly are wheat, barley, triticale and rye. Often the initial sign of infestation is a change in leaf colour to a darker or bluish green. Young plants are likely to be stunted, with leaves that are shorter, broader and more erect than healthy plants.

Hessian fly can cause stunting and yellowing of the crop. Severe infestations will cause death of young plants. As larvae feed at the nodes, infestation during and after stem elongation can result in weakening of the stems, lodging, and lack of head development and seed-set. In some cases 40 to 70 per cent of tillers can be affected.

Currently there are no fly species in Australia that attack cereal plants above the ground, so unexplained lodging of stems or leaf discolouration should be investigated. If you see anything unusual, notify your agronomist or call the Exotic Plant Pest Hotline on 1800 084 881. 

Identifying the fly

The adult hessian fly is a mosquito-like insect, two to four millimetres long. The adults live for two to six days and lay eggs parallel to the veins on the upper surface of the wheat leaf. The eggs are about 0.5mm long, elongated with rounded ends and a glossy red colour that darkens as they age. Their appearance is similar to the early stages of leaf rust. Eggs hatch after three to 12 days.

There are three stages of larval instars. The first instar is 0.5 to 1.7mm long and spends 12 to 15 hours crawling down the leaf to the feeding site between the leaf sheath and stem. The second instar is 1.7 to 4mm and has a long, unevenly cylindrical shape with tapering at the posterior end. It feeds for two to three weeks in high temperatures but as long as two months in cool conditions. It is white while feeding but turns brown and hard. The third instar develops in the second, is not visible and does not feed.

The pupae, embedded in the cereal stems, are dark brown, 2 to 6mm long and commonly known as ‘flaxseeds’. This stage lasts six to 33 days and is the easiest stage at which to detect infestation. 

Look along leaves for eggs and check for maggots or flaxseeds by pulling the leaf sheath away from the stem to the base of the plant. The length of the life cycle is highly temperature dependent, with up to six generations a year reported in warmer climates.

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