Hessian Fly

• Its common name comes from the belief that it reached North America in the straw mattresses of the Hessian mercenary troops during the War of Independence, an origin never confirmed.
• Study of its relationship with wheat led to the description of the gene-for-gene model of resistance: each resistance gene in the plant is matched by a virulence gene in the insect, a concept central to plant breeding.
• The adults live barely one or two days and do not feed: they only mate and lay eggs.
• It is a gall midge: it does not eat the plant but injects effector proteins in its saliva that shut down the plant's defences and redirect its development towards forming a gall.
• Seven per cent of its genome consists of highly diversified genes expressed in the larva's salivary glands, which encode those effectors.
• It has a gene-for-gene relationship with wheat: some 35 resistance genes have been identified in wheat, and each is matched by an avirulence gene in the fly. When the fly's gene mutates and stops working, the larva overcomes that particular resistance.
• On a resistant variety the larva dies within four or five days of hatching; on a susceptible one it keeps growing and forms the gall.
• Plants attacked in autumn lose vigour and die, and those attacked in spring snap easily before harvest.

Skeleton type

Invertebrate - chitin exoskeleton (insect)

Habitat and environment

Wheat, barley and rye crops

Size at birth

Orange elliptical egg under 1 mm; the mature larva reaches 4-6 mm

Sexual maturity

The adult emerges with vestigial mouthparts, does not feed and lives only 1 to 4 days, during which it mates and lays

Gestation / incubation

The eggs hatch in 3-7 days depending on the temperature; after three larval instars the puparium forms and the adult emerges between 6 and 33 days later; the full cycle lasts about 28 days on average

Litter / clutch size

100 to 300 eggs per female, laid in the grooves on the upper surface of the leaves

Sources consulted: https://es.wikipedia.org/wiki/Mayetiola_destructor; LSU AgCenter, ficha Hessian fly; protocolo diagnostico NDP-41; LSU AgCenter; NCBI PMC5013046, receptor de feromona sexual; SDSU Extension; Nature Scientific Reports 2021

Best time: Two generations a year in cold climates (autumn and spring) and up to six in warm regions; it passes the summer and the winter as a puparium, known as the flaxseed