Tolerance as a Mechanism of Hessian Fly Control in Wheat

Host plant resistance genes are a key method in reducing Hessian fly populations and infestations. These gene-for-gene interactions lead to antibiosis of the larvae and survival of the wheat. However, Hessian fly populations can be selected for resistance to these R genes, leading to survival of the larvae and stunting or death of the plant. Tolerance in wheat might hold the key to reducing damage caused by Hessian flies while preventing the flies from gaining resistance. Tolerance allows the plant to survive infestation and to continue growing, potentially pushing larvae out of the leaf sheath and into the environment, making them vulnerable to desiccation and parasitism. Experiments were run using the susceptible lines 25R75 and Newton as well as the tolerant line 25R78. Several sets of time increments were used: 8, 9, 16, and 32 days after infestation. For 16 days, significant differences were observed between the treated lines for tiller number, leaf number, total leaf length, and larvae surface area. There were no significant differences for leaf number or tiller number between the control and treated plants for line 25R78, but there were differences between control and treated plants of 25R75, suggesting that tolerance had a positive effect. The tolerant line experienced significantly more leaf growth, biomass, and tillers versus the susceptible line when both lines were infested with at least one Hessian fly larva. Infestation had a much smaller impact on the tolerant line compared to the susceptible line. There was a 20.74% reduction in leaf length for line 25R78 compared to a 47.08% reduction in leaf length for line 25R78. The tolerant line also showed significantly more visible larvae (50% of plants) present than the susceptible line (0% of plants) and, therefore, more exposed to adverse conditions. An increased number of tillers for the infested tolerant line could lead to more fertile heads and a higher grain yield, compared to the fewer tillers and leaves present in the infested susceptible line.