Effect of temperature on the expression of resistance to Hessian fly (Diptera: Cecidomyiidae) in durum wheat cultivars

Hessian fly, Mayetiola destructor (Say) is a destructive insect pest occurring in many wheat growing areas of the world. The most effective management option for controlling Hessian fly is the use of resistant wheat cultivars carrying specific resistance genes. However, wheat resistance genes to Hessian fly are affected by temperature. Two Moroccan cultivars 'Chaoui' and 'Marouane' and three ICARDA elites DWHF01, DWHF02 and Icamoram7 all carrying resistance to Moroccan Hessian fly populations were evaluated at three different temperatures (20, 25 and 30 degrees C). Results showed that the elite DWHF01 and DWHF02 resistance was less affected by higher temperatures with percentage of resistant plants remaining above 60% at 30 degrees C. However, 'Marouane', 'Icamoram7' and 'Chaoui' lost more than 50% of their resistance at 30 degrees C. Resistance in all these genotypes was expressed only as antibiosis with presence of dead first instars on resistant plants. The number of live larvae on susceptible plants was counted and larval density decreased with increasing temperature. Moreover, length measurements of live larvae showed significant differences across different temperatures, the size of larvae increased as temperature increased and ranged between 3.23 and 4.13 mm. In light of the warming climates and increase occurrence of days above 30 degrees C during the first months of the Moroccan wheat season, the data presented here are meant to help breeders recommend cultivars better adapted to the raising temperatures.