Fitness Cost Of Associated With Virulence Evolution In The Hessian Fly And The Effect Of Wheat Seedling Ages On Its Fitness

The Hessian fly, Mayetiola destructor (Say)(Diptera: Cecidomyiidae), is an importantpest of wheat Triticum spp (Poaceae）throughout most of wheat production areas. Resistantwheat varieties have been proved the most reliable and economical form of management forHessian fly. However, the continued development of virulent biotypes in response to selectionpressure imposed by wide-spread use of resistant cultivars poses great threat to thepermanence of resistance. The wheat-Hessian fly system serves as an excellent model forunderstanding plant-insect interactions, especially those involving gene-for-gene interactions.Fitness cost is believed to influence virulence evolution in insect to resistance genes. However,it has not been investigated for the Hessian fly. Screening resistance materials in wheat andanalyzing virulence of impeding virulent genotypes in Hessian fly will provide usefulinformation for wheat breeding program and for improving control strategies for the insect.Investigating interactions between plant ages and insect fitness will facilitate understandingthe dynamics of population in fields. We investigated the fitness changes under laboratoryconditions to1）test the hypothesis that adaptation to resistance couple with fitness cost inHessian fly;2）understand the effect of plant ages on fitness of Hessian fly;3）screenresistance sources in emmer wheat, and4) identify effectiveness of known H genes for a newadapted strain vH13. The main results are as follows:1. On H-gene-free wheat, two H-adapted strains were shorter to the nonadapted strain inegg-to-adult survival, but they differed in producing adults with shorter wings. By usingknown relationships between wing length and reproductive potential, we found that losses inwing length underestimate reduction in reproductive potential. For example, H9-andH13-adapted females had9%and3%wing reduction, respectively, but they were estimated tohave32%and12%reduction in egg production; for H9-and H13-adapted males, reduction inwing length were5%and3%, respectively, but they were estimated to have18%and11%reduction in reproductive potential.2. On two wheat lines, one conferring H13resistance (referring to as noval host plant）,another one lacking any known gene (natal host plant), H13-adapted (vH13) populationsshowed no difference in growth rate and adult body size between the two hosts, but they differed in survival. Growing on noval host plant significantly decreased larval survivalduring feeding stage, and reflected on survival from egg-to-adult, indicating that adaptation toH resistance incur reduced survival on noval host, and adaptation to noval host do not resultin decreased performance on natal host.3. Ten of300accessions of emmer wheat, including CItr14972, CItr4013, PI154582,PI94634, PI94650, PI254194, PI362500, PI362501, PI355479, and PI377655, exhibitedantibiosis resistance to Hessian fly biotype Great Plains. Five of the10lines, includingCItr14972, CItr4013, PI154582, PI362500, and PI377655, exhibited highly resistance to vH13strain. Virulence analysis showed that seventeen of the tested27resisitance genes, H5, H7H8,H9, H11, H12, H14, H15, H17, H19, H20, H21, H22, H25, H26, H28, H29and H32,conferred high levels of resistance (>80%plants resistant）to vH13strain. Five genes, H3, h4,H13, H18, and H31were susceptible (<50%resistant plants). Nine H genes, including H9,H11, H15, H19, H20, H21, H25, H28, and H29should be recommended as candidate genes inareas where vH13strain would be predominant.4. Plant ages have pleiotropic effects on fitness of the Hessian fly. The insect displayedbetter performance on young seedlings with higher survival from egg to adult and shorteneddevelopment times, with one exception that both females and males were significantly smallerthan those on old seedlings. There was no trade-off between body size and development times.In addition, plant ages lead to a divergence of adult emergence strategy. Relative to adultemergence on young seedlings with one peak, both females and males showed a differentemergence manner with two peaks on old seedlings.