Proximate Cues for Reduced Oviposition by Hessian Fly on Wheat Plants Attacked by Conspecific Larvae.

In a previous study, we showed that female Hessian fly, Mayetiola destructor (Say), oviposits significantly fewer eggs on susceptible wheat plants attacked by conspecific larvae. Here we tested whether proximate cues for reduced egglaying on larval-occupied plants are associated with larvae per se or plant-based cues related to larval attack. We used a novel method, i.e., R gene-defended wheat Triticum aestivum L. genotypes, to decouple Hessian fly larvae from their effects on the plant. On R gene-defended plants, Hessian fly larvae survive for up to 5 d but do not grow. A comparison of egglaying patterns on four near-isogenic wheat genotypes, a susceptible control `Newton' and three R gene wheat genotypes expressing the H6, H9, or H13 gene, showed that the presence of live larvae on plants was not the cause of reduced egglaying. Growth deficits in the youngest leaves, a well-known plant response to Hessian fly larval attack, also were examined as a possible cause of reduced oviposition but showed no consistent relationship with egg numbers. We conclude that Hessian fly females have additional means of distinguishing between larval-occupied and unoccupied plants, perhaps by detecting chemical cues associated with plant stress. [ABSTRACT FROM AUTHOR]