Oviposition behavior of orange wheat blossom midge on low – versus high ranked grass heads

Abstract

The discovery of Sm1 , a highly effective resistance ( R ) gene that targets the first instar of the orange wheat blossom midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae), has created concerns about wheat midge adaptation. Strategies for delaying adaptation to Sm1 include the simultaneous deployment of a resistance trait targeting a different life stage, i.e., the ovipositing adult female. Previous studies have shown that adult females distinguish between wheat genotypes and seed head developmental stages and are attracted by volatiles from young wheat heads. We focused on what happens after the female lands on the seed head, comparing in three tests a seed head of the high-ranked pre-anthesis ‘Roblin’ wheat, Triticum aestivum L. (Poaceae), and a head of one of three lower-ranked types: post-anthesis ‘Roblin’, pre-anthesis ‘Key’ wheat ( T. aestivum ), and pre-anthesis ‘Robust’ barley ( Hordeum vulgare L.). Within each test, high- and low-ranked heads were presented in choice and no-choice assays, with the behavior of wheat midge females scored every 5 min from 20:30 to 23:00 hours, under mid-summer natural light conditions and sunset occurring between 20:50 and 21:20 hours. Head type influenced both proportions of females observed on the head and proportions of females probing with the ovipositor. Head*assay interactions occurred only in the test comparing wheat to barley, with barley reducing females observed on the wheat head and wheat increasing females probing on barley. Results indicate that the wheat midge female detects plant cues while examining the seed head and that this detection contributes to differences in egg counts.