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.
