Browsing by Author "Marion O.H."

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Ovipositing females of a short-lived gall midge take time to assess grass seed heads
(Physiological Entomology, 2008) Ganehiarachchi G.A.S.M.; Marion O.H.
The short-lived adult wheat midge Sitodiplosis mosellana deposits eggs on the seed head of various grasses close to the developing seeds on which larvae feed. The time taken to make egg-laying decisions is investigated using three types of wheat Triticum aestivum seed heads. Young Roblin, Old Roblin and Young Key differ in their effects on ovipositing females (72%, 22% and 6% of eggs in choice tests, respectively) and effects on feeding larvae (75%, 25% and 5% larval survival, respectively). Within seconds of arriving, the female is able to distinguish Young Roblin from the two lower-ranked types. However, the lower-ranked types are not rejected at this time. Instead, all head types are examined before the female eventually flies away. On Young Roblin, probing with the ovipositor is the first behaviour that occurs. Thereafter probing and insertion of the ovipositor occupy most of the female’s time and behavioural transitions tend to be ‘progressive’, signalling a shift from low to high intensity examining. Differences between females visiting Old Roblin and Young Key are significant but take longer to emerge. On both, sitting is the first behaviour but, over the next 5–10 min, the female on Young Key exhibits more sitting, walking and ‘regressive’ transitions than the female on Old Roblin. It is suggested that, when the ovipositing female is short-lived and incapable of controlled flight in all but essentially windless conditions, her behaviour is designed to thoroughly, rather than rapidly, examine a suboptimal host before abandoning it for the uncertain future of finding a better host.
Oviposition behavior of orange wheat blossom midge on low – versus high ranked grass heads
(Entomologia Experimentalis et Applicata, 2007) Ganehiarachchi G.A.S.M.; Marion O.H.
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.