M. W. E. M. Van Tilborg

C4H5N+· ions studied by ion/molecule reactions and photodissociation

Abstract C4H5N+· ions, generated from five different isobaric neutral precursors, have been studied and characterized by ion molecule reactions and their behaviour upon photodissociation, using an ion cyclotron resonance (ICR) spectrometer. It is found that ions derived from methacrylonitrile and pyrrole retain the structures of their parent neutral molecules. Cyclopropyl cyanide and crotonitrile ions partly isomerize to an unreactive C4H5N+· ion, presumably pyrrole, to the extent of 15% and 6%, respectively. Allyl cyanide gives rise to three ionic species: the original structure (25%), crotonitrile (45%) and pyrrole (30%).

State-dependent and odour-mediated anemotactic responses of the predatory mite Phytoseiulus persimilis in a wind tunnel

Anemotaxis in the predatory mite Phytoseiulus persimilis (both well-fed and starved), has previously been studied on a wire grid under slight turbulent airflow conditions yielding weak, yet distinct, gradients in wind speed and odour concentration). Such conditions might have critically influenced the outcome of the study. We repeated these experiments, under laminar airflow conditions on a flat surface in a wind tunnel, thereby avoiding variation in wind speed and odour concentration. Treatments for starved and well-fed mites were (1) still-air without herbivore-induced plant volatiles (HIPV) (well-fed mites only), (2) an HIPV-free air stream, and (3) an air stream with HIPV (originating from Lima bean plants infested by two-spotted spider mites, Tetranychus urticae). Well-fed mites oriented in random directions in still-air without HIPV. In an air stream, starved mites always oriented upwind, whether plant odours were present or not. Well-fed mites oriented downwind in an HIPV-free air stream, but in random directions in an air stream with HIPV. Only under the last treatment our results differed from those of Sabelis and Van der Weel (1993).