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Biomedical subjects

Jan Bruin

Publications and source records attributed to Jan Bruin.

6 recordsLinked to original sources
PubMed2005

Diapause incidence in the two-spotted spider mite increases due to predator presence, not due to selective predation.

We recently reported evidence for increased diapause incidence in the spider mite Tetranychus urticae in presence of the predatory mite Typhlodromus pyri. This effect may arise from (1) selective predation on non-diapause spider mites, (2) predator-induced diapause in spider mites, or (3) both. Using a different strain of T. urticae, we first recovered increased diapause incidence in association with predators. Then, we tested for selective feeding in two-choice experiments with equal numbers of non-diapause and diapause spider mites. We found that the predatory mite had a significant preference for the latter. This indicates that increased diapause incidence in association with predatory mites is not due to selective predation. Therefore, predator-mediated physiological induction of diapause seems a more likely explanation. The cues leading to induction appear to relate to the predators, not their effects, since predation simulated by spider-mite removal or puncturing did not significantly affect diapause incidence. Why spider mites benefit from this response, remains an open question.

Adaptation, Physiological↗
PubMed2004

Predation risk affects diapause induction in the spider mite Tetranychus urticae.

Whenever diapause induction triggers movement into another microhabitat or the development of protective morphological structures, this may also alter predation risk. If the risk of being eaten is lower in the diapause phase, then there may be selection favouring diapause induction in response to predators or their cues. In this article, we studied the effect of the predatory mite Typhlodromus pyri on diapause induction in the spider mite Tetranychus urticae. We used a Greek strain because under long-night photoperiods and low temperature only part of the population enters diapause, thereby leaving room for the impact of another factor. In spider mite groups under predation, the percentage diapause induction increased whenever night-lengths were such that diapause was induced (13-16 h of night). Given this diapause induction in response to predation risk, the question arises whether entering diapause helps spider mites to escape from predation and contribute more offspring to the spring generation next year.

Adaptation, Physiological↗
PubMed2004

A new method for mite extraction from leaf samples.

Debris often hampers the detection of mites in washed leaf samples. We describe in detail a method for the extraction of mites from leaf samples, based on the adherence of mite cuticles to liquid paraffin, at the interface of paraffin and ethanol in a so-called mite-counting channel. We demonstrate its efficacy by comparing the mite numbers in samples before and after extraction. We illustrate the method's reliability by extracting known numbers of a taxonomic variety of plant-inhabiting mites, manually added to mite-free debris: for 13 of the 15 taxa all mites were retrieved. This method can also be used to extract small non-mite arthropods such as scales, whiteflies, thrips, cicadellids, hymenopteran parasitoids and psyllids.

Animals↗
PubMed2003

Intraspecific variation in induction of feeding preference and performance in a herbivorous mite.

Induction of food preference has often been observed in herbivorous insects. The term is used to indicate preference of individuals for the host plant they have already experienced over one they have not experienced. A typical set-up is one where individuals first feed on host X or Y, and are then offered a choice between host X and Y. This set-up--and hence the body of empirical data--has been criticised for lack of a control treatment to untangle the effects of the separate hosts. In this study, we use a design with a third, unrelated host as control to investigate induction of preference in the herbivorous arthropod, Tetranychus urticae. We provide evidence of induced preference, as well as induced performance, and show that there is considerable variation in these two traits among strains. We suggest induced resistance to toxic secondary plant chemicals as one potential explanation for induced performance. This in itself suggests associative learning as the most likely candidate learning mechanism for induction of preference in this species. Phenotypically plastic effects underlying induced performance may be a general aspect of induction of preference in herbivorous arthropods, which warrants closer attention to these phenomena.

Animals↗