We tested the extent to which resistance of common bean (Phaseolus vulgaris) cultivars to the spider mite Tetranychus urticae parallels the extent to which these plants display indirect defenses via the induced attraction of the predatory mite Phytoseiulus persimilis. First, via field and greenhouse trials on 19 commercial bean cultivars, we selected two spider mite-resistant (Naz and Ks41128) and two susceptible (Akthar and G11867) cultivars and measured the spider mite-induced volatiles and the subsequently induced attraction of predatory mites via olfactory choice assays. The two major volatiles, 4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT) and (Z)-3-hexenyl-acetate, were induced in the resistant but not in the susceptible cultivars. However, uninfested susceptible cultivars emitted these volatiles at levels similar to those of mite-infested resistant cultivars. Significant induction of several minor components was observed for all four cultivars except for the infested-susceptible cultivar G11867. Both, the spider mite-resistant cultivar Naz and the susceptible cultivar G11867, attracted more predatory mites when they were infested. In contrast, spider mites induced increased emission of two major and five minor volatiles in Ks41128, but predatory mites did not discriminate between infested and uninfested plants. Overall, the attraction of predatory mites appeared to correlate positively with the presence of TMTT and (Z)-3-hexenyl acetate and negatively with β-caryophyllene and α-pinene in the bean headspace. Taken together, our data suggest that resistance and attraction of natural enemies via induced volatiles are independent traits. We argue that it should be possible to cross predator-attraction promoting traits into resistant cultivars that lack sufficiently inducible indirect defenses.
While searching for food, predators use herbivore induced plant volatiles (HIPV), host plant volatiles and those related to con/heterospecifics to find their prey. Not only the volatile components vary among plant species, but also the predator perception of these components might differ among species and samples. Here, we compared the olfactory response of two samples (Turkey and University of Tehran) of Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) when received herbivore induced plant volatiles (HIPV) from Tetranychus urticae Koch (Acari: Tetranychidae) infested cucumber and bean leaves, along with testing the effect of rearing experience of Turkey sample on its olfactory response in our laboratory conditions. Our data showed that P. persimilis of both samples significantly moved towards leaf odors (either cucumber or bean) when they received clean air from the alternative arm. For both samples, the predator did not make a preference between clean bean and cucumber leaves. When the predators were offered a choice between T. urticae infested bean and cucumber leaves, they significantly moved towards bean leaves in both samples. Rearing experience did not affect the predator choice of host plant species and P. persimilis from both samples preferred odors related to clean leaves rather than clean air. The number of experienced predatory mites moved towards T. urticae infested bean leaves was significantly higher than that preferred T. urticae infested cucumber leaves in both samples. We discussed whether their similar olfactory responses would be related to their experience of previous rearing conditions.
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