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Predatory mite attraction to herbivore-induced plant odors is not a consequence of attraction to individual herbivore-induced plant volatiles.

van Wijk M, De Bruijn PJ, Sabelis MW - J. Chem. Ecol. (2008)

Bottom Line: Attraction to individual compounds was low compared to the full HIPV blend from Lima bean.These results indicate that individual HIPV have no a priori meaning to the mites.Subsequent experiments confirmed that naive predatory mites do not prefer tomato HIPV, which included the attractive compound methyl salicylate, over the odor of an uninfested bean.

View Article: PubMed Central - PubMed

Affiliation: Institute for Biodiversity and Ecosystem Dynamics, 1090 GB, Amsterdam, The Netherlands. wijk@science.uva.nl

ABSTRACT
Predatory mites locate herbivorous mites, their prey, by the aid of herbivore-induced plant volatiles (HIPV). These HIPV differ with plant and/or herbivore species, and it is not well understood how predators cope with this variation. We hypothesized that predators are attracted to specific compounds in HIPV, and that they can identify these compounds in odor mixtures not previously experienced. To test this, we assessed the olfactory response of Phytoseiulus persimilis, a predatory mite that preys on the highly polyphagous herbivore Tetranychus urticae. The responses of the predatory mite to a dilution series of each of 30 structurally different compounds were tested. They mites responded to most of these compounds, but usually in an aversive way. Individual HIPV were no more attractive (or less repellent) than out-group compounds, i.e., volatiles not induced in plants fed upon by spider-mites. Only three samples were significantly attractive to the mites: octan-1-ol, not involved in indirect defense, and cis-3-hexen-1-ol and methyl salicylate, which are both induced by herbivory, but not specific for the herbivore that infests the plant. Attraction to individual compounds was low compared to the full HIPV blend from Lima bean. These results indicate that individual HIPV have no a priori meaning to the mites. Hence, there is no reason why they could profit from an ability to identify individual compounds in odor mixtures. Subsequent experiments confirmed that naive predatory mites do not prefer tomato HIPV, which included the attractive compound methyl salicylate, over the odor of an uninfested bean. However, upon associating each of these odors with food over a period of 15 min, both are preferred. The memory to this association wanes within 24 hr. We conclude that P. persimilis possesses a limited ability to identify individual spider mite-induced plant volatiles in odor mixtures. We suggest that predatory mites instead learn to respond to prey-associated mixtures of volatiles and, thus, to odor blends as a whole.

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Control experiments: 0.5 μl 2,3-dimethyl pyrazine is highly repellent and the mites easily avoid the side of the choice arena that contains this odor. In the absence of odors, the mites are evenly distributed along both sides of the choice arena. A small leaf disks excised from spider mite-infested lima bean leaf is attractive to the mites
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Fig2: Control experiments: 0.5 μl 2,3-dimethyl pyrazine is highly repellent and the mites easily avoid the side of the choice arena that contains this odor. In the absence of odors, the mites are evenly distributed along both sides of the choice arena. A small leaf disks excised from spider mite-infested lima bean leaf is attractive to the mites

Mentions: Validation of the Choice Arena Several tests were conducted to validate the experimental setup. First, the airflow in the choice arena was visualized with smoke derived from droplets of chloric acid and ammonia. This revealed a steady radial airflow along the bottom of the choice arena. When the fumes were applied to one side of the arena, they never entered the other side, while gauze that covered the bottom of the cartridge in the vacuum entrance was progressively covered with NH4Cl salt starting from one side only. This indicated that the separation of the odor plumes extended to the bottom of the cartridge.Unforeseen bias in the setup was investigated with a choice test in the absence of odor sources (Fig. 2). This resulted in an even distribution among both sides of the choice arena. The average preference index was −0.25. None of the six replicate experiments had a significant bias to either side, and the data were not anymore heterogeneous than expected (Gpns, Ghns, Gtns). Subsequently, two positive control experiments were conducted. In the first, an excised, spider mite-infested, lima bean leaf-disc (diam 1.5 cm) was placed on moist filter paper at one side, whereas only moist filter paper was placed at the other side. This resulted for each of the six replicate experiments in a significant attraction of starved P. persimilis, and the overall attraction was also significant (Gp*, Ghns, Gt*). The average preference index was 67.8. Finally, an odor that was a priori known to be highly repellent to the mites, 2,3-dimethyl pyrazine (0.5 μl), was offered at one side, while a control paper was placed at the other. This resulted for each of the six replicate experiments in a significant avoidance of the odor with an overall significant aversion (Gp*, Ghns, Gt*). The average preference index was −87.5.Fig. 2


Predatory mite attraction to herbivore-induced plant odors is not a consequence of attraction to individual herbivore-induced plant volatiles.

van Wijk M, De Bruijn PJ, Sabelis MW - J. Chem. Ecol. (2008)

Control experiments: 0.5 μl 2,3-dimethyl pyrazine is highly repellent and the mites easily avoid the side of the choice arena that contains this odor. In the absence of odors, the mites are evenly distributed along both sides of the choice arena. A small leaf disks excised from spider mite-infested lima bean leaf is attractive to the mites
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2480504&req=5

Fig2: Control experiments: 0.5 μl 2,3-dimethyl pyrazine is highly repellent and the mites easily avoid the side of the choice arena that contains this odor. In the absence of odors, the mites are evenly distributed along both sides of the choice arena. A small leaf disks excised from spider mite-infested lima bean leaf is attractive to the mites
Mentions: Validation of the Choice Arena Several tests were conducted to validate the experimental setup. First, the airflow in the choice arena was visualized with smoke derived from droplets of chloric acid and ammonia. This revealed a steady radial airflow along the bottom of the choice arena. When the fumes were applied to one side of the arena, they never entered the other side, while gauze that covered the bottom of the cartridge in the vacuum entrance was progressively covered with NH4Cl salt starting from one side only. This indicated that the separation of the odor plumes extended to the bottom of the cartridge.Unforeseen bias in the setup was investigated with a choice test in the absence of odor sources (Fig. 2). This resulted in an even distribution among both sides of the choice arena. The average preference index was −0.25. None of the six replicate experiments had a significant bias to either side, and the data were not anymore heterogeneous than expected (Gpns, Ghns, Gtns). Subsequently, two positive control experiments were conducted. In the first, an excised, spider mite-infested, lima bean leaf-disc (diam 1.5 cm) was placed on moist filter paper at one side, whereas only moist filter paper was placed at the other side. This resulted for each of the six replicate experiments in a significant attraction of starved P. persimilis, and the overall attraction was also significant (Gp*, Ghns, Gt*). The average preference index was 67.8. Finally, an odor that was a priori known to be highly repellent to the mites, 2,3-dimethyl pyrazine (0.5 μl), was offered at one side, while a control paper was placed at the other. This resulted for each of the six replicate experiments in a significant avoidance of the odor with an overall significant aversion (Gp*, Ghns, Gt*). The average preference index was −87.5.Fig. 2

Bottom Line: Attraction to individual compounds was low compared to the full HIPV blend from Lima bean.These results indicate that individual HIPV have no a priori meaning to the mites.Subsequent experiments confirmed that naive predatory mites do not prefer tomato HIPV, which included the attractive compound methyl salicylate, over the odor of an uninfested bean.

View Article: PubMed Central - PubMed

Affiliation: Institute for Biodiversity and Ecosystem Dynamics, 1090 GB, Amsterdam, The Netherlands. wijk@science.uva.nl

ABSTRACT
Predatory mites locate herbivorous mites, their prey, by the aid of herbivore-induced plant volatiles (HIPV). These HIPV differ with plant and/or herbivore species, and it is not well understood how predators cope with this variation. We hypothesized that predators are attracted to specific compounds in HIPV, and that they can identify these compounds in odor mixtures not previously experienced. To test this, we assessed the olfactory response of Phytoseiulus persimilis, a predatory mite that preys on the highly polyphagous herbivore Tetranychus urticae. The responses of the predatory mite to a dilution series of each of 30 structurally different compounds were tested. They mites responded to most of these compounds, but usually in an aversive way. Individual HIPV were no more attractive (or less repellent) than out-group compounds, i.e., volatiles not induced in plants fed upon by spider-mites. Only three samples were significantly attractive to the mites: octan-1-ol, not involved in indirect defense, and cis-3-hexen-1-ol and methyl salicylate, which are both induced by herbivory, but not specific for the herbivore that infests the plant. Attraction to individual compounds was low compared to the full HIPV blend from Lima bean. These results indicate that individual HIPV have no a priori meaning to the mites. Hence, there is no reason why they could profit from an ability to identify individual compounds in odor mixtures. Subsequent experiments confirmed that naive predatory mites do not prefer tomato HIPV, which included the attractive compound methyl salicylate, over the odor of an uninfested bean. However, upon associating each of these odors with food over a period of 15 min, both are preferred. The memory to this association wanes within 24 hr. We conclude that P. persimilis possesses a limited ability to identify individual spider mite-induced plant volatiles in odor mixtures. We suggest that predatory mites instead learn to respond to prey-associated mixtures of volatiles and, thus, to odor blends as a whole.

Show MeSH
Related in: MedlinePlus