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Predator efficacy and attraction to herbivore-induced volatiles determine insect pest selection of inferior host plant.

ABSTRACT: Unlike mammals, most invertebrates provide no direct parental care for their progeny, which makes a well-selected oviposition site crucial. However, little is known about the female evaluation of opportunities and threats during host selection. Leveraging the wide range of host plants used by the polyphagous pest, Spodoptera littoralis, we investigate oviposition choice between two plants of different nutritional quality. Females prefer to lay their eggs on the host plant, which has inferior larval development and more natural enemies but provides lower predation rates. On the superior host plant, a major predator shows more successful search behavior and is more attracted to herbivore-induced volatiles. Our findings show that predator efficacy and odor-guided attraction, rather than predator abundance, determine enemy free space. We postulate that predators' behaviors contribute to the weak correlation between preference and performance during host plant selection in S. littoralis and in polyphagous insects in general.

SUBMITTER: Khallaf MA

PROVIDER: S-EPMC9929603 | biostudies-literature | 2023 Feb

REPOSITORIES: biostudies-literature

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Predator efficacy and attraction to herbivore-induced volatiles determine insect pest selection of inferior host plant.

Khallaf Mohammed A MA Sadek Medhat M MM Anderson Peter P

iScience 20230128 2

Unlike mammals, most invertebrates provide no direct parental care for their progeny, which makes a well-selected oviposition site crucial. However, little is known about the female evaluation of opportunities and threats during host selection. Leveraging the wide range of host plants used by the polyphagous pest, <i>Spodoptera littoralis</i>, we investigate oviposition choice between two plants of different nutritional quality. Females prefer to lay their eggs on the host plant, which has infer ...[more]

PMID: 36818286

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Project description: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.

Project description:Beneficial root microbes are among the most frequently used biocontrol agents in cropping systems, since they have been shown to promote plant growth and crop yield. Moreover, they are able to enhance protection against pathogens and insect herbivores by activating plant resistance mechanisms. Plant defense responses against herbivorous insects include the induction of metabolic pathways involved in the synthesis of defense-related metabolites. These metabolites include volatile organic compounds (VOCs), which attract natural enemies of the herbivores as a form of indirect resistance. Considering that beneficial root microbes may affect direct herbivore resistance, we hypothesized that also indirect resistance may be affected. We tested this hypothesis in a study system composed of tomato, the arbuscular mycorrhizal fungus Rhizophagus irregularis, the growth-promoting fungus Trichoderma harzianum, the generalist chewing herbivore Spodoptera exigua and the omnivorous predator Macrolophus pygmaeus. Using a Y-tube olfactometer we found that M. pygmaeus preferred plants with S. exigua herbivory, but microbe-inoculated plants more than non-inoculated ones. We used a targeted GC-MS approach to assess the impact of beneficial microbes on the emission of volatiles 24 h after herbivory to explain the choice of M. pygmaeus. We observed that the volatile composition of the herbivore-infested plants differed from that of the non-infested plants, which was driven by the higher emission of green leaf volatile compounds, methyl salicylate, and several monoterpenes and sesquiterpenes. Inoculation with microbes had only a marginal effect on the emission of some terpenoids in our experiment. Gene expression analysis showed that the marker genes involved in the jasmonic and salicylic acid pathways were differentially expressed in the microbe-inoculated plants after herbivory. Our results pinpoint the role of root symbionts in determining plant-microbe-insect interactions up to the third trophic level, and elucidates their potential to be used in plant protection.

Project description:Plants produce semio-chemicals that directly influence insect attraction and/or repulsion. Generally, this attraction is closely associated with herbivory and has been studied mainly under atmospheric conditions. On the other hand, the relationship between aquatic plants and insects has been little studied. To determine whether the roots of aquatic macrophytes release attractive chemical mixtures into the water, we studied the behaviour of mosquito larvae using olfactory experiments with root exudates. After testing the attraction on Culex and Aedes mosquito larvae, we chose to work with Coquillettidia species, which have a complex behaviour in nature and need to be attached to plant roots in order to obtain oxygen. This relationship is non-destructive and can be described as commensal behaviour. Commonly found compounds seemed to be involved in insect attraction since root exudates from different plants were all attractive. Moreover, chemical analysis allowed us to identify a certain number of commonly found, highly water-soluble, low-molecular-weight compounds, several of which (glycerol, uracil, thymine, uridine, thymidine) were able to induce attraction when tested individually but at concentrations substantially higher than those found in nature. However, our principal findings demonstrated that these compounds appeared to act synergistically, since a mixture of these five compounds attracted larvae at natural concentrations (0.7 nM glycerol, <0.5 nM uracil, 0.6 nM thymine, 2.8 nM uridine, 86 nM thymidine), much lower than those found for each compound tested individually. These results provide strong evidence that a mixture of polyols (glycerol), pyrimidines (uracil, thymine), and nucleosides (uridine, thymidine) functions as an efficient attractive signal in nature for Coquillettidia larvae. We therefore show for the first time, that such commonly found compounds may play an important role in plant-insect relationships in aquatic eco-systems.

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Predator efficacy and attraction to herbivore-induced volatiles determine insect pest selection of inferior host plant.

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Predator efficacy and attraction to herbivore-induced volatiles determine insect pest selection of inferior host plant.

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