Maize mycorrhizas decrease the susceptibility of the foliar insect herbivore Spodoptera frugiperda to its homologous nucleopolyhedrovirus.

BACKGROUND: The multiple nucleopolyhedrovirus of Spodoptera frugiperda (SfMNPV) plays an important role in regulating its natural host and has high potential for use as a bioinsecticide. However, information about how agricultural practices such as fertilization and plant biotic interactions affect the biocontrol efficacy of SfMNPV is limited. In this study, we examined how multitrophic maize-mycorrhiza-insect herbivore interactions affect the biocontrol efficacy of SfMNPV against S. frugiperda under full and reduced mineral nitrogen fertilization. Two fully factorial greenhouse pot experiments with three factors were performed: (i) arbuscular mycorrhizal fungi (AMF) (with and without AMF), (ii) nitrogen fertilization (50% and 100% N), and (iii) insect (with and without of S. frugiperda). The biocontrol efficacy of SfMNPV against S. frugiperda was examined using detached leaves under controlled environmental conditions. RESULTS: Associating maize with AMF resulted in multitrophic cascade effects. Plants with AMF showed suppression of plant growth and increased leaf N and P content, which coincided with increased foliar herbivory and larval biomass that finally reduced the susceptibility of S. frugiperda to SfMNPV. Reduced levels of N fertilization mitigated these observed cascade effects on the biocontrol efficacy of SfMNPV with maize mycorrhizas. CONCLUSION: Our results show that AMF can modulate S. frugiperda-SfMNPV interactions via plant-mediated phenotypic responses to the mycorrhizal association and are most likely linked with increased leaf food quality for S. frugiperda. These results call for further studies to address the mode of interaction and possible implications for pest management in maize agroecosystems. © 2021 Society of Chemical Industry.

In a belowground multitrophic interaction, Trichoderma harzianum induces maize root herbivore tolerance against Phyllophaga vetula.

BACKGROUND: Trichoderma spp. are soil fungi that interact with plant roots and associated biota such as other microorganisms and soil fauna. However, information about their interactions with root-feeding insects is limited. Here, interactions between Trichoderma harzianum and the root-feeding insect Phyllophaga vetula, a common insect pest in maize agroecosystems, were examined. RESULTS: Applications of T. harzianum and P. vetula to the root system increased and decreased maize growth, respectively. Induced tolerance against herbivore attack was provided by T. harzianum maintaining a robust and functional root system as evidenced by the increased uptake of Cu, Ca, Mg, Na and K. Herbivore tolerance also coincided with changes in the emission of root volatile terpenes known to induce indirect defense responses and attract natural enemies of the herbivore. More importantly, T. harzianum induced de novo emission of several sesquiterpenes such as ß-caryophyllene and δ-cadinene. In addition, single and combined applications of T. harzianum and P. vetula altered the sucrose content of the roots. Finally, T. harzianum produced 6-pentyl-2H-pyran-2-one (6-PP) a volatile compound that may act as an antifeedant-signaling compound mitigating root herbivory by P. vetula. CONCLUSION: Our results provide novel information about belowground multitrophic plant-microbe-arthropod interactions between T. harzianum and P. vetula in the maize rhizosphere resulting in alterations in maize phenotypic plant responses, inducing root herbivore tolerance.

Increased maize growth and P uptake promoted by arbuscular mycorrhizal fungi coincide with higher foliar herbivory and larval biomass of the Fall Armyworm Spodoptera frugiperda.

Most plant species naturally associate with arbuscular mycorrhizal fungi (AMF), which are known to promote crop nutrition and health in agroecosystems. However, information on how mycorrhizal associations affect plant biotic interactions that occur aboveground with foliar herbivores is limited and needs to be further addressed for the development of pest management strategies. With the objective to examine the influence of maize mycorrhizas on foliar herbivory caused by larvae of Spodoptera frugiperda, a serious pest in maize agroecosystems, we performed a fully factorial greenhouse pot experiment with three factors: Maize genotype (Puma and Milpal H318), AMF (with and without AMF, and without AMF with mineral P) and Insect herbivory (with and without S. frugiperda). Main results showed that inoculation with AMF improved plant growth and foliar P concentration, which coincided with increased foliar damage from herbivory and higher biomass of S. frugiperda larvae. A significant positive correlation between shoot P concentration and larval biomass was also observed. Finally, foliar herbivory by S. frugiperda slightly increased and decreased AMF root colonization in Puma and H318, respectively. In conclusion, our results show that maize plant benefits from AMF in terms of promotion of growth and nutrition, and may also increase the damage caused from insects by improving the food quality of maize leaves for larval growth, which seems to be linked to increased P uptake by the maize mycorrhizal association.