Digestive activity and organic compounds of Nezara viridula watery saliva induce defensive soybean seed responses

Romina Giacometti,Vanesa Jacobi,Charalampos Panagos,Florencia Kronberg,Arthur S. Edison,Jorge A. Zavala

doi:10.1038/s41598-020-72540-3

Abstract

The stink bug Nezara viridula is one of the most threatening pests for agriculture in North and South America, and its oral secretion may be responsible for the damage it causes in soybean (Glycine max) crop. The high level of injury to seeds caused by pentatomids is related to their feeding behavior, morphology of mouth parts, and saliva, though information on the specific composition of the oral secretion is scarce. Field studies were conducted to evaluate the biochemical damage produced by herbivory to developing soybean seeds. We measured metabolites and proteins to profile the insect saliva in order to understand the dynamics of soybean-herbivore interactions. We describe the mouth parts of N. viridula and the presence of metabolites, proteins and active enzymes in the watery saliva that could be involved in seed cell wall modification, thus triggering plant defenses against herbivory. We did not detect proteins from bacteria, yeasts, or soybean in the oral secretion after feeding. These results suggest that the digestive activity and organic compounds of watery saliva may elicit a plant self-protection response. This study adds to our understanding of stink bug saliva plasticity and its role in the struggle against soybean defenses.

Highlights

The stink bug Nezara viridula is one of the most threatening pests for agriculture in North and South America, and its oral secretion may be responsible for the damage it causes in soybean (Glycine max) crop
To enhance our understanding of the physiology and feeding behaviour of the green stink bug and to provide additional information on the ecological impact of the interaction between N. viridula and the developing soybean pods and seeds, we described the morphology of the mouthparts of this stink bug involved in probing and feeding
Green stink bug mouthparts observed by Scanning Electron Microscopy (SEM) are sophisticated and resemble those described in other piercing-sucking insects, composed of the labium, labrum and a stylet fascicle housed by a long beak (Fig. 1A)

Summary

Introduction

The stink bug Nezara viridula is one of the most threatening pests for agriculture in North and South America, and its oral secretion may be responsible for the damage it causes in soybean (Glycine max) crop. Most research about digestive enzyme secretion in insects has been conducted on aphid midgut c ells[16] or oral secretions and regurgitant of caterpillars This has led to the identification of proteins like β-glucosidase[17,18], peptides named inceptins[19,20], and the well-known amino acidfatty acid conjugates (FACs), while less is known about e ffectors[20]. It has been reported that N. viridula’s gut cells expresses high cysteine protease levels, while salivary glands express high levels of serine proteases and nucleases[14] Since these stink bug enzymes can be inhibited by soybean protease inhibitors accumulated in seeds, N. viridula prefer to feed on developing seeds without induced d efenses[21]

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Conclusion