Selection of soybean pods by the stink bugs, Nezara viridula and Piezodorus guildinii

Lipoxygenases regulate digestive enzyme inhibitor activities in developing seeds of field-grown soybean against the southern green stink bug (Nezara viridula)

Soybean (Glycine max ) is the world's most widely grown seed legume. One of the most important pests that decrease seed quality and reduce yield of soybean crops is the southern green stink bug (Nezara viridula ). Insect damage triggers accumulation of defensive compounds such as protease inhibitors (PIs), isoflavonoids and reactive oxygen species, which are regulated by the lipoxygenase (LOX)-regulated jasmonic acid (JA) to stop insect feeding. This study identified and characterised the role of LOX isoforms in the modulation of chemical defences in seeds of field-grown soybean that decreased digestive enzyme activities of N. viridula after insect attack. Stink bugs attack increased LOX 1 and LOX 2 expression, and activities of LOX 1 and LOX 3 isoenzymes in developing soybean seeds. In addition, stink bug damage and methyl jasmonate application induced expression and activity of both cysteine PIs and trypsin PIs in developing soybean seeds, suggesting that herbivory induced JA in soybean seeds. High PI activity levels in attacked seeds decreased cysteine proteases and α-amylases activities in the gut of stink bugs that fed on field-grown soybean. We demonstrated that LOX isoforms of seeds are concomitantly induced with JA-regulated PIs by stink bugs attack, and these PIs inhibit the activity of insect digestive enzymes. To our knowledge, this is the first study to investigate the participation of LOX in modulating JA-regulated defences against stink bugs in seeds of field-grown soybean, and our results suggest that soybean PIs may inhibit α-amylase activity in the gut of N. viridula .

Plant volatiles guide the new pest Dichelops furcatus to feed on corn seedlings

BACKGROUND

Recently, in temperate and neotropical regions of South America the generalist stink bug Dichelops furcatus (Hemiptera: Pentatomidae) became a new pest of corn (Zea mays) seedlings. Implementation of no-tillage cultivation system left organic matter covering the soil, which shelters adults of stink bugs during winter. In spring, corn is sowed under soybean stubble and D. furcatus adults start to feed on seedlings. To determine corn-derived volatile organic compounds (VOCs) that attract this stink bug species, we evaluated stink bug preferences from two corn hybrids with contrast germplasm backgrounds, a temperate and a tropical hybrid.

RESULTS

Stink bugs preferred to feed on temperate seedlings rather than on the tropical ones. GC-MS and PCA analysis of VOCs suggested that hybrids emitted contrasting blends. Linalool represented 68% of total VOCs emitted from temperate corn, while in the tropical hybrid this compound represented 48%. Olfactometer experiments demonstrated that linalool was attractive to stink bugs. However, 2 h of D. furcatus attack induced emission of 14 additional VOCs in temperate seedlings, and olfactometer bioassay and blend of VOCs emission suggested that perceived volatiles by stink bugs induced feeding avoidance. The increment of VOCs emission was associated with the induction of JA, JA-Ile, ABA, and IAA, and decreasing of SA concentrations.

CONCLUSION

This is the first time showing a complete profile of defensive phytohormones induced by stink bugs feeding on corn, and further demonstrating that a blend of corn seedling-associated VOCs, mainly composed by linalool, modulates D. furcatus adults' behavior and feeding preferences. © 2021 Society of Chemical Industry.

Plant Volatiles Modulate Seasonal Dynamics between Hosts of the Polyphagous Mirid Bug Apolygus lucorum

Plant-derived volatiles play a significant role in host selection of phytophagous insects, but their role in seasonal host shifts remain unclear. The polyphagous mirid bug Apolygus lucorum displays marked seasonal host alternation. During summer, volatiles from flowering plants play a key role in A. lucorum foraging. Though A. lucorum adults deposit overwintering eggs on jujube (Ziziphus jujuba) and grape (Vitis vinifera) during autumn, it is unclear whether plant volatiles equally mediate this host selection behavior. During 2015 and 2016, we found that population densities of A. lucorum adults on cotton (Gossypium hirsutum) during August were higher than those in September, whereas the opposite pattern was observed on fruit trees (i.e., jujube and grape). The dispersal factor of the adult population that dispersed from cotton fields during September was higher than in August, whereas opposite patterns were observed in the neighboring jujube/grape orchard. In Y-tube olfactometer trials, A. lucorum adults preferred cotton plant volatiles over fruit tree odors in August, whereas the opposite patterns were found in September. Three electro-physiologically active volatiles (butyl acrylate, butyl propionate and butyl butyrate) were identified from jujube and grape plants. During September, active volatiles are emitted in considerably greater amounts by jujube and grape than in August, while the amount of volatile emissions in cotton decreases in September. Temporal shifts in plant volatile emission thus may modulate host plant foraging of A. lucorum, and appear to guide its colonization of different host plants. Our findings help understand the role of plant volatiles in the host plant selection and seasonal dynamics of polyphagous herbivores.

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

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.

Assessing the Role of Differential Herbivore Performance Among Plant Species in Associational Effects Involving the Invasive Stink Bug Bagrada hilaris (Hemiptera: Pentatomidae)

Co-occurring plant species can influence the extent of damage to each other by altering the activity or abundance of a shared herbivore. One mechanism by which neighboring host plants exacerbate damage to a focal host is if the neighbor amplifies herbivore populations. We studied the performance of a shared herbivore on a native and an invasive plant, to estimate how strongly the presence of the invasive plant increases local herbivore abundance-in a system in which highly asymmetric spillover herbivory may occur. Specifically, we conducted a series of greenhouse experiments that measured reproduction, development, and survival of the invasive stink bug Bagrada hilaris Burmeister on an invasive annual forb, Sahara mustard (Brassica tournefortii), or a native perennial shrub, four-winged saltbush (Atriplex canescens). All measured aspects of stink bug performance revealed consistently greater performance on Br. tournefortii. Indeed, A. canescens appears to be insufficient for Ba. hilaris to complete its development. Nonetheless, preliminary damage assessments found that both plant species were used as feeding hosts, putative feeding lesions were a more reliable indicator of herbivory than was the degree of yellowing, and higher Ba. hilaris abundance was generally associated with greater sublethal damage to A. canescens. Thus, A. canescens appears to be susceptible to Ba. hilaris herbivory, though more research is needed to assess fitness impacts of this novel herbivore. Our results indicate that differential herbivore performance among host plants may be an important contributor to observed patterns of abundance of a shared herbivore and spillover herbivory between plants.

Early perception of stink bug damage in developing seeds of field-grown soybean induces chemical defences and reduces bug attack

BACKGROUND

Southern green stink bugs (Nezara viridula L.) invade field-grown soybean crops, where they feed on developing seeds and inject phytotoxic saliva, which causes yield reduction. Although leaf responses to herbivory are well studied, no information is available about the regulation of defences in seeds.

RESULTS

This study demonstrated that mitogen-activated protein kinases MPK3, MPK4 and MPK6 are expressed and activated in developing seeds of field-grown soybean and regulate a defensive response after stink bug damage. Although 10-20 min after stink bug feeding on seeds induced the expression of MPK3, MPK6 and MPK4, only MPK6 was phosphorylated after damage. Herbivory induced an early peak of jasmonic acid (JA) accumulation and ethylene (ET) emission after 3 h in developing seeds, whereas salicylic acid (SA) was also induced early, and at increasing levels up to 72 h after damage. Damaged seeds upregulated defensive genes typically modulated by JA/ET or SA, which in turn reduced the activity of digestive enzymes in the gut of stink bugs. Induced seeds were less preferred by stink bugs.

CONCLUSION

This study shows that stink bug damage induces seed defences, which is perceived early by MPKs that may activate defence metabolic pathways in developing seeds of field-grown soybean. © 2015 Society of Chemical Industry.

Host preference and suitability of grasses for Oebalus pugnax

The rice stink bug, Oebalus pugnax (Fabricius) (Hemiptera: Pentatomidae: Carpocorini), though graminaceous, discriminates among its numerous host grass species. This could represent a feeding preference, it could be related to host suitability for growth and development. To clarify the role of host grass discrimination, two laboratory studies were conducted: (1) free-choice tests to evaluate preferences of O. pugnax among 11 wild host grass species found in three rice-producing counties of the central Mississippi Delta (MS, USA), and (2) no-choice tests to evaluate the impact of rice (Oryza sativa L.), junglerice [Echinochloa colona (L.) Link], and dallisgrass (Paspalum dilatatum Poir.) (all Poaceae), on the development of O. pugnax from second instar to adult. In the free-choice test, four experiments were conducted, each with four sets of host grass species and observed 1, 2, 4, 8, and 16 h after release in cages. Approximately 4 h was necessary for O. pugnax to settle on preferred host grasses. Oebalus pugnax showed a feeding preference for junglerice over all 10 other grass species. Bahiagrass, Paspalum notatum Flueggé, was the least preferred. The no-choice tests showed significant effect of host grass species on O. pugnax mean development time of nymphal survival to adults. Survival of nymphs was lower and mean development time was longer on dallisgrass compared to rice and junglerice. Knowledge of O. pugnax rate of growth and development on host grasses could be useful in the future development of rice integrated pest management strategies.