Identification and Expression Profile of Two Putative Odorant-Binding Proteins from the Neotropical Brown Stink Bug, Euschistus heros (Fabricius) (Hemiptera: Pentatomidae)

Brown marmorated stink bug, Halyomorpha halys (Stål), genome: putative underpinnings of polyphagy, insecticide resistance potential and biology of a top worldwide pest

BACKGROUND

Halyomorpha halys (Stål), the brown marmorated stink bug, is a highly invasive insect species due in part to its exceptionally high levels of polyphagy. This species is also a nuisance due to overwintering in human-made structures. It has caused significant agricultural losses in recent years along the Atlantic seaboard of North America and in continental Europe. Genomic resources will assist with determining the molecular basis for this species' feeding and habitat traits, defining potential targets for pest management strategies.

RESULTS

Analysis of the 1.15-Gb draft genome assembly has identified a wide variety of genetic elements underpinning the biological characteristics of this formidable pest species, encompassing the roles of sensory functions, digestion, immunity, detoxification and development, all of which likely support H. halys' capacity for invasiveness. Many of the genes identified herein have potential for biomolecular pesticide applications.

CONCLUSIONS

Availability of the H. halys genome sequence will be useful for the development of environmentally friendly biomolecular pesticides to be applied in concert with more traditional, synthetic chemical-based controls.

Identification and expression profile of odorant-binding proteins in Halyomorpha halys (Hemiptera: Pentatomidae)

The brown marmorated stink bug, Halyomorpha halys, is a devastating invasive species in the USA. Similar to other insects, olfaction plays an important role in its survival and reproduction. As odorant-binding proteins (OBPs) are involved in the initial semiochemical recognition steps, we used RNA-Sequencing (RNA-Seq) to identify OBPs in its antennae, and studied their expression pattern in different body parts under semiochemical stimulation by either aggregation or alarm pheromone or food odorants. Thirty full-length putative HhalOBPs were identified, corresponding to 22 'classic' OBPs and eight 'Plus-C' OBPs. The similarity amongst them ranged from 4.95-70.92%, and with another 325 hemipteran OBPs similarity ranged from 1.94-91.51%, the highest levels being with other stink bug OBPs. Phylogenetic analysis confirmed the monophyly of seven groups of stink bug and other hemipteran OBPs. All 30 HhalOBPs were expressed and about 2/3 were expressed primarily in antennae. The expression of 21 HhalOBPs was higher in the antennae under alarm pheromone stimulus, indicating that multiple OBPs may be responding to this pheromone. Two were highest in antennae under aggregation pheromone stimulus. These findings should provide a basis for understanding the physiological functions of HhalOBPs and the chemosensory perception of this pest, which may help to uncover new control targets for behavioural interference.

Sexual Success after Stress? Imidacloprid-Induced Hormesis in Males of the Neotropical Stink Bug Euschistus heros

Environmental stress in newly-emerged adult insects can have dramatic consequences on their life traits (e.g., dispersion, survival and reproduction) as adults. For instance, insects sublethally exposed to environmental stressors (e.g., insecticides) can gain fitness benefits as a result of hormesis (i.e., benefits of low doses of compounds that would be toxic at higher doses). Here, we experimentally tested whether sublethal exposure to the insecticide imidacloprid would hormetically affect the sexual fitness of newly-emerged adults of the Neotropical brown stink bug Euschistus heros (Hemiptera: Heteroptera: Pentatomidae), which is the most abundant and prevalent insect pest in Neotropical soybean fields. We evaluated the sexual fitness of four couple combinations: unexposed couples, exposed females, exposed males, and exposed couples. Sublethal exposure to dry residues (i.e., contact) of imidacloprid (at 1% of recommended field rate) did not affect insect survival, but led to higher mating frequencies when at least one member of the couple was exposed. However, the average mating duration was shortened when only females were exposed to imidacloprid. Moreover, exposed males showed higher locomotory (walking) activity, lower respiration rates and induced higher fecundity rates when mated to unexposed females. Although the reproductive tracts of exposed males did not differ morphometrically from unexposed males, their accessory glands exhibited positive reactions for acidic and basic contents. Our findings suggest that males of the Neotropical brown stink bug hormetically increase their sexual fitness when cued by impending insecticidal stress in early adulthood.

Transcriptome-Based Identification of Highly Similar Odorant-Binding Proteins among Neotropical Stink Bugs and Their Egg Parasitoid

Olfaction plays a fundamental role in insect survival through resource location and intra and interspecific communications. We used RNA-Seq to analyze transcriptomes for odorant-binding proteins (OBPs) from major stink bug pest species in Brazil, Euschistus heros, Chinavia ubica, and Dichelops melacanthus, and from their egg parasitoid, Telenomus podisi. We identified 23 OBPs in E. heros, 25 OBPs in C. ubica, 9 OBPs in D. melacanthus, and 7 OBPs in T. podisi. The deduced amino acid sequences of the full-length OBPs had low intraspecific similarity, but very high similarity between two pairs of OBPs from E. heros and C. ubica (76.4 and 84.0%) and between two pairs of OBPs from the parasitoid and its preferred host E. heros (82.4 and 88.5%), confirmed by a high similarity of their predicted tertiary structures. The similar pairs of OBPs from E. heros and C. ubica may suggest that they have derived from a common ancestor, and retain the same biological function to bind a ligand perceived or produced in both species. The T. podisi OBPs similar to E. heros were not orthologous to any known hymenopteran OBPs, and may have evolved independently and converged to the host OBPs, providing a possible basis for the host location of T. podisi using E. heros semiochemical cues.