EAG response and behavioral orientation of Dastarcus helophoroides (Fairmaire) (Coleoptera: Bothrideridae) to synthetic host-associated volatiles

Binding characterization of odorant-binding protein BhorOBP29 in Batocera horsfieldi (Hope) with host-plant volatiles

Odorant binding proteins (OBPs) are involved in odorant discrimination and act as the first filter in the peripheral olfactory system. Previous studies have shown that BhorOBP29 is potentially involved in olfactory perception in an important wood-boring pest Batocera horsfieldi (Hope) (Coleoptera: Cerambycidae), however, its function remains unclear. Here, we investigated the ligand-binding profiles of recombinant BhorOBP29 with 22 compounds from its host plant using fluorescence competitive binding assays and fluorescence quenching assays. The results showed that BhorOBP29 could bind to five ligands relying mainly on hydrophobic interactions. Molecular docking analysis indicated that residues Ile48, Leu51, Met52, Trp57, Asn105, and Val119 were extensively involved in the interactions between BhorOBP29 and the five ligands. Furthermore, the site-directed mutagenesis analysis revealed that Leu51 and Met52 residues were indispensable for BhorOBP29-ligands binding. Finally, electroantennogram (EAG) assays confirmed that hexanal, (-)-limonene, and 2-methylbutyraldehyde elicited a concentration-dependent EAG response with a maximum at the concentration of 1/10 v/v. These findings suggest that BhorOBP29 may play a significant role in the perception of host plant volatiles by B. horsfieldi. This study may help to discover novel behavioral regulation and environmentally friendly strategies for controlling B. horsfieldi in the future.

Factors Influencing Copulation Duration in Dastarcus helophoroides (Fairmaire) (Coleoptera: Bothrideridae)

The gregarious ectoparasitic beetle Dastarcus helophoroides (Fairmaire) is considered a primary biocontrol agent for controlling several cerambycid pests in East Asian countries. A thorough study of reproductive behavior is a prerequisite for the mass production of natural insect predators. Nonetheless, little attention has been given to this ectoparasitic beetle. We performed a series of trials to assess whether the adult copulation duration, a key behavioral trait, is differentially influenced by physiological and ecological factors, including body size, mating history, kinship, sex ratio, mating sequence, feeding status, ambient temperature, photoperiod, and time of day. Additionally, the effect of the copulation duration on the reproductive output of this beetle was also investigated. The results indicated that the copulation duration varied considerably, ranging from 1.12 min to 16.40 min and lasting for an average of 9.11 ± 0.12 min. Females with longer copulations laid more eggs and had a greater proportion of eggs hatched. Medium-sized individuals copulated significantly longer than small- and large-sized individuals. The copulation durations were significantly longer when both sexes experienced an asymmetric mating history than when both sexes experienced a symmetric mating history. Inbred couples copulated significantly longer than outbred couples. In terms of the adult sex ratio, increasing the density of females (polygamous group) or males (polyandrous group) led to significantly longer copulation durations than those in the monogamous group. The copulation durations gradually decreased with increasing the mating sequence and temperature. Food-absence couples copulated significantly longer than food-presence couples. The mean copulation duration of the scotophase was significantly longer than that of the photophase. These results demonstrate that all of the analyzed factors emerge as important factors influencing the copulation duration, ultimately affecting the reproductive outputs in this ectoparasitic beetle.

Detection of invasive and native beetle species within trees by chemical analysis of frass

In recent years, several invasive woodborers (Coleoptera: Cerambycidae) have been found in Japan. Aromia bungii is a worldwide important pest of fruits and ornamental species of the genus Prunus. It invaded Japan in the early 2010s and now causes heavy damage to stone fruit trees. Anoplophora glabripennis and Apriona swainsoni are destructive pests of street, ornamental and horticultural trees. The first step in intercepting these beetles is to detect their presence early in their infestation, as accurate identification is crucial for their management. Ejected frass is a major sign of infestation and likely holds information on the insect. We focused on chemicals in both larvae and frass, and conducted a GC-MS analysis of these three invasive beetles and the native Anoplophora malasiaca. In all four species, 4 or 5 species-specific hydrocarbons were detected in both larvae and frass. These results indicate that analysis of hydrocarbons in frass could allow definitive detection of invasive wood-boring pests.

Electrophysiological and Behavioral Responses of Apis mellifera and Bombusterrestris to Melon Flower Volatiles

As important pollinators, honeybees and bumblebees present a pollination behavior that is influenced by flower volatiles through the olfactory system. In this study, volatile compounds from melon flowers were isolated and identified by headspace solid-phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS), and their effects on Apis mellifera and Bombus terrestris were investigated by electroantennogram (EAG) and behavior tests (Y-tube olfactometer). The results showed that 77 volatile compounds were detected in melon flowers, among which the relative content of aldehydes was the highest (61.34%; 82.09%). A. mellifera showed a strong EAG response to e-2-hexenal, e-2-octenal, and 1-nonanal. B. terrestris showed a strong EAG response to e-2-hexenal, e-2-octenal, 2,5-dimethyl-benzaldehyde, benzaldehyde and benzenepropanal. In behavior tests, the volatiles with the highest attractive rate to A. mellifera were e-2-hexenal (200 μg/μL, 33.33%) and e-2-octenal (300 μg/μL, 33.33%), and those to B. terrestris were e-2-hexenal (10 μg/μL, 53.33%) and 2,5-dimethyl-benzaldehyde (100 μg/μL, 43.33%). E-2-hexenal and e-2-octenal were more attractive to A. mellifera than B. terrestris, respectively (10 μg/μL, 10 μg/μL, 200 μg/μL). In conclusion, the volatiles of melon flowers in facilities have certain effects on the electrophysiology and behavior of bees, which is expected to provide theoretical and technical support for the pollination of A. mellifera and B. terrestris in facilities.

Chemical Signals Associated With Gender and Sexual Experience Affect Mating and the Attractiveness of the Poultry Pest, Alphitobius diaperinus (Coleoptera: Tenebrionidae)

Alphitobius diaperinus is one of the most significant pests in the poultry industry. Identifying the role of self-produced chemical signals can help control it. Here, we exposed adults to the olfactory signals of other adults of similar and different genders (either males or females) and sexual experiences (i.e., virgin and experienced) to assess their long-range attractiveness and, at short-range, their mating behavior responses (i.e., touching, mounting, and copulation). In olfactometric experiments, our results indicate that adults are attracted to the olfactory signals of other male adults, independently of gender, or sexual condition, indicating the presence of generalized long-range attractive signals, in contrast to female signals, can be both factor-dependent. However, in mating experiments, virgin males developed more robust mating responses (i.e., they mount and copulate longer with females) compared to sexually experienced males, even though they both have similar precopulatory behavioral responses (i.e., time of antennal and leg touching). These results address the importance of short-range chemical signals in eliciting copulation. Furthermore, when virgins of both genders were tested, their mating responses were significantly longer than any other pair combination, indicating that sexual experience also affects mating behavior. Chemical analyses of adult extracts showed that sexual experience, but not gender, is linked to differences in chemical profiles of adults, primarily involved in short-range signaling. These findings provide new insights into the attractiveness and mating responses of A. diaperinus and the role of sexual experience in shaping the behavior and chemical profile of insects that mate multiple times during their lifetime.

Evolutionarily conserved odorant-binding proteins participate in establishing tritrophic interactions

Attracting herbivores and their natural enemies is a standard method where plant volatiles mediate tritrophic interactions. However, it remains unknown whether the shared attraction has a shared chemosensory basis. Here we focus on the odorant-binding proteins (OBPs), a gene family integral to peripheral detection of odoriferous chemicals. Previous evidence suggests that the herbivorous beetle Monochamus alternatus and its parasitoid beetle Dastarcus helophoroides are attracted to stressed pines. In this study, (+)-fenchone, emitted by stressed pines, is found to be attracted to M. alternatus and D. helophoroides in behavioral assays. Meanwhile, two orthologous OBPs with a slower evolutionary rate, respectively, from the two insects are shown to bind with (+)-fenchone, and the attraction is abolished after RNAi. These results show the ability of evolutionarily conserved OBPs from herbivores and their enemies to detect the same plant volatiles, providing an olfactory mechanism of chemical signals–mediated tritrophic relationships.

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Monochamus alternatus and Dastarcus helophoroides are attracted to (+)-fenchone from host pines

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They harbor evolutionarily conserved odorant-binding proteins (OBPs)

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One pair of the conserved OBPs can bind with (+)-fenchone

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The behavioral preference is lost upon RNAi knockdown of the OBPs

Electroantennographic and olfactory responses of Quadrastichus mendeli to eucalyptus volatiles induced by the gall-forming insect Leptocybe invasa

BACKGROUND

Although parasitoids can precisely locate hidden gall-inducing insects, the host location mechanism is unknown. In this study, our aim was to clarify the olfactory responses of the parasitoid Quadrastichus mendeli to eucalyptus volatiles induced by the gall wasp Leptocybe invasa.

RESULTS

Q. mendeli preferred volatiles from gall-damaged plants compared with those produced by mechanically damaged and undamaged plants. Coupled gas chromatographic-electroantennographic detection results demonstrated that 3-carene, decanal, d-limonene, ethanone,1-(4-ethylphenyl)-, p-cymene and benzene,1-methyl-4-(1-methylpropyl)- from DH 201-2 (Eucalyptus grandis × Eucalyptus tereticornis) elicited significant antennal responses in Q. mendeli in all treatments. Q. mendeli was repelled by decanal and d-limonene and was attracted to 3-carene, benzene,1-methyl-4-(1-methylpropyl)-, ethanone,1-(4-ethylphenyl) and p-cymene. Quaternary blends containing 3-carene, p-cymene, benzene,1-methyl-4-(1-methylpropyl)- and ethanone,1-(4-ethylphenyl)- at a ratio of 1:1:1:1 were attractive to Q. mendeli. However, quaternary blends with added decanal and d-limonene alone or both together induced significant repellence in Q. mendeli.

CONCLUSION

Our report is the first to demonstrate that volatiles produced by galls induced by L. invasa are attractive to Q. mendeli, which suggests that this parasitoid could utilize herbivore-induced plant volatiles to locate its host. The results are beneficial for understanding the function of plant volatiles in host searching by parasitoids of gall-forming insect pests. © 2022 Society of Chemical Industry.

Is the Natural Instinct to Oviposit in Mated Female Oriental Fruit Fly, Bactrocera dorsalis More of a Brain-Independent Act?

What physiological and neuro-molecular changes control the female oviposition behavior post-mating in insects? The molecular changes that occur in a gravid female insect are difficult to dissect out considering the distinct behavioral patterns displayed by different insect groups. To understand the role of the brain center in Oriental fruit fly, Bactrocera dorsalis oviposition, egg-laying behavior was analyzed in γ-octalactone exposed, decapitated mated B. dorsalis females. Interestingly, the females displayed a possible urge to oviposit, which suggests a natural instinct to pass on the gene pool. Expression analysis of certain genes involved in oviposition behavior was also carried out in these insects to explore the molecular aspects of such behavior. This study tries to assess the involvement of brain center in egg-laying and also explore the role of certain neurotransmitter-related receptors in decapitated B. dorsalis oviposition behavior. Our results indicate that B. dorsalis oviposition behavior could potentially have a bypass route of neuronal control devoid of the brain. The study reported here establishes that decapitation in gravid females fails to abolish their ability to sense ovipositional cues and also to oviposit.

Genetic knockout and general odorant-binding/chemosensory protein interactions: Revealing the function and importance of GOBP2 in the yellow peach moth's olfactory system

The GOBP2 protein has a unique function in the yellow peach moth (Conogethes punctiferalis (Guenée)). Several general odorant-binding proteins (GOBPs) have been identified in various lepidopteran species, but the functional difference between GOBP1 and GOBP2 in recognition of host plant odorants is still unknown. The functions of GOBP1 and GOBP2 in the yellow peach moth were evaluated in this study by using the CRISPR-Cas9 system. The results revealed the importance of GOBP2 in the olfaction mechanism in the yellow peach moth. The perception of the GOBP1-knockout larvae toward feeding decreased but did not reach a significant level while knocking out the GOBP2 and GOBP1/2 genes resulted in huge differences. On the other hand, electroantennograms (EAGs) and wind tunnel tests showed that the sensitivity of GOBP2 knockout adults to odorants decreased more than that of GOBP1 knockout individuals. The results of STRING database text mining grabbed our attention in protein-protein interaction studies. In this research, we first proved the existence of physical interactions between GOBPs and chemosensory proteins (CSPs) through the surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC) methods. Interestingly, GOBP1 and GOBP2 could not interact with each other, but they could interact with CSPs. The interaction results indicated that GOBP2 could physically interact with CSP15, CSP5, and OBP17, whereas GOBP1 could bind only with CSP5 and CSP10, and its association constant (k_a) was also more substantial than that of GOBP1. These results strongly suggest the importance of the function of GOBP2 in the perception of host plant odorants by the yellow peach moth.

A Comparison of Fitness-Related Traits in the Coleopteran Parasitoid Dastarcus helophoroides (Coleoptera: Bothrideridae) Reared on Two Factitious Hosts

The coleopteran parasitoid Dastarcus helophoroides (Fairmaire) (Coleoptera: Bothrideridae) is considered an efficient preventative method against the damage caused by a large number of cerambycid pests in China and other East Asian countries. Mass rearing of this parasitoid depends on screening appropriate factitious hosts. In this paper, the fitness-related traits of this parasitic beetle were explored using pupae of the two tenebrionid beetles, Tenebrio molitor Linnaeus and Zophobas morio Fabricius (Coleoptera: Tenebrionidae) as factitious hosts. The results showed that in dual-choice trials, D. helophoroides larvae preferred to attack Z. morio pupae. In no-choice trials, D. helophoroides reared on Z. morio pupae displayed significantly higher pupation and emergence rate, longer developmental duration of larval and larval-pupal stages, larger adult body size, shorter preoviposition period, more egg masses and egg production, and higher relative expected reproduction than those reared on T. molitor pupae. These results demonstrate that Z. morio is a more suitable factitious host for mass rearing of D. helophoroides.