Volatiles from Aquilaria sinensis damaged by Heortia vitessoides larvae deter the conspecific gravid adults and attract its predator Cantheconidea concinna

Chemical ecology of Himalayan eggplant variety's antixenosis: identification of geraniol as an oviposition deterrent against the eggplant shoot and fruit borer

Eggplant (Solanum melongena) suffers severe losses due to a multi-insecticide-resistant lepidopteran pest, shoot and fruit borer (SFB, Leucinodes orbonalis). Heavy and combinatorial application of pesticides for SFB control renders eggplant risky for human consumption. We observed that gravid SFB females do not oviposit on Himalayan eggplant variety RC-RL-22 (RL22). We hypothesized that RL22 contained an antixenosis factor. Females' behavior indicated that the RL22 cue they perceived was olfactory. To identify it, leaf volatile blends of seven eggplant varieties were profiled using solid phase microextraction and gas chromatography mass spectrometry. Seven RL22-specific compounds were detected in the plant headspace. In choice assays, oviposition deterrence efficacies of these candidate compounds were independently tested by their foliar application on SFB-susceptible varieties. Complementation of geraniol, which was exclusively found in RL22, reduced oviposition (> 90%). To validate geraniol's role in RL22's SFB-deterrence, we characterized RL22's geraniol synthase and silenced its gene in planta, using virus-induced gene silencing. Geraniol biosynthesis suppression rendered RL22 SFB-susceptible; foliar geraniol application on the geraniol synthase-silenced plants restored oviposition deterrence. We infer that geraniol is RL22's SFB oviposition deterrent. The use of natural compounds like geraniol, which influence the chemical ecology of oviposition, can reduce the load of hazardous synthetic larvicides.

Repeated mechanical damage enhanced Aquilaria sinensis resistance to Heortia vitessoides through jasmonic acid

Introduction

The leaf-chewing pest Heortia vitessoides severely threatens the growth and development of Aquilaria sinensis. In our previous study, we found that mechanical damage (MD) to stem enhanced A. sinensis sapling resistance to H. vitessoides larvae.

Methods

To reveal the defense mechanisms underlying this observation, we analyzed the types and contents of volatile organic compounds (VOCs), phytohormone contents, and expression of phytohormone-related genes in response to MD and herbivory wounding(HW).

Results

Here, we identified several VOCs, such as the pesticides fenobucarb and 2,4-di-tert-butylphenol, in mature leaf (ML) of MD-treated plants. Compared with salicylic acid (SA) or the ethylene (ET) pathway, jasmonic acid (JA) content and JA-related genes were more strongly upregulated. Interestingly, we found a dramatic difference between JA-related upstream and downstream genes expression in YL and ML, which confirmed that JA-Ile accumulation in MD-ML and HW-ML could be derived from local damaged site.

Discussion

Taken together, we provide evidence that the JA pathway plays a dominant role in the A. sinensis response to MD and HW.

Lethal, transmission, behavioral, and physiological effects of Metarhizium anisopliae against gregarious larvae of Heortia vitessoides and synergistic effects between Metarhizium anisopliae and insecticides

BACKGROUND

Heortia vitessoides Moore is a severe pest of Aquilaria sinensis (Lour.) Gilg, an important source of agarwood. In recent years, large amounts of chemical insecticides have been applied in A. sinensis plantations to deal with the outbreak of H. vitessoides, causing residue problems that reduce the quality and price of agarwood. Herein, we hypothesize that the widely applied biocontrol agent, Metarhizium anisopliae (Metschn.) Sorokin, can effectively kill the gregarious larvae of H. vitessoides through direct contact and horizontal transmission.

RESULTS

At the concentration of 1 × 10⁹ conidia/mL, the three M. anisopliae strains caused 100% mortality of H. vitessoides larvae. In addition, mixing donor larvae (previously treated with M. anisopliae conidia) with receptor larvae (which did not directly contact M. anisopliae conidia) caused significantly higher mortality of receptor larvae than the control receptors. This is due to the horizontal transmission of M. anisopliae conidia among live larvae, which was proven by pictures taken by scanning electron microscopy and induced activities of immunity-related enzymes of donor and receptor larvae. Behavioral bioassays showed that M. anisopliae conidia had little effect on the aggregation tendency of H. vitessoides larvae but may trigger feeding-avoidance behavior depending on M. anisopliae strains and concentrations. Interestingly, joint use of sublethal concentrations of M. anisopliae and chemical insecticides significantly increased larval mortality than each agent alone, indicating synergistic effects between M. anisopliae and insecticide against H. vitessoides.

CONCLUSION

This study may provide a new strategy to suppress H. vitessoides population and reduce the use of chemical insecticides. © 2023 Society of Chemical Industry.

Biotic and abiotic factors that affect parasitism in Trichogramma pintoi (Hymenoptera: Trichogrammatidae) as a biocontrol agent against Heortia vitessoides (Lepidoptera: Pyralidae)

The parasitoid wasp, Trichogramma pintoi, is a promising candidate for inundative release against Heortia vitessoides. Parasitoid females can regulate the sex of their offspring in response to environmental and biological factors. In pest control programs utilizing these parasitoids, male overproduction is not conducive to success. To optimize the production of T. pintoi as an egg parasitoid of H. vitessoides, factors affecting the rates of parasitism and eclosion and the percentage of females among T. pintoi offspring, such as temperature, photoperiod, host age, host density, maternal age, maternal density, and food, were investigated. The proportion of T. pintoi female offspring was significantly affected by temperature, photoperiod, host density, maternal age, and maternal density. The female offspring percentage decreased in response to host density (160 eggs), maternal age (≥ 4 days old), maternal density (≥ 4 females), photoperiods (24:0 and 18:6 L:D), and extremely low temperature (15 °C). However, host age and female diet did not affect the proportion of female offspring. According to the present work, female parasitoid production can be maximized under laboratory conditions of 25 °C, 75% relative humidity, and a photoperiod of 0:24 h (L:D) via exposure of forty 1-day-old H. vitessoides eggs for 24 h or eighty 1-day-old H. vitessoides eggs to a newly emerged, mated female fed a 10% sucrose solution until the female dies. These findings will guide mass production efforts for this parasitoid.

Genome-wide investigation of Cytochrome P450 superfamily of Aquilaria agallocha: Association with terpenoids and phenylpropanoids biosynthesis

Agarwood is a dark resinous wood, produced when Aquilaria tree responds to wounding and microbial infection resulting in the accumulation of fragrant metabolites. Sesquiterpenoids and 2-(2-phenylethyl) chromones are the major phytochemicals in agarwood and Cytochrome P450s (CYPs) are one of the important enzymes in the biosynthesis of these fragrant chemicals. Thus, understanding the repertoire of CYP superfamily in Aquilaria can not only give insights into the fundamentals of agarwood formation, but can also provide a tool for the overproduction of the aroma chemicals. Therefore, current study was designed to investigate CYPs of an agarwood producing plant, Aquilaria agallocha. We identified 136 CYP genes from A. agallocha genome (AaCYPs) and classified them into 8 clans and 38 families. The promoter regions had stress and hormone-related cis-regulatory elements which indicate their participation in the stress response. Duplication and synteny analysis revealed segmental and tandem duplicated and evolutionary related CYP members in other plants. Potential members involved in the biosynthesis of sesquiterpenoids and phenylpropanoids were identified and found to be upregulated in methyl jasmonate-induced callus and infected Aquilaria trees by real-time quantitative PCR analyses. This study highlights the possible involvement of AaCYPs in agarwood resin development and their complex regulation during stress exposure.

Volatile-mediated tritrophic defense and priming in neighboring maize against Ostrinia furnacalis and Mythimna separata

BACKGROUND

Plants respond to attackers by triggering phytohormones signaling associated metabolites, including herbivore-induced plant volatiles (HIPVs). HIPVs can indirectly act against herbivory by recruitment of natural enemies and priming of neighboring plants. Ostrinia furnacalis and Mythimna separata are important insect herbivores of maize plants that have a devastating influence on yield. However, little is known about how maize temporally reconfigures its defense systems against these herbivores and variation of neighboring plant resistance.

RESULTS

This study investigated the effects of HIPVs on the behavior of the dominant predatory beetle Harmonia axyridis and priming in neighboring maize defense against O. furnacalis and M. separata over time. The results showed that maize damaged by either O. furnacalis or M. separata enhanced the release of volatiles including terpenes, aldehydes, alkanes and an ester, which elicited an increased attractive response to H. axyridis after 3 and 12 h, respectively. O. furnacalis damage resulted in accumulations of leaf jasmonic acid (JA) and salicylic acid in maize after 6 and 3 h, respectively, while M. separata damage only raised the JA level after 3 h. Furthermore, HIPVs were able to prime neighboring plants through the accumulation of JA after 24 h. Both larvae showed a significant decrease in weight accumulation after 48 h of feeding on the third leaves of the primed plant.

CONCLUSION

Taken together, the findings provide a dynamic overview of how attacked maize reconfigures its volatiles and phytohormones to defend against herbivores, as well as priming of neighboring plants against oncoming attacks. © 2022 Society of Chemical Industry.

The Role of Green Gram Plant Volatile Blends in the Behavior of Arctiid Moth, Spilosoma obliqua

This study investigated effects of volatile blends released from undamaged (UD), insect-damaged [ID, plants fed by larvae of Spilosoma obliqua Walker (Lepidoptera: Arctiidae)] and mechanically-damaged (MD) plants of three green gram cultivars [PDM 54, Pusa Baisakhi and Samrat] including synthetic blends on the behavior of conspecific adult moths in Y-tube olfactometer bioassays. Females showed attraction towards volatile blends of UD, ID and MD plants of these green gram cultivars against the control solvent (CH₂Cl₂). The components of volatile blends in UD plants of three green gram cultivars are not similar, but no any difference was found among three cultivars in term of the attractive effect on the insect moths when volatile blends from UD plants of these three cultivars were tested against one another. Females were more attracted towards volatile blends of ID plants of a particular cultivar compared to UD plants of the same cultivar. Total amount of volatiles was higher in ID plants than UD plants. Some herbivore-induced plant volatiles - (Z)-3-hexenal, 1-hexanol, (Z)-3-hexenyl acetate, 2-octanol and ocimene were attractive to the insect moths. Females were attracted towards three synthetic blends resembling amounts present in natural volatile blends of ID plants of these three cultivars in Y-tube olfactometer and wind tunnel bioassays, suggesting that involvement of host-specific chemical cues in long-range host location by S. obliqua females. If attraction of adult S. obliqua to these synthetic volatile blends is upheld by field trials then these blends may find practical application in detection and monitoring of S. obliqua populations.

Chromosomal-level reference genome of the moth Heortia vitessoides (Lepidoptera: Crambidae), a major pest of agarwood-producing trees

The moth Heortia vitessoides Moore (Lepidoptera: Crambidae) is a major pest of ecologically, commercially and culturally important agarwood-producing trees in the genus Aquilaria. In particular, H. vitessoides is one of the most destructive defoliating pests of the incense tree Aquilaria sinesis, which produces a valuable fragrant wood used as incense and in traditional Chinese medicine [33]. Nevertheless, a genomic resource for H. vitessoides is lacking. Here, we present a chromosomal-level assembly for H. vitessoides, consisting of a 517 megabase (Mb) genome assembly with high physical contiguity (scaffold N50 of 18.2 Mb) and high completeness (97.9% complete BUSCO score). To aid gene annotation, 8 messenger RNA transcriptomes from different developmental stages were generated, and a total of 16,421 gene models were predicted. Expansion of gene families involved in xenobiotic metabolism and development were detected, including duplications of cytosolic sulfotransferase (SULT) genes shared among lepidopterans. In addition, small RNA sequencing of 5 developmental stages of H. vitessoides facilitated the identification of 85 lepidopteran conserved microRNAs, 94 lineage-specific microRNAs, as well as several microRNA clusters. A large proportion of the H. vitessoides genome consists of repeats, with a 29.12% total genomic contribution from transposable elements, of which long interspersed nuclear elements (LINEs) are the dominant component (17.41%). A sharp decrease in the genome-wide percentage of LINEs with lower levels of genetic distance to family consensus sequences suggests that LINE activity has peaked in H. vitessoides. In contrast, opposing patterns suggest a substantial recent increase in DNA and LTR element activity. Together with annotations of essential sesquiterpenoid hormonal pathways, neuropeptides, microRNAs and transposable elements, the high-quality genomic and transcriptomic resources we provide for the economically important moth H. vitessoides provide a platform for the development of genomic approaches to pest management, and contribute to addressing fundamental research questions in Lepidoptera.

Plant-defense mimicry facilitates rapid dispersal of short-lived seeds by hornets

Rates of seed dispersal have rarely been considered important. Here, we demonstrate through field observations and experiments that rapid dispersal is essential for the unusually short-lived seeds of Aquilaria sinensis (agarwood; Thymelaeaceae), which desiccate and die within hours of exposure by fruit dehiscence in the hot, dry forest canopy in tropical southwest China. We show that three species of Vespa hornets remove most seeds within minutes of exposure. The hornets consume only the fleshy elaiosomes and deposit most seeds in damp shade, where they can germinate, a mean of 166 m from the parent tree. Electrophysiological assays and field experiments demonstrate that the hornets are attracted by highly volatile short-carbon-chain (C5-C9) compounds, including aldehydes, ketones, alcohols, and acids, emitted from the dehiscent fruit capsule. These attractive fruit volatiles share 14 of 17 major electrophysiologically active compounds with those emitted from herbivore-damaged leaves, which attract predators, including hornets. Rapid seed dispersal thus appears to have been achieved in this species by the re-purposing of a rapid indirect defense mechanism. We predict that rapid seed dispersal by various mechanisms will be more widespread than currently documented and suggest that volatile attractants are more effective in facilitating this than visual signals, which are blocked by vegetation.

Attraction of the Biocontrol Agent, Galerucella placida Towards Volatile Blends of Two Polygonaceae Weeds, Rumex dentatus and Polygonum glabrum

The Polygonaceae weed, Rumex dentatus L. grows in association with wheat, mustard and potato, while Polygonum glabrum Willd. grows in association with rice in India. Both larvae and adults of Galerucella placida Baly (Coleoptera: Chrysomelidae) voraciously consume these weeds. Applications of synthetic herbicides to control weeds are harmful to the environment including beneficial organisms. We propose to find volatile organic compounds (VOCs) from both weeds causing attraction of the biocontrol agent, G. placida, in order to attempt to use the insect as a biological weed control. Behavioral responses of G. placida towards volatile blends characteristic of undamaged (UD), insect-damaged (ID), jasmonic acid-treated (JA) or mechanically-damaged (MD) plants were conducted by Y-tube olfactometer bioassays. Cuminaldehyde was predominant in VOCs of UD R. dentatus, ID P. glabrum, and both JA and MD R. dentatus and P. glabrum. Geraniol was predominant in VOCs of UD P. glabrum, while 1,3-diethylbenzene predominated in VOCs of ID R. dentatus. Females were more attracted towards volatile blends of ID plants compared to UD or JA plants. Females did not show attraction towards volatile blends of JA plants. We identified two bioactive synthetics blends, one comprised of seven compounds - 16.65 µg 1,3-diethylbenzene, 10.72 µg acetophenone, 6.52 µg 2,6-(E,Z)-nonadienal, 2.46 µg 1-nonanol, 4.19 µg decanal, 9.86 µg 4-ethylacetophenone and 3.34 µg 1-hexadecene dissolved in 25 µl CH₂Cl₂ and the other containing five compounds - 2.50 µg 2-octanol, 6.84 µg limonene, 0.64 µg dodecane, 6.63 µg 4-ethylacetophenone and 0.24 µg geranyl acetone dissolved in 25 µl CH₂Cl₂. These two blends of volatile compounds could be used to attract the biocontrol agent during early vegetative period of these two weeds, which could lead to eradication of weeds from crop fields.

Feeding of pea leafminer larvae simultaneously activates jasmonic and salicylic acid pathways in plants to release a terpenoid for indirect defense

The pea leafminer, Liriomyza huidobrensis, is an important pest species affecting ornamental crops worldwide. Plant damage consists of oviposition and feeding punctures created by female adult flies as well as larva-bored mines in leaf mesophyll tissues. How plants indirectly defend themselves from these two types of leafminer damage has not been sufficiently investigated. In this study, we compared the indirect defense responses of bean plants infested by either female adults or larvae. Puncturing of leaves by adults released green leaf volatiles and terpenoids, while larval feeding caused plants to additionally emit methyl salicylate and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT). Puncturing of plants by female adults induced increases in jasmonic acid (JA) and JA-related gene expressions but reduced the expressions of salicylic acid (SA)-related genes. In contrast, JA and SA and their-related gene expression levels were increased significantly by larval feeding. The exogenous application of JA+SA significantly triggered TMTT emission, thereby significantly inducing the orientation behavior of parasitoids. Our study has confirmed that larval feeding can trigger TMTT emission through the activation of both JA and SA pathways to attract parasitoids; however, TMTT alone is less attractive than the complete blend of volatiles released by infested plants.

Peach volatile emission and attractiveness of different host plant volatiles blends to Cydia molesta in adjacent peach and pear orchards

The oriental fruit moth (OFM), Cydia (= Grapholitha) molesta, is a highly damaging pest; peaches are its primary host, and pears serve as post-peach secondary hosts during the late season in China. We collected volatiles from detached peach shoots and fruits, and identified them with gas chromatography-mass spectrometry (GC-MS). Antennally active compounds were identified by gas chromatography-electroantennogram detection (GC-EAD), and these were further tested in the laboratory and field. We detected consistent electroantennographic activity was for ten compounds. Significantly more C. molesta females were caught with a mixture of female EAD-active compounds identified from the detached matured peach fruits (nonanal, butyl acetate, 3-methylbutyl acetate, hexyl acetate, (Z)-3-hexenyl acetate, linalool and farnesene) than other mixtures mimicking the volatile profile from detached matured fruits or shoots. We identified a new GC-EAD active mixture from intact peach shoots composed of nonanal, (Z)-3-hexenyl acetate, (E)-β-ocimene, and 6-methyl-5-hepten-2-one. In the field test, the background odour of orchards could affect trap catches, and two peach-derived blends together with two previously known pear-derived blends were proven to be able to monitor the seasonal OFM population dispersal in adjacent orchards. These host plant blends will be effective for further designing candidate attractants for season-long C. molesta population dynamic monitoring.

Potential Use of Trichogramma pintoi as a Biocontrol Agent Against Heortia vitessoides (Lepidoptera: Pyralidae)

Heortia vitessoides Moore is the most serious insect defoliator of Aquilaria sinensis (Lour.) Gilg, an endangered and economically important plant that produces highly prized agarwood. Samples from recently identified indigenous natural populations of Trichogramma pintoi Voegele were collected from H. vitessoides eggs in A. sinensis forests in Yunnan Province, China. To assess the potential capacity of this parasitoid for use as a biological control agent, its functional response, female reproductive potential, and male insemination capacity were investigated in this study. Females successfully parasitized 1- to 4-d-old eggs of H. vitessoides but failed to parasitize 5- to 8-d-old eggs. The parasitoid exhibited a Holling type II functional response, and the estimated maximum numbers of 1- to 4-d-old H. vitessoides eggs parasitized by a single T. pintoi female were 38.1, 29.8, 26.0, and 22.2 eggs over a 24-h period, respectively. Additionally, the parasitoid's average lifetime fecundity was 89.8 ± 2.5 eggs, of which 66.26% were laid within the first 2 d. The average number of total females that mated with a male in his lifetime (4.70 ± 0.13 d) was 10.4, and the average number of total daughters of a male was 292.1. On day 1 of male adult life, the greatest number of females were inseminated by males, and the most daughters were produced; however, the number of copulations and insemination ability decreased rapidly with male age. These results suggest that T. pintoi is a promising candidate for inundative release against H. vitessoides in China, and these findings will guide efforts in achieving mass production of this parasitoid.

The Scent of Stress: Evidence From the Unique Fragrance of Agarwood

Agarwood (Aquilaria spp.) fragrance and its origin in stress make it probably the most suitable model to study stress-induced aroma. Production being confined only to certain small pockets of South and Southeast Asia, agarwood is arguably the costliest wood in the world. Formation of fragrant agarwood resin is the outcome of complex biotic, abiotic, and physical stress on the Aquilaria trees. The intricate mechanism by which some 150 odd fragrant molecules that constitute agarwood aroma is formed is still not clearly understood. The present review therefore aims to bring to focus this less known but highly valuable stress-induced aroma from Asia. Discussions on agarwood species, occurrence, distribution, formation, and products have been included as foundation. Although global trade in agarwood and its products is estimated at US$6 billion to US$8 billion, no reliable data are readily available in literature. Therefore, an effort has been made to review the current status of agarwood trade. The element of stress and its correlation to agarwood aroma is discussed in the subsequent sections. Natural agarwood formation as well as technologies and interventions in agarwood induction are stress-based (natural and artificial injury, insect and fungal attack, chemical induction). The molecular triggers are gradually coming to light as new studies are implicating jasmonate, LOX signaling, and other stress reaction routes as the source of agarwood aroma. This review therefore has strived to compile the information that is scattered across scientific as well as other authentic literature and update the reader on the current status. More information about the specific roles of other vital stressors like insects, abiotic, and genetic factors is eagerly awaited from ongoing and future research to further understand the unique fragrance of agarwood.

Larval Aggregation of Heortia vitessoides Moore (Lepidoptera: Crambidae) and Evidence of Horizontal Transfer of Avermectin

Aquilaria sinensis (Lour.) Gilg is an economically important tree species that produce the highly prized agarwood. In recent years, agarwood production has been seriously threatened by the outbreak of Heortia vitessoides Moore, a leaf-eating pest that shows gregariousness during the larval stage. However, little attention has been paid to the aggregation behavior of H. vitessoides larvae. In the present study, we collected 102 cohorts of H. vitessoides larvae (13,173 individuals in total) in the wild; 54 cohorts were comprised of the same-instar larvae, and 48 cohorts were comprised of larvae with different developmental stages (instars). In general, young larvae (<third instar) tended to form large aggregations, whereas older-instar larvae were either solitary or formed small aggregations. Laboratory studies showed a strong aggregation tendency in the newly hatched and second-instar larvae of H. vitessoides, whenever the individuals originated from the same or different sibling cohorts. In addition, all newly hatched larvae died within two days after they were isolated. When newly hatched larvae were initially assigned in 10-larvae cohorts (containing sibling individuals) or 20-larvae cohorts (either containing individuals originating from the same or different sibling cohorts), their larval survivorship, duration of larval stage, and adult emergence were not significantly different. Interestingly, combining avermectin-treated larvae (donors) with untreated ones (receptors) significantly decreased larval survivorship and adult emergence of receptors, indicating a horizontal transfer of avermectin among H. vitessoides larvae. This study enhances our understanding of the population ecology of H. vitessoides, and may bring novel insights into the management strategies against this pest.