Journal of Chemical Ecology最新文献

Polyploidy is an important driver of the evolution and diversification of flowering plants. Several studies have shown that established polyploids differ from diploids in floral morphological traits and that polyploidization directly affects these traits. However, for floral scent, which is key to many plant-pollinator interactions, only a few studies have quantified differences between established cytotypes, and the direct effects of polyploidization on floral scent are not yet known. We compared the floral scent of established polyploids and diploids from a natural mixed-ploidy population of the plant Lithophragma bolanderi (Saxifragaceae), a species pollinated by two highly specialized moth pollinators of the genus Greya (Prodoxidae). We also compared the floral scent of neopolyploids synthetically generated from diploids with the floral scent of the diploid progenitors to quantify the direct effects of polyploidization on floral scent. Established tetraploids had a higher floral scent emission rate, produced more scent compounds, and emitted a relative scent composition that differed from diploids. Neotetraploids differed in the same direction from diploids as established tetraploids from diploids, but to a lesser extent. Together, our results provide novel insights into the ways in which polyploidization reshapes floral scent, thereby potentially altering interactions between plants and pollinators.

Plant roots are exposed to various organisms that significantly impact plant productivity. Plant-parasitic nematodes (PPNs) such as Meloidogyne spp. and Pratylenchus spp. are microscopic roundworms that damage several crops. In natural populations, M. incognita and P. penetrans were found to infest black mustard (Brassica nigra) plants simultaneously. Considering their different feeding strategies and contrasting effects on plant defense responses, we hypothesized that dual infection may affect each nematode's performance via changes in the root metabolome. Using untargeted and targeted metabolomics, we evaluated how single and dual nematode infections affected B. nigra root metabolome. We combined these metabolic data with measures of early infection success. At three days post-inoculation, dual infection increased M. incognita penetration success, while that of P. penetrans remained unaffected. Compared to single-species infections, dual infections resulted in distinct root metabolic changes by reducing indole glucosinolates (GSL), gluconasturtiin, lignans, and phenylpropanoids. Dual and single-species infections affected different GSL classes. The allyl GSL, sinigrin and its breakdown products increased in P. penetrans-infected plants, while gluconasturtiin and 2-phenylethyl ITC increased in M. incognita-infected plants. This shows that plant defense response to dual nematode infection differ from those of single species, which has consequences to the early infection success of each nematode species.

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is an important herbivorous pest of bottle gourd. We studied the development, reproduction and life table parameters of H. armigera to assess the resistance of eight bottle gourd cultivars, and performed biochemical analysis when H. armigera fed on two more susceptible cultivars [ANKUR AMIT (AMIT) and MALLIKA] and two less susceptible cultivars [KSP-1720 and ANKUR GOLU (GOLU)]. Significantly lower digestive enzymes (amylase, sucrase and lipase), higher detoxification enzymes (carboxylesterase, glutathione-S-transferase and mixed-function oxidase) and greater antioxidant enzymes [superoxide dismutase (SOD), catalase (CAT), polyphenol oxidase (PPO), peroxidase (POD) and ascorbate peroxidase (APX)] were observed in fifth instar H. armigera after feeding on two less susceptible cultivars (KSP-1720 and GOLU) than in two more susceptible cultivars (AMIT and MALLIKA). Further, significantly lower amounts of nutrients (glucose, fructose, sucrose and protein), higher amounts of secondary metabolites (flavonol), and higher activities of antioxidant enzymes (SOD, CAT, POD and APX) and lipoxygenase 3 (LOX3) were recorded in GOLU (less susceptible) than in AMIT (most susceptible), MALLIKA and KSP-1720 when fed by H. armigera caterpillars. The RT-PCR test of three genes for antioxidant enzymes (LsSOD, LsCAT and LsPOD) was more upregulated in GOLU than in AMIT when fed by H. armigera caterpillars, suggesting that GOLU is the less susceptible cultivar and AMIT is the most susceptible cultivar. Therefore, GOLU cultivar suffered lower H. armigera damage by decreasing plant nutrients, and increasing plant secondary metabolites and antioxidant enzymes. This research will help in developing standard regulations to appraise H. armigera-resistant bottle gourds.

Volatile organic compounds are important chemical signals involved in plant-insect interactions. In recent decades, volatiles have been used in many agricultural applications to help control crop pests, but fewer applications have been developed for belowground pests despite volatile signaling and olfactory cues being crucial for orientation and communication of belowground organisms. Volatile signals also depend heavily on soil characteristics which influence both production and diffusion of these volatile compounds. Cover cropping is one agricultural practice that significantly alters soil properties and has been shown to help control certain insect pests, but there is insufficient data on how cover cropping can affect belowground volatile production and recognition. In this study we explored constitutive and root herbivore induced total belowground volatile emissions in two commercial cultivars of maize (Zea mays L.) planted after different cover crop treatments as well as entomopathogenic nematode (EPN) foraging behavior toward plant cues. Contrary to expectation, we found that volatile emission was significantly reduced in response to herbivore feeding and this response was stronger when maize was planted after certain cover crops. In addition, infective juvenile EPN moved equally toward both herbivore-infested and control plants and were not affected by cover crop treatment. Our results suggest that plant responses to insect damage do not always result in adaptive indirect defenses: in some contexts, herbivores may actually reduce their visibility to natural enemies. Moreover, the plasticity and intensity of these responses depend on both plant genotype and soil legacy.

Climate change and rising tropospheric ozone concentration are impacting ecosystems in various ways and can influence the volatile-mediated interactions between insects and their host plants. In this study, individuals of the psyllid species Cacopsylla pyri and C. pyrisuga as well as their host plant Pyrus communis were exposed to elevated but naturally occurring ozone concentrations. The effects on the olfactory perception of the insects and the volatile emission of the plants were examined. Ozone exposure affected the olfactory perception of C. pyri and C. pyrisuga. While the perception threshold of hexanal increased in C. pyri, the perception of the tested compounds was not impaired in C. pyrisuga. Behavioural tests with ozone exposed C. pyri revealed an unchanged repellent effect of nonanal, while hexanal and a synthetic volatile blend became repellent to this species. These findings show only minimal direct effects of moderate ozone concentrations on olfactory perception of pear psyllids. In contrast, chemical analysis of the host plant odours showed a dramatic change in the volatile composition during ozone exposure, with a statistically significant decrease of terpenes and an increase of aldehydes and ketones, showing a greater impact of ozone on the emitter than on the receiver in the pear-psyllid system. This study highlights that moderate ozone levels can alter volatile emissions, potentially disrupting host plant location and impacting other insect-plant interactions that depend specifically on volatile-mediated communication.

Innate behaviours allow solitary animals to complete essential tasks in the absence of social learning. However, we know little about the degree to which ecologically relevant innate preferences can change, and a complete extinction of innate preferences has rarely been shown. The hoverfly Eristalis tenax, a solitary generalist pollinator, is an ideal model for studying innate behaviour in a naturalistic context because its survival depends on the innate ability to identify flowers across many habitats, which could necessitate both learning and unlearning floral objects. Innate behaviour in E. tenax has previously been considered inalterable, but we hypothesised that E. tenax could modulate their innate behaviour after training to a multimodal object derived from chemical and visual cues previously shown to be attractive to hoverflies in field and laboratory assays. To test this, we examined whether E. tenax can extinguish an innate proboscis extension response (PER) to a floral object after undergoing aversive absolute conditioning with quinine, and if flies can acquire PER to an innately unattractive object using sucrose as reinforcement. Finally, we assessed long-term memory retention of these learned behaviours. Here, we report a complete extinction of the PER to an innately attractive floral object following aversive training. Eristalis tenax can also acquire PER to an innately unattractive object after appetitive training. Flies can retain these memories for days after training, and aversive memories last longer than appetitive memories. Ultimately, these findings improve our understanding of how animals integrate innate and learned behaviours to navigate the uncertainties of dynamic objects found in their natural environment.

Plant coloration, predominantly regulated by various natural plant pigments, has been hypothesized to serve crucial ecological functions in plant-animal interactions. Betalains are a rare class of plant pigments synthesized exclusively in specific families within the Caryophyllales order. Their biosynthesis is restricted by the availability of nitrogen. Betalains exhibit significant functions like protecting plants against abiotic stresses, pathogen, and virus; however, their role in plant-herbivore interactions remains largely unknown. In the current study, binary feeding assays revealed that the red leaves of Chenopodium album and the epidermal red salt bladders isolated from the leaves showed defensive effects against Peridroma saucia larvae. Subsequent LC-MS/MS analysis identified betanin as the primary pigment in the red salt bladders, while HPLC quantification revealed a betanin concentration of 0.121 mg/cm² on leaf surface. Bioassays with purified betanin showed dose-dependent defensive efficacy against P. saucia larvae, establishing a direct link between pigment concentration and anti-herbivore activity. This study elucidated the chemical defense function of betanin, discussed the growth-defense trade-off in C. album leaves, and explored its potential coevolutionary dynamics with herbivores, providing novel insights into pigment-driven ecological adaptations.

Plant root exudates serve as critical mediators of rhizospheric cross-kingdom interactions. Beneficial microorganisms have been demonstrated to promote plant fitness by re-assembling the soil nematode community, yet the mechanisms by which beneficial microorganisms alter the nematode community remain unclear. This study elucidates the fungal-induced nematode recruitment mechanisms through root exudate signaling. By testing the chemotactic responses of nematodes to 14 primary metabolites in root exudates, we identified low concentrations of flavonoids (Biochanin A, Isoliquiritigenin, and Quercetin) that significantly attract nematodes. Furthermore, transcriptome analysis of nematodes revealed that genes related to olfactory transduction and neural network pathways were activated when these compounds attracted them. Molecular modeling and docking further showed that the three flavonoids were tightly bound to the proteins of the nematode, Deg-3, Y70D2A.1, Lgc-27, and B0207.7, providing supportive data for flavonoids as signaling molecules for nematode recruitment. Finally, soil microcosm experiments revealed that flavonoids can alter soil nematode community composition, increase community diversity, and selectively enrich omnivorous nematodes. Overall, our findings highlight the pivotal role of flavonoids in mediating plant-nematode interactions and guide us toward novel nematode management strategies.

One of the main characteristics of eusocial insects is an effective division of labor. Termites are one type of eusocial insect that has developed specialized defensive individuals, or soldiers. Although soldiers in termites were viewed as a "burden" due to their high energy costs and inability to feed themselves, studies have revealed that they are essential for other processes, including colony immunity. Soldiers belonging to Nasutitermitinae subfamily have frontal glands that secrete defensive substances. However, little is known about how soldiers and compounds from frontal gland contribute to colony immunity. Here, we investigated the effect of the frontal gland secretion from Nasutitermes corniger on defense against an entomopathogenic fungi. Specifically, we tested the following hypothesizes: (1) the presence of healthy soldiers positively affects the survival of infected workers; (2) the frontal gland extract increases the survivorship of N. corniger workers infected with the fungus; and (3) the growth of Metarhizium anisopliae fungus is negative affects by contact with frontal gland extract of N. corniger soldiers. In general, workers of N. corniger infected with M. anisopliae survived less than those with soldiers or uninfected (control). The groups of N. corniger workers exposed to M. anisopliae survived longer when there was the presence of the soldier's frontal gland compared to groups with only fungi, and the secretions of soldiers have an inhibitory effect on the growth of M. anisopliae. This work contributes to a better understanding of the function of the soldiers, and defense mechanisms that involve chemical secretions.

The peach fruit fly (PFF) Bactrocera zonata (Diptera: Tephritidae) is a major agricultural pest attacking at least 55 plants of economic importance. Previous studies have identified unique compounds in each sex, but none of these appear attractive to either sex. However, it is well known that methyl eugenol (ME) found in nectaries of many plants is strongly attractive to males, while food baits are weakly attractive to both sexes. The present study was designed to find repellent substances for the PFF to implement "push-pull" methods as part of efforts to control the pest and protect orchards. The push-pull method requires an attractant, such as ME, for the fly, and a repellent, which has yet to be discovered. A substance is repellent if it can reduce the attraction of insects to a trap with an attractant as compared to a trap with an attractant alone. The reduction is measured as "trap shutdown", with 100% shutdown being complete repulsion. After systematically screening 82 commercial essential oils (EOs) presented in combinations in field experiments, we found that two EOs, Yarrow and Ylang-ylang, caused over 95% trap shutdown for PFF males and females at different timings and in different orchards (i.e., citrus and mango). We also tested the components of these two EOs and found that artemisia ketone, a component of Yarrow EO, causes a significant trap shutdown of 98% for males and 92% for females. Each component of Ylang-ylang EO tested in the field did not give a sufficient shutdown, suggesting possible synergism among components. However, this EO is inexpensive and thus can be applied wholly in a suitable formulation. We believe that our findings could be developed for the push-pull of other fruit flies known to be attracted to ME.