Momordica cochinchinensis (Cucurbitaceae) leaf volatiles: semiochemicals for host location by the insect pest, Aulacophora foveicollis (Coleoptera: Chrysomelidae)

Components and composition of active volatiles attract on Diorhabda tarsalis (Coleoptera: Chrysomelidae) from Glycyrrhiza uralensis (Rosales: Leguminoseae)

Introduction

Perennial Chinese licorice, Glycyrrhiza uralensis, is an important medicinal plant. Diorhabda tarsalis, a leaf beetle, is a serious insect pest on the plant and cause serious yield losses every year and is attracted to healthy and pest-damaged licorice by plant volatiles.

Aim

The biologically active components of the volatiles released from G. uralensis have not been reported; the components of the volatiles that attract D. tarsalis need to be identified. Such compounds could potentially be used for monitoring and mass-trapping pests.

Methods

GC-EAD, GC-MS, EAG, Y-shaped olfactometer behavioral bioassays, and field trials were performed to identify the components and composition of active volatiles.

Results

Male and virgin female adults were generally attracted to volatiles from licorice, and volatiles from pest-infested plants were more attractive. Four compounds from licorice elicited a significant electrophysiological response (EAD) and were confirmed by EAG, including hexanal, (Z)-3-hexenal, (Z)-3-hexen-1-ol, and (E)-2-hexenal. With the exception of the (E)-2-hexenal, these molecules significantly attracted adults in individual behavioral bioassays, and a proportional mixture corresponding to beetle-damaged licorice of hexanal, (Z)-3-hexenal, (Z)-3-hexen-1-ol, and (E)-2-hexenal (8.78:15.26:57.24:18.72) was most effective for attracting D. tarsalis in the field, attracted a mean of 26 ± 7.19 beetles per trap.

Discussion

D. tarsalis was attracted to volatiles from healthy and herbivore-induced G. uralensis under both laboratory and field conditions. The aforementioned compounds show considerable potential for commercial application to monitor and control D. tarsalis populations.

Short-range attraction and oviposition stimulant of a biocontrol agent, Galerucella placida Baly (Coleoptera: Chrysomelidae) toward weed leaf surface waxes

Two Polygonaceae weeds, Rumex dentatus L. and Polygonum glabrum Willd. are abundant in wheat- and rice-fields, respectively, in India. Galerucella placida Baly (Coleoptera: Chrysomelidae) is a biocontrol agent of these two weeds. The importance of long-chain alkanes and free fatty acids present in leaf surface waxes of these weeds was assessed as short-range attractant and ovipositional stimulant in G. placida females. Extraction, TLC, GC-MS and GC-FID analyses demonstrated 19 n-alkanes from n-C14 to n-C35 and 14 free fatty acids from C12:0 to C22:0 in leaf surface waxes. Hentriacontane was predominant among alkanes in both weeds, while oleic acid and docosanoic acid were predominant among free fatty acids in R. dentatus and P. glabrum, respectively. Females of G. placida were attracted toward one leaf equivalent surface wax of both weeds against the control solvent (petroleum ether) in a short Y-tube olfactometer bioassay. But, the insect could not differentiate between one leaf equivalent surface wax of R. dentatus and P. glabrum, indicating that both weed leaves were equally attractive in females. A synthetic blend of either 2.44, 35.57 and 23.58 μg ml-1 of octadecane, heptacosane and nonacosane, respectively, resembling the amounts present in one leaf equivalent surface wax of R. dentatus or 4.08, 19.54 and 23.58 μg ml-1 of octadecane, palmitoleic acid and docosanoic acid, respectively, resembling the amounts present in one leaf equivalent surface wax of P. glabrum acted as short-range attractant and ovipositional stimulant in G. placida. These results could be a basis for host plant specificity of the biocontrol agent.

Identification of Lathyrus sativus plant volatiles causing behavioral preference of Aphis craccivora

BACKGROUND

The viviparous aphid Aphis craccivora Koch (Hemiptera: Aphididae) is a serious threat to the crop yield of Lathyrus sativus L. (Fabaceae), commonly known as grass pea. The synthetic insecticides applied to control this insect pest are not safe for the environment. Hence, it is necessary to find volatile organic compounds (VOCs) from two cultivars [BIO L 212 Ratan (BIO) and Nirmal B-1 (NIR)] of L. sativus plants causing behavioral preference of A. craccivora.

RESULTS

The VOCs from undamaged (UD), insect-damaged (ID) [plants on which 50 or 100 adults of A. craccivora were fed for 4 h (ID 50 or ID 100)], and mechanically damaged (MD) plants were identified and quantified by gas chromatography-mass spectrometry and gas chromatography-flame ionization detection analyses, respectively. Total VOCs were higher in ID plants compared to UD plants of each cultivar. However, total VOCs were higher in NIR cultivar compared to BIO cultivar for both UD and ID plants. Benzyl alcohol was predominant in volatile extracts of all treatments. In Y-tube olfactometer bioassays, females showed preference towards volatile extracts of UD, ID, and MD plants of each cultivar compared to the control solvent (CH₂ Cl₂ ). Insects preferred certain synthetic blends comparable to volatile extracts of UD, ID, and MD plants of each L. sativus cultivar against the control solvent.

CONCLUSION

Females preferred a synthetic blend of benzyl alcohol, 1,3-diethylbenzene, thymol, and 1-hexadecene at ratios of 142.49: 62.03:1.18:1 dissolved in 25 μL of CH₂ Cl₂ in olfactometer bioassays, which could be used in developing lures to control this insect pest.

The role of Lathyrus sativus flower surface wax in short-range attraction and stimulant for nymph laying by an adult viviparous aphid

Aphis craccivora Koch (Hemiptera: Aphididae) is an important pest of Lathyrus sativus L. plants, and causes retarded plant growth and loss of seed production. The insect sucks cell sap from flowers and lays nymphs on flowers. Hence, an attempt has been made to observe whether flower surface wax compounds (alkanes and free fatty acids) from two cultivars (BIO L 212 Ratan and Nirmal B-1) of L. sativus could act as short-range attractant and stimulant for nymph laying by adult viviparous females. The n-hexane extracts of flower surface waxes were analyzed by TLC, GC-MS and GC-FID analyses. Twenty one and 22 n-alkanes between n-C12 and n-C36 were detected in BIO L 212 Ratan and Nirmal B-1, respectively; whereas 12 free fatty acids between C12:0 and C22:0 were identified in both cultivars. Pentadecane and tridecanoic acid were predominant n-alkane and free fatty acid, respectively. One flower equivalent surface wax of both cultivars served as short-range attractant and stimulant for nymph laying through Y-tube choice experiments and I-tube viviparity assays, respectively, by adult viviparous females. A synthetic blend of nonacosane, tridecanoic acid and linoleic acid, and a synthetic blend of tetradecane, pentadecane, nonacosane, tridecanoic acid and linoleic acid resembling in amounts as present in one flower equivalent surface wax of BIO L 212 Ratan and Nirmal B-1, respectively, served as short-range attractant and stimulant for nymph laying by adult viviparous females. This study suggests that both these blends could be used in lures in the development of baited traps in pest management programmes.

Fruit Volatiles of Creeping Cucumber (Solena amplexicaulis) Attract a Generalist Insect Herbivore

Herbivorous insects employ host plant volatile blends as cue for host recognition. Adults of Aulacophora foveicollis Lucas (Coleoptera: Chrysomelidae) feed on leaves, flowers, and fruits of Solena amplexicaulis (Lam.) Gandhi (syn: Melothria heterophylla) (Cucurbitaceae), commonly known as creeping cucumber. Currently, this pest is controlled by insecticides application. Hence, it is necessary to find out volatile components from fruits attracting the insect, which might be used for eco-friendly pest management program. behavioral responses of females were measured by Y-tube olfactometer bioassays towards volatile blends from undamaged (UD), insect-damaged (ID), and mechanically damaged (MD) fruits with the aim to identify the compounds responsible for host fruit location. Volatile organic compounds were identified and quantified by GC-MS and GC-FID analyses, respectively. Nonanal was predominant in volatile blends of UD, ID, and MD fruits. 1-Octen-3-ol, 3-octanone, 2-octanol, heptadienal (2E,4E), 1-pentadecanol, and 1-hexadecanol were present in volatile blends of ID and MD fruits, but females did not show response to these six compounds. 1-Octanol and 1-heptadecanol were unique in volatile blends of UD fruits after 4 hr of damage, but females did not show response to these compounds. Females were more attracted to volatile blends from UD fruits after 4 hr of damage in comparison to volatile blends released by UD fruits, due to increased emissions of (E,Z)-2,6-nonadienal and 2E-nonenal. A synthetic blend of 3.35 μg (E,Z)-2,6-nonadienal and 1.72 μg 2E-nonenal dissolved in 25 μl CH₂Cl₂ could be used for the development of baited traps to control this insect pest in integrated pest management strategies.

Interference mechanism of Sophora alopecuroides L. alkaloids extract on host finding and selection of the Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera: Psyllidae)

Manipulating insect behavior through the deployment of semiochemicals offers a promising opportunity for protecting crops in a sustainable manner. Therefore, there is still a significant opportunity for the development of natural crop protectants as eco-friendly tools in pest management. In this context, the aim of the current investigation is to find a novel prophylactic against the Asian citrus psyllid (ACP) and to gain a better understanding of the host-finding and selection ability of the ACP towards Murraya paniculata seedlings treated with Sophora alopecuroides alkaloids extract (SAAE). Our results indicate that foliar application of SAAE influences the psyllid host-finding and selection process. The behavioral assay with M. paniculata seedlings treated with 15 and 30 mg/mL of SAAE, with masked visual cues, revealed that only 6.6 and 10.4% psyllids were able to locate the host in the vials. The results also indicate that citrus psyllids mainly rely on both visual and olfaction in host-finding and selection. In choice settling experiments, psyllids settled almost completely on control seedlings rather than on seedlings treated with SAAE at a concentration of 30 mg/mL. Chemical analyses of the alkaloids extract revealed the presence of sophocarpine (33.90%), sophoridine (6.23%), anagyrine (2.77%), matrine (2.38%), lupanine (1.68%) aphylline (0.89%), and sophoramine (0.75%). In further behavioral bioassays with the dominant alkaloids sophocarpine and sophoridine, the alkaloids repelled ACP at higher concentrations of 50 and 70 mg/mL as compared to SAAE. Furthermore, the 50 mg/mL (1:1, v/v) combination of sophocarpine and sophoridine displayed a synergistic effect and showed the maximum behavioral effect as compared to the individual alkaloid. Based on our results, SAAE makes M. paniculata seedlings unattractive to the psyllids, and therefore, alkaloids could be used in reducing the colonization of citrus plants, subsequently curtailing HLB infection.

Two Odorant-Binding Proteins of the Dark Black Chafer (Holotrichia parallela) Display Preferential Binding to Biologically Active Host Plant Volatiles

The dark black chafer (DBC), Holotrichia parallela, is an important pest of multiple crops. Insect host-searching behaviors are regulated by host plant volatiles. Therefore, a better understanding of the mechanism linking the chemosensory system to plant volatiles at the molecular level will benefit DBC control strategies. Based on antenna transcriptome data, two highly expressed antenna-specific odorant-binding proteins (HparOBP20 and 49) were selected to identify novel DBC attractants using reverse chemical ecology methods. We expressed these proteins, mapped their binding specificity, and tested the activity of the plant volatiles in the field. The ligands used in the binding specificity assays included 31 host-plant-associated volatiles and two sex pheromone components. The results showed that (1) HparOBP20 and 49 are involved in odor recognition; (2) these proteins bind attractive plant volatiles strongly and can therefore be employed to develop environmentally friendly DBC management strategies; and (3) the green-leaf volatile (Z)-3-hexenyl acetate shows a high binding affinity to HparOBP20 (Ki = 18.51 μM) and HparOBP49 (Ki = 39.65 μM) and is highly attractive to DBC adults, especially females. In the field test, a (Z)-3-hexenyl acetate trap caught an average of 13 ± 1.202 females per day, which was significantly greater than the corresponding male catch (F2,6 = 74.18, P < 0.0001). (Z)-3-Hexenyl acetate may represent a useful supplement to the known sex pheromone for DBC attraction. In the present study, the binding characteristics of two HparOBPs with host plant volatiles were screened, providing behaviourally active compounds that might be useful for DBC control, based on reverse chemical ecology.

The Role of Leaf Volatiles of Ludwigia octovalvis (Jacq.) Raven in the Attraction of Altica cyanea (Weber) (Coleoptera: Chrysomelidae)

Larvae and adults of Altica cyanea (Weber) (Coleoptera: Chrysomelidae) feed on the rice-field weed Ludwigia octovalvis (Jacq.) Raven (Onagraceae), commonly known as willow primrose, which is considered a biocontrol agent of the weed. Volatile organic compounds from undamaged plants, plants after 4, 12, and 36 h of continuous feeding by A. cyanea larvae or adult females and after mechanical damaging were identified by GC-MS and GC-FID analyses. Twenty nine compounds were identified from undamaged plants. 2Z-Penten-1-ol, geraniol, and 1-tridecanol were present in all plants damaged by larvae. In contrast, feeding by adults caused the release of 2Z-penten-1-ol only after 12 and 36 h; whereas geraniol and 1-tridecanol appeared only after 36 h. Farnesyl acetone was detected after 12 and 36 h of feeding by larvae and after 36 h of feeding by adults. Farnesene was detected after 36 h of feeding by larvae and adults. Linalool was unique after 36 h of feeding by larvae. In Y-shaped glass tube olfactometer bioassays, A. cyanea females were attracted to volatiles after 36 h of feeding by larvae or adults compared to volatiles released by undamaged plants. The insects were attracted to five synthetic compounds: 3-hexanol, α-pinene, linalool oxide, geraniol, and phytol. Synthetic blends were more attractive than individual compounds. Compared to undamaged plants, volatiles released by plants, damaged by conspecific individuals, were more attractive to A. cyanea females, due to elevated emissions of 3-hexanol, α-pinene, linalool oxide, geraniol, and phytol.

Long-chain alkanes and fatty acids from Ludwigia octovalvis weed leaf surface waxes as short-range attractant and ovipositional stimulant to Altica cyanea (Weber) (Coleoptera: Chrysomelidae)

The importance of leaf surface wax compounds from the rice-field weed Ludwigia octovalvis (Jacq.) Raven (Onagraceae) was determined in the flea beetle Altica cyanea (Weber) (Coleoptera: Chrysomelidae). Extraction, thin layer chromatography and GC-MS and GC-FID analyses of surface waxes of young, mature and senescent leaves revealed 20, 19 and 19 n-alkanes between n-C15 and n-C35, respectively; whereas 14, 14 and 12 free fatty acids between C12:0 and C22:0 fatty acids were identified in young, mature and senescent leaves, respectively. Tricosane was predominant n-alkane in young and mature leaves, whilst eicosane predominated in senescent leaves. Heneicosanoic acid, palmitic acid and docosanoic acid were the most abundant free fatty acids in young, mature and senescent leaves, respectively. A. cyanea females showed attraction to 0.25 mature leaf equivalent surface waxes compared with young or senescent leaves in a short glass Y-tube olfactometer bioassay. The insects were attracted to a synthetic blend of 0.90, 1.86, 1.83, 1.95, 0.50 and 0.18 µg ml-1 petroleum ether of hexadecane, octadecane, eicosane, tricosane, palmitic acid and alpha-linolenic acid, respectively, comparable with the proportions as present in 0.25 mature leaf equivalent surface waxes. A. cyanea also laid eggs on a filter paper moistened with 0.25 mature leaf equivalent surface waxes or a synthetic blend of 0.90, 1.86, 1.83, 1.95, 0.50 and 0.18 µg ml-1 petroleum ether of hexadecane, octadecane, eicosane, tricosane, palmitic acid and alpha-linolenic acid, respectively. This finding could provide a basis for monitoring of the potential biocontrol agent in the field.

First Characterisation of Volatile Organic Compounds Emitted by Banana Plants

Banana (Musa sp.) ranks fourth in term of worldwide fruit production, and has economical and nutritional key values. The Cavendish cultivars correspond to more than 90% of the production of dessert banana while cooking cultivars are widely consumed locally around the banana belt production area. Many plants, if not all, produce Volatile Organic Compounds (VOCs) as a means of communication with their environment. Although flower and fruit VOCs have been studied for banana, the VOCs produced by the plant have never been identified despite their importance in plant health and development. A volatile collection methodology was optimized to improve the sensitivity and reproducibility of VOCs analysis from banana plants. We have identified 11 VOCs for the Cavendish, mainly (E,E)-α-farnesene (87.90 ± 11.28 ng/μl), methyl salicylate (33.82 ± 14.29) and 6-methyl-5-hepten-2-one (29.60 ± 11.66), and 14 VOCs for the Pacific Plantain cultivar, mainly (Z,E)-α-farnesene (799.64 ± 503.15), (E,E)-α-farnesene (571.24 ± 381.70) and (E) β ocimene (241.76 ± 158.49). This exploratory study paves the way for an in-depth characterisation of VOCs emitted by Musa plants.

Chemical investigations of volatile kairomones produced by Hyphantria cunea (Drury), a host of the parasitoid Chouioia cunea Yang

In tritrophic 'plants-herbivores-natural enemies' systems, there are relatively few reports concerning the role(s) of kairomones in pupal parasitism. Chouioia cunea Yang (Hymenoptera: Eulophidae), an endoparasitic chalcid wasp, parasitizes pupae of the fall webworm (Hyphantria cunea Drury). The role of host-related kairomones was investigated using electroantennogram (EAG) and behavioral techniques. Chemicals from some host stages (pupae) and host by-products (frass), induced arrestment behavior of female parasitoids, while chemicals from prepupae, were inactive. Gas chromatography-mass spectrometry analysis of volatiles collected from pupae, frass and prepupae using solid-phase microextration revealed seven compounds with carbon chain lengths ranging from C4 to C20. All of the chemicals elicited significant EAG responses in C. cunea. Y-tube olfactometer bioassays demonstrated a significant positive response of mated female C. cunea to 1-dodecene. These data provide a better understanding of the host location mechanisms of pupal parasitoid.