Electrophysiological responses of Philaenus spumarius and Neophilaenus campestris females to plant volatiles

Molecular basis of camphor repellency in Hyphantria cunea

The plant-derived camphor has been used as a natural insect repellent against various insects for >500 years. However, the repellency mechanism behind camphor remains less understood. In this study, we aimed to identify the camphor receptor in Hyphantria cunea by deorphanizing 7 odorant receptors (ORs). The results showed that HcunOR46 is narrowly tuned to Camphor and is only conserved within the family Noctuidae. Further analysis through behavioral and electroantennograms (EAG) assays indicated that H. cunea adults are more sensitive to camphor than larvae, both behaviorally and electrophysiologically. This difference may be due to the lower expression of HcunOR46 at the larval stage. Additionally, a feeding assay indicated that camphor repellency could be related to camphor toxicity to larvae, with the lethal concentration 50 (LC50) value of 69.713 μg/μL. These results suggest that H. cunea may detect camphor through a distinct olfactory pathway from Culicinae mosquitos, providing a novel camphor-based pest management strategy for H. cunea.

Profiles of Volatiles Emitted from Orange Fruits Infested by Ceratitis capitata (Diptera: Tephritidae)

The profiles of volatile organic compounds (VOCs) emitted from orange fruits infested by Ceratitis capitata were examined. VOCs were collected from the headspace of oranges immediately, 24 h, 5 days, 8 days, and 13 days after oviposition and when larvae exit the fruit by applying either static or dynamic sampling techniques. A total of 32 and 47 compounds were detected in infested orange fruits when using static and dynamic techniques, respectively. Differences in the volatile profile of oranges were observed. Classification models were employed, showing that infested fruits emitted a chemical profile distinct from that of non-infested ones. Limonene was associated with cell disruption. (E)-β-Ocimene, (E)-4,8-dimethyl-1,3,7-nonatriene, hexyl butanoate, butyl hexanoate, and hexyl hexanoate were the VOCs that were correlated with the infestation of sweet oranges by C. capitata.

Quick shift in volatile attraction between the third and fifth instar larvae of Endoclita signifier

BACKGROUND

Endoclita signifer is a polyphagous lepidopteran species of eucalyptus that selects its hosts in the third-instar larval period. To understand how it adapts to its host during development, we studied the olfactory responses of late-stage (fifth)-instar larvae to the dynamic chemical environment they encounter.

RESULTS

Thirty-two volatiles from eucalyptus trunk and soil were identified, among which 14 showed electroantennal activity and five were identified as new. Further behavioral bioassay showed that both β-pinene and the imitation ratio of six key volatile in eucalyptus trunk were attractive to the fifth-instar larvae, but both eliminated and increased β-pinene in the mixture decreased the choice ratio and showed no attraction. Although E. signifer larvae shifted their attraction from o-cymene at the third-instar stage to β-pinene at the fifth-instar stage in a single volatile, the appropriate ratio of the main compounds in eucalyptus trunk volatile is the key to the behavior choice of fifth-instar larvae.

CONCLUSION

The switch in olfactory attraction to different compounds between fifth- and third-instar larvae indicated an olfactory plasticity between third- and fifth-instar larvae. And the particular blend mediated the highly specialized communication interactions specificity between fifth-instar larvae and eucalyptus trunk volatile indicated the specialized host adaptation to fifth-instar larvae. This enhances understanding of how the primitive lepidopteran E. signifier, as a native pest, adapts to introduced eucalyptus. Moreover, this study provides knowledge for the screening and development of target volatiles for trapping and managing E. signifer larvae. © 2022 Society of Chemical Industry.

Predicting interactions of the frass-associated yeast Hyphopichia heimii with Olea europaea subsp. cuspidata and twig-boring bark beetles

Bark beetles are destructive insect pests known to form symbioses with different fungal taxa, including yeasts. The aim of this study was to (1) determine the prevalence of the rare yeast Hyphopichia heimii in bark beetle frass from wild olive trees in South Africa and to (2) predict the potential interaction of this yeast with trees and bark beetles. Twenty-eight culturable yeast species were isolated from frass in 35 bark beetle galleries, including representatives of H. heimii from nine samples. Physiological characterization of H. heimii isolates revealed that none was able to degrade complex polymers present in hemicellulose; however, all were able to assimilate sucrose and cellobiose, sugars associated with an arboreal habitat. All isolates were able to produce the auxin indole acetic acid, indicative of a potential symbiosis with the tree. Sterol analysis revealed that the isolates possessed ergosterol quantities ranging from 3.644 ± 0.119 to 13.920 ± 1.230 mg/g dry cell weight, which suggested that H. heimii could serve as a source of sterols in bark beetle diets, as is known for other bark beetle-associated fungi. In addition, gas chromatography-mass spectrometry demonstrated that at least one of the isolates, Hyphopichia heimii CAB 1614, was able to convert the insect pheromone cis-verbenol to the anti-aggregation pheromone verbenone. This indicated that H. heimii could potentially influence beetle behaviour. These results support the contention of a tripartite symbiosis between H. heimii, olive trees, and bark beetles.