Pheromonal cross-attraction in true bugs (Heteroptera): attraction of Piezodorus hybneri (Pentatomidae) to its pheromone versus the pheromone of Riptortus pedestris (Alydidae)

Binding properties of chemosensory protein 4 in Riptortus pedestris to aggregation pheromones

In insects, chemosensory proteins (CSPs) play an important role in the perception of the external environment and have been widely used for protein-binding characterization. Riptortus pedestris has received increased attention as a potential cause of soybean staygreen syndrome in recent years. In this study, we found that RpedCSP4 expression in the antennae of adult R. pedestris increased with age, with no significant difference in expression level observed between males and females, as determined through quantitative real-time polymerase chain reaction (qRT-PCR). Subsequently, we investigated the ability of RpedCSP4 to bind various ligands (five aggregated pheromone components and 13 soybean volatiles) using a prokaryotic expression system and fluorescence competitive binding assays. We found that RpedCSP4 binds to three aggregated pheromone components of R. pedestris, namely, ((E)-2-hexenyl (Z)-3-hexenoate (E2Z3), (E)-2-hexenyl (E)-2-hexenoate (E2E2), and (E)-2-hexenyl hexenoate (E2HH)), and that its binding capacities are most stable under acidic condition. Finally, the structure and protein-ligand interactions of RpedCSP4 were further analyzed via homology modeling, molecular docking, and targeted mutagenesis experiments. The L29A mutant exhibited a loss of binding ability to these three aggregated pheromone components. Our results show that the olfactory function of RpedCSP4 provides new insights into the binding mechanism of RpedCSPs to aggregation pheromones and contributes to discover new target candidates that will provide a theoretical basis for future population control of R. pedestris.

Conditioning Native Telenomus and Trissolcus (Hymenoptera: Scelionidae) Egg Parasitoids to Recognize the Exotic Brown Marmorated Stink Bug (Heteroptera: Pentatomidae: Halyomorpha halys)

Halyomorpha halys (Stål) (Heteroptera: Pentatomidae), the brown marmorated stink bug (BMSB), is a polyphagous fruit and vegetable pest from eastern Asia and now invasive in the United States and Europe. Earlier research revealed that the main volatile from hexane egg extracts of a western North American pentatomid, Euschistus conspersus Uhler, to which two native scelionid egg parasitoids, Telenomus podisi Ashmead and Trissolcus erugatus Johnson are highly attracted, was methyl (2E,4Z)-2,4-decadienoate, the major component of the conspecific male-produced aggregation pheromone. Conversely, extracts of BMSB eggs lacked the male-produced sesquiterpenoid H. halys pheromone components but contained C16,18,20 aldehydes (hexadecanal, octadecanal, and eicosanal); both egg-surface extracts of BMSB eggs and the C16,18,20 synthetic aldehyde blend repelled the female parasitoids. The goal of the present research was to manipulate egg-surface volatiles to induce the scelionid egg parasitoids to adopt BMSB eggs as a host. Here it was demonstrated that individual females of both parasitoids could be conditioned to H. halys egg-surface aldehydes in Y-tube olfactometer experiments, and this positive memory lasted 3-4 d. Furthermore, conditioned wasps successfully parasitized fresh H. halys eggs in no choice tests, and their offspring continued to successfully parasitize fresh H. halys eggs for 2-3 more generations. Eventually, both the individual and generational memories faded. Unconditioned female parasitoids were not attracted to H. halys egg extract or the synthetic blend of egg-surface aldehydes, nor did they parasitize BMSB eggs. Theoretical and practical implications of the research are discussed in the contexts of Hopkins' host selection principle, biological control, and instinct evolution.

The use of the lactone motif in chemical communication

A wide variety of organisms communicate via the chemical channel using small molecules. A structural feature quite often found is the lactone motif. In the present paper, the current knowledge on such lactones will be described, concentrating on the structure, chemistry, function, biosynthesis and synthesis of these compounds. Lactone semiochemicals from insects, vertebrates and bacteria, which this article will focus on, are particularly well investigated. In addition, some ideas on the advantageous use of lactones as volatile signals, which promoted their evolutionary development, will be discussed.