This issue of the Journal of Chemical Ecology honors Professor Kenji Mori, who died on April 16, 2019 at the age of 84. Professor Mori was one of the outstanding chemists of his generation, who will be forever remembered for his work on synthesis of pheromones and other small molecule bioregulators during a career spanning over 60 years. Scopus currently lists 1001 contributions authored by Professor Mori, showing his remarkable drive and determination for science. A book authored by him on his research not only gives an overview of his achievements, but also testifies to his systematic approach to science and his scientific rigor which was never compromised (Mori 2010). His legacy will live on, particularly his pioneering work on the importance of stereochemistry in pheromone research in which he synthesized a wide range of biologically-active molecules, often providing the first synthetic access to these compounds. An equally important contribution to our field of chemical ecology is the network of international collaborators he built up during his lifetime. His endearing charm and enthusiasm, his encouragement of young scientists and his ever-willingness to provide compounds, advice and experience will have enhanced most of our careers at some stage, as evidenced by the contributions in this issue.

The late Wittko Francke published a formal obituary for Professor Mori (Francke 2019). In the first article in this issue, Hirosato Takikawa (2021) provides a personal view of the personality of Mori-sensei and shares some memories of working with him.

The second paper by Dan Bray, David Hall and the Boyd Mori Group in Canada describes identification of the sex pheromone produced by a new species of cecidomyiid midge (Bray et al. 2022). This is a simple but classic confirmation of the importance of stereochemistry in insect pheromones and another example of Professor Mori’s thesis that insects do not always use single stereoisomers. David Hall’s first memory of Professor Mori is receiving a melting point tube containing a few milligrams of the pheromone of the red bollworm moth, Diparopsis castanea, for analysis and field testing, a product of Pheromone Synthesis Part II (Mori 1974).

Kendal Singleton and coworkers from the Gries Group (Singleton et al. 2022) identified an unusual aliphatic ester as the major sex pheromone component produced by females of the click beetle, Agriotes ferrugineipennis, whose wireworm larvae can be important pests. In spite of having only three females and 30 males available, they were able to carry out volatile collections from both sexes and GC-EAD analyses on four different GC columns. Synthesis and field experiments revealed the high activity of the ester that is the only attractive compound among several other EAD-active components.

In their paper, the group of Paulo Zarbin (Gomes et al. 2022) elegantly determined the absolute configuration of the male-produced pheromone of the stink bug, Pellaea stictica, a remarkable achievement considering the three independent stereogenic centers involved. The efficient synthetic strategy is clearly inspired by the work of Professor Mori, combining short reaction sequences with clever use of various chiral building blocks and stereochemical investigations using gas chromatography.

The paper from the Ômura Group (Yoshimori et al. 2022) describes identification and synthesis of compounds from the wing glands of males of the common grass yellow butterfly, Eurema mandarina. Detailed studies of the morphology of the forewing and demonstration of the aphrodisiac activity of the compounds advance our knowledge of chemical communication in these butterflies.

The work presented by the Schulz group (Kuhn and Schulz 2022) describes the identification of a new macrolide that likely plays a role in species-recognition of the frog, Hyperolius cinnamomeoventris. A versatile and enantioselective synthesis of the four possible isomers of the molecule was carried out, making it possible to establish the absolute stereochemistry of the natural product by GC analysis on a chiral phase. This is an impressive illustration of the complexity of structural elucidation with minimal amounts of biologically-active compounds, and is a tribute to the work of Professor Mori who collaborated with research groups around the world, always providing enantiopure compounds.

Tabata (2022) used reference compounds synthesized by Professor Mori to determine the composition of the sex pheromones produced by two mealybug species, Planococcus citri and P. minor and their hybrids. The results of analyses of collections from 595 individuals suggest that the shift of the monoterpene cyclobutane structure in the pheromone of P. citri to its acyclic form in that of P. minor is largely attributable to a single genetic locus.

Kazuaki Akasaka provides a comprehensive review of the development of fluorescence derivatization reagents for highly sensitive and efficient HPLC determination of the absolute configuration and stereoisomer composition of natural products with a chiral branched alkyl chain (Akasaka 2022). Much of this work was inspired by and carried out in collaboration with Professor Mori, and application of the approach to a wide range of insect pheromones and marine natural products is described, illustrating the breadth of Professor Mori’s interests.

The paper by Weliton Silva and the Millar/Hanks Group (Silva et al. 2022) describes the identification of a highly novel trisubstituted tetrahydropyran as a pheromone component of a South American cerambycid beetle. The identification involved elegant NMR experiments and analyses and synthesis of the compound in racemic form. How Professor Mori would have enjoyed the challenge of synthesizing all eight stereoisomers!

Kazama et al. (2022) describe investigations of the stereochemistry of a synthetic plasticizer which was previously shown to inhibit oviposition in the peach fruit moth, Carposina sasakii. Only the (R)-enantiomer elicited an EAG response and inhibited oviposition, a remarkable example of how stereochemistry influences the biological activity even of entirely non-natural compounds.

We sincerely hope Professor Mori would have enjoyed reading these papers as much as we have, and that they constitute a fitting tribute to the indelible legacy left by this giant of chemical ecology.