Distinct Exocrine Glands Contribute to the Chemical Polymorphism Across Developmental Stages and Sexes in Riptortus pedestris

The bean bug Riptortus pedestris is one of the principal soybean pests throughout East Asia. Males release an aggregation pheromone consisting of three compounds—(E)-2-hexenyl (Z)-3-hexenoate (E2HZ3H), (E)-2-hexenyl (E)-2-hexenoate (E2HE2H) and myristyl isobutyrate (MI)—in a ratio of 1:5:1. Although pheromone-based baits have been extensively deployed to control the pest for the past three decades, the glands responsible for producing these volatiles have remained unidentified. Our investigations revealed that the metathoracic glands (MTGs) of males synthesized the two pheromonal esters, E2HZ3H and E2HE2H, along with a suite of auxiliary compounds: (E)-2-hexenal, hexanoic acid, (E)-3-hexenoic acid, (E)-2-hexenoic acid, (E)-2-octenal, and (E)-2-hexenyl hexanoate (E2HH). Female MTGs were morphologically similar to those of males and generated the same auxiliary compounds, but lacked the capacity to produce the pheromonal esters E2HZ3H and E2HE2H. MI was released exclusively from the male abdominal sternites. Its quantity was nearly uniform across all sternal segments, implying secretion from an epidermal glandular patch (GP) that was evenly distributed over the sternites. In nymphs, dorsal abdominal glands (DAGs) emitted several volatiles—including (E)-2-hexenal, 4-oxo-(E)-2-hexenal, (E)-2-octenal, and (E)-2-octenoic acid—some of which are characteristic defensive compounds of heteropterans. Thus, our study clarifies how sex- and stage-specific glands contribute to the chemical polymorphism observed in R. pedestris.