No abstract

Cantharidin is produced by beetles of only two families, the Meloidae and the Oedemeridae. This substance is a defensive terpenoid that is toxic to the enemies of the beetles. Cantharidin also attracts other groups of insects and has been used as a bait to trap them. Cantharidin-baited traps deployed in central Japan captured coleopterans (Anthicidae, Endomychidae, Pyrochroidae, and Scarabaeidae), dipterans (Ceratopogonidae), hymenopterans (Formicidae), and harvestmen (Podoctidae). The seasonal occurrences of these arthropods, their sex ratios, known feeding choices, and mating habits suggest three possible underlying reasons for the attractancy of cantharidin: (i) it is accumulated as a defense against enemies and sometimes for transfer from males to females as a nuptial gift; (ii) it is used as a chemical cue in food searching; and (iii) it is used as an aggregation pheromone by mature arthropod individuals. The group of canthariphilous arthropods we describe represents a cryptic ecological assemblage with rare chemical networking among apparently unrelated species.

Large insect horns function as antipredator armaments, digging implements and intraspecific combat weapons. The sand‐living anthicid beetle Mecynotarsus tenuipes possesses a large horn on the pronotum. Allometric relationships between body size and horn size did not show either a slope of more than 1 or sexual dimorphism, suggesting another function of the horn other than sexual selection via combat. Behavioral observation of individuals using a microvideo camera indicated that the horn is used to dig and move forward in loose sand. Only the horned M. tenuipes could dig into sand, in contrast to the hornless anthicid beetles Stricticollis valgipes and Clavicollis fugiens, which could not dig. When moving in sand, M. tenuipes joins its pronotal horn and head to form a conical shape, with which it pierces into the sand. Then, it opens its horn and head outward to create a space in the sand for forward motion. Although it can dig deeply into sand by repeating these behaviors sequentially, digging speed tends to slow with depth, probably because the weight of the substrate increases.

No abstract

Several insects exhibit strong asymmetry in male genital shape, but the functions of this asymmetry is unknown. In the four species of the family Mantidae belonging to the genera Tenodera, Statilia and Hierodula, male genitalia consist of a more complex left‐side lobe, with two well‐pointed sclerotized processes, the apical process (paa) and the distal process (pda). Female genitalia are symmetric, and the genital opening (gonopore) is concealed by placement of the ovipositor (ovi) into the subgenital plate (sgp). Mating with experimental males, in which either paa or pda was cut, demonstrated that paa is essential for successful copulation. By fluorescence detection of the surface of females mated with males in which the paa was coated with fine fluorescent beads, the paa attachment site was determined to be the left edge of the female sgp. This finding suggests that copulation begins with exposure of the female gonopore by the male hooking the paa to the sgp and unfastening the ovi from the sgp, as associated with other parts of the male genitalia. The extremely asymmetric male genitalia also determine their mating posture. The male, mounting the female, bends his abdomen from the right side of his mate to attach his paa to her sgp. We found no antisymmetry in male genitalia, and never observed reversal (leftward) abdominal bending by the males. This was the fixed mating posture, even in virgin males, suggesting its innateness.