Ultrasonic signal competition between male wax moths

Pair formation in the lesser wax moth, Achroia grisella (Lepidoptera: Pyral idae), is effected by male ultrasonic signals that are attractive to recept ive females within 1-2 m. The males typically aggregate in the vicinity of the larval food resource, honeybee colonies, and signal for 6-10 h each nig ht. Females are known to choose males on a relative basis and evaluate prim arily three signal characters: signal rate (SR), loudness (peak amplitude; PA), and asynchrony interval (AI), a temporal feature reflecting the time i nterval between signals produced by the left and right tymbals. We conducte d a series of experiments to investigate whether and how A. grisella males modify their signals in the presence of neighboring signalers. When separat ed by <40 cm, males increase their SRs by 3-6% upon perceiving a neighbor's signals, but they do not alter their PAs or Als. Increased SRs continue fo r 5-10 min and are more pronounced in males that are silent at the time the y perceive their neighbor By ina easing its SR, a male improves the likelih ood of matching or exceeding its neighbor's SR and may thereby compete more effectively, for local females. SR increases are energetically demanding t hough, and their brief ductation and occurrence primarily at the beginning of signaling bouts may be the most prudent allocation of a male's limited e nergy reserves.