Ultrasonic Signal Competition Between Male Wax Moths

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Pair formation in the lesser wax moth, Achroia grisella (Lepidoptera: Pyralidae), is effected by male ultrasonic signals that are attractive to receptive 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 night. Females are known to choose males on a relative basis and evaluate primarily three signal characters: signal rate (SR), loudness (peak amplitude; PA), and asynchrony interval (AI), a temporal feature reflecting the time interval between signals produced by the left and right tymbals. We conducted a series of experiments to investigate whether and how A. grisella males modify their signals in the presence of neighboring signalers. When separated 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 for 5-10 min and are more pronounced in males that are silent at the time they perceive their neighbor. By increasing its SR, a male improves the likelihood of matching or exceeding its neighbor's SR and may thereby compete more effectively for local females. SR increases are energetically demanding, though, and their brief duration and occurrence primarily at the beginning of signaling bouts may be the most prudent allocation of a male's limited energy reserves.