SEXUAL BEHAVIOR AND SEASONAL MATING ACTIVITY OF TRYPODENDRON LINEATUM (COLEOPTERA: SCOLYTIDAE)

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Abstract
Mating frequency and behavior of five color-coded adults of each sex of Trypodendron lineatum (Olivier) were observed for 1 hour periods in petri dish arenas. Mating activity was evaluated by recording each incident in which a male assumed the "precopulatory" position on a female for a minimum of 10 seconds. Newly emerged brood adults mated with very low frequency. The mating activity of revived overwintering beetles increased throughout the winter. In February there was a sudden rise in activity to an intensity approaching that of sexually active "spring" populations of March and April. This pattern, as well as the recovery of locomotion upon warming throughout the winter, provides evidence that overwintering populations undergo only a reproductive diapause, or hibernation. Mating activity of excavating parents fell to one-half that of spring beetles within 2 weeks of host invasion and declined further after 4 weeks. Parents that had recently emerged from brood logs had negligible mating activity. Flight was not an essential prerequisite to mating. There was no prolonged delay between initial contact of the sexes and mounting, and no observable courtship. Behaviorally, the male was the aggressive partner; the female was passive and nonresisting. Multiple matings by both sexes, with the same or different partners, and mounting of mating couples and other males by males were observed. The average duration of mounting was 1.75 minutes and, when copulation occurred, 3.35 minutes; dissections showed that this period was sufficient for insemination. Pronounced reduction of mounting and copulation activity occurred within 30 to 40 minutes of initial contact with the opposite sex. Mating frequency depended primarily on the maturity and vigor of the male, although the maturity of females had a slight effect.
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