Frass clearing by male pine engraver beetles (Ips pini; Scolytidae): paternal care or paternity assurance

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Male parental care and paternity assurance are often associated with long-duration pair bonds. The mating system of the pine engraver beetle, Ips pini, includes an association between the male and female that persists for most of the prolonged opposition period. The male beetles remove frass that arnmmlatn as the females lay their eggs in die phloem tissue of the host tree. Experiments and field observations were done to test possible benefits to males that stay in the galleries removing frass while die females are ovipositing. Two hypotheses were that clearing frass (1) provides some form of care that results in more offspring being produced and (2) is part of a paternity assurance mechanism. Male removal experiments in the field produced no evidence that male presence significantly influenced any of five measures of offspring production. Laboratory experiments in which virgin females were bred reciprocally to sterile and fertile males showed that, while there is no strong pattern of lastmale precedence, last-male paternity does increase over time. Field observations revealed that female pine engravers often carry sperm from previous maringi when they solicit entry to a male's breeding gallery. The pattern of paternity and the female's sperm storage capacity suggest that males must maintain prolonged mating access to females in order to ensure high paternity. Hence, frass clearing is necessary to maximize paternity. Kiy words: bark beetles, Ips pini, parental care, paternity assurance, sperm precedence. [Befuw Ecol 8:318-325 (1997)]