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Within‐harem competition among Ips females, an overlooked component of density‐dependent larval mortality

1989; Wiley; Volume: 12; Issue: 4 Linguagem: Inglês

10.1111/j.1600-0587.1989.tb00925.x

1600-0587

Lawrence R. Kirkendall,

Entomopathogenic Microorganisms in Pest Control

Intraspecific larval competition is commonly believed to be the major component of egg‐to‐adult mortality in bark beetles. Larval mortality is usually shown to be density dependent. In this study I looked specifically at competition among females in the same gallery system, in a sparse but highly female‐biased population of Ips acuminatus breeding in cut pine branches near Kongsberg, southeastern Norway. Supplementary data from a slightly female‐biased population in western Norway and a population with intermediate female bias in W. Germany are also provided. Survivorship from egg to adult or pupa was measured in laboratory experiments, for the area in which larvae from different arms potentially competed relative to survivorship in areas away from competition. Survivorship was significantly correlated with both average interarm distance (r 2 = 0.76) and food per larva (cm 2 per larva: r 2 = 0.73). There was no evidence that females could detect the presence of other, nearby egg arms: neither egg spacing (on the arm sides nearest each other) nor interarm distance increased when two arms were near each other. Nor did females distribute themselves optimally within harems, though the distribution of egg arms within harems was significantly different from that expected from random settling. analysis of interarm distances and harem sizes in 1984 branches revealed that a minimum of 34% of arm sides could be expected to suffer considerably reduced larval survivorship due to within‐harem competition. Harem size in Ips typographus is reviewed, and data on the distribution of females within harems is presented for Norwegian populations of I. Typographus, Orthotomicus erosus and O. laricis . Evidence from the literature is presented to show that uneven distribution of females between harem sides is not uncommon. I suggest that the findings for Ips acuminatus are applicable to a wide range of harem polygynous scolytids, including I. typographus: the factors influencing density cannot be fully understood without taking into account the distribution of females among males and the distribution of females within harems.