Evidence for Pre‐emergence Mating Among Mature Progeny of Ips Grandicollis (Eichhoff)

Abstract

Diyarrnrcw/ cIf'EnromologI~. Waiti, A,qric~iil/ural Rcsc.arc,h Insti/ure. Universiry qf'Adelaide, Glen Osmond, S. A. 5046. AbstractAdults of/p.s ~~rontlicdlis caught on ipsenol-baited traps. as well as emergents from logs collected from natural infestations. included a high percentage of mated females. However only eight per cent of the laboratory reared mature progeny had mated. The study indicated that the adults mate only under bark. Bark sandwich rearings provided strong evidence for pre-emergence mating, the incidence of which increased with the time the mature progeny stayed under bark. Sister-brother matings resulted in progeny. Both mated and virgin females were accepted into nuptial chambers by the resident males. IntroductionBark beetles of the genus Ips (Coleoptera: Scolytidae) are recognised as secondary pests because they usually attack weakened or dying coniferous trees, predominantly pines and spruces. The males of Ips grandicollis (Eichhoff) usually initiate the attack and produce the aggregating pheromone, ipsenol (Vite and Renwick 1971). This pheromone, in combination with host attractants, directs both sexes to the selected host (Hedden et a/. 1976). Hitherto, it has been assumed that aggregation of the responding beetles, followed by selection of mates is a necessary preliminary to mating.All polygamous Ips species are known to mate within the bark of host trees, following acceptance of females into nuptial chambers by resident males. After they have mated, females typically proceed to construct egg galleries that radiate from the nuptial chamber. Adults from the brood subsequently produced are known to behave in a distinctive manner. Attempts to describe this sequence of behaviour led Cobb et al.(1 968) to propose a generalised system, which has been adapted to the genus Ips in Fig. 1. The term 'emergence', as used here refers to the act of leaving one host tree in search of another; similarly 'dispersal' refers to the act of flying in search of suitable hosts following emergence.In the genus Ips this sequence of behaviour ( Fig. 1) has been recorded by Bungey (1966) and Morgan (1967) avulsus. This scheme implies that all adults emerging for the first time from their brood hosts are virgins; it would appear to negate the possibility that some of them may mate before their first dispersal flight. Thus previous authors have tended to assume that mated beetles found dispersing were parent adults that had already established brood and were moving to new sites, to produce further brood. This assumption appeared reasonable in the light of knowledge that bark beetles produce more than one brood each year and in a number of host trees. Thus, according to previous authors, the females in the flying population at any time should either be parent individuals that had already oviposited, or young female adults that had neither oviposited nor mated. McCambridge (1969a, b) suggested that Ips and related bark beetles mate early following maturation. He found that 15% of the females of Dendrocronus po...

LIFE HISTORY AND BIOLOGY OF IPS LATIDENS (LECONTE) (COLEOPTERA: SCOLYTIDAE)

“…Since mating is necessary before oviposition can occur, even for females that produce all-female broods (Lanier and Oliver 1966), either males andlor females traveled freely between galleries, or females mated prior to introduction into arenas. Pre-emergence mating does occur in I. grandicollis (All and Anderson 1972;Witanachchi 1980), the proportion of mated females increasing with time spent as adults under the bark to as high as 89%.…”

Biology of the bark beetleIps grandicollis Eichhoff (Coleoptera:Scolytinae) and its arthropod, nematode and microbial associates: a review of management opportunities forAustralia

“…It can complete its life cycle in 25–45 days, allowing for up to six generations per year (Morgan ; Schenk & Benjamin ; Raffa ) depending on temperature during development (Anderson ). In south‐eastern Australia, I. grandicollis exhibits three to four generations between early spring and late autumn, and the fourth (the winter generation) between autumn and the following spring takes up to 6 months from eggs to adult emergence (Morgan ; Witanachchi ; Neumann & Morey ).…”

“…Males usually initiate attack by searching a suitable host and constructing nuptial chambers (a chamber in which a male copulates with females). Ips grandicollis adults are polygamous (Witanachchi ); each male mates with one to seven females, either mated or virgin (Witanachchi ; Witanachchi & Morgan ; Kirkendall ; Garraway ). Females copulate with males in the nuptial chamber and construct brood galleries.…”

“…Adults surviving the winter produce a spring brood (Morgan ). The same female can oviposit, re‐emerge and create more than one gallery in the same or different trees without undergoing another feeding phase (Witanachchi ).…”

“…The emergence of adult I. grandicollis mainly depends on ambient temperatures, food availability and population density within the infested trees (Witanachchi ). Winter slows down the development of beetles (e.g.…”