ABSTRACT. Equal numbers of dispersing Ips grandicollis adults were caught on sticky traps held on susceptible and resistant Pinus radiata trees. When beetles were attracted to the same set of trees using baits of ipsenol (aggregation pheromone), some of the beetles that landed on the boles of the trees bored into the bark. The subsequent response of the tree determined whether the tree was accepted or rejected. In resistant trees, the exudation of resin prevented continued boring and led to the retreat of the beetles. In susceptible trees, continued boring led to the establishment of the beetles. Ipsenol was not detected in males that retreated after boring into resistant trees. Beetles that bored into P. radiata logs obtained from slash, continued to bore into the bark, due to the absence of any of the resistance mechanisms; ipsenol was detected in such males. Extracts of groups of male beetles caught from the dispersing population on pheromone‐baited traps, contained little or no ipsenol.

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...

Dispersing males and females of Ips grandicollis, whether mated or virgin, initiated galleries on experimental logs held in a naturally infested P. radiara plantation. A few females initiated galleries despite the presence of adjacent male-initiated galleries. Males responded to logs bearing females by entering 41% of the female-initiated galleries. The pattern of entry of these males differed depending on whether the entrance to the female-initiated gallery was blocked by frass or not. The findings of this study has led to interesting speculations about the behaviour and biology of this species.