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AbstraotCmad. Ent. 98: 98-111 (1966) The dispersal flight of the Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, is oriented toward fresh windthrown and cut trees when these are present in the stand, the beetle being attracted by oleoresin, particularly its alphapinene, camphene, and limonene fractions. In the absence of such material the pioneer beetle dispersal appears to be rather uniform throughout the stand. This host attraction precedes the beetle attraction which is produced by unmated females shortly after entering the host and which results in mass concentration of beetles around the center of attraction. Of these two phases in the attraction process, the secondary attraction is far stronger than that caused by the fractions of the host oleoresin.Attraction centers are established only in freshly downed trees and in standing trees of subnormal physiological condition under both latent and epizootic conditions; however, under epizootic conditions, the beetles can invade even vigorous trees in the perimeter of attraction. The survival of such trees depends on their ability to exude oleoresin, which in turn is influenced greatly by environmental factors. The susceptibility of trees to successful beetle invasion is characterized by their oleoresin exudation pressure, which reflects water disturbances in the tree. Diurnal and seasonal fluctuations of the resin pressure are discussed in relation to beetle flight and invasion, and the resin effects upon the beetle (both mechanical and chemical) are considered. The beetles are found to be repelled by Douglas-fir resin and its fractions, i.e. alpha-and beta-pinene, camphene, limonene, terpineol and geraniol, when tested at close range in the laboratory.

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The vertex‐pronotal stridulatory apparatus of the female is described; the male lacks this sound producing apparatus. Females stridulated in stress, attraction, in‐gallery, and rivalry contexts. In contrast to some Dendroctonus species, I. pini (females) had similar attraction and rivalry chirps, which differed from stress chirps. In‐gallery chirps were longer and had a slower pulse rate than all other chirps, and were multiply interrupted. Their function was not ascertained. Attraction chirps produced by females attempting to enter a hole containing a male plus three females had more pulses/chirp and a faster pulse rate than chirps produced during attempts to enter galleries with either more or fewer females. Olfactory studies showed that the decrease in secondary attraction depended on the relation between the number of females/male in the gallery and elapsed time since the last female entered. However, these results do not indicate whether the aggregation retarding mechanism was the release of an antiattractant or merely cessation of production of the aggregative pheromone. The mean female/male sex ratio of the I. pini attracted to the test situations was 1.4/1.0, indicating a selective advantage to attracting excess males. Early colonisation observations showed that, in Oregon, nuptial chamber construction was completed within 1.4 days and the male accepted three females by 3.3 days. Zusammenfassung Das chemoakustische Verhalten von Ips pint (Say) (Col: Scolytidae) während des Befalles und der Kolonisation des Wirtsbaumes Der Lauterzeugungsapparat des Weibchens von Ips pint wird beschrieben; das Männchen besitzt keinen solchen Apparat. Die Weibchen stridulieren während eines Streß‐, Attraktions‐ und Rivalenverhaltens. Im Gegensatz zu einigen Arten der Gattung Dendroctonus produzieren die Weibchen von Ips pint Attraktion‐ und Rivalensignale, die akustisch ähnlich sind, sich jedoch von den Streß‐Signalen unterscheiden. Die Verhaltensuntersuchungen über die Wahrnehmung der Lockstoffe im Freiland haben gezeigt, daß die Abnahme in der sekundären Attraktion von der Zahl der Weibchen per Mannchen im Fraßgange abhängig ist sowie auch von dem Zeitabschnitt, seitdem das letzte Weibchen in den Fraßgang eindrang. Es ist noch nicht klar, ob diese Attraktionsabnahme durch die Abgabe eines anti‐attraktiven Pheromons oder durch die Beendigung der Pheromonproduktion verursacht wird.