Studies on the population dynamics of the bark beetle Leperisinus varius (Fabr.) (Col., Scolytidae) on European olive (Olea europaea)

Abstract

Within‐generation mortality of the bark beetle L. varius was studied in a Spanish olive orchard by placing cut logs in the field for adult females to breed. Mortality was greatest at the larval stage with only 10% of the original egg number surviving to adulthood. There was no evidence that the density of eggs laid per maternal gallery affects subsequent mortality at the egg, larval or pupal stages. The density of maternal galleries on a log, however, was found to have a positive influence on the mortality of larvae, but not of eggs or pupae. Part of this density‐dependent mortality could be attributed to insect parasitoids, but the effects of intraspecific competition between larvae was also important. However, the relative contribution of each of these components to the density‐dependent relationship was unclear. A simple model showed that the population is regulated by density‐dependent larval mortality at an equilibrium of 11 newly‐emerged females/dm2. Overwintering adult mortality is unlikely to affect this equilibrium significantly. However, year‐to‐year variations in density‐independent egg mortality (or oviposition success) was shown by the model to have a major potential effect on both the equilibrium level and population stability. Zusammenfassung Zur Populationsdynamik von Leperisinus varius (Fabr.) (Col., Scolytidae) in Olivenbäumen (Olea europaea) Die Mortalität des Borkenkäfers Leperisinus varius im Laufe einer Generation wurde in einer spanischen Olivenplantage mit Hilfe ausgelegter Baumabschnitte als Brutplätze untersucht. Die Mortalität war im Larvenstadium am größten mit etwa 10 %. Es gab keine Hinweise darauf, daß die Eidichte pro Muttergang die nachfolgende Mortalität der Eier, Larven und Puppen beeinflußte. Die Dichte der Muttergänge in einem Stammabschnitt jedoch zeigte eine positive Korrelation zur Mortalität der Larven, nicht aber zu jener der Eier und Puppen. Anteil an dieser dichteabhängigen Mortalität hatten zweifellos die Parasitoiden, doch war auch die intraspezifische Konkurrenz zwischen den Larven von Bedeutung. Allerdings blieb der relative Anteil jedes einzelnen der genannten Faktoren unklar. Ein einfaches Modell zeigt, daß die Populationsdichte durch die dichteabhängige Larven‐Mortalität mit einem Gleichgewicht bei elf frischgeschlüpften Weibchen/dm2 reguliert wird. Die Mortalität der überwinternden Adulten nimmt auf dieses Gleichgewicht keinen bedeutenden Einfluß. Jedoch zeigt das Modell, daß Jahr‐zu‐Jahr‐Variationen der dichteunabhängigen Ei‐Mortalität von wesentlicher Bedeutung sowohl für den Gleichgewichtslevel, als auch für die Populationsstabilität sind.

Intraspecific competition of Glyptotendipes paripes (Diptera: Chironomidae) larvae under laboratory conditions

“…During this period, about half of all test larvae died, and this mortality seemed to be density independent. This is consistent with other studies indicating that density independent mortality may strongly affect overall mortality and population dynamics (Lozano et al 1993;Cooke and Roland 2003). The reason for such high mortality in early developmental stages is probably connected with the demanding shift from planktonic to benthic dwelling and associated tube building.…”

The population dynamics of the bark beetle Phloeotribus scarabaeoides (Col., Scolytidae) on European olive (Olea europaea)

“…When this occurs, the larvae come into direct competition for phloem food resources. This type of larval competition has also been observed in the bark beetles Hylesinus varius (LOZANO et al, 1993(LOZANO et al, , 1994 and Scolytus ventralis (STARK and BORDEN, 1965;BERRY-MAN, 1968).…”

“…In order to analyse the relative effects of the different life-stage mortalities (particularly the effects of density dependent larval mortality and adult female establishment) on the insect's population dynamics, it is possible, following the procedure of LOZANO et al (1993), to construct a relatively simple population model using the information available. Thus, we first let: with where , u =proportional female loss and a (the coefficient of density-dependence acting on females) = 27.75 ( fig.…”

The role of parasitism and intraspecific competition in the population dynamics of the bark beetle, Leperisinus varius (Fabr.) (Col., Scolytidae) on European olives (Oka europea L.)

“…Leperisinus varius (Fabr.) is a univoltine, polyphagous bark beetle that attacks a wide range of tree species including olive, ash, pine, oak and beech (LOZANO et al 1993). I n Spanish olive orchards L. varius adults overwinter o n living olive trees in which they excavate subcortical feeding galleries, causing the tumerous 'rose of olive' (CHARARAS 1960).…”