Zur Populationsdynamik der Gemeinen Kiefernbuschhornblattwespe Diprion pini L. (Hym., Diprionidae) in Niedersachsen 1991/92
Authors: Altenkirch W. 
Published: August 2009

Studies on population dynamics of Diprion pini L. (Hym., Diprionidae) in Lower Saxony 1991/92

The paper reports on the gradation of Diprion pini in small areas of Lower Saxony (North‐Western Germany) in 1991/92. The second generation of larvae in autumn 1991 had caused obvious damage on about 20 ha of pine stands. During the winter of 1991/92 the number of cocoons reached 4000/m2 max. around the trunk bases of damaged trees. At these high cocoon‐density rates the proportion of females ready to hatch was significantly lower than at the lower density rates more distant from the trunk. The first strong flight (first wave) happened between 5th and 10th May 1992. The checks of oviposition resulted in a correspondingly high degree of danger. The parasitation of the eggs was low, but fluctuated strongly.

No measures of chemical control were introduced, because we were able to assume that the young shoots and needles growing in May would remain largely unaffected. Feeding‐tests confirmed similar statements found in older literature. As predicted, the feeding‐damage remained within acceptable limits.

Further waves of wasps (in June and July) remained on a very low level. A second generation did not emerge in 1992. The remaining cocoons of autumn 1991 were affected by antagonists ‐ parasites and predators. During the winter of 1992/93 D. pini was found again in the outbreak‐area in the state of latency.

The results show that it is not necessary to stop outbreaks of D. pini in all cases by means of chemical control. But we had to take into account the danger caused by trunk‐inhabitant beetles (Pissodes pini, P. piniphilus, Phaenops cyanea) as secondary pests. Due to the current extreme weather conditions throughout the whole pine area of North‐Eastern Germany, this danger was particularly high.

The data are discussed with regard to the population dynamics of D. pini (see Eichhorn 1991 a. o.). Some questions concerning both the conditions at the start of the outbreaks of D. pini, and the comparatively short extension of the gradation 1991/92, remain unanswered.

Eine kleinräumige Gradation von D. pini war Anlaß, Daten zur Populationsdynamik und Prognose zu sammeln. Die 2. Generation 1991 hatte im Herbst deutliche Fraßschäden auf ca. 20 ha verursacht. Im Winter 1991/92 wurden im Befallsgebiet maximale Kokonzahlen (am Stammfuß) bis zu 4000/m2 gefunden. Die Schlüpfbereitschaft der Weibchen war bei diesen hohen Dichten signifikant niedriger als bei geringer Kokondichte in Entfernung vom Stamm. Es mußte mit einem starken Flug der Wespen (1. Welle) gerechnet werden, der tatsächlich zwischen dem 5. und 10. Mai 1992 eintrat. Die Kontrolle der Eiablage ergab eine entsprechend hohe Gefährdung. Die Eiparasitierung war gering und schwankte stark.

Bekämpfungsmaßnahmen wurden dennoch nicht eingeleitet, da mit einer weitgehenden Fraßverschonung der jungen Mainadeln gerechnet werden konnte. Fütterungsversuche bestätigten entsprechende alte Angaben aus der Literatur. Der Fraß hielt sich denn auch in erträglichen Grenzen.

Weitere Wellen der Blattwespe (im Juni und Juli) flogen nicht oder nur in sehr geringem Umfang. Eine 2. Generation kam 1992 nicht zustande. Die Überlieger vom Herbst 1992 gerieten unter zunehmenden Druck von Parasiten und Räubern. Der Winter 1992/93 zeigte D. pini im Gradations‐gebiet wieder in Latenz.