+6121Ideally studies on the population dynamics of organisms should be holistic, general, precise, and realistic ( 64). Much too often, however, support for research on forest pests approximates the curve of the gradations in time and space, resulting in periodic gathering of bits and pieces of information that differ little from that gathered earlier or elsewhere (68). Therefore it is not surprising that lack of compre hensive, quantitative information on many generations of a field population has handicapped the progress of theoretical thinking on the dynamics of populations, which badly needs "more light and less heat" (86). It has been proposed that research efforts should be coordinated internationally on a few model insects in order to cope with complexity and diversity of population dynamics at a high level of efficiency (25). We consider that the larch bud moth, Zeiraphera diniana, would meet the criteria for being such a model insect (1 8).The coincidence of large-scale insect outbreaks, the availability of effective insecti cides, and economic expansion of industry and tourism after World War II pro moted several extensive control actions against such forest pests as the spruce budworm, Choristoneura fumiferana, in eastern Canada and the larch bud moth, Z. diniana, in Switzerland. Public demand to protect the subalpine larch forests in the recreation area of the Engadine (Switzerland) against the recurring defoliation by the larch bud moth triggered the present research phase. This article is the first attempt to publish the results of the research period comprehensively. In addition, information concerning previous outbreaks of Z. diniana is reviewed on a worldwide base.

The life cycle of Empoasca vitis and its most important parasitoidAnagrus atomus in southern Switzerland can be divided into three phases. In phase I the adults of E. vitis move from overwintering sites, i.e. primarily conifers, over deciduous plants into the vineyards. The parasitoid A. atomus on the other hand, appears to overwinter in leafhopper eggs, mainly on roses and blackberries. It subsequently completes one generation in leafhopper eggs primarily on blackberries and hazelnuts, before it attacks E. vitis eggs in the vineyards. For phase II, a population model with time-varying age structures and stochastic properties was constructed for E. vitis. For this purpose a time-varying distributed delay model with attrition was constructed. Given the calibrated initial density of overwintering females, the model predicts an unacceptable number of E. vitis for the growing season. However, if egg parasitism of A. atomus and Stethynium triclavatum is introduced into the model as an external variable, E. vitis densities are predicted which are economically irrelevant. Inphase III E. vitis adults leave the vineyards for the overwintering sites. The model shows the importance of the parasitoid A. atomus during phase II. A. atomus should be favoured by surrounding the vineyards with host plants carrying leafhoppers' eggs. Consequently, habitat management measures for E. vitis control could be applied to the surroundings of the vineyards.

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There are 109 species of primary and secondary parasitoids associated with Zeiraphera diniana GO,NEE in the Central European Alps. Ninety species are primary, 6 facultative secondary and 13 obligate secondary parasitoids. At family level, the composition of the complex seems to be the same in every outbreak area of the host, with ichneumonids predominating. In the Upper Engadine Valley (Switzerland), where intensive studies were conducted over a period of 3 consecutive outbreak periods (28 years moths into the outbreak areas during the phase of host density increase is very important. The rate of increase of the natural enemies --which are univoltine --can never equal or exceed that of their host ; consequently, control by these natural enemies alone is not possible.

Females of Tetranychus urticae Koch were reared on leaf discs of apple trees and bush beans grown at different N concentrations (0.6–75 mM NO−3. N‐deficiency increased pre‐imaginal development time, pre‐ oviposition period, and decreased female weight, fecundity and oviposition rate of the mites. N, water, amino acid, and sugar content of the apple leaves were positively correlated with weight and egg production and negatively correlated with development time and pre‐oviposition period. The reverse correlations were found with total phenol content of the leaves and above mite parameters. A reduction of leaf N by 50% was related with a tenfold decline in fecundity on apple leaves. The stress mainly affected the oviposition rate and to a lesser extent the oviposition period. On apple leaves the net reproductive rate (av. no. ♀ offspring per ♀, Ro), mean length of a generation (T), and innate capacity for increase (rm) were Ro = 40.3, T = 17.1, and rm = 0.22 for the standard N concentration, and 4.7, 25.0, and 0.06 for strong N‐deficiency, respectively. Zusammenfassung Auswirkungen von Stickstoffmangel der Wirtspflanze auf die Gemeine Spinnmilbe Tetranychus urticae Die polyphage Gemeine Spinnmilbe ist ein wirt‐schaftlich bedeutender Schädling. Die Rolle einzelner Nährstoffe bei der Milbenvermehrung wurde schon von einigen Autoren mit unterschiedlichen Ergebnissen untersucht. Der Stickstoff scheint aber einer der Hauptfaktoren zu sein. Ueber Gewebekulturen klonierte Apfelbäume sowie aus Samen gezogene Buschbohnen wurden in Nährlösungen mit verschiedenen N‐Angeboten kultiviert. Aus solchen Pflanzen wurden Blattscheiben ausgestanzt und mit Weibchen von T. urticae besetzt. Gemessen wurden die tägliche Eiablage bis zum natürlichen Tod, die Entwicklungsdauer und das Weibchengewicht. Mit dem bei N‐Mangel abnehmenden N, Aminosäuren‐ und Zuckergehalt (v.a. Sorbit) im Blatt korrelierend nahmen auch Gewicht, Ablagerate und Fekundität ab, bzw. die Entwicklungsdauer und Praeovipositionsperiode zu. Die umgekehrte Wirkung auf diese Milbenparameter hatte der Gesamtphenolgehalt. Eine Reduktion des N‐Gehalts der Blätter auf die Hälfte (1.5% N) bewirkte auf Apfelblättern eine Abnahme von Fekundität und Ovipositionsrate um das zehnfache, bzw. eine Zunahme der Präovipositionsperiode um mehr als das dreifache. Der Stress beeinflusste v.a. die Maxima der Ablageverläufe und weniger die Lebensdauer. Der Wassergehalt war ebenfalls mit der Fekundität positiv korreliert. Auf Bohnenblättern legten die Tiere mehr Eier und erreichten ein höheres Gewicht als auf Apfel, dies bei gleichem N‐Gehalt beider Pflanzen. Es wirken somit noch andere Faktoren auf die Reproduktion der Spinnmilben. Die Populationsparameter wurden ebenfalls sehr stark beeinflusst. Auf Apfelblättern ergab sich bei der Kontrolle eine Nettoreproduktionsrate Ro von 40.3 und bei starker N‐Defizienz 4.7. Die mittlere Generationsdauer T sowie die spezifische natürliche Wachstumsrate rm betrugen für die Kontrolle 17.1 Tage, bzw. 0.22 und für starken N‐Mangel 25.0 Tage, bzw. 0....