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A model that implies highly inertial regulation of phytophage numbers by entomophages has been applied for the analysis of phytophage–entomophage interactions during different phases of the gradation cycle of phyllophagous insects. The data on population dynamics and the degree of parasite infestation in pupae of the pine looper Bupalus piniarius L. and fir looper Ectropis (=Boarmia) bistortata Gz are used to verify the model. The results of field studies apparently are in good agreement with the model of highly inertial regulation in the “phytophage–entomophage” system. The model that is proposed explains the decisive roles of different factors (entomophages, predators, or diseases) in the population dynamics of phytophages under different conditions.

Given the population dynamics model and the fairly long time series of data, the model parameters can be measured in different segments of this series to get respectively different estimates and a model with time-variable parameters. The variations in model parameters can be caused either by variations in the environmental conditions that affect the population size or by mere demographic stochasticity. A possible approach to the issue is considered based on the example of the data on fluctuations in the population density of pine moth (Bupalus piniarius L.) in Germany. To approximate the data, the well-known Moran-Ricker model is used, which has a rich variety of dynamic regimes. The parameter estimation was carried out by the least-squares method (by 12 out of 58 values). The analysis of trends in the two series of model coefficients, i.e., the maximal growth rate and the coefficient of self-regulation, reveals that the changes in both indicators are low for quite a long period of time (60 years), and the hypothesis of no directed trend in the environment changes turns out to be statistically plausible.

Zusammenfassung Auf der Grundlage der Gedanken von Nicholson (1954), Schwerdtfeger (1956) und Tinbergen & Klomp (1960) uber die Theorie der Dichte-Regulation wurde die Frage untersucht, ob die einzelnen Faktoren-Typen den Massenwechsel in so charakteristischer Weise beeinflussen, das man allein aus der Gestalt der Massenwechselkurve Ruckschlusse auf die steuernden Faktoren ziehen kann. In der Tat durften Regelmasigkeit, Amplitude und Wellenlange der Dichte-Schwankungen in diesem Sinne als diagnostisches Merkmal geeignet sein. Die Dauerlatenz des Kiefernspanners in Niedersachsen scheint — nach diesen Indizien zu schliesen — nicht durch die Ungunst des Klimas, sondern vielmehr durch sofort wirksame dichte-abhangige Faktoren bedingt zu sein. Summary Object of this paper is the question whether different types of factors influence the population dynamics in such a typical manner that their influences can be detected and separated in the fluctuation curves. Considerations which were based on the ideas of Nicholson (1954), Schwerdtfeger (1956) and Tinbergen & Klomp (1960) led to the conclusion that this seems to be true indeed, and that regularity, amplitude and “wave length” of the oscillations may be used in this diagnosis. On the base of such an evaluation of population data it can be concluded that, probably, the action of immediately reacting density-dependent factors is the cause of the permanent latency of the Pine Looper Bupalus piniarius in northwestern Germany.

Zusammenfassung 1. Bei normalen wie auch abweichenden Temperaturen besteht eine totale Koinzidenz zwischen der Eiablage der Tachine Carcelia obesa Zett. und den Zweit- und Drittlarven von Bupalus piniarius L., die fur die Parasitierung in Frage kommen (Abb. 1 und 2). 2. Koinzidenz zwischen Wirts- und Parasitengenerationen tritt in Erscheinung a) bei verschiedenen Wirtsarten (Abb. 3), b) bei univoltinen und bivoltinen Individuen desselben Wirtes (Abb. 3) und c) nach Parasitierung von verschiedenen Larvenstadien desselben Wirtes (Abb. 5). 3. Im letzteren Fall (2, c) konnen theoretisch die beiden Extreme in Abb. 4 auftreten. An Hand der Eiablage an den verschiedenen Larvenstadien von Thera obeliscata last sich nachweisen, das die Verpuppungszeit des Parasiten unabhangig vom Zeitpunkt der Eiablage ist (Abb. 5). 4. Bupalus-Falter sind protandrisch (Abb. 6). Carcelia-Fliegen, die aus mannlichen Bupalus-Puppen schlupfen, erscheinen fruher als die, welche aus weiblichen Bupalus-Puppen zum Vorschein kommen. Dies tritt am deutlichsten nach Trennung der Carcelia-Geschlechter in Erscheinung, da auch der Parasit protandrisch ist (Abb. 6). 5. Aus den angefuhrten Beobachtungen ist zu schliesen, das die Koinzidenz durch Aktivierung der Parasitenlarve wahrend einer bestimmten Phase der Metamorphose des Wirtes zustande kommt. Das erste Larvenstadium des Parasiten wandelt sich nicht zum zweiten Stadium urn, ehe die Entwicklung der Wirtspuppe anfangt (Abb. 1 und 3). Der physiologische Mechanismus der Aktivierung wurde nicht untersucht.

Summary During the autumn of 1964 of several nests of the wasp Paravespula vulgaris the composition of the prey was examined. To this purpose a new type of capture apparatus was made, which could be attached to the entrance of a ground nest in situ or to a hive containing a nest from elsewhere. Samples were taken simultaneously at two nests of about the same size, not more than 75 m apart. Both quality and quantity of the prey differed considerably. In one case the prey that was brought in on one afternoon, consisted for 80% of one species, Dilophus febilus. It was therefore, we investigated whether there could be specialisation on certain prey species. Artificial concentrations of larvae of Bupalus piniarius were planted on shoots of Pinus silvestris. Marked wasps were seen to return frequently to places where they had found a prey once, even several days after all Bupalus larvae had been taken. When the wasps had found a prey, they explored the direct surroundings much longer than when they had found nothing. Thus the differences in composition of the prey brought to the nest could be the consequence of place-specialisation of the wasps.

The succession of infestations by phytophageous pine caterpillars in the Palatinate since 1810 and the causes of their recent decrease. The succession of infestations by phytophageous pine caterpillars (Bupalus piniarius L., Panolis flammea Schiff., Lymantria monacha L., Dendrolimus pini L. and Diprion pini L.) in the Palatinate since 1810 was studied by means of an analysis of historical data in the forestry districts of the state. The outbreaks of these species were evaluated by the extent of economical damage. The most important infestations occurred during 1824–1840 and 1888–1905. Whereas Panolis flammea, Lymantria monacha and Dendrolimus pini predominated at the beginning of the period under study, Bupalus piniarius and Diprion pini occurred mostly at the end of the 19th century. In contrast to previous times the frequency and intensity of infestations have lately become increasingly scarce. It could be shown that this was not caused by an increasing use of insecticides nor were there any clues that the recent development of weather and climate were responsible for this retrogression. From a comparision of the history of infestations of the pine insects (studied) with that of a caterpillar noxious to hard wood trees (Dasychira pudibunda L.) it is concluded that this decrease is probably the result of the increasing cultivation of hard wood trees since 1925/30, particularly beech at the expense of pines. Zusammenfassung Die Zeitfolge des Auftretens nadelfressender Kiefernraupen (Bupalus piniarius L., Panolis flammea Schiff., Lymantria monacha L., Dendrolimus pini L. und Diprion pini L.) in der Pfalz seit 1810 wurde in einer historischen Studie anhand der Originalakten der Staatsforstamter ermittelt. Die ubervermehrungen dieser Arten wurden fur jedes Jahr nach dem Ausmas des wirtschaftlichen Schadens bewertet. Das starkste Schadlingsauftreten fand in den Jahren 1824–1840 und 1888–1905 statt. Wahrend Panolis flammea, Lymantria monacha und Dendrolimus pini zu Beginn des Untersuchungszeitraumes am starksten vorkamen, liegen die Maxima von Bupalus piniarius und Diprion pini in der Zeit um die Jahrhundertwende. ubervermehrungen der funf untersuchten Kiefernraupen sind zunehmend seltener geworden. Es konnte gezeigt werden, das die Ursachen hierfur nicht im vermehrten Einsatz von Insektiziden lag; auch ergaben zufallsstatistische Berechnungen keine Hinweise, das die klimatischen Verhaltnisse fur diesen Ruckgang verantwortlich waren. Dagegen konnte durch Vergleich der Befallsgeschichte nadelfressender Kiefernraupen mit der eines Laubholzschadlings (Dasychira pudibunda L.) wahrscheinlich gemacht werden, das der verstarkte Anbau von Laubholzern, insbesondere Buche, auf Kosten der Kiefer in neuerer Zeit an dieser Entwicklung masgeblichen Anteil hat.

For better determination of the pupae of Bupalus piniarius L. and Semiothisa liturata Cl. German pine forests are irregularly threatened by defoliation due to some noted insect pests, particularly the pine looper and the pine beauty. The densities of the larval stages of these insects are predicted annually by making rough estimates of the numbers of their pupae hibernating in the forest floor. A usable prognosis requires that the species involved are distinguished correctly. This presents difficulties in two geometrids, Bupalus piniarius L. and Semiothisa liturata Cl., the pupae of which may differ with respect to some morphological characteristics, such as weight, size, colour, gloss, mobility of the abdomen, and shape and structure of the cremaster. However, all of these characteristics overlap in some cases to a considerable extent. An absolutely reliable identification has to be based on the surface texture of the caudal parts of the fifth and sixth body segments, the specific differences of which are described and illustrated in the fig. 3 and 4. Zusammenfassung Es konnte deutlich gezeigt werden, das eine zuverlassige Determination der Puppen von B. piniarius und S. liturata auf Grund der Differenzen in der Form und Struktur des Cremasters, in Puppengewicht, Puppendurchmesser, Farbe, Glanz und Beweglichkeit der Puppen unmoglich ist. Eine Unterscheidung der Puppen der beiden Arten ist jedoch moglich an Hand der Unterschiede, die in der kutikularen Struktur der kaudalen Teile des funften und sechsten Abdominalsegmentes bestehen (Abb. 3 und 4).

Comparative studies on the occurrence of phytophageous pine caterpillars in South Germany since 1810. I. Areas of infestation in the Rheinpfalz. The occurrence of phytophageous pine caterpillars in two different regions of the Rheinpfalz since 1810 was examined by means of a thorough study of documents. The following species were taken into account: Bupalus piniarius L., Panolis flammea Schiff., Lymantria monacha L., Dendrolimus pint L. and Diprion pini L. In order to evaluate the frequency of outbreaks, an index rate was calculated for each year, using data on the excessive occurrence of the single species and the extent of economical damage. The results for the Rheinpfalz were compared with those of the forestry district Schwetzingen in the north of Baden. There were considerable differences between the individual species: In the Rheinpfalz, B. piniarius as well as L. monacha and P. flammea predominated. In the forestry district Schwetzingen however, these species were less frequent due to the more continentally influenced climate. Instead, Dendrolimus pini and Diprion pini, whose characteristics are the need of warmth and dryness, caused most of the outbreaks. In all three regions, a more frequent appearence of single species occurred during certain periods, the cause obviously being of a climatic nature. In spite of favourable conditions, the last period of observations (1931–1970) showed a distinct decline in the frequency of outbreaks. Zusammenfassung Mittels eingehender Aktenstudien wurde das Auftreten nadelfressender Kiefernraupen seit 1810 in zwei Schadgebieten der Rheinpfalz untersucht. Folgende Arten wurden berucksichtigt: Bupalus piniarius L., Panolis flammea Schiff., Lymantria monacha L., Dendrolimus pini L. und Diprion pini L. Zur Bewertung des Schadlingsauftretens wurde aus der Zahl der in Ubervermehrung aufgetretenen Arten und dem Ausmas des wirtschaftlichen Schadens fur jedes Jahr ein Indexwert berechnet. Zum Vergleich wurde den rheinpfalzischen Befunden die Schadlingsgeschichte des nordbadischen Forstamtes Schwetzingen gegenubergestellt. Die Summe der Indexwerte fur den gesamten Untersuchungszeitraum als Kennwert der Befallshaufigkeit betragt 248 fur Untersuchungsgebiet I, 67 fur Untersuchungsgebiet II und 183 fur das Forstamt Schwetzingen. Der Anteil der Arten am Gesamtbefall zeigt deutliche Unterschiede: In der Rheinpfalz uberwiegen Kiefernspanner sowie Nonne und Forleule, im klimatisch starker kontinental beeinflusten Forstamt Schwetzingen dagegen treten diese Arten zuruck gegenuber Kiefernspinner und Buschhornblattwespe, fur die besonders hohe Warme- und Trockenheitsanspruche charakteristisch sind. In bestimmten Zeitabschnitten zeigen einzelne Arten in allen Gebieten verstarktes Auftreten, es handelt sich hierbei offenbar um die Wirkung klimatischer Einflusse. Im letzten Beobachtungszeitraum 1931–1970 ist trotz gunstiger klimatischer Bedingungen in der Rheinpfalz und im Forstamt Schwetzingen ein deutlicher Ruckgang der Schadlingshaufigkeit zu verzeichnen. Ein Zusammenhang mit dem seit 1925 grosflachig durchgefuhrten Laubholzunterbau und der Neubegrundung von Mischbestanden wird vermutet; in einer Fortsetzung dieser Studie wird er naher untersucht.

Summary 1 During outbreaks of the pine looper, Bupalus piniarius, its host, Pinus sylvestris, is severely defoliated. The larvae of this geometrid normally feed on mature needles. However, because trees are totally defoliated during outbreaks, the next generation is forced to feed on current-year needles. 2 Bupalus piniarius larvae feeding on previously defoliated trees may show lower performance either because of induced resistance or because larvae have to feed on needles not normally fed upon (current instead of mature). 3 These hypotheses were tested in an experiment where larvae were reared on (i) shoots naturally defoliated the previous year, and thus, bearing only current-year needles, (ii) non-defoliated shoots where larvae had access only to current-year needles, and (iii) control shoots with access to both current and mature needles. 4 There was no support for the induction hypothesis. Survival was lower on naturally defoliated shoots than on control shoots (81.3 vs. 90.9%), but survival was lower also on non-defoliated shoots where larvae had access only to current-year needles (78.8%). Data on larval feeding distribution showed a strong preference for mature needles. 5 Needle nitrogen concentration of current-year needles was 38% higher on defoliated trees than on non-defoliated trees. 6 It is concluded that defoliation affected larval performance primarily through the removal of the preferred type of needles and not because of an induced resistance. Effects of increased concentrations of allelochemicals in defoliated shoots, if present, were probably cancelled out by increased nitrogen concentrations.

The effect of nitrogen-damaged Scots pine (Pinus sylvestris L.) on the developmental success of the pine looper (Bupalus piniarius L. [Lep., Geometridae]): Along an ammonia-input gradient, the predisposition of Scots pine (Pinus sylvestristo the attack of the pine looper) (Bupalus piniarius) was investigated. Pine needles taken from three sites (A, B, C) at different distances (A = 100m, B = 800m, C = 2700m) from an ammonia source (pig fattening station) were fed to 3rd-instar larvae of B. piniarius up to pupation. Biochemical analysis showed that the contents of total and soluble nitrogen, as well as of protein and soluble amino acids, increased in needles closer to the ammonia source (sites A, B). The concentrations of tannins, shikimate, quinate and soluble carbohydrates reached minimum levels near the ammonia source. Insect performance is not consistent with the prevalent ecophysiological hypothesis that high amounts of proteins and low levels of tannins in the food are beneficial for the development of needle-eating insects. Larvae kept on twigs from sites A or B (high ammonia load) showed an increased mortality, prolonged larval development, and a lower growth rate, but pupal weights of the survivors were not significantly different from the control. Zusammenfassung Unter Laborbedingungen wurde der Einflus unterschiedlich stickstoffbelasteter Wirtspflanzen (Pinus sylvestris) auf den Entwicklungserfolg des Kiefernspanners (Bupalus piniarius) untersucht. Die Kiefernnadeln, die in drei unterschiedlichen Entfernungen zu einem Ammoniakemittenten (Schweinemastanlage) entnommen und den Raupen als Nahrung angeboten wurden, wiesen neben einer veranderten Nahrelementkonstellation verminderte Gehalte an loslichen Kohlenhydraten und phenolischen Inhaltsstoffen sowie erhohte Konzentrationen an freien und proteingebundenen Aminosauren auf. Die gangigen okopysiologischen Hypothesen, wonach hohe Protein- und niedrige Tanningehalte die Entwicklung phytophager Insekten begunstigen, werden nicht bestatigt. Die Larven des Kiefernspanners, die mit deutlich belasteten Nadeln ernahrt wurden, entwickelten sich bei signifikant erhohter Mortalitatsrate langsamer und mit geringerem Massezuwachs pro Zeit. Die Puppengewichte der uberlebenden unterschieden sich jedoch nicht signifikant.

The influence of SO2-stressed host plants on the development of Bupalus piniarius L. (Lep., Geometridae) and Dendrolimus pini L. (Lep., Lasiocampidae) The influence of a SO2-conditioned food quality alteration on the successful development of the pine needle pests pine looper (Bupalus piniarius L.) and pine spinner (Dendrolimus pini L.) was investigated under labor conditions from 1989 to 1991. After a 400-hr sulphur dioxid application (960 μg/m3) the needles of four-year-old pines (Pinus sylvestris L.) show besides an increased sulphur and decreased calcium content significant higher concentrations of free aminoacids especially prolin. The concentrations of glucose and fructose are extremely reduced. Likewise the shape of procyanidins in the needles is diminished by about 24 %. The two species of lepidopters show a different sensitivity to the contaminated food. Larvae of B. piniarius, who were fed with SO2-damaged needles, show a delay of larval development together with a diminished biomass rate increase and an increase of mortality. The deterioration of the development success of B. piniarius is attributed above all to the lower carbohydrate concentrations in the needles as well as to the nutrient imbalances. In contrast to this result the rate of biomass increase and the mortality of D. pini is insignificantly reduced. The pine spinner can tolerate the low sugar content of food. That's why the comparatively higher success of development is connected especially with a stress-induced reduction of phenolic needle components. Zusammenfassung Der Einflus einer schwefeldioxidbedingten Anderung der Nahrungsqualitat auf den Entwicklungserfolg der Kiefernnadelschadlinge Bupalus piniarius und Dendrolimus pini wurde in den Jahren 1989 bis 1991 unter Laborbedingungen untersucht. Nach einer 400stundigen Begasung mit Schwefeldioxid (960 μg/m3) wiesen die Nadeln der vierjahrigen Kiefern (Pinus sylvestris) neben erhohten Schwefel- und reduzierten Kalziumgehalten signifikant hohere Konzentrationen an freien Aminosauren, insbesondere Prolin, auf. Die Glukoseund Fruktosekonzentrationen waren drastisch vermindert. Ebenso war der Anteil der Procyanidine in den Nadeln um durchschnittlich 24 % reduziert. Die beiden Lepidopterenarten liesen eine unterschiedliche Sensitivitat gegenuber der schadstoffbe-einflusten Nahrung erkennen. Larven von B. piniarius, die mit SO2-geschadigten Nadeln ernahrt wurden, zeigten eine Verzogerung in der Larvalentwicklung, die von verminderten Biomassezuwachsraten und einer Zunahme der Mortalitat begleitet wurde. Die Verschlechterung des Entwicklungserfolges des Kiefernspanners wird vor allem auf die geringeren Kohlenhydratkonzentrationen in den Nadeln sowie auf Nahrstoffimbalancen zuruckgefuhrt. Im Gegensatz dazu war die Biomassezuwachsrate und auch die Mortalitat von D. pini geringfugig vermindert. Da der Kiefernspinner den niedrigeren Zuckergehalt der Nahrung besser zu tolerieren vermag, steht der vergleichsweise gunstigere Entwicklungserfolg insbesondere mit einer stresbedingten Verminderung phenolischer Nadel-inhaltsstoffe im Zusammenhang.

Zusammenfassung Bei ihrem Fras an Kiefernnadeln vermeiden die Raupen von Bupalus piniarius Kallusgewebe, wie es durch fruheren Fras oder durch Eiablagen von Diprion pini hervorgerufen wird. Ein ahnliches Verhalten wurde bei den Larven von Neodiprion pratti banksianae beobachtet (Ghent 1960). Resume Les chenilles de Bupalus piniarius L. (Lep.) evitent en mangeant le tissu d'endroits ayant ete blesses par un devorement precedent ou par l'introduction d'oeufs. Le meme comportement a ete note chez les larves de Neodiprion (Ghent 1960).

Three habitual parasites of the pine looper are generally not eliminated by the haemocytic defence reaction of their usual host, because the eggs are laid or the larvae settle behind the epithelium of the gut. This acts as a barrier against the passage of blood cells. This conclusion is supported by the observation that larvae of all three species are encapsulated during abnormally long stays in the host's body cavity. In two species this results from the parasitoid's failure to oviposit in the usual way, being either egg deposition at a less favourable site on the host's integument, or in a less suitable larval instar of the host. In the third species encapsulation results from the failure of the parasitoid's larva to enter the mid-gut due to some unknown factor(s) related to superparasitism.

A simulation model is presented which explains the occurrence of protandry (i.e. males emerge on average before females) in the pine looper Bupalus piniarius. The model calculates the fitness of the moths in relation to their date of emergence during the period of emergence. It is investigated how this fitness is affected by: a) the difference between the mean time of emergence of males and females, b) the age of the moths at copulation, c) the mortality rate and longevity of the moths, d) the flight activity of the males, and e) the density of the moths. The input of the model is based on field data and experimental results. The model shows that a) the difference and the mean time of emergence between males and females is maintained by selection of males, such that they on average emerge 2 days before the females, b) 95% of the females mate on the day of emergence, c) the flight activity of the males together with moth density has a significant effect on the difference in time of emergence between the sexes, d) age-dependent copulation success, mortality rate and longevity do not affect the difference in time of emergence between the sexes. From the results it is concluded that mass trapping of males with pheromone traps does not decrease the percentage of females that mate. It is suggested that competitive mate searching has no effect on the occurrence of protandry.

Experiments have been performed showing that the ichneumon wasp Poecilostictus cothurnatus, a parasitoid of the advanced larvae of the pine looper, Bupalus piniarius, is able to locate the host by following the trail left on the needles by the crawling caterpillars. Artificial trails can be prepared by moving the skin of a caterpillar over a sheet of paper, showing that one or more chemicals present in the cuticular layer function as signals (kairomone) for the wasp. When no caterpillar is found when she arrives at the end of the trail, the wasp shows a characteristic behaviour known as area-restricted searching. This type of behaviour has been found in several other species of parasitoids, but in all these cases it was performed immediately after having parasitized a host. The observations suggest that in a pine forest host finding is accomplished by alternating short flights with landings on twigs. After a landing there is a short search for the presence of a trail, and, coming across one, the wasp will try to find the host. If this is found and parasitized she flies away, and will probably soon make a new landing elsewhere.

The respiration of diapausing prepupal stages of the sawfly Cephalcia abietis L. and pupae of Dolerus nigratus F. has been studied by means of a volumetric microrespirometer with a special adaptation for concurrent measuring of respiratory quotients. Contrary to findings on most diapausing pupae, a continuous respiration without pronounced CO 2 bursts has been found. For comparison, the respiration of lepidopterous pupae of Bupalus piniarius L. and Hyphantria cunea Drury of the same body size as the sawflies was investigated. In these a distinctly discontinuous respiration has been found, the amount of CO 2 released in the inter-burst period being, however, greater than in large lepidopterous pupae.

The coloration of forest insects changes as their population density increases or decreases. Using the geostatistical method allowed us to determine the population dynamics’ phase of the pine looper from images of insects’ wings. The color and pattern of the insects’ wings can be successfully used as diagnostic features in determining the phase of the population dynamics.

DURING investigations on the physiological relations between the pine looper, Bupalus piniarius L. (Lep. Geometridae), and its parasite Carcelia obesa Zett. (Dipt. Tachinidae), some interesting facts were discovered, which so far as we know have not hitherto been described.