Interspecific competition between the braconid endoparasitoids Glyptapanteles porthetriae and Glyptapanteles liparidis in Lymantria dispar larvae

The effect of interspecific competition between the solitary endoparasitoid Glyptapanteles porthetriae Muesebeck (Hymenoptera: Braconidae) and the gregarious Glyptapanteles liparidis Bouché (Hymenoptera: Braconidae), was investigated in larvae of Lymantria dispar L. (Lepidoptera: Lymantriidae). Host larvae were parasitized by both wasp species simultaneously in premolt to the 2^nd or the 3^rd host instar or in an additional approach with a 4‐day delay in parasitization by the second wasp species. Host acceptance experiments revealed that both wasp species do not discriminate between unparasitized host larvae and larvae parasitized previously by the same or the other species. In more than 90% female wasps parasitized the larva they encountered first. During the period of endoparasitic development, larvae of the competing parasitoid species never attacked the egg stage of the other species. When host larvae were parasitized simultaneously by both wasp species, the rate of successful development of both species depended on the age of the host larva at the time of its parasitization; G. liparidis emerged successfully from 44% of host larvae parasitized during the premolt to 2^nd instar, G. porthetriae from 28%, and in 20% of the hosts both parasitoid species were able to develop in one gypsy moth larva. However, when host larvae were parasitized simultaneously during premolt to the 3^rd instar, G. liparidis was successful in 90% of the hosts, compared to 8% from which only G. porthetriae emerged. In the experiments with delayed oviposition, generally the species that oviposited first succeeded in completing its larval development. Larvae of the species ovipositing with four days delay were frequently attacked and killed by larvae of the first parasitizing species or suffered reduced growth. As the secondary parasitoid species, G. porthetriae‐larvae were never able to complete their development, whereas G. liparidis developed successfully in at least 12,5% of the multiparasitized host larvae. Thus, multiparasitism of gypsy moth larvae by both Glyptapanteles species corresponds to the contest type; however, G. porthetriae is only able to develop successfully as the primary parasitoid of young host larvae.     

Temperature‐dependent development of the European larch bark beetle,Ips cembrae

The temperature‐dependent development of the European larch bark beetle, Ips cembrae, was studied under long‐day conditions L:D 16:8 at three temperature regimes, 15°C, 20°C and 25°C, using the sandwich plate method. By observing the individual developmental progress, we calculated the developmental times and lower developmental thresholds of one entire generation and various ontogenetic stages. The mean developmental time of one generation was about 120, 64 and 37 days at 15°C, 20°C and 25°C, respectively. The egg stage comprised about 9% of the total development or about 16% of the pre‐imaginal development. The larval stages took about 39% of the entire and about 66% of the pre‐imaginal development. The pupal stage needed about 11% of the total or about 18% of the pre‐imaginal development. The lower developmental threshold for one generation was 11.2°C. The egg stage had the highest lower developmental threshold of 12.0°C, the pupa the lowest of 9.8°C and the total larval stages showed a value of 11.2°C. The thermal requirements for I. cembrae have never been studied in detail before. The results will be a valuable contribution for monitoring and risk assessment models to estimate the beetle's phenology and its potential impacts on forest ecosystems under changing climate conditions.     

Calcite and aragonite distributions in the skeletons of bimineralic bryozoans as revealed by Raman spectroscopy

Abstract. Bryozoans are among a diverse range of invertebrates capable of secreting calcium carbonate skeletons. Relatively little is known about biomineralization in bryozoans, despite the importance of understanding biomineralization processes for nanotechnology and the threats imposed by ocean acidification on organisms having calcareous skeletons. Ten species of cheilostome bryozoans that are reported to have bimineralic skeletons of calcite and aragonite are studied here using Raman spectroscopy. This technique allowed identification of the two mineral phases at submicron spatial resolution, allowing the distributions of calcite and aragonite within bryozoan skeletons to be determined with unprecedented precision. Confirming previous findings based on the use of chemical stains, most of the bimineralic species analyzed exhibited a calcitic skeletal framework, composed of basal, vertical, and inner frontal walls, having aragonite deposited subsequently onto the outer surfaces of the frontal walls. In one species ( Odontionella cyclops ), aragonite formed the superstructure above the autozooids, and in two others, traces of aragonite were detected on the undersides of the frontal shields. Using Raman spectroscopy, it was possible for the first time to determine the mineralogy of small-scale structures, including orificial rims, condyles and hinge teeth, avicularian pivotal bars and rostra, and ascopore rims and sieve plates. Even when surrounded by aragonitic frontal shields, these structures were found typically to be calcitic, the two exceptions being the aragonitic avicularia of Stylopoma inchoans and O. cyclops . Unexpectedly, the first-formed part of the basal wall at the distalmost growing edge of Pentapora foliacea was found to consist mainly of aragonite. This may point to a precursory phase of biomineralization comparable with the unusual mineralogies identified previously in the earliest-formed skeletons of members of some other invertebrate phyla.     

Exceptional seed longevity and robust growth: ancient Sacred Lotus from China

A 1,288 ± 271-yr-old (1,350 ± 220 yr BP, radiocarbon age) seed of Sacred Lotus (Nelumbo nucifera Gaertn.) from an ancient lake bed at Pulantien, Liaoning Province, China, has been germinated and subsequently radiocarbon dated. This is the oldest demonstrably viable and directly dated seed ever reported, the preserved relict of one of the early crops of lotus cultivated by Buddhists at Pulantien after introduction of the religion into the region prior to 372 A.D. A small portion of the dry pericarp of a second lotus fruit from the same locale has been dated as being 332 ± 135-yr-old (270 ± 60 yr BP, radiocarbon age) by accelerator mass spectroscopy at the Lawrence Livermore National Laboratory. This polycentenarian seed not only germinated but is still growing (since March, 1994). Of six old lotus fruits tested, two-thirds germinated, almost all in fewer than 4 d, as rapidly as fruits harvested from the progeny of Pulantien Sacred Lotus plants (under cultivation by the National Park Service in Washington, DC), and more rapidly than fresh fruits of Yellow Lotus [N. lutea (Willd.) Pers.]. Growth of the old lotus is robust: rhizome formation and leaf emergence at rhizome nodes are more rapid than those of the Pulantien progeny, although the leaf width is smaller. Activity of the protein-repair enzyme L-isoaspartyl methyltransferase in the old lotus seed is persistent during germination and is as robust as that in the progeny, and the degree of aspartyl racemization in proteins of the two groups of plants is minimal and essentially identical. The six dated ancient Sacred Lotus fruits range in age from 95 to 1,288 yr (with a mean age of 595 ± 380 yr), evidently reflecting their production, deposition, and preservation at varying times during the intervening millennium.     

Speicherung und mobilisierung von Kohlenhydraten und Lipiden in der Blattwespe Gilpinia hercyniae

Von Larven (drei Populationen, L₃, L₄-, L₄, L₅- und alte L₅-Larven), adulten Weibchen vor (I_v) und nach (I_n) Eiablage, Kokons (K) und Exuvien (E) wurden die Konzentrationen von löslichen Kohlenhydraten, Alanin, Prolin, Glykogen und Lipiden sowie die Frisch- und Trockengewichte bestimmt. Aus den Ergebnissen werden Rückschlüsse auf den Energiestoffwechsel der Entwicklungsstadien Embryo, Larve und Imago gezogen.

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Summary The concentrations of soluble carbohydrates (Fig. 2), alanine and proline (Fig. 3), glycogen and lipids (Fig. 4) and the weights (Fig. 1, Tab. I) of larvae (three populations, L₃, L₄-, L₄, L₅- and old L₅-instar larvae), adult females before (I_v) and after (I_n) oviposition, cocoons (K) and exuviae (E) (Tab. II) were determined. Embryonic, larval and adult stages of development have characteristic types of energy metabolism. The lipid catabolism of the embryonic stage is substituted during larval development by anabolic pathways based on resorbed sugars absorbed from spruce needles. During the first larval stages these soluble carbohydrates are directed to a glycogen pool in relatively large amounts. This pool is only slightly enlarged whereas lipids are synthesized in relatively large amounts between the 14th and 28th day after oviposition. Metamophosis is correlated with a decrease of glycogen. Lipids are used as an energy source by imagines and in eggs. Energy is distributed in the body by movement of trehalose in the larval stage and by a proline-alanine-shuttle in the adult stage.

     

The effect of host age ofLymantria dispar larvae [Lep.: Lymantriidae] on the development ofGlyptapanteles liparidis [Hym.: Braconidae]

The endoparasitic development ofG. liparidis was examined in 3 different host stages of gypsy moth larvae. Hatching ofG. liparidis-larvae occurred 3 to 5 days after oviposition in hosts parasitized during their premoulting period, and after 5 to 7 days in those parasitized in the 3^rd midinstar state. The parasites generally moulted to the 2^nd larval instar between the 11^th and 13^th day in the first group, and between the 13^th and 15^th day in the latter, when they had reached a volume of 0.04–0.05 mm³. The positive correlation between host ecdysis and the ecdysis of 1^st stadium larvae to L₂ suggested that host moulting influenced the development of the parasitoid larvae. Emergence from the host larvae occurred at 20°C after 27 days on average, and coincided with the parasites moulting to the 3^rd instar. Five to 7 days after spinning their cocoons near the developmentally arrested host larva, the male, and 1 to 2 days later the female wasps eclosed. Due to the variation in the number of parasites per host, no difference was observed between the hosts parasitized at various stages; however, a tendency for later parasitized hosts to contain more parasite larvae was evident. The nutritional conditions of the moth parental generation influenced both host and parasite development. On the other hand no influence of host age was observed on emergence dates of larvae and wasps.      

Endokrinologische Untersuchungen an dem Wirt-Parasit-System: Pieris brassicae-Apanteles glomeratus

Die von Apanteles glomeratus L. parasitierten Raupen von Pieris brassicae zeigen in Abhängigkeit des Parasitierungstermins eine deutliche Veränderung des Juvenilhormon (JH)-Titer-Verlaufs während des letzten Larvenstadiums. Dabei tritt ein steiler Anstieg des JH-Gehaltes der Wirtshämolymphe im Zusammenhang mit der Häutung der Parasitenlarven vom 1. zum 2. Larvenstadium auf. Aufgrund von Ligations-experimenten konnte nachgewiesen werden, daß die Parasitenlarven selbst für den erhöhten JH-Titer ihrer Wirtsraupen verantwortlich sind, indem sie während ihrer Häutungsphase anscheinend JH in die Wirtshämolymphe abgeben.Eine durch die Parasitierung gesteigerte Syntheseaktivität läßt sich aus den Befunden histologischer Schnitte der Corpora allata frühparasitierter Raupen nicht feststellen. Dagegen weisen die Prothoraxdrüsen parasitierter Raupen zur Mitte des letzten Stadiums eine deutlich kleinere Querschnittsfläche auf als unparasitierte Tiere. Eine dadurch im Zusammenhang mit dem erhöhten JH-Titer bestehende Beziehung zur Häutungsunfähigkeit parasitierter Pieris-Raupen am Ende des letzten Larvenstadiums wird diskutiert.

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Summary The effects of parasitism by Apanteles glomeratus on the hemolymph juvenile hormone (JH) titers of Pieris brassicae during the last larval instar were determined using the Galleria bioassay.Depending on the time of parasitization, a significant increase of the JH titer could be observed when moulting of the parasites from the first to the second larval instar occurred.As neck-ligatured, parasitized Pieris larvae showed a similar increase of the JH titer at this time, it is concluded that the parasite larvae themselves are responsible for the elevation of the titer by delivering JH during their ecdysis into the host's hemolymph.This is supported by histological results from the corpora allata of parasitized and unparasitized caterpillars at the first and third day of the last larval instar, indicating no differences in its secretory activity. The prothoracid glands of parasitized host larvae, however, appear significantly smaller than those of comparable unparasitized ones in the middle of the last instar. A reduced secretory activity at this time, which is assumed from their decreased size, combined with an elevated JH titer may explain why parasitized larvae fail to moult at the end of their larval development.