Flight propensity and diapause incidence in five populations of the bark beetle Ips typographus in Scandinavia

Emergence from brood logs, take-off activity and the duration of tethered flight was recorded in the first laboratory generation of the bark beetle Ips typographus L. (Coleoptera: Scolytidae) from five locations (ca 300 km apart) in Sweden and Denmark. Beetles of northerly origin emerged later from brood logs. This pattern was associated with an increasing proportion on non-fliers towards the north. After overwintering, both the rate of development of flight activity and the proportion of non-fliers were the same among populations. Flight duration of fliers was similar among populations and appeared unaffected by outbreak conditions.     

Behavior of male and female spruce bark beetles,Ips typographus,on the bark of host trees during mass attack

The behavior of 118 spruce bark beetles, Ips typographus,was observed on trees under colonization. Most individuals were followed from when they landed until they entered or left the tree. Both males and females spent most time inspecting crevices and searching for a place to start boring or for a hole to enter. These behaviors accounted for 87 and 70% of all behavioral acts recorded for males and females, respectively. Females entered galleries with males only after a period of pushing at the gallery entrance. Males spent on average 3 min and females 4 min on the bark before entering or leaving the tree. Thirty-three percent of the beetles eventually entered the tree, 31% flew away, 35% dropped from the host, and one beetle was eaten by a predator. The results are discussed in relation to the question of mate choice in bark beetles and to studies on attack dynamics of spruce bark beetle populations.     

Neural and hormonal control of pheromone biosynthesis in the bark beetle, Ips paraconfusus

ABSTRACT. Synthetic juvenile hormone (JH) induced the synthesis of the three pheromones, ipsenol, ipsdienol and 2-phenylethanol, by Ips paraconfusus males and enhanced the conversion of (–)-α-pinene to a fourth pheromome, cis -verbenol. Synthetic JH also mimicked the stimulatory effect of feeding on the metabolism of myrcene to ipsdienol and ipsenol. Implantations of corpora allata and/or corpora cardiaca from fed or newly-emerged males into intact or decapitated males were performed. The results indicated that JH acts indirectly by stimulating the release of brain hormone, and the release of JH in unfed males is prevented by neural inhibition which is removed by the stretching of the gut during normal feeding. Failure of any hormonal treatment or gland implantation to stimulate cis -verbenol synthesis in the absence of exogenous α-pinene is presented as evidence that no endogenous precursor for this pheromone is present. An apparent seasonal variation in the ability of males to produce ipsdienol and ipsenol when treated with JH was observed.     

Constant association of ophiostomatoid fungi with the bark beetle <Emphasis Type="Italic">Ips subelongatus</Emphasis> invading Japanese larch logs

Ceratocystiopsis, Ceratocystis, Grosmannia, and Ophiostoma species were isolated from Ips subelongatus and beetle-infested Japanese larch logs collected at several areas in central and northern Honshu Island, Japan, to determine constant associates of I. subelongatus. Ceratocystiopsis minuta, two species of Ceratocystis, three species of Grosmannia, and four species of Ophiostoma were isolated. Of the fungi isolated in the present study, G. laricis, O. brunneociliatum, and O. piceae were constant associates of the beetles. Ceratocystis fujiensis, Ceratocystiopsis minuta, and Ophiostoma sp. F were occasionally isolated with high frequencies of occurrence but were not consistent associates. Ceratocystis fujiensis was most often isolated as the leading fungal invasion in the sapwood of Japanese larch logs invaded by I. subelongatus, confirming that the fungus acts as a primary invader of sapwood in beetle-attacked logs. Contribution No. 221, Laboratory of Plant Parasitic Mycology, Graduate School of Life and Environmental Sciences, University of Tsukuba     

Plasticity in life-history traits of the bark beetle Ips calligraphus as influenced by phloem thickness

Summary Reproduction and development of Ips calligraphus (Germar) (Coleoptera: Scolytidae) occur primarily in the phloem (inner bark) tissue of its pine hosts. In slash pine (Pinus elliottii Engelm. var. elliottii), phloem thickness can vary widely from tree to tree. We compared adult residence time and fecundity and progeny development time, body size, and sex ratio of this beetle when reared in slash pine bolts and bark slabs with phloem thicker or thinner than average adult body width. Most studies were conducted at 20°, 25°, and 30° C. Residence time of parent males and females decreased with increasing temperature but it was not affected by phloem thickness. Residence time of parent males was about 2 days shorter than that of parent females at each temperature. Reproductive fitness was greater in thick phloem at all temperatures as measured by faster larval development, earlier emergence of progeny (F ₁ ) adults, and emergence of more progeny adults per parent female. Progeny survival was similar between phloem those from thick phloem, and their sex ratio was female biased (1:2 vs 1:1, male:female). When allowed to inhabit thick phloem, the progeny (F ₂) of adults from thin phloem were just as large and of similar sex ratio (1:1) as were progeny of F ₁ adults from thick phloem. The high degree of plasticity in the life-history traits of this beetle may enable it to successfully colonize pines that vary widely in phloem thickness.     

Characterization of microsatellite loci in the spruce bark beetle Ips typographus (Coleoptera: Scolytinae)

Ips typographus is an economically important pest of Norway spruce stands. We developed five polymorphic microsatellite markers using a biotin enrichment protocol. The number of alleles ranged from three to 11 per locus and no strong evidence for null alleles was found. Heterozygosity ranged from 0.3 to 0.97. These markers could be useful tools to study the population structure and genetic consequences of I. typographus population outbreaks.     

Programmed cell death in flight muscle histolysis of the house cricket

We have characterized the process of flight muscle histolysis in the female house cricket, Acheta domesticus, through analysis of alterations of tissue wet weight, total protein content, and percent shortening of the dorsal longitudinal flight muscles (DLMs). Our objectives were to (1) define the normal course of histolysis in the cricket, (2) analyze the effects of juvenile hormone (JH) removal and replacement, (3) determine the effects of cycloheximide treatment, and (4) examine patterns of protein expression during histolysis. Our results suggest that flight muscle histolysis in the house cricket is an example of an active, developmentally regulated cell death program induced by an endocrine signal. Initial declines of total protein in DLMs indicated the JH signal that induced histolysis occurred by Day 2 and that histolysis was essentially complete by Day 3. Significant reductions in tissue weight and percent muscle shortening were observed in DLMs from Day 3 crickets. Cervical ligation of Day 1 crickets prevented histolysis but this inhibition could be reversed by continual topical treatments with methoprene (an active JH analog) although ligation of Day 2 crickets did not prevent histolysis. A requirement for active protein expression was demonstrated by analysis of synthesis block by cycloheximide and short-term incorporation of (35)S-methionine. Treatment with cycloheximide prevented histolysis. Autofluorographic imaging of DLM proteins separated by electrophoresis revealed apparent coordinated regulation of protein expression.     

A correlation between juvenile hormone deficiency and vitellogenic oocyte degeneration inDrosophila melanogaster

Summary It is known from previous work that juvenile hormone (JH) is required to initiate vitellogenin uptake into maturing oocytes ofDrosophila melanogaster, but additional requirements for this hormone during oocyte maturation have not been fully understood. To determine if early vitellogenic oocytes (stages 8 and 9) require JH for continued development, these oocytes were transplanted toDrosophila female and male hosts which were rendered deficient in JH by three methods. Implanted stage 9 and usually stage 8 oocytes were found to degenerate in JH-deficient hosts unless ZR-515, a JH analogue, was applied to the host shortly after implantation.These results were confirmed during in situ ovary development. JH deficiency was produced in gravid females, and ovaries examined at subsequent time intervals were found to be deficient in stage 8–10 oocytes as early as 6 h after treatment. Degenerating oocytes corresponding to these stages were commonly found. ZR-515 prevented oocyte degeneration during at least the first 8 h and continued to support stage 8–10 oocyte development 24 h after application to these females. The results suggest that JH is required not only for initiation but also for continuation of vitellogenin uptake and oocyte development.     

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.     

Age-specific flight behavior in relation to body weight and lipid content of Ips calligraphus reared in slash pine bolts with thick or thin inner bark (phloem)

Rearing larvae of Ips calligraphus (Germar) (Coleoptera: Scolytidae) in bolts of typical slash pine, Pinus elliottii Engelm. var. elliottii, with thin (TN; 0.5–1.5 mm) phloem (inner bark) relative to adult beetle body width significantly reduced body weight and lipid content of emerging adults compared with thick (TK; 2.5–3.5 mm) phloem-reared adults. Unmated (pre-nuptial) TK beetles averaged 2-fold longer daily and life-time flight duration than TN beetles. Daily flights were highly variable, averaging <20 min (longest daily flight=173 min). TK and TN beetles initiated flight, and the greatest number flew, on the first or second day after emergence form their rearing bolt; % of beetles flying and survival gradually declined to zero by day 9. Males (both TK and TN) averaged 2.5 days of flight, ca. 1 day longer than females. Fliers lived ca. 2-fold longer than non-fliers. Among TK and TN fliers, significant but weak positive correlations occurred between body weight and lifetime flight duration. Poor correlation between lifetime flight duration and longevity suggests little physiological cost to flight, but effects on fecundity were not assessed. Flight by mated, egg-laying (post-nuptial) beetles was substantially delayed (peaking on day 6), suggesting degeneration and subsequent regeneration of flight muscles.

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Résumé Le comportement de vol d'Ips calligraphus GERMAR (Scolytidae) a été examiné au laboratoire par une technique de vol captif. La génération parentale avait été artificiellement introduite, suivant la taille des adultes (1,6 à 2,1 mm) dans des morceaux de Pinus elliottii Engelm. variété elliottii au phloeme épais (TK=2,5 à 3,5 mm) ou fin (TN=0,5 à 1,5 mm) les larves se sont développées dans ces morceaux de pin. Le poids et la teneur en lipide des adultes obtenus à partir de TN étaient significativement inférieure à ceux de TK. Le poids des mâles les plus gros a été plus réduit que celui des femelles; les mâles les plus petits semblaient être moins efficaces dans l'initiation des attaques sur les arbres, et les femelles les plus petites ont eu une fécondité réduite.Les durées de vol quotidiennes pendant la vie des mâles TK vierges étaient en moyenne deux fois plus longues que celles des mâles TN. Les durées de vol quotidiennes étaient très variables: en moyenne moins de 20 minutes, mais la plus longue a été de 173 mn. En moyennes les adultes TN et TK ont commencé à voler, et volaient en plus grand nombre, le premier et le second jour après l'émergence. Ensuite la fréquence d'adultes volants et le pourcentage de surviveants, ont graduellement diminué jusqu'à tomber à zéro le neuvième jour. Les mâles TN et TK avaient des vols quotidiens plus longs et volaient environ 1 jour de plus que les femelles. L'activité de vol accrue des mâles reflète leur besoin de trouver dans la nature des arbres convenables; les vols des femelles peuvent généralement être plus brefs, étant plus directement orientés comme une réponse aux phéromones mâles.Les voiliers ont vécu environ 2 fois plus longtemps que les non-voiliers. Parmi les voiliers TK et TN il y avait une corrélation positive étroite entre le poids du corps et la durée totale des vols. Il n'y en a qu'une faible corrélation entre cette durée totale des vols et la longévité, suggérant un faible coût physiologique du vol. L'influence de cette durée des vols et du prélèvement consécutif de lipides sur la fécondité n'a pas été examinée. L'initiation au vol chez les individus fécondés a été sérieusement retardée (maximum le sixième jour) par rapport aux vierges, ce qui suggère un dégénérescence des muscles du vol associée à la reproduction, suivie d'une régénération importante, comme cela a été signalé chez d'autres Scolytes.Ces résultats contribuent à notre compréhension des facteurs conditionnant le comportement de vol et d'autres aspects fondamentaux de la biologie des insectes des pins. Une telle connaissance est nécessaire au développement d'une politique efficace de protection.

     

Ultrastructure of the neurosecretory system of the Colorado potato beetle,Leptinotarsa decemlineata (Say)

Summary The ultrastructure of seven types of neurosecretory cells (NSC) in the medial and lateral groups of the protocerebrum is described. The differences among cell types established earlier by light microscopy parallel differences in size and appearance of the neurosecretory particles observed in electron micrographs. No relationship was found between the affinity for Gomori's paraldehyde fuchsin stain and the nature of the particles.The secretions of the A-, A₁-, and C-types of NSC of the medial group are characterized by electron-dense neurosecretory granules of 1250 Å dia., medium-dense granules of 2100 Å, and electron-lucent vesicles of 1700 Å, respectively. The L-type NSCof the lateral group contain smaller (1300 Å) or larger (1700 Å) neurosecretory granules. The medial B- and E-types of NSC and the lateral L_B-type contain granulated vesicles (1200 Å) of the same appearance. These cell types differ in other respects and most likely have separate functions.The author wishes to thank the Laboratory of Virology of the Agricultural University for the use of the electron microscope, Mr. J. Groenewegen and Miss J. van Rinsum for technical assistance, and Professor J. Lattin for correcting the English text. Part of the work has been done while the author was in the service of the Netherlands Organization for the Advancement of Pure Research (ZWO, grant 942-48), and the National Council for Agricultural Research (TNO).     

Aggregation response of European engraver beetles of the genus Ips mediated by terpenoid pheromones

Upon exposure to vapours of the host tree's monoterpene (–)--pinene, Ips acuminatus produces the terpene alcohol cis-verbenol which, besides ipsdienol and ipsenol, is a component of its aggregation pheromone. I. cembrae transforms the same monoterpene predominantly into myrtenol and trans-verbenol but little into cis-verbenol, which interrupts pheromone response under field conditions.On the other hand, I. cembrae releases, upon feeding in the bark, the terpene alcohol amitinol in major amounts. Amitinol significantly enhances field response to the aggregation pheromone that also includes ipsdienol, ipsenol, and 3-methyl-3-buten-1-ol. However, amitinol reduces pheromone response in I. acuminatus and I. erosus. Also, males of I. sexdentatus release amitinol which appears to increase response to its attractive principle pheromone component, racemic ipsdienol. There is some evidence that present knowledge of the chemical communication systems among European Ips spp. still lacks satisfactory explanation of the naturally occuring aggregation en masse, perhaps with the exception of I. erosus and I. typographus.     

Effect of juvenile hormone on acid phosphatases in the degenerating flight muscles of the Douglas-fir beetle, Dendroctonus pseudotsugae

Changes in acid phosphatase activity were used to estimate flight muscle degeneration in Dendroctonus pseudotsugae. Acid phosphatase positive sites increased numerically as well as in size in flight muscles of beetles attacking the host logs and those maintained on host bark chips. Topical treatment of beetles with a juvenile hormone analogue further increased the phosphatase activity. Juvenile hormone produced similar effects when applied to insects injected with eserine. An increase in the activity of acid phosphatases was also observed after incubation in culture medium with added juvenile hormone. The rôle of nerves and hormones in the degenerating muscles of D. pseudotsugae is compared with that in the permanently degenerating muscles during metamorphosis of some moths.     

In vitro induced pinocytotic activity by a juvenile hormone analogue in oocytes of Drosophila melanogaster

Summary Pinocytotic activity has been analyzed in Drosophila oocytes following either in vivo or in vitro exposure to horseradish peroxidase. The enzyme tracer gains access to the yolk spheres only when supplied to the oocyte in vivo. In oocytes cultured in vitro, peroxidase remains restricted to the residual coated vesicles and to the tubular profiles formed in excess in the cortical ooplasm.In an attempt to induce peroxidase uptake by oocytes cultured in vitro, various incubations were tested. Among these, hemolymph from both sexes is capable of promoting peroxidase uptake up to a level comparable to that detectable in vivo. On the other hand, fat body extracts fail to promote such cellular activity. Finally, the juvenile hormone analogue ZR-515 is shown to be the only factor required to promote pinocytotic activity under the experimental conditions tested. The observations are interpreted to indicate that vitellogenin has no inductive role on pinocytosis but simply acts by adhering to the forming coated vesicles which in turn are produced by the oolemma in response to the action of juvenile hormone.     

Effect of different semiochemicals blends on spruce bark beetle,Ips typographus (Coleoptera: Scolytidae)

The spruce bark beetle, Ips typographus, is a recent new introduction to the Qilian Mountains of China. An outbreak of these beetles has infested over 0.03 million hectares of spruce forests in this area. Although primary attraction to volatiles has been clearly demonstrated for I. typographus, the existence and role of attraction to insect‐produced pheromones have been widely debated. Currently, commercial lures for I. typographus include only the volatiles ipsdienol, cis‐verbenol, trans‐verbenol, 2‐methyl‐3‐buten‐2‐ol and 2‐phenylethanol in Europe. Several potential pheromone candidates have been identified for I. typographus. Our GC–MS and GC–FID analyses volatiles from hindgut extracts of I. typographus in different attack phases demonstrated that the 2‐methyl‐3‐buten‐2‐ol, ipsdienol, cis‐verbenol and trans‐verbenol as major hindgut components, and ipsenol, 2‐phenylethanol, trans‐ myrtenol and verbenone as minor components. We tested various combinations of semiochemical candidates, to determine an optimal blend. Our results suggest that addition of 2‐methyl‐3‐buten‐2‐ol to either ipsenol alone, or to blends of ipsenol and other semiochemical candidates, significantly enhanced attraction of I. typographus. Therefore, a simple lure consisting of ipsenol and 2‐methyl‐3‐buten‐2‐ol would be an optimal blend of I. typographus in the Qilian Mountains, China. We conclude that this optimal semiochemical blend may provide an effective biological pest control method for use in forest ecosystem against I. typographus.     

Ultrastructure of spermiogenesis in a freshwater stingray, Himantura signifer

Ultrastructural changes of spermatids during spermiogenesis in a freshwater stingray, Himantura signifer, are described. Differentiation of spermatids begins with modification of the nuclear envelope adjacent to the Golgi apparatus, before the attachment of the acrosomal vesicle. A fibrous nuclear sheath extends over the nuclear surface from the site of acrosomal adherence. The conical apical acrosome is formed during nuclear elongation. At the same time, chromatin fibers shift from an initially random arrangement, assume a longitudinal orientation, and become helical before final nuclear condensation. An axial midpiece rod is formed at the posterior end of nucleus and connects to the base of the sperm tail. Numerous spherical mitochondria surround the midpiece axis. The tail originating from the posterior end of the midpiece is composed of the usual 9 + 2 axoneme accompanied by two longitudinal columns, which are equal in size and round in cross section. The two longitudinal columns are absent at the end piece. A distinctive feature of freshwater stingray sperm is its spiral configuration.