Probing behavior of Adelges laricis Vallot (Hemiptera: Adelgidae) on Larix decidua Mill: Description and analysis of EPG waveforms.

Adelgidae are a sister group of Aphididae and Phylloxeridae within Hemiptera, Aphidoidea and occur exclusively on Pinaceae. The piercing-sucking mouthparts of Adelgidae are similar to those of aphids and it is believed that adelgids ingest sap from both the non-vascular and vascular (phloem) tissues. The aim of the present study was to identify and characterize the adelgid stylet activities during their penetration in plant tissues. The probing behavior of Adelges laricis Vallot (Hemiptera: Adelgidae) on European larch Larix decidua Mill. and sucrose diets was monitored using the DC-EPG (Electrical Penetration Graph technique = electropenetrography). The EPG waveforms were described based on amplitude, frequency, voltage level, and electrical origin of the observed traces, and associated with putative behavioral activities based on analogy with aphid activities. Waveform frequency, duration, and sequence were analysed as well. A. laricis generated EPG signals at two clearly distinct voltage levels positive and negative, suggesting extracellular and intracellular stylet penetration, respectively. The adelgid EPG patterns were ascribed to four behavioral phases, which were non-probing, pathway, phloem, and xylem phases. Non-probing referred to the position of the stylets outside the plant tissues. Pathway phase was represented by three waveform patterns that visualized extracellular stylet penetration in non-vascular tissues without potential drops (AC1), with serial short (1.2-1.5 s) potential drops (AC2), and with 'aphid-like' (5-10 s) potential drops (AC3). Phloem phase comprised three waveform patterns at intracellular level, which in all probability represented phloem salivation (AE1), and phloem sap passive (AE2) and active ingestion (AE3). AE3 was a newly described waveform, previously unreported from Hemiptera. Waveform AG represented the ingestion of xylem sap. The comparative analysis demonstrated that the gymnosperm-associated adelgids show certain similarities in probing behavior typical of aphids and phylloxerids on angiosperm plants. The present work is the first detailed analysis of specific adelgid stylet activities on gymnosperms.

Genome Analysis of an Alphabaculovirus Isolated from the Larch Looper, Erannis ankeraria.

The larch looper, Erannis ankeraria Staudinger (Lepidoptera: Geometridae), is one of the major insect pests of larch forests, widely distributed from southeastern Europe to East Asia. A naturally occurring baculovirus, Erannis ankeraria nucleopolyhedrovirus (EranNPV), was isolated from E. ankeraria larvae. This virus was characterized by electron microscopy and by sequencing the whole viral genome. The occlusion bodies (OBs) of EranNPV exhibited irregular polyhedral shapes containing multiple enveloped rod-shaped virions with a single nucleocapsid per virion. The EranNPV genome was 125,247 bp in length with a nucleotide distribution of 34.9% G+C. A total of 131 hypothetical open reading frames (ORFs) were identified, including the 38 baculovirus core genes and five multi-copy genes. Five homologous regions (hrs) were found in the EranNPV genome. Phylogeny and pairwise kimura 2-parameter analysis indicated that EranNPV was a novel group II alphabaculovirus and was most closely related to Apocheima cinerarium NPV (ApciNPV). Field trials showed that EranNPV was effective in controlling E. ankeraria in larch forests. The above results will be relevant to the functional research on EranNPV and promote the use of this virus as a biocontrol agent.

The symbiotic complex of Dendroctonus simplex: implications in the beetle attack and its life cycle.

The eastern larch beetle (Dendroctonus simplex Le Conte) is recognized as a serious destructive forest pest in the upper part of North America. Under epidemic conditions, this beetle can attack healthy trees, causing severe damages to larch stands. Dendroctonus species are considered as holobionts, as they engage in multipartite interactions with microorganisms, such as bacteria, filamentous fungi, and yeasts, which are implicated in physiological processes of the insect, such as nutrition. They also play a key role in the beetle's attack, as they are responsible for the detoxification of the subcortical environment and weaken the tree's defense mechanisms. The eastern larch beetle is associated with bacteria and fungi, but their implication in the success of the beetle remains unknown. Here, we investigated the bacterial and fungal microbiota of this beetle pest throughout its ontogeny (pioneer adults, larvae and pupae) by high-throughput sequencing. A successional microbial assemblage was identified throughout the beetle developmental stages, reflecting the beetle's requirements. These results indicate that a symbiotic association between the eastern larch beetle and some of these microorganisms takes place and that this D. simplex symbiotic complex is helping the insect to colonize its host tree and survive the conditions encountered.

Co-existence of periodic bursts and death of cycles in a population dynamics system.

We study the dynamics of a discrete-time tritrophic model which mimics the observed periodicity in the population cycles of the larch budmoth insect which causes widespread defoliation of larch forests at high altitudes periodically. Our model employs q-deformation of numbers to model the system comprising the budmoth, one or more parasitoid species, and larch trees. Incorporating climate parameters, we introduce additional parasitoid species and show that their introduction increases the periodicity of the budmoth cycles as observed experimentally. The presence of these additional species also produces other interesting dynamical effects such as periodic bursting and oscillation quenching via oscillation death, amplitude death, and partial oscillation death which are also seen in nature. We suggest that introducing additional parasitoid species provides an alternative explanation for the collapse of the nine year budmoth outbreak cycles observed in the Swiss Alps after 1981. A detailed exploration of the parameter space of the system is performed with movies of bifurcation diagrams which enable variation of two parameters at a time. Limit cycles emerge through a Neimark-Sacker bifurcation with respect to all parameters in all the five and higher dimensional models we have studied.

Introduced and Native Parasitoid Wasps Associated With Larch Casebearer (Lepidoptera: Coleophoridae) in Western Larch.

The larch casebearer [Coleophora laricella (Hubner)], a non-native insect, continues to impact western larch (Larix occidentalis Nutt.) through defoliation events in the Pacific Northwest. Biological control programs starting in the 1960s released seven species of parasitoid wasps to control C. laricella outbreaks. However, information about current population dynamics of C. laricella and associated parasitoids remains lacking. Therefore, the goal of this study was to document the presence, current distributions, densities, and parasitism rates of introduced and native parasitoid wasps occurring on C. laricella throughout the Northwestern U.S. range of L. occidentalis. We sampled L. occidentalis trees at multiple sites in Oregon, Washington, Idaho, and Montana. C. laricella was present at all sites with average state densities ranging from 6.2 to 13.1 moths/100 buds. We recovered two introduced hymenopteran biological control agents; Agathis pumila (Ratzeburg: Braconidae) at 79% of the sites, and Chrysocharis laricinellae (Ratzeburg: Eulophidae) at 63% of the sites. Fourteen species of native parasitic wasps were also recovered. The most common species were: Bracon sp., Spilochalcis albifrons, and Mesopolobus sp. The average native species parasitism rate across the four states was 9.0%, which was higher than the introduced species Ch. laricinellae (2.9%), but not as high as A. pumila (19.3%). While survey results suggest that native species may be more important for the control of C. laricella than previously thought, A. pumila remains the major source of regional control. However, further research is needed to better understand how introduced and native parasitoids interact to control invasive pest populations.

[Life-cycle of Bursaphelenchus mucronatus Mamiya et Enda, 1979 (Nematoda: Aphelenchida)].

Postembryonic development of Bursaphelenchus mucronatus has been studied. First molt takes place within the egg-shell, and three subsequent molts after hatching. Structure of all juvenile stages are described, as well as molting juveniles and adults. Juvenile stages differ in genital primordium structure, copulatory structures primordial and the body length. In juveniles of 3rd and 4th stage the sex of juvenile was distinguished: male juveniles have cloacal primordium, whereas female juveniles have vulval primordium. Adults differ from juveniles in presence of vulva in females and spicules in males. The key to identify juvenile stages and their sex is given. Male has the terminal bursal flap and 3 pairs of iail papillae: p1 anadanal; p2 and p3 at the bursal flap base: p2 close to mid-line of the ventral body surface, p3 located laterally to p2 at the same level. Unpaired papilla is present on the upper cloacal lip, on the ventral mid-line.

Three centuries of insect outbreaks across the European Alps.

Knowledge of the persistence of regular larch budmoth outbreaks is limited in space and time. Although dendrochronological methods have been used to reconstruct insect outbreaks, their presence may be obscured by climatic influences. More than 5000 tree-ring series from 70 larch host and 73 spruce nonhost sites within the European Alps and Tatra Mountains were compiled. Site-specific assessment of growth-climate responses and the application of six larch budmoth detection methods considering host, nonhost and instrumental time-series revealed spatiotemporal patterns of insect defoliation across the Alpine arc. Annual maps of reconstructed defoliation showed historical persistence of cyclic outbreaks at the site level, recurring c. every 8-9 yr. Larch budmoth outbreaks occurred independently of rising temperatures from the Little Ice Age until recent warmth. Although no collapse in outbreak periodicity was recorded at the local scale, synchronized Alpine-wide defoliation has ceased during recent decades. Our study demonstrates the persistence of recurring insect outbreaks during AD 1700-2000 and emphasizes that a widely distributed tree-ring network and novel analysis methods can contribute towards an understanding of the changes in outbreak amplitude, synchrony and climate dependence.

Ultrastructural observations on antennal sensilla of Coleophora obducta (Meyrick) (Lepidoptera: Coleophoridae).

Coleophora obducta (Meyrick) is an important defoliator of larch in northeast China. To further describe the mechanism of insect-plant chemical communication, we observed the antennae and their sensilla of C. obducta by scanning and transmission electron microscopy. In both sexes, antennae were threadlike, and in total there were eight types of sensilla found on the antennae: Sensilla placodea, Sensilla basiconica, Sensilla coeloconica, Sensilla styloconica, Sensilla trichodea, Sensilla squamiformia, Sensilla furcatea and Böhm bristles, respectively. We described ultrastructures and discussed possible functions. We inferred from their ultrastructures as chemoreceptors that S. placodea, S. basiconica and S. trichodea were innervated by sensory neurons. The neuron of S. styloconica terminated in a tubular structure which suggested gustatory/mechanosensory function, and the terminal sensory pegs might function as contact-chemoreceptors depending on their locations.

Dynamics of discrete-time larch budmoth population models.

The larch budmoth (LBM) population in the Swiss Alps is well known for its periodic outbreaks and regular oscillations over several centuries. The ecological mechanisms that drive these oscillations, however, have not been unambiguously identified, although a number of hypotheses have been proposed. In this article, we investigate several LBM resulting from these different ecological hypotheses. We first study a leaf quality-moth population model and then two moth-parasitoid models. Existence and stability of equilibria are investigated and sufficient conditions for which populations can persist are derived. We then provide conclusions based on our analysis.

[Effects of different elicitors on olfactory response and oviposition selection of Dendrolimus superans (Butler)].

This paper studied the behavioral responses of Dendrolimus superans larvae and adults to Z-jasmone, methyl jasmonate (MeJA) and methyl salicylate (MeSA), and to Larix gmelinii seedlings treated with different elicitors including mechanic wounding, insect feeding, jasmonic acid (JA), salicylic acid (SA), Z-jasmone, MeJA, MeSA, and JA + SA. The results showed that D. superans larvae were repelled by MeJA and MeSA at the concentrations of 0.1%-10% V/V. L. gmelinii seedlings were induced resistance by wounding, JA, MeJA, Z-jasmone and MeSA, which decreased the feeding selection of D. superans larvae. D. superans adults exploited evident electroantennogram (EAG) responses to Z-jasmone and MeSA, and the sensitivity of the females was enhanced with the increasing concentration of Z-jasmone and MeSA. Significantly low amount of eggs was observed on the L. gmelinii seedlings treated with test elicitors.