Claude Guertin

Variation in the Susceptibility of the Forest Tent Caterpillar (Lepidoptera: Lasiocampidae) to Bacillus thuringiensis variety kurstaki HD-1: Effect of the Host Plant

Abstract Host-mediated effect on the efficacy of Bacillus thuringiensis Berliner against larvae of the forest tent caterpillar, Malacosoma disstria Hübner, was investigated under controlled conditions. Host plants used in this study were quaking aspen, Populus tremuloides Michx., a preferred host, and sugar maple, Acer saccharum Marsh., a secondary host. Larvae were reared in the laboratory on leaves of these hosts, and upon reaching the third, fourth, and fifth instar, they were fed leaves treated with one of a range of concentrations of B. thuringiensis variety kurstaki HD-1 suspensions. Larvae were tested on the host on which they were feeding before the 4-d bioassays. The estimated LC50s were 100-fold greater on quaking aspen than on sugar maple. Also, there was a decrease in efficacy over the whole ranges of concentrations with larval age on both hosts. LC50s varied approximately two-fold between third and fifth instar. These results indicate that host-mediated effects on B. thuringiensis efficacy warrant more interest. In particular, they strongly indicate that the host plant modifies the interaction between B. thuringiensis and a target insect, and offer the opportunity to investigate the mechanism(s) that may be involved in the enhancement of B. thuringiensis toxicity.

The complex symbiotic relationships of bark beetles with microorganisms: a potential practical approach for biological control in forestry

Bark beetles, especially Dendroctonus species, are considered to be serious pests of the coniferous forests in North America. Bark beetle forest pests undergo population eruptions, causing region wide economic losses. In order to save forests, finding new and innovative environmentally friendly approaches in wood-boring insect pest management is more important than ever. Several biological control methods have been attempted over time to limit the damage and spreading of bark beetle epidemics. The use of entomopathogenic microorganisms against bark beetle populations is an attractive alternative tool for many biological control programmes in forestry. However, the effectiveness of these biological control agents is strongly affected by environmental factors, as well as by the susceptibility of the insect host. Bark beetle susceptibility to entomopathogens varies greatly between species. According to recent literature, bark beetles are engaged in symbiotic relationships with fungi and bacteria. These types of relationship are very complex and apparently involved in bark beetle defensive mechanisms against pathogens. The latest scientific discoveries in multipartite symbiosis have unravelled unexpected opportunities in bark beetle pest management, which are discussed in this article.

Towards the Development of an Autocontamination Trap System to Manage Populations of Emerald Ash Borer (Coleoptera: Buprestidae) With the Native Entomopathogenic Fungus, Beauveria bassiana

ABSTRACT Emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) is an invasive species from Asia that was discovered in North America Canada, in 2002. Herein, we describe studies to develop an autocontamination trapping system to disseminate Beauveria bassiana to control beetle populations. The standard trap for emerald ash borer in Canada is a light green prism trap covered in an insect adhesive and baited with (Z)-3-hexenol. We compared of green multifunnel traps, green intercept panel traps (both with and without fluon coating) and green prism traps for capturing emerald ash borer in a green ash plantation. The coated green multifunnel traps captured significantly more males and more females than any other trap design. We examined the efficacy of two native B. bassiana isolates, INRS-CFL and L49–1AA. In a field experiment the INRS-CFL isolate attached to multifunnel traps in autocontamination chambers retained its pathogenicity to emerald ash borer adults for up to 43 d of outdoor exposure. Conidia germination of the INRS-CFL isolate was >69% after outdoor exposure in the traps for up to 57 d. The L49–1AA isolate was not pathogenic in simulated trap exposures and the germination rate was extremely low (<5.3%).Mean (±SEM) conidia loads on ash borer adults after being autocontaminated in the laboratory using pouches that had been exposed in traps out of doors for 29 d were 579,200 (±86,181) and 2,400 (±681) for the INRS-CFL and the L49–1AA isolates, respectively. We also examined the fungal dissemination process under field conditions using the L49–1AA isolate in a green ash plantation. Beetles were lured to baited green multifunnel traps with attached autocontamination chambers. Beetles acquired fungal conidia from cultures growing on pouches in the chambers and were recaptured on Pestick-coated traps. In total, 2,532 beetles were captured of which 165 (6.5%) had fungal growth that resembled B. bassiana. Of these 25 beetles were positive for the L49–1AA isolate.

Molecular characterization of three new avian infectious bronchitis virus (IBV) strains isolated in Quebec.

Three unrecognized field isolates of Infectious Bronchitis Virus (IBV) were recovered from commercial broiler chickens vaccinated with live Mass viral strain (H120). These isolates were identified by immunofluorescence using monoclonal antibodies produced against reference serotypes: Mass, Conn, and Ark. RT-PCRs were performed on viral RNAs to amplify S1 gene using a specific set of primers S1OLIGO3′ and S1OLIGO5′. Restriction polymorphism (RFLP) of PCR products was determined by the use of HaeIII restriction enzyme. As expected, patterns of PCR products were different from common pattern of strains assigned to Mass serotype M41, Beaudette, H120, and Florida. Molecular analysis showed a nucleotide insertion in hypervariable region one (HVR-1) of S1 gene of only Quebec isolates (Qu16, Qu_mv and Q_37zm). However, New Brunswick IBV isolate (NB_cp) did not display these insertions. Major amino acid changes involved insertion of two stretches (aa118–119: Arg–Ser and aa141–145: Sys–Ser–Asn–Ala–Ser–Cys) located at N-terminal and C-terminal regions of HVR-2. It is speculated that cysteine residue located upstream and downstream of Cys–Ser–Asn–Ala–Ser–Cys segment might be involved in the formation of loop structure and disulfide bond that could trigger important epitope changes. Insertion of new NXT and NXS (X≠P) glycosylation motifs scattered along S1 region and insertion of cysteine residues in HVR are contributing to the antigenic shifting of Quebec isolates. Fragment insertions were thought to be induced by inter-serotype recombination between vaccine strain (H120) that belongs to Mass serotype and another strain belonging to Ark serotype. Phylogenetic tree based on amino acid sequences showed that Quebec isolates formed a new phylogenetic cluster.

Sequence analysis and expression of the polyhedrin gene of Choristoneura fumiferana cytoplasmic polyhedrosis virus (CfCPV).

The segmented double-stranded RNA genome of Choristoneura fumiferana cytoplasmic polyhedrosis virus (CfCPV) was extracted, polyadenylated, reverse-transcribed into cDNA and cloned. The cDNA clones that hybridized to the smallest genomic segment (segment 10) were identified, and its nucleotide sequence was determined. Genome segment 10 of CfCPV was found to be 1171 nucleotides in length with a single open reading frame in one strand capable of coding a predicted protein of 258 residues (Mr of 29,795), consistent with an apparent Mr of 30.5 kDa determined by SDS-PAGE of purified polyhedrin. Comparison of the nucleotide and amino acid sequences of the polyhedrin gene of CfCPV with those of other CPVs and with several nuclear polyhedrosis viruses revealed no particular homology. Analysis of the hydrophilic profiles and predicted secondary structures of Bombyx mori (BmCPV), Euxoa scandens (EsCPV) and CfCPV indicated the presence of seven similar regions located at the amino terminus of the polyhedrin polypeptide of the three viruses. The expression of the cloned CfCPV polyhedrin gene in Escherichia coli demonstrated that this polyhedrin has the property of self-assembly, since the production of crystal-like occlusion with a well-defined crystalline lattice structure was observed.

Efficacy of Beauveria bassiana (Bals.) Vuill. against the tarnished plant bug, Lygus lineolaris L., in strawberries

Beauveria bassiana has a high insecticidal potential to control the tarnished plant bug, Lygus lineolaris, a significant pest of strawberries. Screening experiments showed that L. lineolaris adults were susceptible to several B. bassiana isolates. Another screening test with Coleomegilla maculata, a natural enemy found in strawberries, was also performed in order to select the isolate having lower entomopathogenic impact on this insect. Based on data obtained from both insect species and on the ecozone origin of the B. bassiana isolates, INRS‐IP and INRS‐CFL isolates were selected for further experiments. The LC50 values of these two isolates against L. lineolaris adults were 7.8 × 105 and 5.3 × 105 conidia/ml, and average survival time (AST) values were 4.46 and 4.37 days at a concentration of 1 × 108 conidia/ml respectively. Results also indicated that L. lineolaris nymphs are susceptible to the selected isolates. During field experiments, using a randomized block design with four replicates, INRS‐IP and INRS‐CFL isolates were applied at two rates (1 × 1011 and 1 × 1013 conidia/ha) weekly during a period of 4 weeks. These multiple applications triggered a significant reduction of L. lineolaris nymphal populations in strawberries. Twenty‐four days after the first application, a significant difference was observed between the mean population densities of surviving nymphs in all B. bassiana‐treated plots (less than one insect per five plants) compared with those in control plots (four insects per five plants). During the field experiment, persistence of insecticidal activity and viability of B. bassiana conidia were also monitored. The results showed the presence of viable and infective conidia up to 6 days after each application on strawberry foliage. Moreover, the multiple applications of B. bassiana at the rate of 1 × 1013 conidia/ha triggered a significant reduction in strawberry fruit injuries induced by L. lineolaris feeding behaviour compared with the control plots.

Surveying the endomicrobiome and ectomicrobiome of bark beetles: The case of Dendroctonus simplex

Many bark beetles belonging to the Dendroctonus genus carry bacterial and fungal microbiota, forming a symbiotic complex that helps the insect to colonize the subcortical environment of the host tree. However, the biodiversity of those bacteria at the surface of the cuticle or inside the body parts of bark beetles is not well established. The aim of this study was to characterize the bacterial microbiome associated with the eastern larch beetle, Dendroctonus simplex, using bacterial 16S rRNA gene pyrosequencing. The ecto- and endomicrobiome and the subcortical galleries were investigated. Several bacterial genera were identified, among which Pseudomonas, Serratia and Yersinia are associated with the surface of the beetle cuticle, and genera belonging to Enterobacteriaceae and Gammaproteobacteria with the interior of the insect body. The index of dissimilarity indicates that the bacterial microbiome associated with each environment constitutes exclusive groups. These results suggest the presence of distinct bacterial microbiota on the surface of the cuticle and the interior of D. simplex body. Additionally, the bacterial diversity identified in the galleries is substantially different from the ectomicrobiome, which could indicate a selection by the insect. This study reports for the first time the identification of the eastern larch beetle microbiome.

Identification and sequence analyses of the granulin gene of Choristoneura fumiferana granulovirus

SummaryThe nucleotide sequence of the granulin gene of Choristoneura fumiferana granulovirus (CfGV) was determined. The gene encodes a protein of 248 amino acids with a predicted Mr of 29.299 kDa. The granulin genes of Trichoplusia ni, Pieris brassicae and Cryptophlebia leucotreta granuloviruses showed homologies ranging from 76.7–80.5 % for nucleotide sequences and 84.2–88.3 % for amino acid sequences when compared to CfGV. The secondary structure of CfGV granulin protein, including the hydrophilic (polar) and hydrophobic (basic) regions, was predicted and found to be similar to other granulins. A very late baculovirus promoter motif, ATAAG, was found within the putative promoter region of the CfGV granulin gene.

Land-use influences the distribution and activity of high affinity CO-oxidizing bacteria associated to type I-coxL genotype in soil

Soil carboxydovore bacteria are the biological sink of atmospheric carbon monoxide (CO). The initial oxidation of CO is catalyzed by a CO-dehydrogenase (CODH), and the gene coxL encodes the large subunit of the enzyme. Only a few carboxydovore isolates were shown to oxidize atmospheric CO and little is known about the potential impact of global change on the ecophysiology of this functional group. The main objective of this study was to assess the impact of land-use and soil properties on coxL gene diversity and identify molecular indicators for the soil uptake of atmospheric CO. Soil samples were collected in three neighboring sites encompassing different land-use types, namely deciduous forest, larch plantation and maize field. CO uptake activity was related to total carbon and nitrogen content in soil, with the highest activity observed in deciduous forest. An extensive coxL database was assembled to optimize a PCR detection assay targeting sequences belonging to functional type I-CODH and hypothetical type II-CODH. Fully replicated coxL gene libraries unveiled a unique molecular signature in deciduous forest soil, with enrichment of type I sequences. Genetic profiles of larch and maize monocultures were not statistically different and showed higher level of coxL gene richness than deciduous forest. Soil water content and CO uptake activity explained 38% of the variation of coxL gene profiles in a canonical ordination analysis, leading to the identification of sequences belonging to the δ-Proteobacteria cluster as indicator for high affinity CO uptake activity. Enrichment of type I and δ-Proteobacteria coxL sequences in deciduous forest were confirmed by qPCR in an independent soil survey. CO uptake activity in model carboxydovore bacteria suggested that a significant fraction of detected putative high affinity CO oxidizers were active in soil. Land-use was a driving force separating coxL diversity in deciduous forest from monocultures.

Assessment of genetic and pheromonal diversity of the Cydia strobilella species complex (Lepidoptera: Tortricidae)

Combining pheromone trapping and genetic analyses can be useful when trying to resolve complexes of closely related insect taxa that are difficult to distinguish based on morphological characters. Nearctic and Palearctic populations of the spruce seed moth, Cydia strobilella L., have been considered taxonomically synonymous since 1983, but more recent work revealing distinct sex pheromones for Canadian and Swedish moths suggest that populations in the two regions belong to different species. In order to test this hypothesis, we performed field trapping using different pheromone lures at ten sites in North America, Europe and Asia, and reconstructed phylogenetic relationships among trapped moths using mitochondrial (cytochrome oxidase subunit I) and nuclear (elongation factor 1 alpha) DNA sequence data. Trapping data and tree topologies for both genes revealed distinct pherotypes in North America and Eurasia. A genetically distinct population from China was investigated further with respect to its sex pheromone. Electrophysiological data indicated that Chinese females produce a deviant ratio of the sex pheromone components (dienic acetates) compared to Swedish females. However, trapping experiments in both areas revealed a similar broad response profile in males to a wide range of acetate ratios, and these populations should be considered taxonomically synonymous. A previous suggestion of an agonistic effect on the attraction of C. strobilella males in Sweden when adding the corresponding alcohols to the binary acetate blend was also tested in Sweden as well as in China, with no observed effect on attraction of males. In conclusion, our study demonstrates the great potential of using pheromone trapping as a tool for identification and delimitation of taxa within cryptic species complexes. Based on our data, Nearctic and Palearctic populations of C. strobilella should be considered different species, and C. youngana Kearfott stat. rev. is resurrected here as valid name for North American populations, which was the case before the revision in 1983.