Michel Cusson

Expression of a Tranosema rostrale polydnavirus gene in the spruce budworm, Choristoneura fumiferana

The endoparasitic wasp Tranosema rostrale (Ichneumonidae) transmits a polydnavirus (PDV) to its host, Choristoneura fumiferana, during oviposition. Unlike most other PDVs examined, the virus of T. rostrale (TrPDV) does not appear to play an important role in suppressing the host cellular immune response. However, it inhibits host metamorphosis. In the present study, TrPDV gene expression was examined in parasitized and virus-injected last-instar caterpillars. Northern analysis with viral DNA as a probe revealed only one detectable mRNA, of about 650 bp. The corresponding cDNA, termed TrV1, was cloned and sequenced and found to encode a protein of 103 amino acids which, following cleavage of the putative signal peptide, has a predicted molecular mass of 9.3 kDa. This protein displays limited similarity to the VHv1.4 cysteine-rich protein from the PDV of Campoletis sonorensis, mostly within the signal peptide region. By using a TrV1-specific probe, the TrV1 gene was localized to segment G of the TrPDV genome. The cuticle and fat body were identified as the principal sites of TrV1 transcription, with little transcription observed in haemocytes and midgut. Western analysis of proteins extracted from selected tissues of parasitized insects suggested that the TrV1 protein is secreted in the haemolymph. As observed for other PDVs, injection of TrPDV did not suppress transcription of the gene that encodes juvenile hormone esterase, the activity of which is inhibited by the virus. We speculate that the TrV1 protein may play a role in the inhibition of C. fumiferana metamorphosis.

JUVENILE HORMONE PRODUCTION AND SEXUAL MATURATION IN TRUE ARMYWORM, PSEUDALETIA UNIPUNCTA (HAW.) (LEPIDOPTERA : NOCTUIDAE) : A COMPARISON OF MIGRATORY AND NON-MIGRATORY POPULATIONS

Previous work on North American populations of the true armyworm, Pseudaletia unipuncta, has shown that (1) ovarian development, pheromone synthesis, and the onset of calling (behavior associated with the emission of the sex pheromone) in virgin females are positively correlated with an increase in juvenile hormone (JH) production, and (2) sexual maturation is delayed under short-day, low-temperature conditions. Based on these results and on the observation that this insect is unable to survive the low temperatures of the Canadian winter, it has been hypothesized that armyworm moths undertake seasonal north-south migrations in response to predictable habitat deterioration. Recently we obtained material from the Azores, a volcanic archipelago in the Atlantic Ocean where the armyworm sustains populations all year round. We, therefore, undertook a comparative study to test the hypothesis that the earlier onset of calling behavior observed in this non-migrant population, relative to the North American population under identical conditions, was associated with an earlier induction of JH biosynthesis and a more rapid ovarian development. The results clearly supported this hypothesis: JH biosynthesis increased at a significantly younger age in Azorean females, although there were no differences in the relative proportions of the three JH homologues produced in vitro by CA of females sacrificed on their first night of calling. The early production of JH was reflected in a more rapid ovarian maturation although the data suggest that sexual maturation in the Azorean population may require a lower JH titer. The importance of the observed differences are discussed with respect to the presence or absense of migration in each population.

Regulation of Pheromone Production in Lepidoptera: The Need for an Ecological Perspective

Recently a graduate student in molecular biology, working on aspects of insect reproduction, was asked what he knew about the life history and ecology of the species he was studying. While the initial response “Oh, it lives in the rearing room down the hall” was accompanied by a telltale grin, it became clear after further discussion that the student’s knowledge of his subject species did no extend far beyond the lab bench. The object of this story is not to slight molecular biologists—because behavioral ecologists and evolutionary biologists would not fare better if asked about the physiology or biochemistry of the species they work with each day—but rather to point out that we all tend to work within a somewhat narrow context.

Cloning, expression and characterization of four serpin-1 cDNA variants from the spruce budworm, Choristoneura fumiferana

Four cDNAs (Cfserpin-1a, Cfserpin-1b, Cfserpin-1c and Cfserpin-1d) of the Choristoneura fumiferana serpin-1 gene were cloned from an epidermis cDNA library. Analysis of the deduced amino acid sequences indicated that the cloned cDNAs encode four different proteins displaying identical N- but distinct C-termini, the latter region containing the inhibitory loop. The entire CfSerpin-1 gene is transcribed while the variants are generated. Antibodies generated against the purified recombinant serpins cross-reacted with the other three. Each of the four Cfserpin-1 cDNA variants was transcribed throughout larval development, from the 4th to the 6th instar, but transcript levels during the intermolt phases were generally higher than during the molting phase. The epidermis and fat body had higher levels of Cfserpin-1 transcripts than the midgut. Cfserpin-1 proteins, detected with the Cfserpin-1a antibody, were found in the epidermis, midgut, fat body, plasma and molting fluid of 6th instar larvae and pre-pupae. Prepupal and pupal insects had higher levels of the proteins than the 6th instar feeding larvae, despite a drop in transcript levels. Cfserpin-1a could bind with the serine proteinase elastase and form a complex in vitro. We hypothesize that the cloned serpins could be involved in the regulation of cuticle degradation during the insect molting cycle.

Cloning, expression and localization of a trypsin-like serine protease in the spruce budworm, Choristoneura fumiferana

Abstractu2002 A trypsin‐like molting‐related serine protease cDNA (CfMRSP) was cloned from the spruce budworm, Choristoneura fumiferana. The full‐length CfMRSP complementary DNA (cDNA) encoded a 43 kDa protein that contained a trypsin‐like serine protease catalytic domain, but no clip domain. The C‐terminal extension contained five cystein residues, which may allow the protein to form a homodimer through interchain disulfide bonds and regulate the activity of CfMRSP. Phylogenetic tree analysis showed that CfMRSP clusters with lepidopteran homologues such as serine protease 1 of Lonomia obliqua, hemolymph proteinase 20 (HP20), pattern recognition serine proteinase precursor (ProHP14) and a trypsin‐like protein of Manduca sexta. Northern blot analysis of developmental expression of CfMRSP indicated that its transcripts were found primarily in the epidermis and were produced during all of the tested stadia, from 4th instar larvae to pupae, but increased levels of CfMRSP transcripts were always found after each molt. A high level of the protein was found in the epidermis by immunohistochemistry analysis. Altogether these data suggest that CfMRSP plays a role in the epidermis during molting and metamorphosis.

Biosurveillance of forest insects: part I—integration and application of genomic tools to the surveillance of non-native forest insects

Invasive species pose significant threats to forest ecosystems. Early intervention strategies are the most cost-effective means to control biological invasions, but are reliant on robust biosurveillance. State-of-the-art genomic approaches can provide an unprecedented opportunity to access detailed information on the invasion process and adaptive potential of invasive insects that pose an immediate threat to forests environments. Genomics can improve diagnostics of the invader and identify its route of invasion by determining the source population(s), assess its probability of establishment and patterns of spread, as well as provide evidence of adaptation. Applied biosurveillance efforts by plant health regulatory agencies will benefit substantially from the detailed insights that genomic data bring to our understanding of biological invasions.