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PubMed2002

Heterochromatic banding patterns on chromosomes of twelve weevil species (Insecta, Coleoptera, Curculionoidea: Apionidae, Curculionidae).

The C-banding patterns of twelve weevil species are presented. The obtained results confirm the existence of two groups of species: with a small or large amount of heterochromatin in the karyotype. The first group comprises seven species (Apionidae: Holotrichapion pisi; Curculionidae: Phyllobius urticae, Ph. pyri, Ph. maculicornis, Tanymecus palliatus, Larinodontes turbinatus, Cionus tuberculosus). In weevils with a small amount of heterochromatin, tiny grains on the nucleus in interphase are visible, afterwards in mitotic and meiotic prophase appearing as dark dots. The absence of C-bands does not indicate a lack of heterochromatin but heterochromatic regions are sometimes so small that the condensation is not visible during the cell cycle. The second group comprises five species (Otiorhynchus niger, O. morio, Polydrusus corruscus, Barypeithes chevrolati, Nedyus quadrimaculatus) which possess much larger heteropicnotic parts of chromosomes visible during all nuclear divisions. The species examined have paracentromeric C-bands on autosomes and the sex chromosome X, except for Otiorhynchus niger, which also has an intercalary bands on one pair of autososomes. All the species examined differ in the size of segments of constitutive heterochromatin. The y heterochromosome is dot-like and wholly euchromatic in all the studied species.

Animals↗

PubMed2026

Development of a Droplet-Based RNA Interference Feeding Assay for Neonates of the Citrus Root Weevil Diaprepes abbreviatus.

The citrus root weevil, Diaprepes abbreviatus, is an economically important pest of citrus and ornamental crops whose subterranean larval feeding damages roots and predisposes plants to secondary pathogen infection. Development of efficient RNA interference (RNAi) delivery methods for early larval stages is essential for functional genomics studies and the evaluation of RNAi-based pest management strategies. In this study, we developed a droplet-based feeding assay for oral delivery of double-stranded RNA (dsRNA) to neonates of D. abbreviatus using chitin synthase 2 (DaCHS2) as a model RNAi target to validate the assay. Feeding solutions containing dsRNA were supplemented with sucrose and bromophenol blue dye, with bromophenol blue used to visually confirm ingestion. Across three independent biological replicates, all neonates exposed to DaCHS2-dsRNA, GFP-dsRNA, and water control droplets were confirmed to have ingested the feeding solution (45/45 neonates per treatment; 100% feeding success). Oral delivery of dsRNA targeting DaCHS2 reduced transcript abundance and was associated with developmental abnormalities and mortality, including incomplete molting, abnormal pigmentation, cuticular deformities, defective pupation, and malformed adults. Regression analysis demonstrated moderate and significant relationship between dsRNA concentration and neonate mortality and developmental abnormalities. RT-qPCR further confirmed reduced DaCHS2 transcript abundance following oral dsRNA exposure. The developed assay provides a simple, reproducible, and minimally invasive proof-of-concept platform for oral dsRNA delivery to D. abbreviatus neonates. The assay requires only small dsRNA volumes, provides visual confirmation of ingestion, and may facilitate laboratory-based screening of additional RNAi target genes in D. abbreviatus and other coleopteran pests.

Animals↗

PubMed2006

Site of pheromone biosynthesis and isolation of HMG-CoA reductase cDNA in the cotton boll weevil, Anthonomus grandis.

Isolated gut tissue from male cotton boll weevil, Anthonomus grandis (Coleoptera: Curculionidae), incorporated radiolabeled acetate into components that co-eluted with monoterpenoid pheromone components on HPLC. This demonstrates that pheromone components of male A. grandis are produced de novo and strongly suggests that pheromone biosynthesis occurs in gut tissue. A central enzyme in isoprenoid biosynthesis is 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-R), and a full-length HMG-R cDNA was isolated from A. grandis. The predicted translation product was 54 and 45% identical to HMG-R from Ips paraconfusus and Drosophila melanogaster, respectively. HMG-R gene expression gradually increased with age in male A. grandis, which correlates with pheromone production. However, topical application of JH III did not significantly increase HMG-R mRNA levels.

Age Factors↗

PubMed2006

Molecular mapping of genes for resistance to the bean pod weevil (Apion godmani Wagner) in common bean.

The bean pod weevil (Apion godmani Wagner) is a serious insect pest of common beans (Phaseolus vulgaris L.) grown in Mexico and Central America that is best controlled by host-plant resistance available in Durango or Jalisco genotypes such as J-117. Given unreliable infestation by the insect, the use of marker-assisted selection is desirable. In the present study, we developed a set of nine molecular markers for Apion resistance and mapped them to loci on chromosomes 2, 3, 4 and 6 (linkage groups b01, b08, b07 and b11, respectively) based on genetic analysis of an F (5:10) susceptible x resistant recombinant inbred line population (Jamapa x J-117) and two reference mapping populations (DOR364 x G19833 and BAT93 x JaloEEP558) for which chromosome and linkage group designations are known. All the markers were derived from randomly amplified polymorphic DNA (RAPD) bands that were identified through bulked segregant analysis and cloned for conversion to sequence tagged site (STS) markers. One of the markers was dominant while four detected polymorphism upon digestion with restriction enzymes. The other markers were mapped as RAPD fragments. Phenotypic data for the population was based on the evaluation of percentage seed damage in replicated trials conducted over four seasons in Mexico. In single point regression analysis, individual markers explained from 3.5 to 22.5% of the variance for the resistance trait with the most significant markers overall being F10-500S, U1-1400R, R20-1200S, W9-1300S and Z4-800S, all markers that mapped to chromosome 2 (b01). Two additional significant markers, B1-1400R and W6-800R, were mapped to chromosome 6 (b11) and explained from 4.3 to 10.2% of variance depending on the season. The latter of these markers was a dominant STS marker that may find immediate utility in marker-assisted selection. The association of these two loci with the Agr and Agm genes is discussed as well as the possibility of additional resistance genes on chromosome 4 (b07) and chromosome 3 (b08). These are among the first specific markers developed for tagging insect resistance in common bean and are expected to be useful for evaluating the mechanism of resistance to A. godmani.

Animals↗

PubMed2005

Antifeedants against Hylobius abietis pine weevils: an active compound in extract of bark of Tilia cordata linden.

Linden (Tilia cordata) bark was shown to contain an antifeedant effective against the large pine weevil, Hylobius abietis. Soxhlet extraction of inner and outer bark resulted in an extract that showed antifeedant activity in a microfeeding assay. The extract was fractionated by chromatography on silica gel using gradient elution with solvents of increasing polarity. The content of the fractions obtained was monitored by thin layer- and gas chromatography. Fractions of similar chemical composition were merged. Two of the 17 fractions showed antifeedant activity in the microfeeding assay. Nonanoic acid was identified in both of these fractions. Subsequent testing in the microfeeding assay showed that nonanoic acid possessed strong antifeedant activity against H. abietis adults.

Animals↗

PubMed2006

Electrophysiological and behavioral responses of a Cuban population of the sweet potato weevil to its sex pheromone.

The sex pheromone of feral sweet potato weevils Cylas formicarius elegantulus from Cuba was found, via solid-phase microextraction analysis, to be identical to (Z)-3-dodecenyl (E)-2-butenoate, a previously reported compound. Females emitted 20 pg pheromone d(-1). In scanning electron microscopy studies carried out on the male antenna, we identified several types of sensilla: sensilla trichoidea of type 1 (ST1) as long hairs (100-150 microm), sensilla trichoidea of type 2 as short hairs (50-60 microm), sensilla basiconica of type 1 as thick pegs (20-25 microm), sensilla basiconica of type 2 as curved pegs (10-15 microm), and sensilla basiconica of type 3 as thin and straight short pegs (15-20 microm). The same types were observed in female antennae but ST1 were far less abundant than in males. Sensilla chaetica were also found on the flagellum subsegments in both sexes. In electrophysiological tests, the crotonate function in the pheromone structure proved to be critical for activity since regular depolarizations (0.6-0.8 mV) were obtained with puffs on 1 microg of the attractant, but not with puffs of the formate, acetate, propionate, or butyrate analogue of the pheromone. In a double dual-choice olfactometer, males showed maximum activity between the 4th and the 8th hr of scotophase at a dose of 50-1000 ng of pheromone. In field tests, a correlation between the contents of the Z,E isomer in the pheromone formulation with activity was noticed, and baits containing this isomer of stereomeric purity >94% showed the highest attractivity. The presence of 5% of the Z,Z isomer in the lure did not induce any synergistic or inhibitory effect, and the alcohol precursor of the pheromone was inactive. The results show that use of a stereomerically pure pheromone may not be necessary in pest control strategies.

Animal Structures↗

PubMed2006

Structure-activity relationships of benzoic acid derivatives as antifeedants for the pine weevil, Hylobius abietis.

Aromatic organic compounds found in the feces of the pine weevil, Hylobius abietis (L.) (Coleoptera: Curculionidae), have been shown to deter feeding behavior in this species, which is a serious pest of planted conifer seedlings in Europe. We evaluated 55 benzoic acid derivatives and a few homologs as antifeedants for H. abietis. Structure-activity relationships were identified by bioassaying related compounds obtained by rational syntheses of functional group analogs and structural isomers. We identified five main criteria of efficiency as antifeedants among the benzoic acid derivatives. By predicting optimal structures for H. abietis antifeedants, we attempted to find a commercial antifeedant to protect conifer seedlings against damage by H. abietis in regenerating forests. New, highly effective antifeedants are methyl 2,4-dimethoxybenzoate, isopropyl 2,4-dimethoxybenzoate, methyl 2-hydroxy-3-methoxybenzoate, methyl (3,5-dimethoxyphenyl)acetate, and methyl (2,5-dimethoxyphenyl)acetate. Of these, methyl 2,4-dimethoxybenzoate and isopropyl 2,4-dimethoxybenzoate have the highest antifeedant indices of all substances tested and are the best candidates for practical applications in order to protect planted seedlings in the field.

Alcohols↗

PubMed2004

A diverse family of serine proteinase genes expressed in cotton boll weevil (Anthonomus grandis): implications for the design of pest-resistant transgenic cotton plants.

Fourteen different cDNA fragments encoding serine proteinases were isolated by reverse transcription-PCR from cotton boll weevil (Anthonomus grandis) larvae. A large diversity between the sequences was observed, with a mean pairwise identity of 22% in the amino acid sequence. The cDNAs encompassed 11 trypsin-like sequences classifiable into three families and three chymotrypsin-like sequences belonging to a single family. Using a combination of 5' and 3' RACE, the full-length sequence was obtained for five of the cDNAs, named Agser2, Agser5, Agser6, Agser10 and Agser21. The encoded proteins included amino acid sequence motifs of serine proteinase active sites, conserved cysteine residues, and both zymogen activation and signal peptides. Southern blotting analysis suggested that one or two copies of these serine proteinase genes exist in the A. grandis genome. Northern blotting analysis of Agser2 and Agser5 showed that for both genes, expression is induced upon feeding and is concentrated in the gut of larvae and adult insects. Reverse northern analysis of the 14 cDNA fragments showed that only two trypsin-like and two chymotrypsin-like were expressed at detectable levels. Under the effect of the serine proteinase inhibitors soybean Kunitz trypsin inhibitor and black-eyed pea trypsin/chymotrypsin inhibitor, expression of one of the trypsin-like sequences was upregulated while expression of the two chymotrypsin-like sequences was downregulated.

Amino Acid Sequence↗

PubMed2005

Effect of temperature on the termination of prolonged larval diapause in the chestnut weevil Curculio sikkimensis (Coleoptera: Curculionidae).

Adults of the chestnut weevil Curculio sikkimensis emerged over a 3-year period under laboratory and quasi-field conditions due to a prolonged diapause that occurred at the mature larval stage. Variable proportions of the larvae remained in diapause after a single cold (5 degrees C) treatment of 120 days. Extension of the chilling period to as long as 540 days did not increase the percentage of diapause termination, and excessively long chilling actually reduced the percentage. Chilling was not indispensable to the termination of larval diapause. Diapause intensity was very high and variable, and more than 1000 days at 20 degrees C was necessary to reactivate all diapause larvae. When the diapause larvae were exposed to cycles of low (5 degrees C for 120 days) and high (20 degrees C for 240 days) temperatures, the percentage of diapause termination reached 100% after two or three such cycles. Thus, the prolonged diapause of C. sikkimensis has characteristics similar to the common short winter diapause in other insects, but has unique characteristics that ensure polymodal reactivation over several years.

Adaptation, Physiological↗

PubMed2005

Testing and mapping non-stationarity in animal behavioral processes: a case study on an individual female bean weevil.

Statistical analysis based on two characteristics of a small-world network, and on Lempel-Ziv's measure of Kolmogorov-Chaitin's algorithmic complexity are first proposed to scan through an individual behavioral sequence for possible existence of non-stationarity. Due to fixed window width, these tests have drawbacks in mapping out regions of non-stationarity. A non-parametric approach based on sparse coding schemes is employed to segment the whole behavioral sequence into unequal length segments, thus resultant avoiding further efforts for grouping. Then attempts are made to entangle the resultant segmentation with other non-local behavioral patterns onto such sequence to ascertain that the non-stationarity corresponds to a sequence of different categories of underlying driving force. It is of potential importance that this segmentation, represented by a hierarchy of code sequences, provides a natural platform for detecting intrinsically coherent behavioral patterns based on continuously recorded data. Illustrations throughout the developments are made exclusively on data encoded from a nearly 4-h video-recording of a female bean weevil's behavior.

Algorithms↗

PubMed2004

snRNPs are present in the karyosome capsule in the weevil germinal vesicle.

Within the oocyte nucleus of the apple blossom weevil, Anthonomus pomorum (Insecta, Coleoptera) highly condensed and transcriptionaly inactive chromosomes form the karyosome. During its formation, within the nucleoplasm numerous, variably sized spherical inclusions termed nuclear bodies occur. As oogenesis progresses, the karyosome is gradually surrounded by a prominent sheath, the karyosome capsule. The function and molecular composition of both the nuclear bodies and the karyosome capsule are largely unknown. Using cytochemical methods we demonstrate that DNA is confined to the karyosome and there is no extrachromosomal DNA accumulations within the nucleoplasm. In addition, none of the oocyte nucleus subdomains contain argyrophilic proteins. Our immunoEM study revealed that in contrast to similar structures in germinal vesicles in other insect species, the nuclear bodies of A. pomorum do not cross-react with antibodies recognising small nuclear ribonucleoproteins, coilin or the splicing factor SC-35. Unexpectedly, we found that as the karyosome capsule develops, mature small nuclear RNAs and proteins containing the Sm epitope associate with the capsule material. We suggest that the karyosome capsule is a storage site for small nuclear ribonucleoprotein particles, which may be used during early embryonic development.

Animals↗

PubMed2004

Soyacystatin N inhibits proteolysis of wheat alpha-amylase inhibitor and potentiates toxicity against cowpea weevil.

Genetic engineering may be used to introduce multiple insect resistance genes with different modes of action into crop plants. We explored the possible interactions of two differing gene products fed in the diet of cowpea weevil, Callosobruchus maculates (F.), a stored grain pest. The soybean cysteine protease inhibitor soyacystatin N (scN) and alpha-amylase inhibitor (alphaAI) from wheat have defensive function against this coleopteran. When artificial seeds containing both scN and alpha(AI) were infested with eggs of C. maculatus, the delays in larval development were longer than was predicted by summing the developmental delays seen when larvae were fed a diet containing the individual proteins, indicating that the effects of scN and alpha(AI) are synergistic. Alpha(AI) was readily hydrolyzed when incubated with insect gut extract. This proteolytic degradation was inhibited by scN, but not by Kunitz inhibitor (a serine protease inhibitor). Thus, degradation of alpha(AI) was due to proteolysis by insect digestive cysteine proteases. These data suggest that C. maculatus uses digestive enzymes not only to function in food protein digestion but also to defend the insects themselves by helping reduce the concentration of a toxic dietary protein.

Animals↗

PubMed2004

Protein-enriched pea flour extract protects stored milled rice against the rice weevil, Sitophilus oryzae.

Studies were conducted to evaluate the effect of a protein-enriched pea (Pisum sativum var. Bonneville) flour extract against the rice weevil, Sitophilus oryzae in its repellency, toxicity, effect on fecundity, stability and sensory properties. Milled rice admixed with pea flour extract at 1% concentration significantly repelled S. oryzae. Mortality of S. oryzae was found to increase and fecundity was markedly suppressed, in rice treated with 1% pea flour extract. The toxicity and reproductive effects of the pea protein-enriched rice were found to be stable for a period of 5 months. The sensory characteristics of stored rice when eaten were not affected by the treatment with pea flour extract. This study indicates that the protein-enriched flour extract obtained from the Bonneville pea may be feasible to protect stored milled rice from insect attack.

Animals↗

PubMed2004

Endosymbiont phylogenesis in the dryophthoridae weevils: evidence for bacterial replacement.

Intracellular symbiosis is widespread in the insect world where it plays an important role in evolution and adaptation. The weevil family Dryophthoridae (Curculionoidea) is of particular interest in intracellular symbiosis evolution with regard to the great economical and ecological features of these invasive insects, and the potential for comparative studies across a wide range of host plants and environments. Here, we have analyzed the intracellular symbiotic bacteria of 19 Dryophthoridae species collected worldwide, representing a wide range of plant species and tissues. All except one (Sitophilus linearis) harbor symbiotic bacteria within specialized cells (the bacteriocytes) assembled as an organ, the bacteriome. Phylogenetic analysis of the 16S rDNA gene sequence of the Dryophthoridae endosymbionts revealed three endosymbiotic clades belonging to gamma3-Proteobacteria and characterized by different GC contents and evolutionary rate. The genus name Candidatus Nardonella was proposed for the ancestral clade infesting Dryophthoridae 100 MYA and represented by five of nine bacterial genera studied. For this clade showing low GC content (40.5% GC) and high evolutionary rate (0.128 substitutions/site per 100 Myr), a single infection and subsequent cospeciation of the host and the endosymbionts was observed. In the two other insect lineage endosymbionts, with relatively high GC content (53.4% and 53.8% GC), competition with ancestral pathogenic bacteria might have occurred, leading to endosymbiont replacement in present-day last insects.

Animals↗

PubMed2004

Ecomorphological adaptation of acorn weevils to their oviposition site.

Comparisons between closely related species in different habitats provide a window into understanding how biotic factors shape evolutionary pathways. Weevils in the genus Curculio have radiated extensively across the Palearctic, where similar ecomorphs have evolved independently on different hosts. We examined ecological and morphological data for 31 Curculio species using multivariate statistics to determine which morphological traits covary and which correlate with the host seed size. A subset of 15 taxa for which phylogenetic relationships were known were used for comparative analyses and inferring historical patterns of trait evolution. The morphological analyses suggest rostrum size increased proportionately to body size in both males and females and that both rostrum and body size correlate with host seed size but that rostrum shape does not correlate with any of the seed traits used in the analyses. Host shifts from small seeds to considerably larger seeds or vice versa have occurred several times independently and historical trait evolution indicates that these host shifts were accompanied by morphological changes in rostrum size. These patterns suggest that seed size is an important selective agent for changes in rostrum length along with body size and thus may be a key factor promoting morphological differentiation in the genus Curculio.

Adaptation, Biological↗

PubMed2004

Divergence in replicated phylogenies: the evolution of partial post-mating prezygotic isolation in bean weevils.

By tradition, speciation research has been focused on processes leading to either premating or post-zygotic reproductive isolation. The processes which generate isolation after mating but before zygote formation are less well understood. Here, we study divergence in characters which contribute to post-mating prezygotic isolation, such as egg production and remating rate. We propose that 'replicated' laboratory phylogenies with known histories can be used to yield insights into the processes of divergence. We performed a series of cross-matings between populations within two strains of the bean weevil Callosobruchus maculatus. Each strain has a unique and independent origin and both have been kept in the same set of laboratories during the last few decades. Our results show that divergence has occurred between laboratory populations within strains with regards to the effects that mating has on female reproductive behaviour, showing that the evolution of partial post-mating prezygotic isolation can be rapid. More importantly, the pattern of divergence across populations was distinct in the two strains, suggesting that coevolutionary trajectories are not determined by environmental factors but are to some extent arbitrary. We discuss the limitations of the novel empirical strategy employed here, and conclude that our results lend support to the hypothesis that post-mating sexual selection is capable of rapidly generating post-mating prezygotic isolation.

Animals↗

PubMed2006

Host PGRP gene expression and bacterial release in endosymbiosis of the weevil Sitophilus zeamais.

Intracellular symbiosis (endosymbiosis) with gram-negative bacteria is common in insects, yet little is known about how the host immune system perceives the endosymbionts and controls their growth and invasion without complete bacterial clearance. In this study, we have explored the expression of a peptidoglycan recognition protein gene of the weevil Sitophilus zeamais (wPGRP); an ortholog in Drosophila (i.e., PGRP-LB) was recently shown to downregulate the Imd pathway (A. Zaidman-Remy, M. Herve, M. Poidevin, S. Pili-Floury, M. S. Kim, D. Blanot, B. H. Oh, R. Ueda, D. Mengin-Lecreulx, and B. Lemaitre, Immunity 24:463-473, 2006). Insect challenges with bacteria have demonstrated that wPGRP is induced by gram-negative bacteria and that the level of induction depends on bacterial growth. Real-time reverse transcription-PCR quantification of the wPGRP gene transcript performed at different points in insect development has shown a high steady-state level in the bacteria-bearing organ (the bacteriome) of larvae and a high level of wPGRP up-regulation in the symbiotic nymphal phase. Concomitantly, during this stage fluorescence in situ hybridization has revealed an endosymbiont release from the host bacteriocytes. Together with the previously described high induction level of endosymbiont virulence genes at the nymphal phase (C. Dale, G. R. Plague, B. Wang, H. Ochman, and N. A. Moran, Proc. Natl. Acad. Sci. USA 99:12397-12402, 2002), these findings indicate that insect mutualistic relationships evolve through an interplay between bacterial virulence and host immune defense and that the host immunity engages the PGRP gene family in that interplay.

Animals↗

PubMed2005

Synthesis of the four stereoisomers of 2,6-dimethyloctane-1,8-dioic acid, a component of the copulation release pheromone of the cowpea weevil, Callosobruchus maculatus.

A diastereomeric mixture and the four stereoisomers of 2,6-dimethyloctane-1,8-dioic acid (2), a copulation release pheromone of the cowpea weevil, Callosobruchus maculatus, were synthesized. The stereoisomeric purities of the four synthetic isomers of 2 were determined by the HPLC analyses of their bis-2-(2,3-anthracenedicarboximide)-1-cyclohexyl esters.

Acyclic Monoterpenes↗