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PubMed2003

The potential of virulent Wolbachia to modulate disease transmission by insects.

A virulent strain of Wolbachia has recently been identified in Drosophila that drastically reduces adult lifespan. It has been proposed that this phenotype might be introduced into insect disease vector populations to reduce pathogen transmission. Here we model the requirements for spread of such an agent and the associated reduction in disease transmission. First, a simulation of mosquito population age structure was used to describe the age distribution of mosquitoes transmitting dengue virus. Second, given varying levels of cytoplasmic incompatibility and fecundity effect, the maximum possible longevity reduction that would allow Wolbachia to invade was obtained. Finally, the two models were combined to estimate the reduction in disease transmission according to different introduction frequencies. With strong CI and limited effect of fecundity, an introduction of Wolbachia with an initial frequency of 0.4 could result in a 60-80% reduction of transmitting mosquitoes. Greater reductions are possible at higher initial release rates.

Age Factors↗
PubMed2003

Comparison of non-linear temperature-dependent development rate models applied to in vitro growth of entomopathogenic fungi.

Five non-linear models with three to five parameters, built to quantify the effect of temperature on insect development and microbial growth, were tested to describe the influence of temperature on in vitro-measured growth rates of entomopathogenic hyphomycetes. Data from two isolates of each of the four fungal species, Paecilomyces fumosoroseus, Beauveria bassiana, Metarhizium anisopliae, Metarhizium flavoviride, were used to assess the features of each model. Criteria for model evaluation included the statistical quality of parameters estimates, the goodness of fit to data, as well as the ability to provide estimates of several key parameters: the upper and lower development thresholds, the thermal optimum and the maximal growth rate at thermal optimum. The second model proposed by Brière et al. (1999) was found to be the best, and Ratkowsky's model (1983) also exhibited good features.

Hot Temperature↗
PubMed2001

Fungal populations on sunflower (Helianthus annuus) anthosphere and their relation to susceptibility or tolerance to Sclerotinia sclerotiorum attack.

Analysis of the fungal flora from different floret parts of various sunflower (Helianthus annuus) varieties showed that there are differences in both fungal species and frequency, depending on whether the sunflower variety is susceptible (SV) or tolerant (TV) to attack of the flower heads by the ascomycete pathogen Sclerotinia sclerotiorum. The sunflower varieties analyzed were SV: HA 300 and Z 20028, and TV: HA 302, Z AV 8410 and Z 30629. The isolates showed different "in vitro" behavior as biocontrol agents. The most common types of interaction with Sclerotinia sclerotiorum were D2 and D2+ (hyphal contact) for isolates from SV and TV, while some of the isolates from TV displayed antibiosis. The microorganisms that colonize TV florets play a part in an indirect mechanism that protects flowers from ascospore germination and pathogen growth.

Ascomycota↗
PubMed2004

Evaluation of prey-stage preference as an indicator of life-style type in phytoseiid mites.

Discriminant analysis (DA) models were developed and applied to examine the use of prey-stage preference (Tetranychus urticae Koch egg versus larval prey) in the classification of phytoseiid mites into life-style types. Prey-stage preferences and developmental times when preying on T. urticae, and relative ovipositional rates on six food categories were determined for four phytoseiid species occurring on apple in central and eastern Oregon, USA: Galendromus flumenis (Chant), Galendromus occidentalis (Nesbitt), Metaseiulus citri (Garman and McGregor) and Typhlodromus caudiglans Schuster. In terms of all three aspects studied, the phytoseiid species showed a consistent polarization of G. occidentalis < or = G. flumenis < or = T. caudiglans < M. citri. Specifically, G. occidentalis ('The Dalles' strain) had a significant preference for eggs, G. flumenis had no preference, and T. caudiglans and M. citri had significant preferences for larvae; G. occidentalis had the shortest developmental time, followed by G. flumenis and T. caudiglans, while M. citri had the longest developmental time; and diet breadth was most narrow for G. occidentalis and progressively broader from G. flumenis, T. caudiglans through M. citri, which was able to sustain oviposition on the broadest range of prey and pollens. Species were classified somewhat differently depending on which traits were considered in a given DA. Prey-stage preference was not included as an indicator in the parsimonious DA model when all species and all traits were considered, but in general this trait performed well as an indicator alone (single-trait DA) and somewhat improved the classifications of multitrait discriminant analyses.

Animals↗
PubMed2003

Release of invasive plants from fungal and viral pathogens.

Invasive plant species both threaten native biodiversity and are economically costly, but only a few naturalized species become pests. Here we report broad, quantitative support for two long-standing hypotheses that explain why only some naturalized species have large impacts. The enemy release hypothesis argues that invaders' impacts result from reduced natural enemy attack. The biotic resistance hypothesis argues that interactions with native species, including natural enemies, limit invaders' impacts. We tested these hypotheses for viruses and for rust, smut and powdery mildew fungi that infect 473 plant species naturalized to the United States from Europe. On average, 84% fewer fungi and 24% fewer virus species infect each plant species in its naturalized range than in its native range. In addition, invasive plant species that are more completely released from pathogens are more widely reported as harmful invaders of both agricultural and natural ecosystems. Together, these results strongly support the enemy release hypothesis. Among noxious agricultural weeds, species accumulating more pathogens in their naturalized range are less widely noxious, supporting the biotic resistance hypothesis. Our results indicate that invasive plants' impacts may be a function of both release from and accumulation of natural enemies, including pathogens.

Ecosystem↗
PubMed1998

Overcoming cytoplasmic incompatibility in Drosophila.

The endocellular microbe Wolbachia pipientis infects a wide variety of invertebrate species, in which its presence is closely linked to a form of reproductive failure termed cytoplasmic incompatibility (CI). CI renders infected males unable to father offspring when mated to uninfected females. Because CI can dramatically affect fitness in natural populations, mechanisms that abate CI can have equally large impacts on fitness. We have discovered that repeated copulation by Wolbachia-infected male Drosophila simulans significantly diminishes CI. Repeated copulation does not prevent Wolbachia from populating developing spermatids, but may reduce the time during spermatogenesis when Wolbachia can express CI. This restoration of fertility in premated infected males could have important implications for Wolbachia transmission and persistence in nature and for its exploitation as an agent of biological pest control.

Animals↗
PubMed2006

EST analysis of cDNA libraries from the entomopathogenic fungus Beauveria (Cordyceps) bassiana. I. Evidence for stage-specific gene expression in aerial conidia, in vitro blastospores and submerged conidia.

The entomopathogenic fungus Beauveria (Cordyceps) bassiana holds much promise as a pest biological control agent. B. bassiana produces at least three in vitro single cell infectious propagules, including aerial conidia, vegetative cells termed blastospores and submerged conidia, that display different morphological, biochemical and virulence properties. Populations of aerial conidia, blastospores and submerged conidia were produced on agar plates, rich liquid broth cultures and under conditions of nutrient limitation in submerged cultures, respectively. cDNA libraries were generated from mRNA isolated from each B. bassiana cell type and approximately 2,500 5' end sequences were determined from each library. Sequences derived from aerial conidia clustered into 284 contigs and 963 singlets, with those derived from blastospores and submerged conidia forming 327 contigs with 788 singlets, and 303 contigs and 1,079 contigs, respectively. Almost half (40-45 %) of the sequences in each library displayed either no significant similarity (e value >10(-4)) or similarity to hypothetical proteins found in the NCBI database. The expressed sequence tag dataset also included sequences representing a significant portion of proteins in cellular metabolism, information storage and processing, transport and cell processes, including cell division and posttranslational modifications. Transcripts encoding a diverse array of pathogenicity-related genes, including proteases, lipases, esterases, phosphatases and enzymes producing toxic secondary metabolites, were also identified. Comparative analysis between the libraries identified 2,416 unique sequences, of which 20-30 % were unique to each library, and only approximately 6 % of the sequences were shared between all three libraries. The unique and divergent representation of the B. bassiana transcriptome in the cDNA libraries from each cell type suggests robust differential gene expression profiles in response to environmental conditions.

Animals↗
PubMed1993

Effect of phenotypic plasticity on epiphytic survival and colonization by Pseudomonas syringae.

The bacterial epiphyte Pseudomonas syringae MF714R was cultured on agar or in broth or collected from colonized leaves; it was then inoculated onto greenhouse-grown bean plants incubated in a growth chamber at low relative humidity or in the field or onto field-grown bean plants. Cells cultured in liquid medium survived the least well after inoculation of leaf surfaces under all conditions. Cells cultured in solid medium exhibited the highest percent survival and desiccation tolerance in the growth chamber but generally survived less well in the field than did cells harvested from plants. Cells harvested from plants and inoculated onto plants in the field usually exhibited the highest percent survival, started to increase in population earlier, and reached a higher number than did cells cultured in vitro. Differences in field survival were apparently not attributable to differential UV tolerance. The observed effects of phenotypic plasticity on epiphytic survival and colonization should be considered in risk assessment studies, in studies of bacterial epidemiology, and in the use of microbial antagonists for biological pest control.

Bacteriological Techniques↗
PubMed2002

Grasses and gall midges: plant defense and insect adaptation.

The interactions of two economically important gall midge species, the rice gall midge and the Hessian fly, with their host plants, rice and wheat, respectively, are characterized by plant defense via R genes and insect adaptation via avr genes. The interaction of a third gall midge species, the orange wheat blossom midge, with wheat defense R genes has not yet exhibited insect adaptation. Because of the simple genetics underlying important aspects of these gall midge-grass interactions, a unique opportunity exists for integrating plant and insect molecular genetics with coevolutionary ecology. We present an overview of some genetic, physiological, behavioral, and ecological studies that will contribute to this integration and point to areas in need of study.

Adaptation, Physiological↗
PubMedDate not supplied

Time trends of occupational pesticide-related injuries in Costa Rica, 1982-1992.

To evaluate time trends of occupational pesticide-related injuries in Costa Rica, a survey was carried out three times over a ten-year period at a national reporting system for occupational accidents and diseases among wage-earning workers. The sample comprised the accidents reported during the months of June of the years 1982, 1987, and 1992. The overall incidence rates were 1.8, 2.7, and 2.5 per 1,000 agricultural workers, respectively. Rates among female workers increased (3.1, 3.7, 5.4) and were elevated as compared with male workers (1.7, 2.6, 2.3). The trend for topical lesions was upgoing (1.2, 1.4, 2.1), consistent with an increased use of fungicides and lack of safety measures for pesticides with low acute toxicity. Systemic poisonings peaked in 1987 (0.6, 1.2, 0.5), declining in 1992 with increased use of biologic pest control and pyrethroid insecticides less toxic than cholinesterase inhibitors, and improved safety during nematocide applications on banana plantations. In 1992, despite the largest decline of systemic poisonings in the banana-producing Atlantic Region, poisonings as well as topical injuries were still four times more frequent in this region than in the rest of the country. Restriction of highly toxic pesticides together with implementation of occupational safety measures can reduce systemic poisonings in developing countries. Such policies need to be extended to other pesticides to prevent less life threatening but often disabling skin and eye injuries.

Accidents, Occupational↗
PubMed2002

Effects of row spacing and plant density on corn rootworm (Coleoptera: Chrysomelidae) emergence and damage potential to corn.

Planting corn, Zea mays L., in row spacings less than the conventional width of 76 cm has been shown to increase grain yields. This study was conducted to determine if row spacing and plant density affected corn rootworm, Diabrotica virgifera virgifera LeConte and D. barberi Smith & Lawrence, adult emergence, larval injury to the roots, and plant tolerance to injury. Field experiments were conducted at Ames and Nashua, IA, in 1998, 1999, and 2000. Treatments were row spacings of 38 and 76 cm, and plant populations of 64,500 and 79,600 plants per hectare. Adult emergence was 31% greater in 38 cm compared with 76-cm rows. However, root injury was not significantly different between row spacings or plant populations. Row spacing alone did not significantly influence tolerance to injury, measured as root size and the amount of root regrowth. However, at one environment where precipitation was low, plants in 38-cm rows produced 25% more regrowth compared with plants in 76-cm rows. Root dry weight and regrowth were suppressed by 16 and 32%, respectively, at the high plant population. Although lodging was 51% lower in the 38-cm rows compared with the 76-cm rows, grain yields were not significantly different between row spacings. Reducing the row spacing of field corn from 76-38 cm should not increase the potential for injury from corn rootworm larvae.

Agriculture↗
PubMed2002

Developmental rates and host specificity for Pseudacteon parasitoids (Diptera: Phoridae) of fire ants (Hymenoptera: Formicidae) in Argentina.

This study extends our comparative knowledge of Pseudacteon interactions with Solenopsis fire ant workers. Reported in this work are development times for seven Argentinean parasitoid species reared on two hosts, Solenopsis richteri Forel and Solenopsis invicta Buren, under laboratory temperature regimes comparable with those of the climatic zones occupied by these host species. Developmental times spanned 31-66 d across phorid species, and in general did not differ between genders or host species, but were longer at lower temperatures. The size distribution of flies reared was bimodal, with a group of large (Pseudacteon borgmeieri, Pseudacteon nocens, Pseudacteon obtusus and Pseudacteon tricuspis) and small (Pseudacteon cultellatus, Pseudacteon curvatus, and Pseudacteon nudicornis) species. P. borgmeieri was exceptional with respect to length of developmental time. Also reported are results of initial oviposition and developmental studies of some of these phorid species on other Argentinean Solenopsis ant species; P. curvatus was the only species able to complete its development on nonhost fire ants. These results support the concept of incorporating several complementary species of Pseudacteon in the biological control of pest fire ants.

Animals↗
PubMed2001

Oviposition preferences of Episyrphus balteatus.

A crucial aspect of predator oviposition behaviour is host plant choice, especially in hoverflies where the newly hatched offspring are unable to move a great distance to search for the appropriate prey. Such offspring must generally feed on the host plant aphids previously selected by the mother. Some factors involved in the selection of the oviposition site of Episyrphus balteatus De Geer include aphids associated to chemical stimuli, aphid colony size and host plant characteristics. Here we tested the hypothesis that there will not only be a rank order hierarchy of preference for aphid prey species reared on the same host plant but that a similar hierarchy of different host plant of one aphid species could be established. Therefore we compared the number of eggs laid on different combinations of host plant and aphid species. Vicia faba L., secondary metabolites free, Brassica napus L. and Sinapis alba L., containing low and high levels of glucosinolates respectively were used. The latter compounds are well known allelochemicals from Brassicaceae having a strong influence on specialist and generalist insects from both phytophagous and entomophagous levels. These experiments enhance the importance of tritrophic interactions in biological control of pests by underlining the host plant influence on aphidophagous predators, either directly or through the odours emitted by the phytophagous prey.

Animals↗
PubMedDate not supplied

[Recent experience with mites in stored products].

The A.A. refer a recent experience about the isolation and identification of same species of storaged timber mites. They believe that these mites are responsible of dermatitis at the trunk and the arms of timber workers. Mites are the most elderly living species on the earth, they can live and grow in different environments, such as plants, flowers, animals, men, earth, lake and sea waters, organical rubles, houses, mattresses, old books etc. There are free-living, saprophitic, parasitic and predator mites. Generally, primary mites live either freely or as commensals feeding on conserved foodstuff and on what they find available. Secondary mites, i.e. parasites and predators, live off primary mites and insects infesting foodstuff. Direct damage to foodstuff are not to be considered important, whereas indirect damages are more serious, due to the contamination of bodies and stools of mites that are rich in nitrogen. Some secondary mites may attack foodstuff workers causing characteristic dermatitis: they can act either directly, by sting and bites, or indirectly, provoking on allergic hypersensitivity. In this study the A.A. used the floating method to isolate timber mites, and then, these have been photographed at the microscope to obtain an easier and more complete identification. The A.A. describe a heterogeneous fauna consisting of both adult and larval-status insects, some species of free-living mites (Oribatula Tibialis) and, in particular, of two species secondary mites, predator, belonging to the Prostigmata sub-order. The Cheyletus Eruditus (Cheylatidae family) is a whitish mite feeding mostly on insect larva and primary mites living in foodstuff. When no prey is available, the Cheyletus Eruditus eats individuals of its own species. The Pyemotes Herfsi (Pyemotidae family) is a little white mite feeding on insect larva. It lives in conserved foodstuff and may attack man causing characteristic dermatitis such as those described by the A.A. The A.A. conclude dealing with the possible preventive and therapeutic measures tend to keep phisic-chemicals parameters of foodstuff and others conserved products afar from the values suitable for the growth of parasites (water content min. 13%, environmental humidity min. 60-65%, appropriate temperature etc.). Therapeutic procedure are based either on physical media: infra-red rays, gamma-rays, electric fields for the transformation of temperature or using chemical mixtures containing methyl bromide, carbon tetrachloride and hydrogen sulphide. Among the therapeutic procedures, however, the biological pest control using chemical media associated with antagonist mites of the infesting species is to be preferred.

Animals↗