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At least 397 records · Page 22Linked to original sources
PubMed2003

Low-temperature isolation of disease-suppressive bacteria and characterization of a distinctive group of pseudomonads.

The influence of environmental factors during isolation on the composition of potential biocontrol isolates is largely unknown. Bacterial isolates that efficiently suppressed wheat seedling blight caused by Fusarium culmorum were found by isolating psychrotrophic, root-associated bacteria and by screening them in a bioassay that mimicked field conditions. The impact of individual isolation factors on the disease-suppressive index (DSI) of almost 600 isolates was analyzed. The bacteria originated from 135 samples from 62 sites in Sweden and Switzerland. The isolation factors that increased the probability of finding isolates with high DSIs were sampling from arable land, Swiss origin of samples, and origination of isolates from plants belonging to the family Brassicaceae. The colony morphology of the isolates was characterized and compared to DSIs, which led to identification of a uniform morphological group containing 57 highly disease-suppressive isolates. Isolates in this group were identified as Pseudomonas sp.; they were fluorescent on King's medium B and had characteristic crystalline structures in their colonies. These isolates were morphologically similar to seven strains that had previously been selected for suppression of barley net blotch caused by Drechslera teres. Members of this morphological group grow at 1.5 degrees C and produce an antifungal polyketide (2,3-deepoxy-2,3-didehydrorhizoxin [DDR]). They have similar two-dimensional polyacrylamide gel electrophoresis protein profiles, phenotypic characteristics, and in vitro inhibition spectra of pathogens. In summary, in this paper we describe some isolation factors that are important for obtaining disease-suppressive bacteria in our system, and we describe a novel group of biocontrol pseudomonads.

Biological Assay↗
PubMed1970

Genetics and ecology.

Explore the source record for details and available documents.

Adaptation, Physiological↗
PubMed2000

Plant-toxin interactions in transgenic Bt cotton and their effect on mortality of Helicoverpa armigera (Lepidoptera: Noctuidae).

In Australia, transgenic cotton plants expressing the cry1Ac gene from Bacillus thuringiensis Berliner variety kurstaki are less toxic to first-instar Helicoverpa armigera (Hübner) after the plant is producing fruit. We developed two bioassay methods (leaf mush, leaf disk) to test if the physiological state of the plants explained changes in toxicity and a third method (diet incorporation) was developed to quantify the toxicity of Bt leaves when mixed in chickpea diet. Cry1Ac protein was less toxic to H. armigera larvae when the protein was mixed with leaves from fruiting versus presquare conventional cotton. Differences in LC50 varied from 2.4- to 726-fold, depending on the source of toxin and conventional plant material. These results suggest that plant-toxin interactions in fruiting cotton are reducing the toxicity of the Cry1Ac protein. The possible role of tannins in these changes is discussed.

Animals↗
PubMed2001

Interactions between Nosema pyrausta (Microsporidia: Nosematidae) and Bacillus thuringiensis subsp. kurstaki in the European corn borer (Lepidoptera: Pyralidae).

Larval susceptibility to Bacillus thuringiensis was determined for Nosema pyrausta-infected and uninfected European corn borers, Ostrinia nubilalis (Hübner), in bioassays using a commercial formulation of B. thuringiensis subsp. kurstaki, Dipel ES, incorporated into diet. LC50 values for N. pyrausta-infected larvae were significantly lower (P<0.0001) than for uninfected larvae and declined with increasing levels of infection. LC50 values for a 15-d bioassay using field-colony first instars were 0.006 and 0.027 mg of Dipel ES/kg of diet for larvae moderately infected by N. pyrausta and uninfected larvae, respectively. Nosema pyrausta-infected larvae reared on Dipel ES-amended diets produced 70-fold fewer spores (P<0.0001) than larvae reared on standard diet. For example, 15 d after placement as first instars on standard diet, infected field-colony larvae produced 7.6-8.7 million N. pyrausta spores per larva; similar larvae placed on diet containing 0.09 mg of Dipel ES/kg of diet produced 85-103 thousand spores per larva. Infected larvae also weighed less and failed to mature on Dipel ES-amended diets. Increased susceptibility of N. pyrausta-infected larvae to Dipel ES and reduced N. pyrausta spore production in larvae feeding on diet containing Dipel ES suggest that Bt corn will have a direct adverse effect on the survival and continual impact of N, pyrausta as a regulating factor on European corn borer populations.

Animals↗
PubMedDate not supplied

Quantitative assessment of the infection rate of the entomophthoraceous fungus, Zoophthora anhuiensis against the green peach aphid Myzus persicae.

A two-step method was developed to quantitatively assess the infection rate of the entomophthoraceous fungus, Zoophthora anhuiensis (Li) Humber, on the green peach aphid, Myzus persicae (Sulzer). Firstly, a standard time-dose-mortality relationship, established by modeling data from bioassay 1 at varying conidial dosages (0.4 - 10.4 conidia/mm2) of Z. anhuiensis F97028, was used to yield an estimate of expected mortality probability at a given dosage. Secondly, bioassay 2 was conducted by simultaneously exposing six < or = 4-day-old nymphal colonies to a shower of Z. anhuiensis conidia at each of four dosages (resulting from exposures of 0.3 - 8.0 min). Subsequently, the colonies were separately immersed in a 0.1% chlorothalonil solution for 0.5 min to disinfect all surviving conidia on the host integument from 1 - 12 h after exposure under temperature treatments of 15 and 20 degrees C, respectively. The infection rate during a specific period from the end of the exposure to the immersion was then estimated as the ratio of the observed mortality over the expected mortality probability at a particular dosage. The results showed that the infection of M. persicae from Z. anhuiensis was highly rapid with little difference between aphid colonies maintained at 15 and 20 degrees C before being immersed in the fungicidal solution after exposure. The first 6-hour period after exposure was most crucial to successful infection of the fungus with the infection rate greatly depending on conidial dosages. It took < or = 1 h to infect > 50% of the aphids at a dosage of > 1.5 conida/mm2 and > 90% at > 50 conidia/mm2.

Animals↗
PubMed2004

Autodissemination of the entomopathogenic fungus Metarhizium anisopliae amongst adults of the malaria vector Anopheles gambiae s.s.

BACKGROUND: The entomopathogenic fungus Metarhizium anisopliae is being considered as a biocontrol agent for adult African malaria vectors. In the laboratory, work was carried out to assess whether horizontal transmission of the pathogen can take place during copulation, as this would enhance the impact of the fungus on target populations when compared with insecticides. METHODS: Virgin female Anopheles gambiae sensu stricto were exposed to conidia whilst resting on fungus-impregnated paper. These females were then placed together for one hour with uncontaminated males in proportions of either 1:1 or 1:10 shortly before the onset of mating activity. RESULTS: Males that had acquired fungal infection after mating indicate that passive transfer of the pathogen from infected females does occur, with mean male infection rates between 10.7 +/- 3.2% and 33.3 +/- 3.8%. The infections caused by horizontal transmission did not result in overall differences in survival between males from test and control groups, but in one of the three experiments the infected males had significantly shorter life spans than uninfected males (P < 0.05). CONCLUSION: This study shows that autodissemination of fungal inoculum between An. gambiae s.s. mosquitoes during mating activity is possible under laboratory conditions. Field studies are required next, to assess the extent to which this phenomenon may augment the primary contamination pathway (i.e. direct contact with fungus-impregnated targets) of vector populations in the field.

Animals↗
PubMed2000

Biological control of Bactocera oleae (Diptera: Tephritidae) using a Greek Bacillus thuringiensis isolate.

Bacillus thuringiensis, isolate 114A, was used in toxicity experiments against the wild population ofthe olive pest Bactroceria oleae (Gmelin). In laboratory experiments, spores and crystals of the B.t. were delivered to the insects with the food. Longevity, oviposition period, number of eggs produced, and percent hatch were recorded. Olive fruits from the oviposition test were dipped into a suspension containing spores and crystals of B. thuringiensis 114A after the eggs were deposited. In field experiments, four to six sprayings per year of B.t. 114A isolate were applied for three successive years. It was found that, in addition to the longevity of B. oleae, the oviposition period, number of eggs and percent egg hatch decreased. Also, the percentage of pupation and emergence was reduced when olive fruits with eggs in their mesocarp were dipped in the solution of spores and crystals. Field applications with the toxins of 114A isolate of B. thuringiensis have resulted in significant protection of the olive production.

Animals↗
PubMed2006

Effects of temperature on predation by the stinkbugs Picromerus bidens and Podisus maculiventris (Heteroptera: Pentatomidae) on noctuid caterpillars.

Environmental risks associated with the use of non-indigenous organisms for augmentative biological control have received growing attention. In Europe, the native pentatomid predator Picromerus bidens (Linnaeus) has been considered a potential alternative to the North American pentatomid Podisus maculiventris (Say) for the control of lepidopteran, coleopteran and hymenopteran defoliator pests. In the current study, prey consumption and developmental duration of the predatory stages of P. bidens and P. maculiventris were investigated at three temperatures (18, 23 and 27 degrees C) in the laboratory using caterpillars of Spodoptera littoralis as prey. Development time from second to fifth instar was longer for P. bidens than for P. maculiventris, taking on average 17-44 and 14-32 days, respectively, at the different temperatures. Total nymphal consumption of fourth instar S. littoralis caterpillars indicated a greater voracity of P. bidens as compared with P. maculiventris at both the low and high temperatures tested (18 and 27 degrees C). At 23 degrees C, however, the predation rate of P. maculiventris nymphs exceeded that of P. bidens nymphs. Effect of temperature on the functional response of P. bidens to densities of fourth instar Spodoptera exigua was assessed on potted green bean plants. Female adults of P. bidens exhibited a type II functional response at 18 and 23 degrees C but a type III response at 27 degrees C. Searching efficiency was not affected by temperature but handling time decreased from 4.2 to 1.4 h as temperature increased from 18 to 23 degrees C. However, the predator spent twice as much time handling prey at 27 degrees C (2.9 h) than at 23 degrees C. This study indicates high predation rates of P. bidens at a wide range of temperatures and suggests that the species may be a valuable asset for the biological control of defoliating caterpillars, provided that obstacles to its mass production can be overcome.

Animals↗
PubMed2006

Use of Bacillus thuringiensis toxin as an alternative method of control against Haemonchus contortus.

The biocide activity of Bacillus thuringiensis (B. thuringiensis) IB-16 strain was evaluated against the blood-feeding nematode Haemonchus contortus (H. contortus) in vitro and in vivo assays. Twenty experimental jirds (Meriones unguiculatus) and 32 sheep were infected with H. contortus by oral route. Fourteen days post infection 10 jirds were treated with 0.2 mg per mL of IB-16 soluble toxin by intraperitoneal (i.p.) route and 8 sheep were treated with 0.5 mg of toxin per kg of body weight by intramuscular route 35 days after H. contortus infection. Same number of treated jirds and sheep were used as control. Fecal and blood samples were analyzed from experimental sheep to estimate the number of parasitic eggs, percentage of eosinophils, packed cell volume (PCV), and IgG title. All experimental jirds and 16 sheep (8 treated and 8 controls) were sacrificed at days 5, 7, and 30 after B. thuringiensis treatment. The percentage of nematode reduction was estimated from L(4) and H. contortus adults. The percentage of protection was 80.0 to jirds and 73.8 and 53.3 to sheep, sacrificed at days 7 and 30, respectively. Moreover, nonsignificant difference (P > or = 0.05) was detected from parasitic eggs, eosinophils, and PCV parameters. Significance level of IgG was observed only before H. contortus treatment with B. thuringiensis soluble toxin (P < or = 0.05) but nonsignificant difference was observed after treatment. These results showed that B. thuringiensis activity was similar to those observed by anthelmintic treatment and it could be used as an alternative biological method.

Analysis of Variance↗
PubMed2002

Binary insecticidal crystal protein from Bacillus thuringiensis, strain PS149B1: effects of individual protein components and mixtures in laboratory bioassays.

A family of novel binary insecticidal crystal proteins, with activity against western corn rootworm, Diabrotica virgifera virgifera LeConte, was identified from Bacillus thuringiensis Berliner. A binary insecticidal crystal protein (bICP) from B. thuringiensis strain PS149B1 is composed of a 14-kDa protein (Cry34Abl) and a 44-kDaprotein (Cry35Ab1). These proteins have been co-expressed in transgenic maize plants, Zea mays L., and effectively control western corn rootworm larvae under field conditions. Laboratory experiments were conducted to better understand the contribution of each component protein to the in vivo activity of the bICP. The 14-kDa protein is active alone against southern corn rootworm, Diabrotica undecimpunctata howardi Barber, and was synergized by the 44-kDa protein. In mixtures, the concentration of the 14-kDa protein had a greater impact on efficacy than the 44-kDa component. Although both proteins are clearly required for maximal insecticidal activity, laboratory results did not support the formation of a stable, fixed-ratio complex of the two component proteins.

Animals↗
PubMed1997

Insect chitinases: molecular biology and potential use as biopesticides.

Chitin, an insoluble structural polysaccharide that occurs in the exoskeletal and gut linings of insects, is a metabolic target of selective pest control agents. One potential biopesticide is the insect molting enzyme, chitinase, which degrades chitin to low molecular weight, soluble and insoluble oligosaccharides. For several years, our laboratories have been characterizing this enzyme and its gene. Most recently, we have been developing chitinase for use as a biopesticide to control insect and also fungal pests. Chitinases have been isolated from the tobacco hornworm, Manduca sexta, and several other insect species, and some of their chemical, physical, and kinetic properties have been determined. Also, cDNA and genomic clones for the chitinase from the hornworm have been isolated and characterized. Transgenic plants that express hornworm chitinase constitutively have been generated and found to exhibit host plant resistance. A transformed entomopathogenic virus that produces the enzyme displayed enhanced insecticidal activity. Chitinase also potentiated the efficacy of the toxin from the microbial insecticide, Bacillus thuringiensis. Insect chitinase and its gene are now available for biopesticidal applications in integrated pest management programs. Current knowledge regarding the molecular biology and biopesticidal action of insect and several other types of chitinases is described in this mini-review.

Amino Acid Sequence↗
PubMed2005

Tadpoles of four common Australian frogs are not effective predators of the common pest and vector mosquito Culex annulirostris.

In a laboratory investigation of tadpoles of 4 Australian frogs, Limnodynastes peronii, Limnodynastes tasmaniensis, Litoria aurea, and Litoria peronii, there was no evidence of active predation on larvae of Culex annulirostris. The mortality of larvae was greatest when exposed to the tadpoles of Litoria spp., which may have been the result of specific foraging behavior. Results indicate that Litoria spp. tadpoles may have a minor impact on mosquito populations, but they are unlikely to be useful biological control agents in Australia.

Animals↗
PubMed1998

Examination of New Zealand's endemic Wiseana nucleopolyhedrovirus by analysis of the viral polyhedrin gene.

Insects of the genus Wiseana (Lepidoptera: Hepialidae) are major agricultural pests in New Zealand. Singly enveloped nucleopolyhedroviruses (SNPVs) isolated from three of the seven described Wiseana species have potential as biological control agents. As part of an effort to characterise the Wiseana SNPV genome the polyhedrin gene was cloned and the nucleotide sequence determined. The gene sequence was used, in conjunction with morphological and restriction endonuclease analysis, to compare isolates from different sites and species of Wiseana. Heterogeneity was detected within a single site, as well as between SNPV from separate Wiseana species. The extent of divergence between the nucleotide sequences was small enough, however, to consider three SNPVs from W. signata, W. cervinata and W. umbraculata as different strains of a single SNPV species. This improves the likely practicability of developing a single viral agent to control this pest complex. In addition, the virus polyhedrin gene sequence was used to estimate the phylogenetic relatedness of a W. signata SNPV to 16 other NPV from diverse insect genera. These comparisons suggest the Wiseana SNPV was unique within the Baculoviridae, but was more closely related to the group II NPVs.

Animals↗
PubMed2006

Use of Bacillus thuringiensis toxins for control of the cotton pest Earias insulana (Boisd.) (Lepidoptera: Noctuidae).

Thirteen of the most common lepidopteran-specific Cry proteins of Bacillus thuringiensis have been tested for their efficacy against newly hatched larvae of two populations of the spiny bollworm, Earias insulana. At a concentration of 100 microg of toxin per milliliter of artificial diet, six Cry toxins (Cry1Ca, Cry1Ea, Cry1Fa, Cry1Ja, Cry2Aa, and Cry2Ab) were not toxic at all. Cry1Aa, Cry1Ja, and Cry2Aa did not cause mortality but caused significant inhibition of growth. The other Cry toxins (Cry1Ab, Cry1Ac, Cry1Ba, Cry1Da, Cry1Ia, and Cry9Ca) were toxic to E. insulana larvae. The 50% lethal concentration values of these toxins ranged from 0.39 to 21.13 microg/ml (for Cry9Ca and Cry1Ia, respectively) for an E. insulana laboratory colony originating from Egypt and from 0.20 to 4.25 microg/ml (for Cry9Ca and Cry1Da, respectively) for a laboratory colony originating from Spain. The relative potencies of the toxins in the population from Egypt were highest for Cry9Ca and Cry1Ab, and they were both significantly more toxic than Cry1Ac and Cry1Ba, followed by Cry1Da and finally Cry1Ia. In the population from Spain, Cry9Ca was the most toxic, followed in decreasing order by Cry1Ac and Cry1Ba, and the least toxic was Cry1Da. Binding experiments were performed to test whether the toxic Cry proteins shared binding sites in this insect. 125I-labeled Cry1Ac and Cry1Ab and biotinylated Cry1Ba, Cry1Ia, and Cry9Ca showed specific binding to the brush border membrane vesicles from E. insulana. Competition binding experiments among these toxins showed that only Cry1Ab and Cry1Ac competed for the same binding sites, indicating a high possibility that this insect may develop cross-resistance to Cry1Ab upon exposure to Cry1Ac transgenic cotton but not to the other toxins tested.

Animals↗