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PubMed2004

Entomopathogenic fungi from 'El Eden' Ecological Reserve, Quintana Roo, Mexico.

Entomopathogenic fungi were isolated and identified from insects collected from the tropical forest and an agricultural area at El Eden Ecological Reserve, Quintana Roo, Mexico. These fungi were studied to determine their potential as biological control agents of greenhouse Trialeurodes vaporariorum (Homoptera: Aleyrodidae), and to contribute to the knowledge of biodiversity of this area. No pest insects were observed in the tropical forest. In contrast, all insects collected in the agricultural area were considered important pests by the local farmers, with the whitefly, as the most relevant, plentiful in Cucurbitaceae plants. From approximately 3400 collected insects in three different surveys, different anamorphic Ascomycetes were recovered. One isolate of Aspergillus sp., two of Penicillium sp., three of Paecilomyces marquandii, and three of Verticillium sp. out of 308 insects (2.9%) from three insect orders, Hymenoptera, Diptera and Isoptera in the tropical forest. In contrast, a higher number of fungal isolates were recovered from the agricultural area: three isolates from Aspergillus parasiticus, 100 of Fusarium moniliforme, one of Aschersonia sp., and 246 of Fusarium oxysporum out of 3100 insects (11.3%) from three insect orders, Homoptera, Coleoptera and Lepidoptera. The results of this study show Fusarium moniliforme and F oxysporum as highly virulent to infected insects in the agricultural area, with 100 and 246 isolates respectively, out of 350 infected insects of 3100 studied specimens. Laboratory whitefly nymph bioassays with isolates Ed29a of F. moniliforme, Ed322 of F. oxysporum, and Ed22 of P marquandii showed 96 to 97.5% insect mortality with no significant differences (P < 0.05) among them. F. oxysporum Ed322 produced no mortality when inoculated on tomato, bean, squash and maize seedlings (with and without injuries) compared to the 100% mortality caused by phytopathogenic strains, F. oxysporum f. sp. lycopersici and F. oxysporum f. sp. radicis lycopersici.

Animals↗
PubMed2002

Mayolenes: labile defensive lipids from the glandular hairs of a caterpillar (Pieris rapae).

Larvae of the European cabbage butterfly, Pieris rapae (Pieridae), are beset with glandular hairs, bearing droplets of a clear oily secretion at their tip. The fluid consists primarily of a series of chemically labile, unsaturated lipids, the mayolenes, which are derived from 11-hydroxylinolenic acid. In bioassays with the ant Crematogaster lineolata, the secretion was shown to be potently deterrent, indicating that the fluid plays a defensive role in nature.

Animals↗
PubMed1994

Reversal of resistance to Bacillus thuringiensis in Plutella xylostella.

Continued success of the most widely used biopesticide, Bacillus thuringiensis, is threatened by development of resistance in pests. Experiments with Plutella xylostella (diamondback moth), the first insect with field populations resistant to B. thuringiensis, revealed factors that promote reversal of resistance. In strains of P. xylostella with 25- to 2800-fold resistance to B. thuringiensis compared with unselected strains, reversal of resistance occurred when exposure to B. thuringiensis was stopped for many generations. Reversal of resistance was associated with restoration of binding of B. thuringiensis toxin CryIA(c) to brush-border membrane vesicles and with increased biotic fitness. Compared with susceptible colonies, revertant colonies had a higher proportion of extremely resistant individuals. Revertant colonies responded rapidly to reselection for resistance. Understanding reversal of resistance will help to design strategies for extending the usefulness of this environmentally benign insecticide.

Animals↗
PubMed1993

Occurrence and distribution in Rhode Island of Hunterellus hookeri (Hymenoptera: Encyrtidae), a wasp parasitoid of Ixodes dammini.

The wasp Hunterellus hookeri Howard parasitizes several species of ixodid ticks including Ixodes dammini Spielman, Clifford, Piesman & Corwin, the vector of Lyme disease spirochetes, Borrelia burgdorferi, in the northeastern United States. We detected the occurrence and evaluated the distribution of this wasp parasitoid in populations of I. dammini in Rhode Island. There has been no intentional introduction of a tick parasitoid recorded anywhere in Rhode Island; yet, we found this wasp at one of the six study sites (Prudence Island), where it parasitized 21 (n = 243) and 17% (n = 284) of nymphal I. dammini collected during 1988 and 1989, respectively. The proportion of nymphs parasitized was greatest during May (46%) and was less in June (18%), July (18%), and August (11%). In Rhode Island, the wasp was only found parasitizing ticks at the site with the highest (by a factor of 2) tick population, confirming similar observations in Massachusetts and New York. It is suggested that establishment as well as the distribution of H. hookeri depends upon a super abundant deer tick population. The usefulness of this parasitoid as a biological control agent is yet unknown.

Animals↗
PubMed2004

Endophytic bacterial communities of field-grown potato plants and their plant-growth-promoting and antagonistic abilities.

To study the effect of plant growth on potato-associated bacteria, the composition and properties of bacteria colonizing the endosphere of field-grown potato were analyzed by a multiphasic approach. The occurrence and diversity of potato-associated bacteria were monitored by a cultivation-independent approach, using terminal restriction fragment length polymorphism analysis of 16S rDNA. The patterns obtained revealed a high heterogeneity of community composition and suggested the existence of plant-specific communities. However, endophytic populations correlated to a certain extent with plant growth performance. Endophytes were also isolated from plants that grew well or grew poorly and were identified by partial sequencing of the 16S rRNA genes. A broad phylogenetic spectrum was found among isolates and differently growing plants hosted different bacterial populations. In an approach to investigate the plant-growth-promoting potential of potato-associated bacteria, a total of 35 bacteria were screened by dual testing for in vitro antagonism towards (i) the fungal pathogens Verticillium dahliae, Rhizoctonia solani, Sclerotinia sclerotiorum, and Phytophthora cactorum and (ii) the bacterial pathogens Erwinia carotovora, Streptomyces scabies, and Xanthomonas campestris. The proportion of isolates with antagonistic activity was highest against Streptomyces sp. (43%) followed by those against Xanthomonas sp. (29%). As all plants showed more or less severe disease symptoms of scab disease caused by Streptomyces scabies, we assume that the presence of the pathogen induced the colonization of antagonists. The antifungal activity of the isolates was generally low. The biotechnological potential of endophytic isolates assessed by their antagonistic activity and by in vitro production of enzymes, antibiotics, siderophores, and the plant growth hormone indole-1,3-acetic acid was generally high. Overall, seven endophytes were found to antagonize fungal as well as bacterial pathogens and showed a high production of active compounds and were therefore considered promising biological control agents.

Antibiosis↗
PubMed1991

Non-target and environmental hazards of pesticides.

When compared with pesticide pollution from other sources and pollution by other agents, the hazards of atmospheric pollution by pesticides appear relatively insignificant. The high persistency in the environment observed especially with the organochlorines suggests that there could be a gradual accumulation of residual pesticides in the atmosphere. Thus, in addition to the function of redistributing pesticides by air currents and aerial drifts, the atmosphere may become a major reservoir for drift prone finely divided particulate pesticides and highly volatile compounds. Indiscriminate aerial spraying should be avoided. A more selective approach should be adopted whereby forest areas are sprayed without contaminating streams, lakes and inland waters. Improvement in spraying devices are needed such that pesticides are more precisely delivered to target. Direct spraying of water bodies should be avoided as much as possible. Treatment of waste water for pesticide removal or neutralization prior to effluence from factories and disposal of effluence to legally designated sites in addition to chemical treatment of contaminated water are more ways of reducing water pollution. Pesticide residues in soil, in addition to eliminating or reducing parasitic microbes, are also toxic to the non-parasitic and ecologically useful soil microbial and vertebrate population. Pesticides may reduce certain microorganism populations while they stimulate the growth of others, especially the saphrophytic and spore forming types. Soil chemical properties may also be altered by accumulation of residual pesticides and their metabolites. These processes may disrupt the ecological balance in the soil microenvironment, first by simplifying the microbial population, and possibly by reducing soil fertility and its ability to support life. Non-target or residual pesticide toxicity would also disrupt the population of some of the valuable soil invertebrates like earthworms, predatory mites, centipedes and carabid beetles. Accumulation of pesticides in resistant or tolerant species may provoke episodes of toxicity to organisms higher in the food chain. The chlorinated hydrocarbons are likely to be most ecotoxic. Use of such pesticides ought to be restricted. Efforts to find alternatives to pesticides, especially research into biological control, should be intensified.

Air Pollution↗
PubMedDate not supplied

The repellence of Aristolochia aff. orbicularis roots against the corn borer Sitophilus zeamais.

The repellence of Aristolochia aff. orbicularis root, a native of Xochipala, Guerrero, Mexico, to the corn borer Sitophilus zeamais (Coleoptera) was investigated. The essential oil was isolated from the aromatic root and its repellent effect was assessed. About 40 components of the oil were identified using gas chromatography-mass spectrometry and other spectroscopic methods. The repellence of the roots, the oil and the chromatography fractions were also evaluated. Some fractions had a higher repellence than the total oil.

Animals↗
PubMed2006

Effects of long-term storage on potency of TM Biocontrol-1, the registered viral insecticide of Orgyia pseudotsugata (Lepidoptera: Lymantriidae).

The article presents the results of bioassaying 39 samples of TM Biocontrol-1, a viral insecticide, from 10 different lots and various sizes of vacuum-sealed packages that were stored at -10 degrees C for 5-15 yr. This is the first study to present potency data for a registered virus product stored for this length of time. Laboratory bioassays in insects from the same colony from which the TM Biocontrol-1 was produced showed that the stored viral insecticide is still effective, although it lost approximately 30% of its effectiveness during storage. A direct correlation of this loss with the length of time in storage is not apparent. Bioassays also showed that there are significant differences in the susceptibility of Douglas-fir tussock moth, Orgyia pseudotsugata (McDunnough), larvae from different geographic regions to OpMNPV (family Baculoviridae, genus Nucleopolyhedrovirus) infection. Package size did not affect the potency of stored TM Biocontrol-1. There were no clear, significant differences in the effectiveness among lots of TM Biocontrol-1 processed by different organizations.

Animals↗
PubMed2000

Development of diagnostic concentrations for monitoring Bacillus thuringiensis resistance in European corn borer (Lepidoptera: Crambidae).

Two candidate diagnostic concentrations of the Cry1Ab and Cry1Ac toxins from Bacillus thuringiensis corresponding to the LC99 and EC99 (effective concentration that causes 99% growth inhibition) for European corn borer, Ostrinia nubilalis (Hübner), were determined based on previously obtained baseline data. Validation experiments using field-collected European corn borer populations from across North America showed that for Cry1Ab, a concentration corresponding to the upper limit of the 95% confidence interval of the LC99, produced mortality > 99% for all populations tested. However, for Cry1Ac, adjustments and further validation are probably necessary. Development of B. thuringiensis resistance monitoring programs that rely on diagnostic techniques are discussed.

Animals↗
PubMed2001

Impact of Bt cottons expressing one or two insecticidal proteins of Bacillus thuringiensis Berliner on growth and survival of noctuid (Lepidoptera) larvae.

A series of laboratory assays were performed to compare the relative impact of commercial and experimental cultivars of cotton, Gossypium hirsutum (L.), expressing zero, one, or two insecticidal proteins of Bacillus thuringiensis Berliner, on several lepidopteran pests. Assays in which larvae were fed fresh plant tissue indicated that dual-toxin B. thuringiensis (Bt) cultivars, expressing both Cry1Ac and Cry2Ab endotoxins of B. thuringiensis, were more toxic to bollworms, Helicoverpa zea (Boddie), fall armyworms, Spodoptera frugiperda (J. E. Smith), and beet armyworms, Spodoptera exigua (Hubner), than single-toxin cultivars expressing Cry1Ac. Assays in which lyophilized plant tissue was incorporated into artificial diet also indicated improved activity of the dual-toxin Bt cultivar compared with single-toxin plants. Both bollworm and tobacco budworm, Heliothis virescens (F.), growth was reduced by Bt cotton, particularly the dual-toxin cultivar. Although assays with lyophilized tissues were done using largely sublethal doses, bollworm survival was reduced by the dual-toxin cultivar. It appears that this newly developed Bt cotton expressing two toxins will be more effective and have a wider range of activity on these lepidopteran pests.

Animals↗
PubMed2001

Sesquiterpene carboxylic acids from a wild tomato species affect larval feeding behavior and survival of Helicoverpa zea and Spodoptera exigua (Lepidoptera: Noctuidae).

The sesquiterpene carboxylic acids (SCA), (+)-(E)-alpha-santalen-12-oic, (-)-(E)-endo-alpha-bergamoten-12-oic, and (+)-(E)-endo-beta-bergamoten-12-oic acid, are produced in glandular trichomes of Lycopersicon hirsutum f. typicum Humb. & Bonpl. accession (LA) 1777, which is highly resistant to a range of pests of cultivated tomatoes. L. esculentum Mill. Exposure of the larvae of two key tomato pests, tomato fruitworm [Helicoverpa zea (Boddie)] and beet armyworm [Spodoptera exigua (Hübner)], to these compounds in diets and on leaf surfaces resulted in reduced development rates and survival and deterred feeding. These effects were observed when levels of SCA, in artificial insect diet, applied to leaflets of susceptible cultivars, or synthesized in trichomes of leaves of plants, exceeded 2 mg SCA/g of diet or fresh leaf weight. This study suggests that cultivated tomatoes capable of synthesizing SCA, at 2 mg SCA/g of leaf tissue or greater, on their leaves and fruit would display enhanced host plant resistance to H. zea and S. exigua and other insect pests.

Animals↗
PubMed2002

Resistance monitoring of Helicoverpa armigera (Lepidoptera Noctuidae) to Bacillus thuringiensis insecticidal protein in China.

Sensitivities of Helicoverpa armigera (Hübner) field populations to Bacillus thuringiensis (Bt) insecticidal protein CrylAc were monitored during 1998-2000 in China. A total of 41 strains was sampled, and most of them were collected from Bt cotton planting regions. The range of IC50 values (concentration producing 50% inhibition of larval development to third instar) among different populations in 1998,1999, and 2000 were 0.020-0.105 microg/ml, 0.016-0.099 microg/ml, and 0.016-0.080 microg/ml, respectively. Diagnostic concentration studies (IC99) showed that the percentage of individuals reaching third instar ranged from 0 to 4.35%, with only eight of the 41 tested populations showing values above 0%. Also interesting was a trend over successive years in which fewer populations contained individuals that survived the diagnostic concentration by reaching third instar. Considering these data, it was determined that the field populations sampled during the 3-yr study were susceptible to CrylAc protein, and that movement toward resistance among H. armigera populations was not apparent.

Animals↗
PubMed2005

Suppressive effects of Calendula micrantha essential oil and gibberelic acid (PGR) on repro ductive potential of the Mediterranean fruit fly Ceratitis capitata Wied. (Diptera: Tephritidae).

The volatile oil of Calendula micrtantha plant was extracted and the components were identified by Gc/Ms. Adulticidal efficiency of the volatile oil and gibberelic acid "plant growth promoting hormone" as well as their mixture was assessed against the Mediterranean fruit fly Ceratitis capitata. The result showed that the two compounds capable have characteristic resembling to insect juvenile hormones and have suppressive effect on reproductive potential. They induced the significant disturbances in the ovarian protein fraction and the amino acids patterns.

Animals↗
PubMed1990

Isolation of indigenous larvicidal microbial control agents of mosquitos: the Malaysian experience.

A nationwide screening program searching for microbial control agents of mosquitos was initiated in Malaysia in 1986. A total of 725 samples were collected and 2,394 bacterial colonies were isolated and screened for larvicidal activity. From such screening, 20 Bacillus thuringiensis, 6 B. sphaericus, 1 Clostridium bifermentans and 2 Pseudomonas pseudomallei larvicidal isolates were obtained. Of these, a new B. thuringiensis named as subspecies malaysianensis was found, while the C. bifermentans was also a new anaerobe individualized as serovar malaysia. It was concluded that this screening program was highly successful.

Animals↗
PubMed1995

Structure, function and engineering of Bacillus thuringiensis toxins.

Nature has provided potent insecticidal toxins as fermentation products of many Bacillus thuringiensis strains. Elucidation of structure-function relationships for this class of natural toxins is in its early stages. Both direct experimentation and application of theoretical structure-function principles emerging from the rapidly growing field of protein structure are accelerating understanding of these toxins. Coupled with the increasing demand for biologically sound pesticides, the benefits from engineering nature's toxins for improved performance set the stage for exciting, fast growth in discovery, characterization and commercialization of new active ingredients for biopesticides and transgenic plants.

Animals↗
PubMed2005

New resistance mechanism in Helicoverpa armigera threatens transgenic crops expressing Bacillus thuringiensis Cry1Ac toxin.

In Australia, the cotton bollworm, Helicoverpa armigera, has a long history of resistance to conventional insecticides. Transgenic cotton (expressing the Bacillus thuringiensis toxin Cry1Ac) has been grown for H. armigera control since 1996. It is demonstrated here that a population of Australian H. armigera has developed resistance to Cry1Ac toxin (275-fold). Some 70% of resistant H. armigera larvae were able to survive on Cry1Ac transgenic cotton (Ingard) The resistance phenotype is inherited as an autosomal semidominant trait. Resistance was associated with elevated esterase levels, which cosegregated with resistance. In vitro studies employing surface plasmon resonance technology and other biochemical techniques demonstrated that resistant strain esterase could bind to Cry1Ac protoxin and activated toxin. In vivo studies showed that Cry1Ac-resistant larvae fed Cy1Ac transgenic cotton or Cry1Ac-treated artificial diet had lower esterase activity than non-Cry1Ac-fed larvae. A resistance mechanism in which esterase sequesters Cry1Ac is proposed.

Animals↗
PubMed1992

In vivo passage through calves of nematophagous fungi selected for biocontrol of parasitic nematodes.

The experiment was designed to test the survival and performance of stress selected nematophagous fungi after passage through the gastro-intestinal tract of cattle. Ruminating calves were fed daily with a fixed amount of fungal material grown on barley grains. The excreted dung was collected on days four and five after the start of the feeding experiment. Barley grains were washed out of the excreted dung and incoculated on water-agar plates. After incubation for one week, nine of ten fungal isolates were re-isolated from these plates. The predatory capacity of the fungi in the excreted faeces was tested in a dung pat bioassay and a faecal culture system. In the dung pat bioassay, two fungi of the genus Arthrobotrys and six of the genus Duddingtonia reduced the development of Ostertagia ostertagi third stage larvae by 85% (61%-93%), compared to the number of larvae developed from fungus-free control pats. In seven out of these eight isolates, the reduction of larvae in the faecal cultures was 92% (76%-99%).

Animals↗