Direct and indirect estimates of Pandora neoaphidis conidia in laboratory bioassays with aphids.
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Animals↗
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Results for “Pest Control, Biological”
Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.
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Evaluating the impacts of refuge width on source-sink dynamics between transgenic and non-transgenic cotton.
Resistance management for Bt-transgenic crops relies in part on the production of sufficient numbers of susceptible insects in non-toxic refuges. Simulation models suggested that source-sink dynamics could interact with the structure of refuges to impact the production of insects in these areas. We tested the hypothesis that altering isolation between refuges and transgenic cotton by manipulating the width of refuges embedded within cotton fields would alter the density of Heliothis virescens and Helicoverpa zea eggs oviposited in refuges. Three categories of refuge widths were tested over two years: they included narrow (16-24 m wide), medium (32-48 m wide) and wide (80-96 m wide) refuges. Isolation between the two habitats increased as refuge width increased. In 1996, eggs of H. virescens from H. zea were not distinguished, but a significant increase in the density of eggs and a significant decrease in relative yield (refuge yield compared to the yield from immediately surrounding Bt-cotton) was found as refuge width increased. In 1997, eggs from H. virescens were analyzed separately from H. zea using an ELISA test. The density of H. virescens eggs increased with increasing refuge width, and there was a significant decline in density of H. virescens eggs with increasing distance from the refuge. In contrast, there was no impact of refuge width on the density of H. zea eggs, nor was the slope of a regression of egg density and distance from the refuge significantly different from zero. We suggest that these differences reflect differences in the biology of the two insects.
Animals↗
Ecology. Aquaculture--a gateway for exotic species.
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Animals↗
Plant chemistry and natural enemy fitness: effects on herbivore and natural enemy interactions.
Tremendous strides have been made regarding our understanding of how host plant chemistry influences the interactions between herbivores and their natural enemies. While most work has focused on plant chemistry effects on host location and acceptance by natural enemies, an increasing number of studies examine negative effects. The tritrophic role of plant chemistry is central to several aspects of trophic phenomena including top-down versus bottom-up control of herbivores, enemy-free space and host choice, and theories of plant defense. Furthermore, tritrophic effects of plant chemistry are important in assessing the degree of compatibility between biological control and plant resistance approaches to pest control. Additional research is needed to understand the physiological effects of plant chemistry on parasitoids. Explicit tests are required to determine whether natural enemies can act as selective forces on plant defense. Finally, further studies of natural systems are crucial to understanding the evolution of multitrophic relationships.
Animals↗
Computer simulation of management strategies for Psorophora columbiae in the rice agroecosystem.
Various control strategies were evaluated using a previously-described and validated (Focks et al. 1988a, 1988b) simulation model (PcSim) of the population dynamics of Psorophora columbiae breeding in the rice agroecosystem. As expected from field experience, focally-applied ground or aerial ULV aerosols of insecticides were seen to provide local control of peak populations. Similar control was predicted for larvicides when also used in and around urban and suburban areas. Both of these measures were predicted by simulation to provide only short term control of adults as a result of immigration of adults from surrounding, untreated provide only short term control of adults as a result of immigration of adults from surrounding, untreated areas. Evaluations of the effectiveness of diapause egg control or the elimination of early spring broods to provide lasting, season-long suppression were not encouraging if only conventional methods such as insecticides or tillage were used. This was primarily because the ability of Ps. columbiae to recolonize treated areas during the course of a breeding season would require the treatment of prohibitively large, parish- (i.e., county-) sized areas. Evaluations of host management (either removal or residual insecticide treatment of cattle) in and around urban and suburban areas were more encouraging. This technique, by providing continuing pressure on populations, has the potential to offset the impact of immigration and thereby afford long-term suppression in local areas. Finally, evaluations of the impact of modifications to irrigation practices indicated that this approach warrants consideration as a supplemental control technique. These results suggest that field evaluations of model predictions would be useful. They emphasize the need to better understand the movement and spatial distribution of Ps. columbiae. These factors would bear directly on the cost and therefore, the practicality of several of the long-term suppression strategies evaluated as they determine the size of the treatment area surrounding population centers needed to offset the impact of immigration from surrounding, untreated areas.
Agriculture↗
An alternative bioassay employing neonate larvae for determining the toxicity of suspended particles to mosquitoes.
An alternative bioassay using neonate larvae of Aedes aegypti is described for determining the toxicity of suspended particles, particularly insecticidal bacteria, to mosquitoes. This new assay is comparable in precision to the 4th instar bioassay recommended by the World Health Organization, but is quicker and requires much less space. Values obtained using neonate larvae as the test insect showed less variation within and between replicates in regard to LC50 and slope of the regression line, and in general required fewer replicates to fulfill the requirements for a statistically valid bioassay than the W.H.O. assay. The precision of the neonate larval bioassay in combination with its requirements for less time and space may make it especially useful for screening large numbers of samples.
Aedes↗
Fungal siderophores in plant-microbe interactions.
Siderophores are low-molecular-weight high specificity, ferric iron chelating agents. They are produced under iron starvation by most microorganisms. Systems such as siderophores, involved in the acquisition of iron under iron limited conditions, may play a major role in microbial interactions. Some siderophores are virulence factors in animal and in plant pathogens. Moreover, siderophores have been demonstrated to play a major role in plant disease suppression by some bacterial biocontrol agents which inhibit the growth or the activity of plant pathogens by sequestering iron. This latest type of mechanism has been extensively studied in bacteria. However, the role of these iron chelating compounds in disease suppression by fungal biocontrol agents has not been clearly determined.
Bacteria↗
[Characterization of insecticidal crystal proteins of Bacillus thuringiensis subsp. chinensis CT-43].
Bacillus thuringiensis subsp. chinensis CT-43, no flagellum, produces various shaped parasporal crystals, which consist of 140000, 130000, and 65000 proteins. Based on two kinds of mutant, 140000 and 130000 crystal protein individually forms bipyramidal crystal and the 65000 protein forms cubidal crystal, and that the 140000 and 130000 protein is activated by trypsin into 55000 and 66000 proteins and 60000 protein, respectively. Bioassay were conducted to 3rd instar Plutella xylostella larvae with crystals, soluble crystal proteins, and activated crystal proteins, respectively, and it indicated that high toxic mutants can be obtained by curing low toxic crystal genes, and that the toxicity of crystals can be improved 16.3 to 58.4 times after solubilization.
Animals↗
Epidemiological concepts and strategies for parasite control: what changes are likely to occur?
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Animals↗
Host-host-pathogen models and microbial pest control: the effect of host self regulation.
A model has been investigated of the dynamics of the interaction between two hosts that are both attacked by a common pathogen with free-living infective stages, where the hosts are also subject to self-regulation. If either host interacted with the pathogen alone, two types of dynamics would be possible: an uninfected state where the host settles at its carrying capacity, and an infected state where the host settles at, or cycles around, a density lower than the carrying capacity. The three possible combination of two hosts have been investigated: uninfected-uninfected (both hosts uninfected if alone with the pathogen), infected-uninfected and infected-infected. A range of dynamics is generated, depending on parameter values, including infected co-existence of the two hosts (arrived at by a variety of routes), uninfected co-existence of the two hosts, exclusion of one host by the other which remains in an infected state, and a number of outcomes contingent on the initial densities in the system. Free-living infective stages make uninfected co-existence more likely and introduce additional contingency into the dynamics. The implications for microbial pest control are into the dynamics. The implications for microbial pest control are markedly different from those derived from related models without host self-regulation. There appears to be little chance of a non-target host undermining pest control, relatively little chance of the non-target enhancing pest control and a small but non-negligible threat to non-targets when parameter values are appropriate. The application of the results is commended but great caution is urged.
Animals↗
[Biochemical diagnosis of the presence of poisoning by Bacillus thuringiensis serotype "H3a,3b" in two lepidopterans].
A detailed biochemical analysis has shown that during larval development on artificial medium, the amounts of K+, Na+, and Ca2+ in the hemolymph of healthy Choristoneura fumiferana varied from 85 to 110 mg/100 mL, 29 to 33 mg/100 mL, and 4.8 to 7.3 mg/100 mL, respectively. Similar results were obtained with Malacosoma disstria. Intoxication by Bacillus thuringiensis "H3a,3b" (B. t.) considerably modified the amounts of the cations. Thus, after 4 h, the quantity of K+ in M. disstria increased from 99 to 229 mg/100 mL and Na+ from 26.5 to 50.3 mg/100 mL while that of Ca2+ decreased from 5.8 to 1.2 mg/100 mL. Similar results were observed with C. fumiferana, but these variations occurred after 2 to 4 days of B. t. intoxication. The variations detected during the bacillosis, with respect to the cationic composition of the insect hemolymph, are rapidly detectable, well before light microscope observation can confirm the presence of this intoxication. Aspartate aminotransferase, alanine aminotransferase, alpha-hydroxybutyrate dehydrogenase, and isocitrate dehydrogenase activity fluctuated very slightly in the hemolymph of either healthy or bacillosed larvae of the two insects under study. These results suggest that it is possible to diagnose biochemically the presence of a B. t. intoxication in lepidopteran forest pests following treatments by this biological insecticide for their control.
Alanine Transaminase↗
Pathogenicity of Bacillus thuringiensis isolated from two species of Acromyrmex (Hymenoptera, Formicidae).
The control of Acromyrmex leaf-cutting ants is necessary due to the severe damage they cause to diverse crops. A possibility was to control them using the bacterium Bacillus thuringiensis (Bt) that characteristically produces insecticidal crystal proteins (ICPs). The ICPs have been effective in controlling lepidopterans, dipterans, and coleopterans, but their action against hymenopterans is unknown. This paper describes an attempt to isolate Bt from ants of two Acromyrmex species, to evaluate its pathogenicity towards these ants, and to test isolates by PCR. Bacterial isolates of Bt obtained from A. crassispinus and A. lundi have been assayed against A. lundi in the laboratory. The bioassays were carried out in BOD at 25 degrees C, with a 12-hour photoperiod, until the seventh day after treatment. The Bt isolates obtained were submitted to total DNA extraction and tested by PCR with primers specific to cry genes. The results showed Bt presence in 40% of the assessed samples. The data from the in vivo assays showed a mortality rate higher than 50% in the target population, with the Bt HA48 isolate causing 100% of corrected mortality. The PCR results of Bt isolates showed a magnification of DNA fragments relative to cry1 genes in 22% of the isolates, and cry9 in 67%. Cry2, cry3, cry7, and cry8 genes were not detected in the tested samples, and 22% had no magnified DNA fragments corresponding to the assessed cry genes. The results are promising not only regarding allele identification in new isolates, but also fort the assays aimed at determining the Bt HA48 LC50's, which can eventually be applied in controlling of Acromyrmex leaf-cutting ants.
Animals↗
Habitat association in two genetic groups of the insect-pathogenic fungus metarhizium anisopliae: uncovering cryptic species?
Strains of insect-pathogenic fungi with high virulence toward certain pest insects have great potential for commercial biological control applications. Identifying such strains has been a central theme in using fungi for biological control. This theme is supported by a persistent paradigm in insect pathology which suggests that the host insect is the predominant influence on the population genetics of insect-pathogenic fungi. In this study, a population genetics analysis of the insect-pathogenic fungus Metarhizium anisopliae from forested and agricultural habitats in Ontario, Canada, showed a nonrandom association of alleles between two distinct, reproductively isolated groups (index of multilocus association = 1.2). Analyses of the mitochondrial DNA showed no differences between the groups. The two groups were associated with different habitat types, and associations with insect hosts were not found. The group from forested areas showed an ability for cold-active growth (i.e., 8 degrees C), while the group from the agricultural area showed an ability for growth at high temperatures (i.e., 37 degrees C) and resilience to UV exposure. These results represent a significant paradigm shift; habitat selection, not host insect selection, drives the population structure of these insect-pathogenic deuteromycetous fungi. With each group we observed recombining population structures as well as clonally reproducing lineages. We discuss whether these groups may represent cryptic species. Worldwide, M. anisopliae may be an assembly of cryptic species, each adapted to certain environmental conditions. The association of fungal genotypes with habitat but not with host insects has implications on the criteria for utility of this, and perhaps other, fungal biocontrol agents.
Agriculture↗
Use of baculoviruses as biological insecticides.
Naturally occurring baculoviruses can be used to control a wide range of insect pests. Most baculoviruses are used as biopesticides, that is, they are sprayed onto high-density pest populations in a manner akin to the use of synthetic chemical pesticides. However, other strategies that use the biological features of the viruses are also possible and should increase as we expand our knowledge of baculovirus ecology. In order to develop a baculovirus control program, several areas need to be studied before progressing to large scale field studies and commercialization. These range from laboratory efficacy testing and the development of production systems to detailed study of pest behavior and the development of appropriate application strategies.
Animals↗
Bioactivities of seven chrysanthemum species flowers powder on Spodoptera littoralis (Boiduval) larvae.
We have screened seven Chrysanthemum species, collected from different biotope in Tunisia for the antifeeding and growth regulatory activity against S. littoralis (Lepidoptera: Noctuidae) an insect pest of tomato. The flowers powder was added to the Poitout and Bues (1974) artificial diet at three concentrations: 4, 8, and 16%. After ten days of treatment, the consumed quantity determination revelled that these species have an antifeeding activity proportional to the concentration, more considerable for the C. fuscatum and C. Myconis flowers powder. At the concentration of 16% the larvae weight was significantly delayed in the average time to the control, these results were compared to the effect of Cestrum parquii on S. littoralis and Pieris brassicae The moulting date determination showed an elongation of the third, fourth and fifth stages at the high concentration probably due to the presence of juvenile hormones Analogues.
Animals↗
Predacious activity of Duddingtonia flagrans within the cattle faecal pat.
Two studies were conducted to investigate the growth and activity of the fungus, Duddingtonia flagrans, within cattle faecal pats. Artificial faecal pats were constructed with the centre separated from the outer layer by a nylon mesh. Eight treatments were tested, by varying the presence/absence of Cooperia oncophora eggs and fungal spores within each layer. With parasite eggs in the centre layer, a statistically lower recovery of larvae was observed compared to both pats with parasite eggs in the periphery and pats with parasite eggs throughout both layers. Regardless of location within the pat, if co-located with the parasite egg, D. flagrans was found to be effective in trapping developing larvae. The reduction in recovery of larvae from pats with parasite eggs and fungal spores in the centre was found to be significantly higher than when parasite eggs were in the centre and fungal spores in the periphery. In the second study, pats were made up in two treatments: pats containing fungal spores and C. oncophora eggs (fungus) and pats containing C. oncophora eggs (control). The pats were incubated at low or high humidity. Ten pats were used in a cross over where five pats incubated at low humidity for 7 weeks were removed, water added and then incubated at a high humidity for 1 week. Another five pats were incubated at a high humidity for 7 weeks, aerated and incubated at a low humidity for 1 week. There was no apparent growth of fungus in faecal pats incubated at a high humidity and less than 20% of larvae were recovered. The growth of D. flagrans was observed in faecal pats incubated at a low humidity, but a corresponding reduction in the percentage recovery of larvae did not occur, except in week 4. No statistical difference between fungal and control pats was seen in the change over pats. Nematophagous activity was assessed throughout the study and observed in the first 4 weeks within the pats containing fungus.
Animals↗
Translocation induced outgrowth of fungi in nutrient-free environments.
The study of alternatives to chemical methods of nematode control in agriculture has received significant recent interest. One such method is biological control using nematode trapping fungi such as Arthrobotrys superba. To understand how these fungi can be implemented as effective nematicides, it is essential to study their outgrowth into soil from localized nutrient resources. In this paper, we use a mathematical model to investigate the outgrowth of fungi into an environment essentially without available nutrients capable of supporting net growth. By comparing model solutions with experimental results, we show that in such circumstances, continual mycelial expansion can only be obtained if internal metabolites are actively translocated through the mycelium. Predictions are made concerning the maximal extension possible from a given quantity of nutrients and a testable functional relationship between the two is derived. Using this modelling technique we are able to map not only biomass extent but also biomass distribution at each stage. The type of environmental heterogeneity investigated here is encountered by many species of fungi in nature and is of relevance for the introduction of specific fungi into soil for biological control or bioremediation purposes.
Animals↗
Exploiting genotypic diversity of 2,4-diacetylphloroglucinol-producing Pseudomonas spp.: characterization of superior root-colonizing P. fluorescens strain Q8r1-96.
The genotypic diversity that occurs in natural populations of antagonistic microorganisms provides an enormous resource for improving biological control of plant diseases. In this study, we determined the diversity of indigenous 2,4-diacetylphloroglucinol (DAPG)-producing Pseudomonas spp. occurring on roots of wheat grown in a soil naturally suppressive to take-all disease of wheat. Among 101 isolates, 16 different groups were identified by random amplified polymorphic DNA (RAPD) analysis. One RAPD group made up 50% of the total population of DAPG-producing Pseudomonas spp. Both short- and long-term studies indicated that this dominant genotype, exemplified by P. fluorescens Q8r1-96, is highly adapted to the wheat rhizosphere. Q8r1-96 requires a much lower dose (only 10 to 100 CFU seed(-1) or soil(-1)) to establish high rhizosphere population densities (10(7) CFU g of root(-1)) than Q2-87 and 1M1-96, two genotypically different, DAPG-producing P. fluorescens strains. Q8r1-96 maintained a rhizosphere population density of approximately 10(5) CFU g of root(-1) after eight successive growth cycles of wheat in three different, raw virgin soils, whereas populations of Q2-87 and 1M1-96 dropped relatively quickly after five cycles and were not detectable after seven cycles. In short-term studies, strains Q8r1-96, Q2-87, and 1M1-96 did not differ in their ability to suppress take-all. After eight successive growth cycles, however, Q8r1-96 still provided control of take-all to the same level as obtained in the take-all suppressive soil, whereas Q2-87 and 1M1-96 gave no control anymore. Biochemical analyses indicated that the superior rhizosphere competence of Q8r1-96 is not related to in situ DAPG production levels. We postulate that certain rhizobacterial genotypes have evolved a preference for colonization of specific crops. By exploiting diversity of antagonistic rhizobacteria that share a common trait, biological control can be improved significantly.
Antifungal Agents↗