Use Of Microbial Control Agents Research Articles

Microbial agents for the control of ticks Rhipicephalus microplus.

Ticks are ectoparasites responsible for the transmission of various pathogens to vertebrates. They represent one of the major threats to livestock production worldwide due to their impact on the health, production and welfare of livestock destined for human consumption. The development of resistance to the main families of ixodicides used for their control has led to the search for new alternatives, where microbial control is an option. The use of microbial control agents against the tick Rhipicephalus microplus is reviewed in this paper. Bacteria such as Bacillus thuringiensis, Serratia marcescens and Staphylococcus spp. the nematodes Steinernema spp. and Heterorhabditis spp. as well as the fungi Metarhizium anisopliae and Beauveria bassiana are the most studied organisms for use as biological control agents against ticks. Laboratory, stable and field trials with free-living and parasitised ticks have shown that microbial agents can control both susceptible and ixodicide-resistant tick populations. However, multidisciplinary studies using novel tools like genomics, transcriptomics and proteomics should be carried out to understand the virulence factors which microbial agents use to induce pathogenesis and virulence in ticks. In addition, applied research will be carried out with the aim of improving techniques for large-scale application, as well as the improvement of cultivation, storage, formulation and application methods.

Biocontrol of the cat flea, Ctenocephalides felis, by entomopathogenic nematodes and fungi

The cat flea, Ctenocephalides felis (Bouche) (Siphonaptera: Pulicidae), is the most important ectoparasite of domestic pets. Its control is mainly based on chemical insecticides. In this study, the potential of fungi and nematodes to control this pest was evaluated. The various life stages of the cat flea were exposed to several variables: strains and species of entomopathogenic nematodes and fungi at different ambient temperatures and levels of relative humidity (RH), as well as in\\on filter paper, sand or carpet as substrates. The nematode Steinernema feltiae (Nematoda: Steinernematidae) was most virulent against flea larvae, cocoons and adults, and the nematode Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae) was highly effective against flea cocoons on all substrates evaluated. Overall, the nematodes were most effective at 28o C and 95% RH. The fungus Metarhizium robertsii 2575 (Bischoff) (Hypocreales: Clavicipitaceae), was highly virulent against adult fleas. Flea eggs were resistant to both nematodes and the fungus evaluated. The results indicate high potential for use of microbial control agents against cat fleas. While the fungus, M. robertsii, could be effective in killing adult fleas on infested vertebrates, the nematodes S. feltiae and H. bacteriophora could be successful in controlling pre-imaginal stages on the soil.

Research and Application of Entomopathogenic Fungi as Pest Management Option: A Review

Entomopathogenic fungi are myco-biocontrol, potentially the most versatile biological control agents with a wide host range and are an environmentally sound and effective means of reducing insect-pests. The use of microbial control agents particularly entomopathogenic fungi, have been investigated for the control of a wide range of orchard and field crop pests and are a widespread component of most terrestrial ecosystems. Entomopathogenic fungi are a major component of integrated pest management techniques as biological control agents against insect pests and other arthropods in horticulture, forestry and agriculture and are found in the divisions of Zygomycota, Ascomycota, Deuteromycota, Chytridiomycota and Oomycota, which were previously classified within fungi. Insect control using entomopathogenic fungi is achieved when sufficient infective propagules, conidia contact a susceptible host and conditions are suitable for a lethal mycosis to develop. A wide range of fungi occur in the soil environment and they have various ecological functions. Most of these fungi, along with a range of bacteria, can grow on artificial media in vitro . Several methods have been used to describe the variation within a species of entomopathogenic and mycoparasitic fungi including morphological characteristics of spores and colonies, extracellular protein profiles, pathogenecity, growth and nutrient requirements. Furthermore, immune taxonomic and chemotaxonomic methods have been used, though only with limited success. Taxonomic procedures are becoming more and more complex and it is generally accepted that some forms of molecular identification techniques are needed in addition to the traditional morphological characteristics formally used to classify fungal species. During the last four decades, over 80 companies worldwide have developed 171 mycoinsecticides and myco-acaricides. Use of mycoinsecticdes is likely to rise if research is focus on; improving its performance under challenging environmental conditions, formulations that will increase persistence, longer shelf life, ease of application, pathogen virulence and wider spectrum of action. Keywords: Eco-friendliness, fungi , insect pest , myco-acaricides, mycoinsecticdes DOI: 10.7176/JEES/10-3-03 Publication date: March 31 st 2020

Laboratory Bioassay of <i>Chilodonella uncinata</i>, an Entomopathogenic Protozoan, against Mosquito Larvae

Background & objectives Use of microbial control agents provides alternative method for adequate insect management. We evaluated laboratory bioassay of Chilodonella uncinata , a natural protozoan parasite of mosquito larvae. Methods Two formulations and four strains: North India (Monsoon and Pre-monsoon) strain, South India strain, updated strain of Chilodonella uncinata were tested against Anopheles stephensi , Culex quinquefasciatus and Aedes aegypti larvae at four institutes. Results & Interpretation Delayed development was noted in mosquito larvae exposed to Ch. uncinata formulation that produced better effect in all larval species. Efficacy of this biolarvicide is not dose dependant as least dose produced maximum mortality with minimum post exposure. An. stephensi larvae were most sensitive followed by Cx. quinquefasciatus and Ae. aegypti which required longer post exposure. Of the four strains, updated strain was most effective and stable; south India strain had rapid killing effect; Pre-monsoon strain was more effective than Monsoon strain as the later required 20x higher dose (cs/ml) to induce satisfactory mortality in An. stephensi larvae with higher values for LT 50 (4.71) and LT 90 (6.84) as against LT 50 (2.5) and LT 90 (3.57) of former strain. Tea bag formulation is easy to store, transport and treat, was found to have a shelf life of >18 months resulting in satisfactory efficacy against An. stephensi with LT 50 (5.16) and LT 90 (7.69) noted at 0.25 g even after 6 months of storage. These laboratory test data suggest that a lower dose of this protozoan formulation can be used as a potential biolarvide to control mosquito larvae as an alternative to chemical insecticides under integrated vector management.

Combined effect of microbial and chemical control agents on subterranean termites

Termite mortality was measured when fungi were combined with bacteria or a chemical termiticide to determine whether a synergistic effect occurred. The fungus Beauveria bassiana was combined with the non-repellant chemical termiticide imidacloprid. Of the three B. bassiana strains tested one, B. bassiana ATCC 90519, was sufficiently pathogenic on its own that the advantage of a supplementary chemical treatment was marginal. The mortality caused by another fungal strain, B. bassiana ATCC 26037, was improved in combination with imidacloprid at both of the tested chemical concentrations over the first 14 days. The remaining fungal strain, B. bassiana ATCC 90518, demonstrated an overall mortality rate in combination with imidacloprid of 82.5%, versus a rate of 65.0% for the fungus alone. The fungus Isaria fumosorosea (Ifr) was combined with the bacterium Bacillus thuringiensis (Bt). On day 5, Ifr, Bt, and the combined treatment at a 10(6) spores or cells/ml dosage caused 8.8%, 22.5%, and 15.0% mortality, respectively. The Bt and combined mortality rates are not significantly different. Control mortality on day 5 was 5.0%. On day 13 the combined 10(6) treatment mortality rate was 91.3%, which was significantly higher than all other treatments: control at 17.5%, Ifr at 36.3% and Bt at 35.0%. When Ifr and Bt were applied at a 10(9) spores or cells/ml dosage, Ifr alone caused a mortality rate of 97.5% as early as day 5. The combination with Bt could not significantly increase the effectiveness of this dosage. These data demonstrate the potential for synergistic effects of fungal and chemical treatment methods, thereby broadening the use of microbial control agents and reducing the quantity of chemical agents necessary to effect control.

Microbial control in Southeast Asia

Beginning in the 1980s, concerns about the deleterious effects of synthetic pesticides have driven a significant Southeast Asian research and development effort directed towards alternative pest control strategies, including the use of microbial control agents. Despite this effort, use of microbial control agents has grown slowly in the region. This is the result of an interplay between internal factors such as economics, national research programs, farmer education, manufacturing capabilities and regulatory frameworks, and external factors such as the influence of neighboring countries (particularly China), the availability of competitive pest control products, import regulations on pesticide residues and the activities of donor agencies. The role of these factors in providing both incentives and barriers to the adoption of microbial control are explored, and examples of promising projects are examined as a means of pointing the way forward towards increased progress in the future.

Insect Pathogens as Biological Control Agents: Do They Have a Future?

Naturally occurring entomopathogens are important regulatory factors in insect populations. Many species are employed as biological control agents of insect pests in row and glasshouse crops, orchards, ornamentals, range, turf and lawn, stored products, and forestry and for abatement of pest and vector insects of veterinary and medical importance. The comparison of entomopathogens with conventional chemical pesticides is usually solely from the perspective of their efficacy and cost. In addition to efficacy, the advantages of use of microbial control agents are numerous. These include safety for humans and other nontarget organisms, reduction of pesticide residues in food, preservation of other natural enemies, and increased biodiversity in managed ecosystems. As with predators and parasitoids, there are three basic approaches for use of entomopathogens as microbial control agents: classical biological control, augmentation, and conservation. The use of a virus (Oryctes nonoccluded virus), a fungus (Entomophaga maimaiga), and a nematode (Deladenus siricidicola )a s innoculatively applied biological control agents for the long-term suppression of palm rhinoceros beetle (Oryctes rhinoceros), gypsy moth (Lymantria dispar), and woodwasp (Sirex noctilio), respectively, has been successful. Most examples of microbial control involve inundative application of entomopathogens. The most widely used microbial control agent is the bacterium Bacillus thuringiensis. The discovery of new varieties with activity against Lepidoptera, Coleoptera, and Diptera and their genetic improvement has enhanced the utility of this species. Recent developments in its molecular biology, mode of action, and resistance management are reviewed. Examples of the use, benefits, and limitations of entomopathogenic viruses, bacteria, fungi, nematodes, and protozoa as inundatively applied microbial control agents are presented. Microbial control agents can be effective and serve as alternatives to broad-spectrum chemical insecticides. However, their increased utilization will require (1) increased pathogen virulence and speed of kill; (2) improved pathogen performance under challenging environmental conditions (cool weather, dry conditions, etc.); (3) greater efficiency in their production; (4) improvements in formulation that enable ease of application, increased environmental persistence, and longer shelf life; (5) better understanding of how they will fit into integrated systems and their interaction with the environment and other integrated pest management (IPM) components; (6) greater appreciation of their environmental advantages; and (7) acceptance by growers and the general public. We envision a broader appreciation for the attributes of entomopathogens in the near to distant future and expect to see synergistic combinations of microbial control agents with other technologies. However, if future development is only market driven, there will be considerable delays in the implementation of several microbial control agents that have excellent potential for use in IPM programs.

Bacillus thuringiensis: fermentation process and risk assessment. A short review.

Several factors make the local production of Bacillus thuringiensis (Bt) highly appropriate for pest control in developing nations. Bt can be cheaply produced on a wide variety of low cost, organic substrates. Local production results in considerable savings in hard currency which otherwise would be spent on importation of chemical and biological insecticides. The use of Bt in Brazil has been limited in comparison with chemical insecticides. Although Bt is imported, some Brazilian researchers have been working on its development and production. Fermentation processes (submerged and semi-solid) were applied, using by-products from agro-industries. As the semi-solid fermentation process demonstrated to be interesting for Bt endotoxins production, it could be adopted for small scale local production. Although promising results had been achieved, national products have not been registered due to the absence of a specific legislation for biological products. Effective actions are being developed in order to solve this gap. Regardless of the biocontrol agents being considered atoxic and harmless to the environment, information related to direct and indirect effects of microbials are still insufficient in many cases. The risk analysis of the use of microbial control agents is of upmost importance nowadays, and is also discussed.

Fungal Entomopathogen Effect on Numbers and Spatial Patterns of the Russian Wheat Aphid (Homoptera: Aphididae) on Preferred and Nonpreferred Host Plants

Effects of plant-host type, either wheat, Triticum aestivum L., or oat, Avena sativa L., and the fungal entomopathogen Beauveria bassiana (Balsamo) Vuillemin, on numerical and spatial distributions of Russian wheat aphid, Diuraphis noxia Kurdyumov, populations were investigated. Untreated adult aphids or aphids inoculated with conidial suspensions of the pathogen were released onto the center seedlings of an Bl-seedling grid in a cage. After 17 d, the numbers of live adults, live nymphs, and sporulating cadavers were recorded for each plant, along with plant height and dry weight. Aphid populations were consistently lower on oat than on wheat, and lower in B. bassiana treatments. Spatial statistics (geostatistics) were used to compare patterns of aphid distribution on plants. On wheat without the pathogen present, adult aphid populations were highest in approximately concentric rings near the outermost plants in grids. Addition of B. bassiana to the system reduced the amount of variation caused by spatial orientation, thereby changing the spatial distribution of aphid populations. On oat, aphid populations generally were highest near the center of the grid, but addition of the pathogen changed the spatial structure of the aphid population. Results suggest that aphid movement behavior, which is intimately linked to host-plant quality, is an important determinant of epizootic proliferation. Elucidation of these relationships may eventually lead to a synergistic use of microbial control agents and host-plant resistance in pest management strategies.