Biocontrol Research Research Articles

Overview and relevance of Wolbachia bacteria in biocontrol research

Wolbachia bacteria are an unsuspected, but potentially important, component of many biocontrol programs. To heighten awareness of these bacteria, we review current knowledge of Wolbachia and their possible application in biocontrol research. Wolbachia promote their spread by altering the reproductive success of their arthropod hosts. This ability frequently is identified as having potential either to reduce populations of pest species, or to increase populations of beneficial species. However, only 19 and 1% of peer-reviewed research articles (n=844) on Wolbachia appear in arthropod- and biocontrol-specific journals, respectively. Although Wolbachia will not have application for all programs, their prevalence cannot be denied. We screened for Wolbachia in populations of arthropods of current interest to biocontrol programs in Canada. Infections were detected in 47% of 177 populations, representing 46% of the 105 species tested. Greater awareness, in combination with the rapidly expanding knowledge base of Wolbachia and similar endosymbionts, offers new directions for research in biocontrol programs. We recommend that all arthropod species in biocontrol programs be screened for these bacteria.

Biocontrol of Korean Ginseng Root Rot Caused by Phytophthora cactorum Using Antagonistic Bacterial Strains ISE13 and KJ1R5

In this biocontrol research, we evaluated disease suppressive effects of antagonistic bacterial strains ISE13 and KJ1R5 against Korean ginseng root rot caused by P. eaetorum. We also examined the effects of nutrient solution in the hydroponic culture system for Korean ginseng on biological activity of the bacterial strains. As results of dual culture tests of the bacterial strains on <TEX>$V_{8}$</TEX> juice agar, the strain ISE13 showed antifungal activity against P. eaetorum and other plant pathogenic fungi, but the strain KJ1R5 did not. When their inhibitory effects against infection of P. eaetorum on the roots grown in either nutrient solution or water were tested, the strains ISE13 and KJ1R5 inhibited the disease severity of Korean ginseng roots only grown with water, compared to buffer-treated, inoculated controls. However, the nutrient solution used for hydroponic cultures of ginseng in pots caused higher levels of disease severity by the strains ISE13 and KJ1R5 from <TEX>418.8\%$</TEX> to <TEX>40.0\%$</TEX> and from <TEX>24.3\%$</TEX> to <TEX>45.0\%$</TEX>, respectively. In this study, the bacterial strains ISE13 and KJ1R5 could be potentially biocontrol agents to suppress Korean ginseng root rot caused by P. eaetorum. However, more attention using nutrient solution in hydroponic cultures for Korean ginseng production should be applied in biocontrol of plant diseases using the antagonistic microorganisms.

Dangers of New Zealand Possum Biocontrol Research to Endogenous Australian Fauna

Dangers of New Zealand Possum Biocontrol Research to Endogenous Australian Fauna

New cell lines from Ephestia kuehniella: Characterization and susceptibility to baculoviruses

New cell lines from embryos of Ephestia kuehniella were recently developed. Primary cultures were initiated in September 2002 from 2 to 4 day old eggs in either modified TC-100 or ExCell 400 medium. From these initial cultures, one, originally isolated in the Ex-Cell medium, produced sufficient cell growth to allow subcultivation and eventually led to the establishment of two cell strains, one that forms multicellular vesicles in suspension and one consisting of tightly attached epithelial-like cells. The strains were compared to an extract from E. kuehniella eggs by isozyme analysis and shown to be from the same species. Both strains were inoculated with various insect viruses, including nucleopolyhedroviruses from Autographa californica, Anagrapha falcifera, Anticarsa gemmatalis, Galleria mellonella, Heliothis armigera, Helicoverpa zea, Lymantria dispar, Plutella xylostella, and Rachoplusia ou. Both strains were highly susceptible to most of the nucleopolyhedroviruses (with the exception of the viruses from Helicoverpa zea and Lymantria dispar which did not show cytopathology to either cell strain) with large numbers of occlusion bodies produced in most of the inoculated cells. Our results suggest these new lines can be useful in biocontrol research.

Using parasite databases to identify potential nontarget hosts of biological control organisms

Biological control organisms undergo host range studies to identify potential nontarget hosts. The selection criterion for host range studies is primarily based on the target host's taxonomy. Thus, inaccuracies in host taxonomy may compromise the validity of host range studies. We propose that biocontrol researchers use internet‐available databases to identify potential nontarget organisms that share parasites (biotrophic pathogens and pests) with target hosts, and add these organisms to host range tests. Marijuana (Cannabis sativa) has been targeted for biocontrol, and host range studies have focused upon the Moraceae. A list of Cannabis parasites was compared with database lists of pests and pathogens for hosts in the order Urticales. The databases revealed seven Cannabis biotrophic parasites that were shared by hosts in the family Urticaceae, one biotroph shared by a host in the Celtidaceae, and no biotrophs shared by hosts in the Moraceae, Cercropiaceae, or Ulmaceae. These results suggest that biocontrol host range studies of Cannabis parasites should focus on the Urticaceae and Celtidaceae as well as the Moraceae. These results also suggest that taxonomic relationships within the Uricales be reassessed.

Pathogenicity and Host Specificity of Mycovellosiella lantanae var. lantanae, a Potential Biocontrol Agent for Lantana camara in South Africa

Lantana camara is a poisonous, bushy shrub from South and Central America that has invaded much of the moist, warm sub-tropical areas of South Africa. In the last decade, evidence of a conspicuous and damaging mycobiota on lantana in the Neotropics has persuaded biocontrol researchers to consider fungi as potential biocontrol agents for this plant. Samples of diseased L. camara leaves were collected during field surveys in South, North and Central America from 1987 to 1997. Pathogenicity tests showed the leaf spot fungus, Mycovellosiella lantanae var. lantanae to be a promising biocontrol pathogen. Inoculations onto South African biotypes of L. camara and a number of closely related species within the family Verbenaceae were made under quarantine conditions to determine the pathogenicity and host specificity of the fungus. Inoculation of L. camara biotypes resulted in necrotic, grey lesions (20-60 per leaf), necrosis of flower buds and stalks, as well as defoliation of certain biotypes after three weeks. None of the other plant species tested showed any disease symptoms. This indicates a very restricted host range, making this pathogen a suitable candidate for application as a biological control agent. It is expected that the fungus will reduce the vigour and reproductive potential of L. camara. Due to the variation in virulence of M. lantanae var. lantanae when tested on South African lantana biotypes, release strategies may include the use of combinations of the isolates to target a wider range of lantana biotypes in the field. Permission to release M. lantanae var. lantanae in South Africa was granted in September 2001. The pathogen will be released as a classical biocontrol agent in South Africa.

Regulation of antibiotic production in root-colonizing Peudomonas spp. and relevance for biological control of plant disease.

Certain strains of fluorescent pseudomonads are important biological components of agricultural soils that are suppressive to diseases caused by pathogenic fungi on crop plants. The biocontrol abilities of such strains depend essentially on aggressive root colonization, induction of systemic resistance in the plant, and the production of diffusible or volatile antifungal antibiotics. Evidence that these compounds are produced in situ is based on their chemical extraction from the rhizosphere and on the expression of antibiotic biosynthetic genes in the producer strains colonizing plant roots. Well-characterized antibiotics with biocontrol properties include phenazines, 2,4-diacetylphloroglucinol, pyoluteorin, pyrrolnitrin, lipopeptides, and hydrogen cyanide. In vitro, optimal production of these compounds occurs at high cell densities and during conditions of restricted growth, involving (i) a number of transcriptional regulators, which are mostly pathway-specific, and (ii) the GacS/GacA two-component system, which globally exerts a positive effect on the production of extracellular metabolites at a posttranscriptional level. Small untranslated RNAs have important roles in the GacS/GacA signal transduction pathway. One challenge in future biocontrol research involves development of new strategies to overcome the broad toxicity and lack of antifungal specificity displayed by most biocontrol antibiotics studied so far.

Biocontrol of the pathogen Phytophthora parasitica by arbuscular mycorrhizal fungi is a consequence of effects on infection loci

The impact of colonization by the arbuscular mycorrhizal fungus (AMF) Glomus mosseae on tomato root necrosis caused by the soil‐borne pathogen Phytophthora parasitica was investigated. Studies in situ permitted infection loci to be identified and the effects of the AMF on numbers to be elucidated. Effects were significant and, 7 and 16 days after inoculation with zoospores of the pathogen, roots of plants colonized by the AMF had 39% and 30%, respectively, fewer infection loci than those that were not. Concurrent studies of the rate of spread of necrosis within roots showed no changes caused by the AMF. At harvest, 26 days following inoculation with the pathogen, 61% of roots of noncolonized plants were necrotic compared with only 31% in AMF‐colonized plants. It is concluded that effects on numbers of infection loci are one mechanism via which AMF achieve biocontrol of this pathogen in tomato. Measures of the effects of the AMF on root system architecture suggest that no significant changes occur and are thus not the reasons for the reduction in infection loci. The implications of these data for agricultural practice and biocontrol research are discussed.

Modular Habitat Refugia Enhance Generalist Predators and Lower Plant Damage in Soybeans

Promoting generalist predators in agriculture via habitat manipulation has gained much interest in biocontrol research. Straw shelters have been used by Chinese farmers for >2,000 yr to provide temporary spider refugia during cyclic farming disturbances. This method, however, has not been systematically investigated on larger scales in western-style agriculture. Our preliminary observations indicated a significant decrease in the abundance of spiders (76%) and their egg sacs (75%), after conventional tillage of soybeans [Glycine max (L.) Merr.]. We hypothesized that providing alternative habitats in tilled fields could conserve predatory assemblages following this major disturbance. We used modular habitat refugia constructed of chicken wire loosely filled with bedding straw to provide temporary habitats for epigeic predators in a soybean field. Refugia held 5–36 times the spider density compared with open field, and the production of spider egg sacs was enhanced 18–87 times. Almost 60% more spider species were found in refugia than in open field. Abundance of harvestmen, carabids, and staphylinid beetles also significantly increased in habitat refugia. Increased habitat cover and provision of alternative prey in habitat refugia may have caused this dramatic predator increase. Soybean seedlings grown within 1 m of habitat refugia suffered 33% less insect damage compared with plants at control locations. Decrease in seedling damage, however, did not significantly increase soybean seed production. Applications of discrete habitat refugia may provide an alternative to habitat manipulation techniques to conserve and augment arthropod predators in agroecosystems.

Modular Habitat Refugia Enhance Generalist Predators and Lower Plant Damage in Soybeans

Promoting generalist predators in agriculture via habitat manipulation has gained much interest in biocontrol research. Straw shelters have been used by Chinese farmers for >2,000 yr to provide temporary spider refugia during cyclic farming disturbances. This method, however, has not been systematically investigated on larger scales in western-style agriculture. Our preliminary observations indicated a significant decrease in the abundance of spiders (76%) and their egg sacs (75%), after conventional tillage of soybeans [Glycine max (L.) Merr.]. We hypothesized that providing alternative habitats in tilled fields could conserve predatory assemblages following this major disturbance. We used modular habitat refugia constructed of chicken wire loosely filled with bedding straw to provide temporary habitats for epigeic predators in a soybean field. Refugia held 5–36 times the spider density compared with open field, and the production of spider egg sacs was enhanced 18–87 times. Almost 60% more spider species were found in refugia than in open field. Abundance of harvestmen, carabids, and staphylinid beetles also significantly increased in habitat refugia. Increased habitat cover and provision of alternative prey in habitat refugia may have caused this dramatic predator increase. Soybean seedlings grown within 1 m of habitat refugia suffered 33% less insect damage compared with plants at control locations. Decrease in seedling damage, however, did not significantly increase soybean seed production. Applications of discrete habitat refugia may provide an alternative to habitat manipulation techniques to conserve and augment arthropod predators in agroecosystems.

Fighting Fire With Fire

BIOLOGICAL CONTROLWEST BOULDER RIVER, MONTANA-- As the menace posed by biological invaders grows, many scientists and governments are fighting fire with fire by importing natural enemies of exotic weeds and pests. But the good exotics may become problems themselves, attacking nontarget native species or reshuffling ecosystems in unwanted ways. And even biocontrol researchers admit that the long-term fate of introduced agents is often unknown.

Hurdles and bottlenecks on the road to biocontrol of plant pathogens

Despite the progress in biocontrol research that has placed about 40 commercially available biocontrol products on the shelf, many hurdles to the wide adoption of biocontrol remain. Biocontrol works well under conditions of low biological diversity, such as in soil-less potting mix, but is more difficult to demonstrate in the field, and biocontrol is often less consistent than chemical control. Is biocontrol not working, or is it our inability to deliver and establish the biocontrol organism in the appropriate physiological state, in the right place at the right time? A greater understanding of the ecology of the organisms involved, as well as the epidemiology of the system, will help us to develop ecologically rational approaches to disease management. More efficient and effective ways of growing and formulating biocontrol organisms are needed in many cases in order to make biocontrol economically viable. Research on safety and environmental fate of biocontrol agents is lacking in some cases. Trends that may encourage more research into biocontrol of plant diseases include the increased public interest in ‘organic’ foods, the public’s concern over non-target effects of chemical pesticides in the environment, and the loss of many chemical pesticides, or uses of those pesticides, from the market.

Biocontrol Research with Nematodes Against Insect Pests in Korea

Biocontrol Research with Nematodes Against Insect Pests in Korea

The grape berry moth,Lobesia botranaDenis &amp; Schiffermueller (Lepidoptera: Tortricidae), in pear orchards in Israel1

Abstract The European grape berry moth, Lobesia botrana Denis & Schiffermueller (Lepidoptera: Tortricidae) is, in its larval stage, one of the most serious pests of grapes. It is also a pest of roses in greenhouses and of many ornamental and wild plants. During the past decade in Israel, Lobesia botrana has begun to cause damage to pear (Pyrus communis) orchards. Integrated pest management methods were implemented which resulted in a drastic decrease in the cumulative use of non‐selective pesticides and in the number of treatments. The objectives of the present study were to examine the efficacy of some new pheromone preparations, visual determination of damage to fruit yield, and assessment of pesticide formulations for application. To monitor pest populations in pear orchards during the flight period traps baited with pheromones were introduced. Biocontrol research was carried out using Bacillus thuringiensis Berliner preparations. The efficiency of these formulations against the pest has been established.

Citrus blackfly in Florida: Eradication or bio-control?

The citrus blackfly (CBF) invaded south Florida in January 1976. It was considered by scientists to be a major threat to the Florida citrus industry located in the central part of the state. The CBF was successfully contained in a 1000 square mile tri-county quarantined area surrounding Ft. Lauderdale for several months before breaking out to an area near the commercial citrus production area. During this time federal and state research agencies were evaluating a bio-control approach involving two tiny wasps which were introduced in south Florida in 1976 by the United States Department of Agriculture. By late 1978 it had become clear to most of the leading scientists and some of the industry leaders that the spray program for eradication was failing and that research showed conclusively that the bio-control agents (two wasps) could be a permanent solution to the problem. After considerable deliberation, research administrators announced on 18 January 1979 that they were convinced that the CBF was under bio-control and was no longer a threat to the citrus industry. Although there was some resistance to giving up the concept of eradication with a spray program, it was announced on 8 March 1979, that the regulatory agencies would abandon the initial goal of eradication for a containment program and in August 1979 all spray programs were terminated. The bio-control agents have successfully kept the CBF under bio-control for 10 years. It was a low-cost, environmentally sound solution of a serious threat to the Florida citrus industry. The decision to support a bio-control program was approved (although perceived by some to be risky in 1979) and resulted in millions of dollars in savings to the people of Florida. Furthermore, since the bio-control agents continue to be well established in Florida at low levels, the state can be assured it will not be invaded again by CBF. The success of the CBF bio-control program engendered an increased credibility in this approach to management of other foreign pests. Increased emphasis on bio-control research will lead to more applications in Florida as well as worldwide with benefits of cost saving and reductions to environmental degradation.