Recognition of the potential of Beauveria bassiana (Balsamo) Vuillemin as a control agent of grasshoppers and locusts occurred as early as 1936, in South Africa. Field testing of B. bassiana as an inundative control agent of grasshoppers and locusts has been facilitated by development of a solid substrate method for mass-production of the fungus and has resulted in the registration of a strain against grasshoppers in the United States. In some, but not all field trials, application has resulted in substantial reductions in grasshopper populations. Numerous environmental constraints, including temperature and ultraviolet (UV) radiation, may limit field efficacy of the fungus. Laboratory studies suggest that low humidity does not limit the ability of the fungus to initiate disease. Sunlight is the major cause of mortality of conidia on leaf surfaces. The incorporation of UVB protectants in formulations can increase conidial survival; however, these have not yet been evaluated for their effects on field efficacy of B. bassiana against insects. Thermoregulation by grasshoppers has been implicated in resistance to mycosis. Results of laboratory studies indicate that grasshoppers infected with B. bassiana preferentially seek temperatures between 40 and 42 degrees C and these temperatures are inhibitory to disease development. In field-cage trials, a higher prevalence and more rapid development of disease were observed in grasshoppers placed in shaded cages than in grasshoppers placed in cages exposed to full sunlight. In laboratory experiments simulating grasshopper thermoregulation during daylight periods, application of both Metarhizium flavoviride Gams and Rozsypal and B. bassiana simultaneously resulted in a final prevalence of disease that was greater than M. flavoviride alone in the hot temperature environment, and equal to B. bassiana alone in the cool temperature environment. Incorporation of sublethal levels of Dimilin with conidia of B. bassiana increased efficacy of the fungus against grasshoppers in laboratory and field trials. Once environmental constraints are better quantified, it may be possible to overcome them through improved formulation, strain selection, genetic or phenotypic manipulation, and inoculum targeting. Ultimately, success of B. bassiana as a microbial control agent will depend on our ability to overcome environmental and other constraints and/or to predict its efficacy under various environmental conditions.
Three leading entomopathogens isolated from Madagascar's migratory locust, Locusta misgratoria ia capita Sauss, were evaluated in field and laboratory tests. In a field trial in Madagascar in 1994, two isolates of Metarhizium flavoviride Gams and Rozsypal (SP3 and SP9) and an isolate of Beauveria bassiana (Balsamo) Vuillemin (SP16) were tested against L. migratoria capita. Locusts from field plots treated with SP9 experienced 100% mortality in 8 days, a higher death rate than that found in locusts treated with M. flavoviride SP3 or B. bassiana SP16. However, locusts treated with M. flavoviride SP3 or B. bassiana SP16 had significantly higher mortality than did the untreated controls. In separate field and laboratory trials in Cape Verde in 1994, SP9 was also tested against the Senegalese grasshopper, Oedaleus senegalensis Krauss. Oedaleus senegalensis treated in small-scale field plots with SP9 experienced 100% mortality in 8 days, a significantly higher death rate than that of the untreated controls. An extensive laboratory bioassay with SP9 revealed a dose-response for rate of mortality to O. senegalensis. Results from these trials in Madagascar and Cape Verde suggest that one or more of the Malagasy strains evaluated have good potential for biocontrol of locusts and grasshoppers.
Two isolates of the fungus Beauveria bassiana (Balsamo) Vuillemin, GHA and BF, were evaluated in Cape Verde in 1991 and 1992 for infectivity to the Senegalese grasshopper, Oedaleus senegalensis (Krauss), and the migratory locust, Locusta migratoria migratorioides (Reiche and Fairmaire). Evaluations included laboratory bioassays and small-scale field trials. Laboratory bioassays evaluated five different formulations. Four of the formulations tested showed strong dose-response patterns and significantly higher mortality than the untreated control or carriers minus spores. All four formulations achieved high mortality levels when applied at economically feasible dose rates. The GHA and BF isolates, formulated in an oil carrier with an emulsifier, were equally infectious to migratory locust nymphs. Six different formulations of GHA were evaluated in field trials. Field trials evaluated both direct effects (treatment of field plots infested with O. senegalensis) and indirect effects (treatment of plots without grasshoppers, after which grasshoppers were introduced). In both cases, all six formulations showed good biocontrol potential. Grasshoppers exposed to treated plots up to 72 h after application exhibited comparatively high mortality levels, indicating that large numbers of spores remained viable in the field for at least 3 days. This was confirmed by analysis of the viability of conidia from Vegetation samples obtained in the field following treatment. In open-plot, small-scale field trials, two different formulations (oil and clay-based) of GHA resulted in high rates of infection and approximately 45% reductions in grasshopper densities in the treated plots 7 days after application, even though density-reduction results were "diluted" by grasshopper migration into and out of the test plots. Results of the Cape Verde evaluations demonstrate that biopesticides developed from B. bassiana represent a promising alternative to chemical pesticides for grasshopper and locust control.
Protozoa known to infect Acrididae include certain Amoebida (Phylum Rhizopoda), Eugregarinida, Neogregarinida (Phylum Apicomplexa) and at least one species from the Phylum Ciliophora, but are mainly Microsporida (Phylum Microspora). Among the Microsporida, Nosema locustae Canning has been the most common subject of large-scale field testing as a potential microbial control of grasshoppers and locusts. Although there have been demonstrations of significant impacts of Protozoa such as Nosema spp. on survival, development, reproduction and feeding of grasshoppers and locusts, these candidates have not met the requirements for fast-acting control of Acrididae. However, recently discovered and as yet undiscovered Microspora and other Protozoa may offer reliable non-chemical control of grasshoppers and locusts. Research on candidates such as Nosema locustae has not been wasted effort; at a minimum, research invested toward development of methods of formulation, application, assessment and ecological fate of these potential microbial control agents has provided useful information needed to prepare for the eventuality of discovery of more fast-acting protozoa, and has contributed to development of field methods required for testing of other microbial agents. With improvements in understanding of insect behavioral and physiological responses, satisfactory short-term efficacy (perhaps resulting from combined formulations with behavioral modifiers or stressors) may allow N. locustae, N. cuneatum Henry, N. acridophagus Henry or Johenrea locustae Lange et al. to also serve a role in limiting acridid abundance and activity, either as an agent of biological control in sites requiring special care, or within a rangeland IPM context.
Trials on the use of Metarhizium flavoviride Gams and Roszypal conidia in oil-based formulation for the control of grasshoppers, particularly Hieroglyphus daganensis Krauss, in Malanville, north Benin, are described. Preliminary work examined sprayer types, application rate, and time of application. In a trial on 4-ha plots with three replicates, M. flavoviride mycoinsecticide application to H. daganensis nymphs resulted in field population reductions of 70% after 14 days. In samples incubated in cages, mortality was higher in the samples taken 3 or 7 days after application than in the sample taken immediately after application, indicating the possibility of residual pick-up compared with direct spray impact in this environment. Significant mortality was still bring observed in samples collected 37 days after application; to investigate this further, a method for bioassaying the spore load in the field was developed and used to monitor the spore load in the field. The possibility that the results indicate the occurrence of secondary infections resulting from horizontal transmission of M. flavoviride is discussed.
The use of chemical insecticides, especially as ultra low volume (ULV) formulations, against locusts and grasshoppers will continue for the foreseeable future; therefore application techniques for microbial agents should be as compatible as possible with existing practice. Low volume and ULV spraying of deuteromycete conidia in oil-based formulations have produced very promising acridid control results in the field, although baiting, dusting, and hydraulic application techniques have also been tested for a wide range of pathogens.The key problems for further research and development appear to be the logistics and supply of consistently reliable formulations for application on a large scale, and the determination of mechanisms for effective dose transfer in the field. The application of suspended particulate matter can present special problems with rotary and other atomizers.
Entomophaga grylli (Fresenius) Batko (North American pathotype 1) is a fungal pathogen of the clearwinged grasshopper, Camnula pellucida (Scudder). We present results from a field experiment conducted in Arizona in 1984, designed to investigate factors associated with seasonal patterns of cadaver persistence and sporulation by E. grylli. Rangeland plots at two sites were monitored daily for 8 weeks for the appearance of new cadavers of diseased grasshoppers during a natural epizootic. Cadavers were individually marked and revisited on subsequent days. when it was noted whether or not conidial sporulation was underway. Environmental variables were recorded by electronic data loggers. Daily probabilities of cadaver disappearance and fungal sporulation were analysed in relation to site, date, and Various measures of cadaver status, sporulation history, and environmental variables by logistic regression analysis. The average daily rate of cadaver disappearance was 0.22, yielding an expected time to 50% disappearance of 2.8 days. The environmental factor most significantly associated with cadaver disappearance was rainfall, and the most important host factor was age of the cadaver. The probability that conidia would be discharged from a cadaver over the next 24 h was most dependent on whether or not conidial sporulation was underway already. This probably reflects a state of readiness for sporulation on the part of the fungus. Although the probability of sporulation declined with increasing age of a cadaver, high rates of sporulation were predicted under conditions of prolonged leaf wetness and high humidity at night, regardless of age of the cadaver. These results, together with the observation that in some cadavers sequences of sporulation were interspersed with periods of no sporulation, suggest that E. grylli may undergo cycles of dehydration and rehydration, in which conidial production is interrupted and then resumes in response to changing environmental conditions.
Microbial control agents offer a method of pest control using organisms that are a natural component of the environment and are usually much more selective than chemical pesticides. Furthermore, they can usually be integrated with other methods of control, and may provide prolonged control by establishment within the host population. However, microbial control agents also possess properties that can pose human and environmental risks depending on the nature of the pathogen and its pattern of use. We present an overview of issues concerning the safety and registration of microbial control agents with emphasis on pathogens of locusts and grasshoppers. The potential safety issues and other consequences of concern from the deployment of microorganisms for pest control are: (1) pathogenicity to non-target organisms, (2) toxigenicity to non-target organisms, (3) competitive displacement of microorganisms, and (4) allergenicity. Inundative control methods pose unique risks because the pathogens must be produced in large quantities, stored, transported, and applied, usually in concentrations much higher than would normally ever occur naturally. The overriding concern in introducing an exotic agent is the risk to non-target beneficial organisms, because once the agent becomes established. it will in most situations be impossible to eradicate. However, if indigenous organisms are used, there is relatively little risk of irreversible, long-term detrimental effects. A synopsis of safety testing results of some of the more promising microbial control agents for grasshoppers and locusts and an evaluation of their potential hazards are presented. Safety to vertebrates is evaluated by a tiered series of laboratory test requirements. Assessments on hazards to non-target invertebrates are based principally on results of laboratory bioassays. Safety tests should be chosen with regard to the biological characteristics of the agent and should not impose standards that are more stringent than those imposed on other forms of pest control. Regulatory oversight should assure the integrity of the environment and safety of the public, while at the same time not unduly hampering the development, registration, and use of more sustainable pest control methods.
A total of 181 isolates of Merarhizium anisopliae (Metschnikoff) Sorokin, M. flavoviride Gams and Rozsypal, Beauveria bassiana (Balsamo) Vuillemin, and Sorosporella sp. was found in a survey of Orthoptera in West Africa, Madagascar, Oman, and Pakistan between 1990 and 1993. Prior to this survey, there were only 28 isolates of hyphomycete fungi from Orthoptera held in international culture collections. Seventeen of the recently acquired Merarhizium isolates have been determined to be highly Virulent during screening tests as part of a research programme for the development of a microbial insecticide against locusts and grasshoppers in Africa. Ninety-five isolates came from Benin which was the country where survey activities were most concentrated, and 63 of these isolates were found in Malanville, northern Benin, between 1991 and 1992 during an epizootic of M. flavoviride. Recordings from Oman and Pakistan represent the first specimens from these countries to be deposited in international culture collections. No deductions can be made on the best method for survey; both incubation of live grasshoppers and field searches for cadavers yielded results. Soil baiting with Orthoptera was used with some success. Limited soil screening using selective agar media was not found to be particularly useful.
Several species of entomopathogenic deuteromycetous fungi can produce epizootics in populations of grasshoppers and locusts. Consequently there is considerable interest in development of these fungi as biocontrol agents. To this end we need information about the genetic and molecular basis of deuteromycete pathogenesis in acridids to develop a rational plan for strain improvement. Herein we present an overview of the infection processes of deuteromycetous fungi in acridids. These fungi penetrate through the cuticle which is composed primarily of proteins. Hydrophobic interactions, appressoria formation, and mucus production by the fungus are involved in fungal adhesion to the acridid cuticle. Extracellular proteases produced by Beauveria bassiana (Balsamo) Vuillemin and Metarhizium anisopliae (Metchnikoff) Sorokin solubilize cuticle proteins, which assists penetration and provides nutrients for further growth. Fungal infection through the locust gut is rare because indigenous gut microflora produce antifungal metabolites. Little is known of the events providing host specificity or those that lead to insect death once the cuticle is breached by the fungus; however, mechanical damage, nutrient deprivation, and toxic metabolites may be involved.
Four research programmes are investigating the entomopathogenic fungal genera Metarhizium and Beauveria for locust and grasshopper control in Africa. In the LUBILOSA programme, surveys for pathogen isolates revealed a morphologically distinctive Metarhizium flavoviride Gams and Rozsypal attacking acridoids in West Africa, Madagascar, and elsewhere. Metarhizium anisopliae (Metschnikoff) Sorokin isolates with virulence to acridoids were also obtained, including several from non-orthopteran hosts. Natural epizootics of both genera are rare in acridoid populations, but do occur. A standardized screening method discriminated virulent from non-virulent isolates. The great majority of the most virulent isolates were from the acridoid group of M. flavoviride. A Niger isolate chosen for development from this group had low Virulence to honey bees and parasitic Hymenoptera and was not infective to insects in several other orders. Field tests were carried out on formulations of oil mixtures, using ULV application rates of 1-2 L/ha and 2-5 x 10(12) conidia per hectare. In preliminary tests, target insects were sprayed successfully in small field arenas and in large cages. Trials in 1993 on variegated grasshopper gave an approx. 90% reduction in field populations after 15 days. Trials on various acridids, predominantly Hieroglyphus daganensis Krauss, in dense grass in northern Benin showed slower mortality, although up to 70% population reduction was achieved. Trials using a vehicle-mounted ULV sprayer (the Ulva-Mast) in open grassland in Niger gave >90% mortality in samples of mixed acridids. In Mall, a Malian isolate of M. flavoviride was shown to be slightly more virulent than the standard Niger isolate; both isolates gave significant population reductions against nymphs of Oedaleus sengalensis Krauss and Kraussella amabile (Krauss) in 1-ha plots. Successful small-scale field trials have also been carried out using the standard M. flavoviride isolate in South Africa against brown locust and in Australia using an Australian isolate against wingless grasshopper. In Mauritania, a trial using the Niger isolate against desert locust nymph bands gave up to 90% mortality in caged samples by day 9 after spraying. The uncaged treated bands were completely destroyed by predators while untreated bands fledged. Oil-based ULV formulations of M. flavoviride are capable of causing high mortality in the field populations of all acridoids against which they have been field tested and show great promise for development as components of IPM strategies for these pests.
Large-scale applications of non-persistent but broad-spectrum chemical insecticides in Africa during the 1980s for control of acridoid pests, particularly the desert locust (Schistocerca gregaria Forskal) and Sahelian pest grasshoppers, raised concern about environmental damage and human safety. Similar concerns have been expressed in Australia, the United States, and Canada and have led to a search for alternative strategies. To lessen dependence on chemicals, an integrated pest management (IPM) approach for grasshopper control has been encouraged in the United States with emphasis on biological control as an important component and this is also desirable elsewhere, but additional biocontrol components are needed. Current strategies for most pest acridoids rely on short-term destruction of outbreak populations. Nymphs are the preferred target wherever possible and inundative augmentation of entomopathogenic deuteromycete fungi formulated as biopesticides could replace chemical spraying in some cases, especially where the major threat is to crops remote from the pest breeding areas. Entomopathogens are slower acting than chemicals and thus best suited for use where the pest is not immediately threatening to crops. Schistocerca gregaria and Oedaleus senegalensis Krauss pose particularly difficult problems because of the very large area and inaccessibility of their potential breeding grounds, their Very sudden upsurges, and their great mobility as adult swarms. Fast-acting chemicals are likely to be needed when rapid intervention is required to control these pests, but an IPM strategy could incorporate biopesticide application in the early stages of upsurges and also be used for swarm control in some cases. However, improved prediction and monitoring are needed to facilitate the use of biopesticides and other IPM techniques against these pests.
Only one isolate of Metarhizium flavoviride Gams and Roszypal group 3 has been isolated from a field-infected acridid in Australia. This is isolate FI985 (ARSEF 324) obtained from a spur-throated locust, Austracris guttulosa (Walker), near Rockhampton, Queensland, in 1979. In terms of conidial size and shape as well as phialide morphology, FI985 is intermediate between Metarhizium anisopliae (Metschnikoff) Sorokin and M. flavoviride. It has been compared with other group 3 isolates using RAPDs and sequence analysis of the ITS region and found to be very similar. However the analysis shows that these group 3 isolates are genetically closer to M. anisopliae than to M. flavoviride sensu stricto. Laboratory bioassays have shown that FI985 is virulent for five species of acridid pests in Australia. Comparative bioassays with other isolates of Metarhizium, including other group 3 isolates from Africa and Asia, have not yet revealed any isolate more virulent than FI985. This isolate is amenable to mass-production on rice and has been formulated in oil as a mycoinsecticide. The results from six field tests, mostly against wingless grasshopper, Phaulacridium vittatum (Sjostedt), using, doses of 2-7x10(12) conidia per hectare and plot sizes up to 50 ha are summarized. These trials (with the exception of the first against the Australian plague locust) have given high levels of disease-related mortality in caged samples of the target collected within 3 days of spraying. In the four trials with wingless grasshopper, population reductions were detected 10-30 days after application; however these reductions were much less than suggested by cage samples as a result of movement of the target acridids. In contrast, positive control plots sprayed with fenitrothion gave a very high initial kill (>90% in 1 day) but were then more rapidly reinvaded. Consequently, 3-4 weeks after spraying the density in the plots treated with chemical insecticide and those treated with mycoinsecticide were similar. Further field trials are needed especially against the Australian plague locust and evaluating lower doses. The results obtained to date show that a mycoinsecticide based on FI985 is likely to be effective over a wide range of target acridids and weather conditions.
Initial promising results with the microsporidium Nosema locustae Canning as a means of controlling grasshoppers have been followed by some cases of limited field performance. However, at sublethal doses this entomopathogen can reduce grasshopper feeding, reproduction and development, suggesting that the damage caused to range, forages and crops might be reduced if the prevalence of infection in the field could be increased over previously achieved levels. In a field experiment, we treated plots totalling 780 ha with bran bait containing N. locustae at either 2.5 or 5.0 x 10(9) spores per ha in each of two consecutive years, and grasshopper populations and the prevalence and degree of infection were monitored every two weeks during the summers, for three years. Little or no background infection occurred in the untreated plots. Infections of grasshoppers with N. locustae in the treated plots during the first year of application, typically increased from less than 5% by the 4(th) week to 10-15% by the 8(th) week after application The higher application rates resulted in only slightly higher percentages infected. Most of the infections were classified by microscopic examination as trace to moderate, although heavy infections were observed in the second year. Up to 35% of some Melanoplus species collected from the treated plots were found to contain N. locustae spores, but intensive monitoring indicated population reductions that were inconsistent among sites and generally less than 50%. Other species, notably Aeropedellus clavatus, Ageneotettix deorum, Bruneria brunnea and Camnula pellucida, failed to acquire significant infection by N. locustae. The presence. of these apparently less susceptible species did not account for the poor overall performance of the treatments. Two annual applications of N. locustae did not greatly increase the rate or severity of infections in grasshopper populations, although at one of the three sites, trace infections were found in the treated plots six years later.Although Nosema may eventually have value as a component of an integrated grasshopper pest management system, the low virulence cannot be readily overcome by repeated applications.
A new isolate of Metarhizium flavoviride Gams and Rozsypal (Hyphomycetes) (CG 423) found in Northeast Brazil infecting Schistocerca pallens (Thunberg) was identified using arbitrarily primed PCR. Cluster analysis of DNA markers revealed a high level of homogeneity (>83% similarity) among the Brazilian (CG 423) and two other M. flavoviride isolates from Nigeria (CG 366 = IMI 330189) and Australia (CG 291). However, M. flavoviride isolates were very distinct when compared with two isolates of Metarhizium anisopliae (Metschnikoff) Sorokin (6.4% similarity). Bioassays showed that strain CG 423 is as virulent as other isolates of M. flavoviride (CG 291, CG 366), M. anisopliae (CG 087), and Beauveria bassiana CB (Balsamo) Vuillemin (CG 425) against the grasshopper Rhammatocerus schistocercoides (Rehn) (Orthoptera: Acrididae), an important pest in Central Brazil. However, the Brazilian isolate of M. flavoviride (CG 423) is more virulent than the Brazilian isolate of B. bassiana (CG 250). Because conidia used in bioassays were formulated in soybean oil containing 5% kerosene, the effect of the kerosene present in the oil formulation was tested. Kerosene (0-10%) did not affect the virulence (P>0.3) of M. flavoviride against R. schistocercoides. The native isolate of M. flavoviride (CG 423) is now being developed as a mycoinsecticide against grasshoppers in Brazil.
The relationship of nematodes and nematomorphs with grasshoppers and locusts is reviewed, emphasizing the actual or potential role of these parasitoids in microbial management. There are records of mermithids parasitizing grasshoppers worldwide, and they are considered important biological control agents in some grassland ecosystems of Europe, North and South America, Papua New Guinea, New Zealand, and Australia. Nematomorphs, although widely distributed, are uncommon parasitoids of grasshoppers, and their dependence on free-standing water for host infection and apparent host specificity are considered drawbacks to their use in biological control programmes. The ascaridids, spirurids, and acanthocephalans are parasites of birds and mammals, and may use grasshoppers as intermediate hosts. They have been shown to debilitate grasshopper hosts in laboratory studies, but their primary role as parasites of vertebrates precludes any consideration as biological control agents. Rhabditids do not naturally parasitize grasshoppers, but recent advances in mass-culturing techniques have given them a potential role as bioinsecticides for the control of grasshoppers. Quantitative data on the effects of nematodes and nematomorphs on agricultural pests, including grasshoppers and locusts, are generally lacking. However, there is evidence that some, particularly mermithids, are important in the population dynamics of grasshoppers and locusts. Keys to the identification of the Various 'worms' found in grasshoppers and locusts are provided, including keys to the species of mermithids.
The biology, ecology, disease etiology, and biological control potential of different members of the Entomophaga grylli species complex are discussed. This complex is represented by several pathotypes that include members that produce both conidia and resting spores within a single season, and members that produce only resting spores. This complex is known as a major pathogen of acridids from most areas of the world where populations of these insects are found, including Africa, Asia, Australia, Europe, North America, and South America. Pathogens from this species complex commonly cause disease epizootics in their host populations and are known to reduce significantly outbreaks of grasshoppers, particularly following periods of rain or high humidity. Specific factors that either limit or enhance disease processes and host mortality are discussed in relation to both epizootiology and biological control programmes. Recent biological control efforts are discussed and the potential of using members of the E. grylli species complex in both augmentation and introduction programmes is considered.
Entomopoxviruses (EPVs) are insect poxviruses that are often found infecting grasshoppers and locusts. Nearly 15 grasshopper and locust EPVs have been reported in the literature. This review describes our current knowledge of the biology of grasshopper and locust EPVs including virus ultrastructure, host range, production in cell culture, pathology, process of infection, epizootiology, and field evaluations of the Viruses to assess their potential as biological control agents. The most extensively studied has been the Melanoplus sanguinipes EPV (MsEPV). Trypsin-like protease activity has been identified in association with MsEPV occlusion bodies but its importance in the infection process is not known. Mortality from MsEPV has been found to occur in two distinct time frames over 6 weeks or longer. MsEPV is also the only grasshopper EPV that has been grown in vitro and been shown to produce virus that is both infectious and virulent to M. sanguinipes. Horizontal transmission of grasshopper EPVs is apparently by consumption of infected cadavers. Field evaluations of MsEPV at an application rate of 1 x 10(10) occlusion bodies per hectare resulted in a 23% prevalence after 13 days despite a considerable amount of dispersal of grasshoppers between plots. Epizootiological studies of EPVs will continue to be an area requiring additional research. Virus production and a limited host range are the two most critical issues affecting the development of EPVs as microbial control agents.
The success of microbial control programmes often depends on an adequate mass-production method for the agent used. The pathogens with potential for use against grasshoppers and locusts Vary widely in the ease with which they can be mass-produced. Obligate pathogens such as grasshopper entomopoxviruses, mermithid nematodes and Nosema locustae Canning are currently restricted to culture in living systems. Liquid fermentation is usually employed for the production of non-obligate pathogens such as bacteria, some fungi and nematodes, but in some cases the propagules produced in liquid culture are not amenable to formulation and application. Conidia of hyphomycete fungi can be produced on the surface of liquid media, on solid substrates or in diphasic systems. Production on solid substrates has been adopted for production of steinemematid and heterorhabditid nematodes and some fungi. Diphasic liquid-solid fermentation combines the benefits of both systems and is used mostly for mass-production of hyphomycete fungi such as Metarhizium flavoviride Gams & Rozsypal and Beauvelia bassiana (Balsamo) Vuillemin. Increased commercial interest in biological control is likely to accelerate the development of improved and more economical methods for the mass-production of microbial control agents.
