Influence of biotic and abiotic factors on the persistence of a Beauveria bassiana biopesticide in laboratory and high-rise poultry house settings

Recent studies suggest the potential for use of oil formulations of the entomopathogenic fungus, Beauveria bassiana, as residual sprays for control of house flies in poultry production facilities. The current study investigated the influence of biotic and abiotic factors on biopesticide persistence. We found that flies physically removed and deactivated conidia, with higher fly densities and greater cumulative exposure hastening the decline. Nonetheless, very low densities of viable conidia were still able to cause rapid mortality, suggesting the potential for relatively long re-treatment intervals as fly populations are controlled. Considering abiotic factors, we found that fungal spray treatments remained viable for up to 13 weeks under laboratory conditions. Periodic exposure of flies to the spray residue showed high levels of mortality, with very little decline in mortality rate over time. Equivalent treatments placed in a commercial poultry house showed much more rapid decline. One trial at the end of summer showed conidia to remain viable up to seven weeks. However, repeats during the winter months revealed decay in 1–2 weeks, with fly mortality rates influenced accordingly. The exact reasons for the more rapid decay remain unclear but could be linked to high concentrations of ammonia in the basement areas, especially during winter when ventilation is minimal. The combined data suggest the potential for adaptive treatment regimes with weekly spray intervals in conditions with very high fly populations and/or high ammonia levels, and potentially monthly spray intervals when fly populations and ammonia levels are reduced.     

Virulence of Different Isolates and Formulations of Beauveria bassiana for House Flies and the Parasitoid Muscidifurax raptor

Adult house flies (Musca domestica) were susceptible (94-100% mortality) to Beauveria bassiana when conidia of the Hf88 isolate were applied to plywood boards at 10⁷ conidia/cm²; a starch dust formulation was more effective than a liquid suspension. Adult flies were also susceptible (90-99% mortality) to this isolate when they were con fined with treated water (10⁸ conidia/ml) or food (10⁸ conidia/100 mg). House fly larvae were not affected by treatments with up to 10⁸ conidia/cm³ of rearing medium. A 2-year survey of house flies cm from New York dairies indicated that most natural infections of house flies occurred in September and October, although prevalence rates never exceeded 1%. Thirteen single-fly isolates obtained during this survey were compared with the Hf88 isolate for virulence against flies; the 2 most virulent isolates were slightly more virulent for flies than for the fly parasitoid Muscidifurax raptor. Incorporation of conidia into a sucrose bait (10⁸ conidia/100 mg) in cages gave high levels of house fly control (78-100% mortality) 5 days after exposure.     

Evaluation of Beauveria bassiana applications against adult house fly, Musca domestica, in commercial caged-layer poultry facilities in New York state

Applications of a commercially produced Beauveria bassiana product, balEnce, were compared with pyrethrin treatments for the control of adult house flies in New York high-rise, caged-layer poultry facilities. An integrated fly management program, which included the release of house fly pupal hymenopteran parasitoids, was used at all facilities. Adult house fly populations were lower in B. bassiana-treated facilities during the spray and post-spray periods, as recorded on spot cards. Concurrently, the numbers of house fly larvae recovered in B. bassiana-treated facilities were less than one-half that of the pyrethrin-treated facilities. House fly pupal parasitism levels were low, but similar under both treatment regimes. The numbers of adult and larval Carcinops pumilio, a predatory beetle, recovered from B. bassiana-treated facilities were 43 and 66% greater than from the pyrethrin-treated facilities, respectively.     

Host age and pathogen exposure level as factors in the susceptibility of the house fly,Musca domestica (Diptera: Muscidae) to Beauveria bassiana

Adult house flies, Musca domestica L., of four ages, <1, 3, 7, and 14 day post-eclosion, were exposed to three strains of Beauveria bassiana (P89, L90 and 447). Flies were exposed to moistened filter paper treated with either a low (1.57×10⁴ conidia/cm²) or high (1.57×10⁵ conidia/cm²) concentration of each fungal strain for 6 h. Strain 447 was superior to the two house fly-derived B. bassiana strains in inducing host infection and mortality. Significant spikes in infection and mortality occurred as early as 5 days post-exposure with higher concentration exposures acting more quickly. Few differences were observed in either infection or mortality among the four fly age classes. On Day 10 post-exposure, 77% of the high-concentration, 447-exposed flies were infected, compared with only 24% of the flies from the P89 low-concentration exposure. Potential applications of these results in integrated house fly management programs are discussed.     

Stable fly, house fly (Diptera: Muscidae), and other nuisance fly development in poultry litter associated with horticultural crop production

Poultry litter usage in horticultural crop production is a contributor to nuisance fly populations, in particular stable flies (Stomoxys calcitrans L.) and house flies (Musca domestica L.). Extrapolation of adult emergence data suggests that approximately 1.5 million house flies and 0.2 million stable flies are emerging on average from every hectare of poultry litter applied as a preplant fertilizer for vegetable production in Perth, Western Australia. To a lesser extent, sideband applications to established crops may allow for the development of 0.5 million house flies and 45,000 stable flies per hectare. However, up to 1 million house flies, 0.45 million lesser house flies, Fannia cannicularis L., and 11,000 stable flies per hectare may be produced from surface dressings of poultry litter associated with turf production. Other nuisance flies present in poultry litter included the false stable fly, Muscina stabulans (Fallén), bluebodied blowfly, Calliphora dubia Hardy, black carrion fly, Hydrotaea rostrata Robineau-Desvoidy, Australian sheep blowfly, Lucilia cuprina Wiedemann, and flesh flies (Sarcophagidae). Only house flies developed in poultry litter for the first 4 d after application in the field. Stable flies were not present in poultry litter until 4-7 d after application, and were the only fly species developing in litter > 9 d after application.     

Potential for biocontrol of house flies,Musca domestica,using fungal biopesticides

Chemical control of house flies in poultry production facilities is becoming increasingly difficult due to insecticide resistance and regulatory constraints. Biopesticides based on entomopathogenic fungi could provide an alternative approach. Here we evaluated population control potential of two fungal pathogens, Beauveria bassiana and Metarhizium anisopliae. Cohorts of adult flies were established in large plastic boxes in the laboratory and were exposed to residues of oil-formulated fungal conidia sprayed on strips of plastic sheeting attached to the box walls. Exposure to the biopesticide barrier treatments caused 100% mortality in adult populations within 8–16 days, depending on the fungal species. In contrast, control flies survived until 96–110 days. Additionally, fungal infections caused 13–20% reduction in egg viability and >70% reduction in fecundity of flies prior to death. The combined lethal and pre-lethal impacts resulted in 21- to 26-fold reduction in basic reproductive rate in the fungus-exposed populations relative to controls. Based on these promising proof-of-principle results, further research is currently under way to determine the feasibility of developing a biopesticide product for operational use.     

Microbial biological control potential of three strains of Beauveria bassiana s. l. against greenhouse shore fly Scatella tenuicosta: Assessment of virulence,mass production capacity,and effects on shore fly reproduction

The microbial biological control potential of three strains of Beauveria bassiana sensu lato originally isolated from the shore fly Scatella tenuicosta (Diptera: Ephydridae) was assessed in a series of laboratory bioassays. Comparisons were made to two commercially-available strains of B. bassiana. Two of the shore fly strains proved 27–67 times more virulent than the commercial strains in terms of LC₅₀ (14–17 vs. 458–942 conidia/mm²) and killed shore flies more rapidly. B. bassiana s. l. strain ST1 exhibited a mass production capacity comparable to the commercial B. bassiana stain GHA, producing 2.8 × 10¹² conidia/kg barley-based solid substrate in ventilated mushroom spawn bags. The shore fly strains of Beauveria sporulated on a higher percentage of killed adult shore flies and produced substantially greater numbers of conidia per cadaver than the commercial strains, indicating that these pathogens are well adapted to this host. Female shore flies treated with strain ST1 survived for only 5 days, with longevity being reduced by 8–10 days compared to control insects. This reduction in survival had a large impact on total lifetime egg production, reducing it by 78–88%, depending on the time of treatment relative to the pre-oviposition period. However, fungal growth within infected female shore flies had no effect on egg production or egg viability until the day before the flies succumbed to mycosis (day 4 post-inoculation). As a consequence, the intrinsic rate of shore fly population increase and population doubling time were little affected by fungal infection (0.4357 vs. 0.4152 and 1.6 vs. 1.7 days for control vs. Beauveria-treated populations, respectively). These findings underscore the challenges involved with use of slow-acting pathogens for control of highly fecund greenhouse pests and the fundamental necessity of integrating these agents into integrated pest management systems.     

Susceptibility of different life stages of the European cherry fruit fly,Rhagoletis cerasi,to entomopathogenic fungi

The effects of six fungus isolates on the mortality of different life stages of the European cherry fruit fly, Rhagoletis cerasi (Diptera: Tephritidae), were assessed in a series of laboratory experiments to find an isolate suitable for biological control. In a first step, the effects of fungus treatments on mortality, mycosis and fecundity of adult flies at a concentration of 10⁷ conidia/ml were evaluated. All fungus isolates caused mycosis but virulence varied considerably among the isolates. Beauveria bassiana and Isaria fumosorosea caused 90–100% mortality and had the strongest influence on fecundity. Metarhizium anisopliae also induced high rates of mortality, while the pathogenicity of Isaria farinosa was low. The effects of lower conidia concentrations and the influence of the age of flies were assessed in a second step. Higher conidia concentrations generally resulted in a higher mortality. B. bassiana was most efficient at low concentrations. Young flies showed lower mortality rates than older flies but, sub‐lethal effects on eclosion rate of eggs were greater in younger flies. Finally, the effects on L₃ larvae were tested: none of the fungus isolates induced mortality in more than 25% of larvae. As L₃ larvae and pupae are not susceptible to fungus infection, field control of R. cerasi should be focused on adult flies.     

Simultaneous use of SIT plus disseminator devices of Beauveria bassiana enhances horizontal transmission in Anastrepha ludens

Beauveria bassiana is an entomopathogenic fungus widely used to control different insect pests including Anastrepha ludens (Diptera: Tephritidae), a key pest of citrus and mangoes. Currently, to control this pest, sterile A. ludens males of the Tap-7 genetic sexing strain are released weekly by aircraft at a density of 1,000 males/ha as part of an integrated pest management programme (IPM) in Southern Mexico. Our objective here was to determine whether the sterile insect technique (SIT) could be enhanced by augmenting it with horizontal transmission of fungus conidia by using Beauveria bassiana disseminator devices (DBb) designed to distribute it with minimal impact on non-target species. Four treatments were established: DBb only, DBb + SIT, SIT only and untreated control, and fruit fly populations were monitored using two Multilure traps baited with 250 ml of CeraTrap per plot. We found that the presence of B. bassiana disseminator devices in areas where A. ludens sterile males were released resulted in higher proportions of infected wild fruit flies in the field, and that high relative humidity (rainy season) played an important role in the efficiency of horizontal conidia transmission to the wild populations. We conclude that the simultaneous use of both strategies (SIT + DBb) increases the conidia transmission to wild populations, and that this approach could be incorporated to an integrated pest management for the better suppression of fruit fly populations.     

Natural Infections Caused by the Fungus <Emphasis Type="Italic">Beauveria bassiana</Emphasis> as a Pathogen of <Emphasis Type="Italic">Musca domestica</Emphasis>in the Neotropic

A survey for entomopathogenic fungi of Musca domestica adults was conducted in poultry houses in La Plata, Buenos Aires province, Argentina, during the years 2002 and 2003. Adult house flies were found infected with the fungus Beauveria bassiana (Bals.) Vuill. (Deuteromycotina: Hyphomycetes) from field collections, with a natural infected prevalence between 0.4–1.45%. This is the first record of natural infections of house flies caused by B. bassiana for the neotropics. Pathogenicity assays under laboratory conditions showed 94% adult mortality at 14 days post challenge. CIC fellow     

Influence of substrate and relative humidity on the efficacy of three entomopathogenic fungi for the hide beetle,Dermestes maculatus (Coleoptera,Dermestidae)

Dermestes maculatus De Geer (Coleoptera: Dermestidae) is a carrion feeder that is also a pest of poultry houses, museums, silkworm culture, and many stored foods. The Hypocreales, Beauveria bassiana (Balsamo) Vuillemin, Metarhizium anisopliae (Metschnikoff), and Isaria fumosorosea Wize, were tested for efficacy against D. maculatus larvae on concrete, plastic, leather, and wood surfaces. Only wood had a significant negative effect on efficacy, and B. bassiana was the most efficacious species. The conidia of all three species lost viability quickly on wood with various responses on the other surfaces. When beetle larvae were exposed to deposited B. bassiana and incubated at 43, 56, 75, or 82% relative humidity, mortality was greatest at the lowest humidity suggesting enhancement of fungal infection by desiccation stress. The results indicate that entomopathogenic Hypocreales, especially B. bassiana, may be useful for control of hide beetles when applied at a low dose to surfaces that do not impact the viability of conidia.     

Laboratory studies on the biology ofSpalangia nigra [Hym.: Pteromalidae]

At 21 °C,Spalangia nigra Latreille (Hymenoptera: Pteromalidae) averaged 29.3 days between exposure and emergence of 1^st progeny from host house flies,Musca domestica L. (Diptera: Muscidae). At 27 °C, the average developmental time to 1^st emergence was reduced to 26.6 days, and a majority of adult wasps emerged from host house fly puparia between 29 and 40 days postoviposition. The sex ratio of progeny ranged from 1.4 to 1.8 female-to-male, but all progeny of virgin females were male. Male wasps lived from 6.8–15 and females 11–17.8 days at 27 °C; honey as a food source increased longevity. No significant differences in parasitism byS. nigra were associated with host house fly pupal densities ranging from 1 to 200 pupae per female-male pair of wasps, but average percent parasitism decreased at host densities greater than 50. House fly pupae exposed to parasitism at ages ranging from 4 to 96 h did not differ in subsequent production of adult flies.S. nigra did not demonstrate preference for house flies or stable flies,Stomoxys calcitrans (L.) (Diptera: Muscidae) as hosts. The results of these studies indicate thatS. nigra may contribute significantly to previously unexplained mortality of house flies and stable flies.      

Activity of pupal parasitoids of the stable fly Stomoxys calcitrans and prevalence of entomopathogenic fungi in the stable fly and the house fly Musca domestica in Denmark

A survey was conducted on confined dairy cattle farms and a pig farm from May–October in 1999 to determine the activity and relative abundance of pupal parasitoids and the prevalence of entomopathogenic fungi in populations of the haematophagous stable fly, Stomoxys calcitrans (Diptera: Muscidae), in Denmark. Four species of pteromalids were found with Spalangia cameroni as the predominant. The other parasitoids were S. nigripes, S. nigra and Phygadeuon fumator (Ichneumonidae). Peak activity of the parasitoids was observed to be late in the summer and the beginning of autumn (August–September) when approximately 10% of the collected stable fly pupae were parasitised. Adult stable flies were infected with four species of entomopathogenic fungi: Entomophthora muscae, E. schizophorae, Beauveria bassiana and Verticillium lecanii. All fungi occurred in low percentages (max. 4%) and remained at this level throughout the sampling period. Likewise, adult house flies were infected with B. bassiana and V. lecanii,but Metarhizium anisopliae, Paecilomyces fumosoroseus and V. fusisporum were also recorded. The overall hyphomycete prevalence in house flies was 0.3%, and single species rarely exceeded 0.1%. The prevalence remained low in spite of increasing house fly numbers in August–September.     

Efficacy of Beauveria bassiana (Bals.) Vuill. against the tarnished plant bug, Lygus lineolaris L., in strawberries

Beauveria bassiana has a high insecticidal potential to control the tarnished plant bug, Lygus lineolaris, a significant pest of strawberries. Screening experiments showed that L. lineolaris adults were susceptible to several B. bassiana isolates. Another screening test with Coleomegilla maculata, a natural enemy found in strawberries, was also performed in order to select the isolate having lower entomopathogenic impact on this insect. Based on data obtained from both insect species and on the ecozone origin of the B. bassiana isolates, INRS‐IP and INRS‐CFL isolates were selected for further experiments. The LC₅₀ values of these two isolates against L. lineolaris adults were 7.8 × 10⁵ and 5.3 × 10⁵ conidia/ml, and average survival time (AST) values were 4.46 and 4.37 days at a concentration of 1 × 10⁸ conidia/ml respectively. Results also indicated that L. lineolaris nymphs are susceptible to the selected isolates. During field experiments, using a randomized block design with four replicates, INRS‐IP and INRS‐CFL isolates were applied at two rates (1 × 10¹¹ and 1 × 10¹³ conidia/ha) weekly during a period of 4 weeks. These multiple applications triggered a significant reduction of L. lineolaris nymphal populations in strawberries. Twenty‐four days after the first application, a significant difference was observed between the mean population densities of surviving nymphs in all B. bassiana‐treated plots (less than one insect per five plants) compared with those in control plots (four insects per five plants). During the field experiment, persistence of insecticidal activity and viability of B. bassiana conidia were also monitored. The results showed the presence of viable and infective conidia up to 6 days after each application on strawberry foliage. Moreover, the multiple applications of B. bassiana at the rate of 1 × 10¹³ conidia/ha triggered a significant reduction in strawberry fruit injuries induced by L. lineolaris feeding behaviour compared with the control plots.     

Effects of four commercial fungal formulations on mortality and sporulation in house flies (Musca domestica) and stable flies (Stomoxys calcitrans)

The house fly Musca domestica L. (Diptera: Muscidae) and stable fly Stomoxys calcitrans (L.) (Diptera: Muscidae) are major pests of livestock. Biological control is an important tool in an integrated control framework. Increased mortality in filth flies has been documented with entomopathogenic fungi, several strains of which are commercially available. Three strains of Beauveria bassiana (Balsamo‐Crivelli) Vuillemin (Hypocreales: Cordycipitaceae) and one strain of Metarhizium brunneum (Petch) (Hypocreales: Clavicipitaceae) were tested in commercial formulations for pathogenicity against house flies and stable flies. There was a significant increase in mortality of house flies with three of the formulations, BotaniGard^® ES, Mycotrol^® O, and Met52^® EC, during days 4–9 in comparison with balEnce? and the control. In stable flies, mortality rates were highest with Met52^® EC, followed by Mycotrol^® O, BotaniGard^® ES and, finally, balEnce?. There was a significant fungal effect on sporulation in both house flies and stable flies. Product formulation, species differences and fungal strains may be responsible for some of the differences observed. Future testing in field situations is necessary. These commercial biopesticides may represent important tools in integrated fly management programmes.     

Sporulation by Entomophthora schizophorae (Zygomycetes: Entomophthorales) from housefly cadavers and the persistence of primary conidia at constant temperatures and relative humidities

The duration of discharge of Entomophthora schizophorae (Zygomycetes: Entomophthorales) conidia from house fly (Musca domestica, Diptera) cadavers was measured at 7, 18, and 25 degrees C. The higher the temperature, the shorter the duration of conidia discharge. Significantly more conidia were produced per cadaver at 7 degrees C over a period of 120 h than at 18 and 25 degrees C. At 25 degrees C, the initial discharge over the first 10 h was much larger than at the other temperatures, and at 7 degrees C, no peak in discharge was observed. The persistence of E. schizophorae primary conidia was measured on fabricated non-host surfaces typically found in stables (straw, wood, plaster, and glass) at 7, 18, and 25 degrees C or constant relative humidities of 45, 65, and 85%. Persistence, as measured by the subsequent ability to infect flies, was usually only a few days and depended on the temperature and type of surface. It was greatest on straw, followed by wood, glass, and plaster, and at 7 degrees C, followed by 18 and 25 degrees C. Limited transmission took place between flies exposed to conidia and previously unexposed mates.     

Sterile males of Ceratitis capitata (Diptera: Tephritidae) as disseminators of Beauveria bassiana conidia for IPM strategies

Sterile Mediterranean fruit fly, Ceratitis capitata (Wied.), males were evaluated as vectors to spread Beauveria bassiana (Bals) conidia to wild C. capitata populations under field conditions. The inoculated sterile males were released by air, using the chilled adult technique over 7000 ha of coffee growing in Chimaltenango, Guatemala, Central America. The impact of releases was determined using dry traps baited with a food attractant. The effects of these releases on Apis mellifera, Linnaeus (honey bee), Hypothenemus hampei, Ferrari (coffee berry borer) and the parasitic mite Varroa destructor (Oudeman) were also evaluated. Inoculated sterile males were able to transmit fungal spores to 44% of the wild C. capitata flies captured in traps, which likely were infected through intra- and intersexual interactions during leks, mating or mating attempts. There was no transmission of the fungal spores to non-target insect species such as coffee berry borer, honey bees or varroa. We conclude that sterile males of Mediterranean fruit fly inoculated with B. bassiana can act as effective vectors of conidia to wild populations, constituting a safe, environmentally friendly and selective alternative for suppressing the medfly under a Sterile Insect Technique-based IPM approach.     

Production of conidia of Beauveria bassiana in solid-state culture: current status and future perspectives

Beauveria bassiana is an important entomopathogenic fungus widely commercialized in the world. Recent progress and achievements on conidia production have focused on a yield goal of 10⁹ to 10¹⁰ conidia per gram of dry substrate. Due to cost-competitive perspectives, these yields should be associated with better production rates or productivities. This study presents a review of relevant studies of B. bassiana conidia production on solid-state cultures and the parameters that should be taken into account to maintain constant quality in the product to be commercialized. Conditions for maximizing production and infectivity of B. bassiana conidia are also analysed.     

Light stimulates conidiation of the entomopathogenic fungus Beauveria bassiana

Beauveria bassiana is a commercially important entomopathogenic fungus. Like other insect fungal pathogens, B. bassiana usually produces asexual reproductive bodies, conidia, for dispersal, transmission and infection of insects. Adequate mass-production of high quality conidia is crucial to development of an efficient B. bassiana insecticide. However, little is known about details of conidiation in this fungus in response to environmental signals, which limits understanding of the mechanism of conidiation and improvement in conidia production. Here, morphologenetic changes of B. bassiana under different light conditions are reported. When cultured in total darkness, B. bassiana hyphae can grow continuously with few reproductive structures differentiated, while illumination with white light resulted in prolific formation of conidiophores bearing abundant conidia, indicating that light could stimulate conidiation of B. bassiana. Among the single colour lights tested, blue light was the most effective to stimulating sporulation. Colonies became adapted for blue light stimulus only after hyphae had grown in total darkness for at least 96 h, whereas the photoadaptation obviously declined after 144 h. For the exposure time, 3 min of blue light pulse was enough to stimulate conidiation in the photoadapted mycelia, while prolonged light exposure over 3 min resulted in a decrease in conidia yield. Our results provided useful clues for understanding the mechanism of conidiation mediated by light in B. bassiana.