Flavoviride Gams Research Articles

Nilaparvata lugens (Hemiptera: Delphacidae) Midgut Microbial Community Responses to Exposure to Metarhizium flavoviride (Sordariomycetes: Hypocreales)

Abstract Changes to the community of symbiotic bacteria and fungi in the brown planthopper, Nilaparvata lugens Stål, were measured at different times after exposure to conidial suspensions of Metarhizium flavoviride Gams and Roszypal. Over all concentrations tested, bacterial species associated with N. lugens comprised 8 phyla, 17 classes, 22 orders, 26 families, and 31 genera of which the relative proportions of Arsenophonus, Burkholderia, Enterobacter, Pseudomonas, Stenotrophomonas, and Bacteroides were highest. The relative abundance and diversity of bacteria were highest in the carrier control (0.05% Tween-80 only). Fungi comprised 1 phyla, 5 classes, 10 orders, 13 families, and 18 genera, with Metarhizium being the dominant taxon in specimens from all treatment groups. Metarhizium spp. was greatest in the concentrations of 107 and 108 conidia/ml at 72 hours after exposure, reaching 94.82% and 93.74% of taxonomic units, respectively. We deduced that M. flavoviride competes for nutrition with midgut microorganisms; therefore, exposure to a pathogenic fungus will change the abundance and diversity of bacterial and fungal microorganisms in the midguts of hosts, and pathogens will impact the structure of bacterial communities in the host midgut with an alteration in the bacterial species composition. We observed that following the exposure of N. lugens to M. flavoviride, Metarhizium spp. dominated in the midgut of the host, the abundance and diversity of midgut fungal microorganisms decreased, and the dominant bacterial species in the midgut shifted.

Entomopathogenic Fungal Screening against Two Spotted Spider Mites, Tetranychus urticae Koch in Tomato and Broad Mite, Polyphagotarsonemus latus (Banks) in Chilli

Background: Entomopathogenic fungi are microorganisms that specifically infect and often kill insects and other arthropods. Most are non-pathogenic to plants and relatively non-toxic to humans and animals. Use of fungal entomopathogens can be an alternative to insecticides and could help in bio-intensive pest management. The current study aimed to study the pathogenicity of entomopathogenic fungal isolates against two Spotted Spider Mites, Tetranychus urticae Koch in tomato and broad Mite, Polyphagotarsonemus latus (Banks) in chilli. Methods: An extensive survey for the natural occurrence of entomopathogenic fungi on insects and mites was made in different agro climatic regions of Tamil Nadu during 2013 and 2014. Survey revealed the occurrence of two entomopathogenic fungi viz., Beauveria bassiana (Balsamo) Vuillemin and Metarhizium flavoviride Gams and Rozsypal var. minus. Laboratory experiment was conducted to evaluate the pathogenicity of fourteen isolates of Beauveria bassiana, Metarhizium anisopliae and Lecanicillium lecanii against Tetranychus urticae and Polyphagotarsonemus latus. Result: In opposition to T. urticae, the Beauveria bassiana isolate Bb 112 showed the highest toxicity of all the other isolates tested, with low LC50 value of 0.6 x106 spores ml-1 and LT50 of 92.60h. Against P. latus, Bb 112 had high virulence with low LC50 value of 0.3x106 spores ml-1 and LT50 value of 92.32h. Hence, there is potential for use of entomopathogenic fungi in the field conditions as an alternate control method in combating the insect pests and other arthropod pests since they are considered natural mortality agents and are environmentally safe.

EVALUATION OF ENTOMOPATHOGENIC FUNGI AGAINST TOMATO THRIPS, THRIPS TABACI LINDEMAN

AUTHOR(S) S. Hemalatha*, K. Ramaraju and S. Jeyarani ABSTRACT Eleven fungal isolates belonging to Beauveria bassiana (Balsamo-Crivelli) Vuillemin Metarhizium anisopliae (Metschinikoff) Sorokin, Lecanicillium lecanii (Zimmerman) Zare and Gams and Metarhizium flavoviride Gams and Rozsypal var minus with different host origins were assayed for their pathogenicity against the tomato thrips, Thrips tabaci Lindeman. The tomato thrips were found susceptible to all the examined isolates of entomopathogenic fungi. The fungal isolate Bb111 of B. bassiana was found highly virulent to T. tabaci with an LC50 of 1.6 × 105 spores/mL as evidenced by its non overlapping fiducial limits to other isolates. Mycosis on T. tabaci by Bb111 isolate had fast lethal effect after treatment with conidial suspensions at the concentration of 108conidia/mL. The values of the median lethal time required for 50% mortality (LT50) of the respective isolate was 104.91 h. The rest of the tested isolates showed higher LC50 and LT50 values, indicating the intermediate or low virulence to T. tabaci. The results of the present investigation revealed that the Bb111 could be further exploited on a field scale against T. tabaci.

Investigation of native isolates of entomopathogenic fungi for the biological control of three citrus pests

The pathogenicity of 15 isolates of Beauveria bassiana (Balsamo) Vuillemin, five isolates of Metarhizium anisopliae (Metschnikoff) Sorokin and one isolate of M. flavoviride (Gams and Rozsypal) were tested under laboratory conditions against the subterranean life stages of the citrus pests, Ceratitis rosa Karsch, C. capitata Wiedemann (Diptera: Tephritidae) and Thaumatotibia leucotreta Meyrick. (Lepidoptera: Tortricidae). When these citrus pests were treated with a concentration of 1×107 conidia mL−1, fungal isolates had a significantly greater effect on the adults of C. rosa and C. capitata than they did on the puparia of these two fruit fly species. Further, C. rosa and C. capitata did not differ significantly in their response to entomopathogenic fungi when adult and pupal mycosis were considered. Depending on fungal isolate, the percentage of T. leucotreta adults which emerged from fungal treated sand ranged from 5 to 60% and the percentage of pupae with visible signs of mycosis ranged from 21 to 93%. The relative virulence of the four most promising fungal isolates, as well as the commercially available B. bassiana product, BroadBand® (Biological Control Products, South Africa), were compared against one another as log-probit regressions of mortality against T. leucotreta which exhibited a dose-dependent response. The estimated LC50 values of the three most virulent B. bassiana isolates ranged from 6.8×105 to 2.1×106 conidia mL−1, while those of the least pathogenic ranged from 1.6×107 to 3.7×107 conidia mL−1.

Mortality of the Nut-Leaf Weevil Strophosoma Melanogrammum (Forster) and Damage Rate of Needles After Treatment with Entomopathogenic Fungi

The susceptibility of the nut-leaf weevil, Strophosoma melanogrammum (Forster) (Coleoptera; Curculionidae) to the select- ed strains of Beauveria bassiana (Bals.-Criv.) Vuillemin, Isaria farinosa (Holm) Brown & Smith, I. fumosorosea (Wize) Brown & Smith, Metarhizium anisopliae (Metschnikoff) Sorokin and M. flavoviride Gams & Rozsypal, was tested under laboratory conditions. Two ways of insect exposure to fungus were studied; direct inoculation of weevils and indirect by contact with inoculated A. procera twigs that served as food for S. melanogrammum. All of the tested isolates were pathogenic to S. melanogrammum. Direct inoculation of adult weevils in fungal spore suspensions resulted in the greatest mortality compared to indirect inoculation where A. procera twigs were immersed in spore suspensions. Direct inoculation with B. bassiana and Metarhizium spp. isolates caused over 80% mortality after 28 days at 20°C, while LT 50 values ranged from 15.0 to 21.6 days. Indirect inoculation with the most effective isolate M. anisopliae (275) resulted in 72% mortality after 28 days with a LT 50 value of 22.1 days. Both direct and indirect spore application failed to reduce needle damage compared with the control. However, significant differences between particular isolates have appeared.

Selection of global Metarhizium isolates for the control of the rice pest Nilaparvata lugens (Homoptera: Delphacidae)

This study was initiated to search for fungal candidates for microbial control of brown planthopper (BPH) Nilaparvata lugens Stål, to which little attention has been paid in the past two decades. Thirty-five isolates of Metarhizium anisopliae (Metschnikoff) Sorokin and M. flavoviride Gams & Rozsypal from different host insects worldwide were bioassayed for their lethal effects against third-instar BPH nymphs at 25 degrees C and a 14:10 h light:dark photoperiod at ca 1000 conidia mm(-2). On day 9 post-treatment, mortality attributable to mycosis ranged from 6.5 to 64.2% and differed significantly among the tested isolates with no apparent relationship to their host origin. Only two BPH-derived M. anisopliae isolates from the Philippines (ARSEF456) and Indonesia (ARSEF576) killed >50% of the nymphs. Both isolates were further bioassayed for time-concentration-mortality responses of the nymphs to the sprays of 19-29, 118-164 and 978-1088 conidia mm(-2) in repeated bioassays. The resultant data fitted a time-concentration-mortality model very well. Their LC(50) values were estimated as 731 and 1124 conidia mm(-2) on day 7 and fell to 284 and 306 conidia mm(-2), respectively, on day 10. The two M. anisopliae isolates are potential biocontrol agents of BPH for further research. This is the first report of the lethal effects of global Metarhizium isolates on the rice pest.

Effects of drying on the survival of conidiosphores of Metarhizium anisopliae var. acridum Driver & Milner

Metarhizium anisopliae var. acridum Driver & Milner (= Metarhizium flavoviride Gams & Rozsypal), isolate CG423, is being developed as a mycoinsecticide against grasshoppers in Brazil. Conidia were harvested and stored in a drying chamber during a study period of 260 d, in a room at ∼25°C. Water content (dry weight) of fresh and dried conidia was 70 and 4%, respectively. Conidia from fresh and dry preparations produced similar in vitro germination patterns and were both infective of the American grasshopper Schistocerca americana Drury. The drying process greatly enhanced the survival of CG423 conidia, as witnessed by nearly 100% germination rates after more than a 100-d desiccation period. Prolonged 135 and 176-d storage in the drying chamber at room temperature decreased viability to 72.5% and 28.5% respectively. In contrast, fresh conidia sealed in plastic bags and stored at ambient conditions for 52 d were inactive (<10% viable). The low germination rate (28.5%) of conidia exposed to 176 d in dry storage was altered by exposure of the dry conidia to high humidity (96% RH). Dry conidia exposed to a 4-h rehydration period had germination rates of ∼50%, whereas 24-h preincubation at high humidity resulted in ∼90% germination rates. However, the germination rates were reduced at 204 (81%), 323 (70%) and 260 (23%) days in storage. In addition, preincubation of the CG423 dry conidia in water produced similar positive effects on germination as compared to germination of fresh conidia. At 24h post-inoculation, dry conidia produced significantly lower germination rates (21%) than rehydrated conidia (germination rates > 91.7%, p < 0.05). However, after 48h on SDAY plates, the germination rate of dry conidia (88.3%) was comparable to the germination of conidia rehydrated in water, water Tween-20, or in high humidity.

Food consumption of Rhammatocerus schistocercoides Rehn (Orthoptera: Acrididae) infected by the fungus Metarhizium flavoviride Gams &amp; Rozsypal

Foliage consumption by nymphs and adults of the grasshopper Rhammatocerus schistocercoides Rehn infected with the fungus Metarhizium flavoviride Gams &amp; Rozsypal was evaluated. Sixth and eighth instar nymphs and female adults consumed on average (±SEM) 6.9 ± 0.36 cm² (60.7 ± 2.92 mg of dry matter), 11.0 ± 1.35 cm² (74.9 ± 9.24 mg d.m.), and 16.0 ± 0.50 cm² (126.5 ± 6.35 mg d.m.) of sugarcane leaves per day, equivalent to 85.4, 35.9 and 41.9% of the insect body weights, respectively. Eighth instar nymphs and female adults inoculated with M. flavoviride (5,000 conidia / insect) ingested less food from day three onward and showed at day 10 an average consumption 74.5 and 45.6% lower than control insects, respectively. Adult females topically treated with a sub-lethal dosage (3 ml of a 8 ppm suspension / insect) of the chemical insecticide diflubenzuron showed consumption rates comparable to untreated insects (P=0.065). The combination fungus + chemical did not show results different from those obtained with the fungus alone (P=0.405). A strong correlation (r²=0.998) between production of fecal pellets by R. schistocercoides and food consumption was observed. These results confirmed the high voracity of R. schistocercoides and showed a remarkable adverse effect of the fungus on food intake by infected nymphs and adults.

Natural Incidence of Metarhizium flavoviride Infection in Two Grasshopper Communities in Northern Benin

The infection of grasshoppers by naturally occurring entomopathogenic fungi was monitored at two sites in Malanville, northern Benin, Africa. Grasshoppers were collected during the monsoon seasons of 1993, 1994 and 1995. At the first site, 982 individuals of 38 grasshopper species were incubated. At the second site, 899 individuals of 33 grasshopper species were incubated. Two hyphomycete fungi (Deuteromycotina: Hyphomycetes), Metarhizium flavoviride Gams and Rozsypal and Sorosporella sp., were found infecting grasshoppers. The mean incidence of M. flavoviride infection was 0.3-1.7% at the first site and 1.2-3.2% at the second site for all grasshopper species. Sorosporella sp. was only collected from two grasshopper individuals in 1993. The majority of infected species had adult quiescence or continuously reproducing life cycles, and were either arboricolous or terricolous. Comparisons are made with a previous study of the two sites performed during 1992.

Polymorphism of the grasshopper Schistocerca pallens (Thunberg) (Orthoptera: Acrididae) and its natural pathogen Metarhizium flavoviride Gams &amp; Rozsypal (Hyphomycetes), revealed by RAPD analysis

The genetic variability of 27 individuals from two distinct populations (Northeast and Central Brazil) of the grasshopper Schistocerca pallens (Thunberg) and eight isolates of its natural pathogen, the fungus Metarhizium flavoviride Gams &amp; Rozsypal, was investigated using RAPD analysis. For the grasshoppers, ten different 10-mer oligonucleotide primers of arbitrary sequence were selected for analysis, resulting in 79 scorable binary characters. The program RAPDDIP applied to S. pallens revealed nucleotide diversity of 2.3 and 2.2% for the populations from Rio Grande do Norte (Northeast Brazil) and Federal District (Central Brazil), respectively. These values indicate the presence of high genetic variability within these populations. Conversely, the value for nucleotide divergence (0.004) showed almost no distinction between the two populations. In the case of M. flavoviride, thirty-one 10-mer oligonucleotide primers of arbitrary sequence were selected for analysis, producing 388 scorable binary characters. A dendrogram obtained for M. flavoviride, using the program NTSYS, revealed high homogeneity (similarity ≥79.5%) among the 8 isolates analyzed. The Brazilian isolates, all from the same geographical area and host (S. pallens), were even more homogeneous (≥98.3%).

Microbial Control of Schistocerca americana (Orthoptera: Acrididae) by Metarhizium flavoviride (Deuteromycotina): Instar Dependent Mortality and Efficacy of Ultra Low Volume Application Under Greenhouse Conditions

The entomopathogenic fungus Metarhizium flavoviride Gams & Rozsypal has been widely tested for the suppression of African grasshoppers, but there has been no research on Nearctic species. We examined the potential of M. flavoviride for the control of the American grasshopper, Schistocerca americana (Drury). When tested under conidial dosages of 1.2 x 10 3 , 1.2 x 10 4 , and 1.2 x 10 5 , 4th-instar S. americana were significantly more susceptible to M. flavoviride than 6th-instar and adult S. americana. At the conidial dosage of 1.2 x 10 5 , M. flavoviride produced 89.7, 12.8, and 17.6% mean mortality 7 d after treatment in 4th-instar, 6th-instar, and adult S. americana, respectively. By the 14th d after treatment, the M. flavoviride conidial dosage of 1.2 x 10 5 produced 99.4, 86.1, and 80.8% mean mortality in 4th-instar, 6th-instar, and adult S. americana, respectively. The LD 50 estimates for M. flavoviride of 1.7 x 10 4 conidia for the 4th-instar, 1.3 x 10 4 conidia for the 6th-instar, and 3.1 x 10 4 conidia for the adult S. americana are generally greater than those used for other acridids. Furthermore, mortality in M. flavoviride-treated S. americana was positively dosage dependent, as described by mean percentage of cumulative mortality and LT 50 estimates. Greenhouse trials evaluating ultra low volume application to grasshoppers, foliage, or grasshoppers and foliage produced from 78.1 to 92.0% mean mortality 14 d after treatment. In this simulated field trial, grasshoppers and M. flavoviride were exposed to temperatures ranging from 10 to 40°C, which demonstrated the potential of M. flavoviride to be effective under large temperature fluctuations, as may occur in the field.

Behavioural fever in the Senegalese grasshopper, Oedaleus senegalensis, and its implications for biological control using pathogens

1. Thermoregulatory behaviour of the Senegalese grasshopper, Oedaleus senegalensis (Krauss), was investigated in the field following a spray application of an oil‐based formulation of Metarhizium flavoviride Gams and Rozsypal in Niger, West Africa.2. Measurements of environmental temperature, wind speed and solar radiation were made in conjunction with measurements of internal body temperatures of grasshoppers from a control (unsprayed) and treated plot using microthermocouples and hand‐held thermometers. Grasshoppers were monitored for 4 days from the third day after application.3. Oedaleus senegalensis utilized a range of thermoregulatory behaviours to maximize body temperatures during periods of low insolation and ambient temperature, and to minimize excessive heat loading during the hottest periods. Preferred body temperature of uninfected grasshoppers was 39 °C, with a range from 24 °C in the early morning to a high of 46 °C during periods of high insolation and ambient temperature.4. Infected grasshoppers altered their thermoregulatory behaviour and showed a behavioural fever response to the pathogen. Preferred body temperatures of infected individuals were raised to a new set point of ≈ 42 °C. This is believed to be the first evidence for a behavioural fever in response to a microbial infection for any natural population. In the present study, its effects appeared to provide little therapeutic advantage to hosts infected following application. Preliminary evidence from other studies, however, indicates that modifications to host thermoregulation could be a significant constraint to the pathogen and may limit its impact under certain conditions.

Pathogenicity of Beauveria bassiana and Metarhizium flavoviride (Deuteromycotina) to Schistocerca americana (Orthoptera: Acrididae)

The entomopathogenic fungi Beauveria bassiana (Balsamo) Vuillemin and Metarhizium flavoviride Gams and Rozspal have been widely tested for the suppression of grasshoppers. However, with the exception of Melanoplus sanguinipes (F.), there has been little research on Nearctic species. We examined the potential of these 2 microbial agents for control of the American grasshopper, Schistocerca Americana (Drury), and the migratory grasshopper, M. sanguinipes. M. flavoviride was much more virulent than B. bassiana to both grasshopper species. At the conidial dosage of 1.2 x 105, M. flavoviride produced 69.2 and 74.2% mean mortality 7 d after treatment in S. americana and M. sanguinipes, respectively. In contrast, B. bassiana produced 1.7 and 11.7% mean mortality 7 d after treatment in S. americana and M. sanguinipes, respectively. Treatment with M. flavoviride also caused a significant reduction in feeding beginning 48 h after treatment of 6th-instar S. americana. Furthermore, M. flavoviride-treated S. americana showed an average reduction of 36.6% mean cumulative consumption, 5-8 d after treatment, when compared with untreated grasshoppers.

Field Treatment of Desert Locust ( Schistocerca gregaria Forskal) Hoppers in Mauritania Using an Oil Formulation of the Entomopathogenic Fungus Metarhizium flavoviride

A field trial was conducted to test the efficacy of an oil formulation of the entomopathogenic fungus , Metarhizium flavoviride Gams & Rozsypal (Deuteromycotina: Hyphomycetes) , as a control agent for the desert locust , Schistocerca gregaria Forskal (Orthoptera: Acrididae) , in Mauritania . The treatment was applied to hopper bands in the field . In caged samples of the treated insects , 99% mortality was observed in 15 days . On average during application only 51% of the hoppers received spray droplets directly , the additional mortality being due to pick - up of spores from the spray residue . This mortality was assessed by exposing insects to a treated plot at intervals , and monitoring disease levels during subsequent incubation in cages . The spray residue remained highly infective for a period of 6 days after application . The number of nymphs in the hopper bands was estimated using a computer - based photographic image - processing technique . Unfortunately , most of the hopper bands dispersed into small groups , but a population reduction could be demonstrated for one hopper band . Maximal daily mortality in the field was observed 10 - 11 days after application , compared with 6 - 10 days in cages .

Viability of Stored Conidia of Metarhizium flavoviride Gams and Rozsypal, Produced under Differing Culture Regimes and Stored with Clays

Conidia of Metarhizium flavoviride were cultured under a range of conditions and stored , with or without clays and silica gel , as powder or in oil . Fungal biomass was produced in shake flasks in liquid media containing nutrients before being added to sterilized rice for conidial production . Conidia pre - cultured under a low C:N ratio , or dried over a 9 - day period compared with 2 days before being placed in storage , showed greatest loss of viability . Conidia stored at 10 o C survived better than those stored at + 30 o C . A range of clays had no significant effect on storage of dried conidia but montmorillonite K10 clay was often harmful in terms of conidial viability . Conidia survived better when stored as dry powder than when stored in a mixture of mineral and vegetable oils . The addition of silica gel proved beneficial even when dried conidia were being stored .

Infection of Schistocerca gregaria (Orthoptera: Acrididae) hoppers by Metarhizium flavoviride (Deuteromycotina: Hyphomycetes) conidia in an oil formulation applied under desert conditions

In the framework of the LUBILOSA programme (Lutte Biologique contre les Locustes et les Sauteriaux), a field trial was carried out on hopper bands of the desert locust, Schistocerca gregaria (Forskal) (Orthoptera: Acrididae), in south-central Mauritania. The objective of the trial was to show that conidia of the entomopathogenic funbws Metarhizill171 flavoviride Gams and Roszypal formulated in oil would be able to infect and kill hoppers under desert climatic conditions. LUBILOSA is a research programme on the biological control of locusts and grasshoppers carried out by the International Institute of Biological Control (IIBC), Ascot, UK, the International Institute of Tropical Agriculture

Essais sur l'utilisation d'un biopesticide à base des conidies de Metarhizium flavoviride pour le contrôle des sauteriaux au Mali

Abstract: Investigation on the use of a biological insecticide based on Metarhizium flavoviride for the control of grasshoppers in Mali. Metarhizium flavoviride Gams &amp; Rozsypal (Deuteromycotinae; Hyphomycetes) was produced in diphasic culture, firstly in a sucrose‐yeast medium, with sporulation on rice. Spores were extracted in kerosene or sieved and dried. For application, the spores were formulated with a mixture of peanut oil and kerosene. The spore formulation was applied with spinning disk sprayers at Ultra‐Low Volume. From 1992 to 1994 several species of grasshoppers were treated with this formulation containing M. flavoviride conidia. Field applications resulted in mortality rates of 92% for Oedaleus senegalensis (Orth., Acrididae) (Krauss) treated with the Niger strain (IMI 330189) kept in field cages in 1992. In 1993, experiments compared two strains of M. flavoviride, the Niger strain (IMI 330189) and one from Mali (192–794). Mortality rates obtained for samples incubated in cages were between 31 % and 93%, respectively, for IMI 330189 (Day 0) and 192–794 (Day 3) for Krausella amabile (Orth., Acrididae) (Krauss). Field applications in 1994 resulted in cage mortality rates between 50% and 99% for O. senegalensis and K. amabile, respectively when treated with IMI 330189 and 192–794, with between 26% and 83% of dead insects showing external sporulation. Field counts in the 1994 experiment showed a population reduction of 85%.

SURVEYS FOR FUNGAL PATHOGENS OF LOCUSTS AND GRASSHOPPERS IN AFRICA AND THE NEAR EAST

AbstractA total of 181 isolates of Metarhizium 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 Metarhizium 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.

DEVELOPMENT OF METARHIZIUM SPP. FOR THE CONTROL OF GRASSHOPPERS AND LOCUSTS

AbstractFour 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 × 1012 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 &gt;90% mortality in samples of mixed acridids. In Mali, 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 senegalensis 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.

Use of Metarhizium flavoviride for control of Zonocerus variegatus: A model, linking dispersal and secondary infection from the spray residue with mortality in caged field samples

AbstractA field trial was conducted using an oil formulation of the entomopathogenic fungus, Metarhizium flavoviride Gams &amp; Rozyspal (Deuteromycotina: Hyphomycetes), to control the variegated grasshopper, Zonocerus variegatus L. (Orthoptera: Pyrgomorphidae). The influence of dispersal and secondary pick‐up from the spray residue on mortality was assessed by sampling insects from the treated plots at intervals and monitoring disease levels during subsequent incubation in the laboratory. The cumulative mortality curves showed the pathogen to be highly effective, even in samples taken 8 days after spraying. A model was developed to link the influence of mortality, incubation, secondary pick‐up of spores and insect dispersal, on the shape of these cumulative mortality curves. The model proved useful for data received from an experiment using small plot sizes, where insect dispersal is a big problem. The spray residue had an important influence on overall insect mortality. The model also indicated a difference in speed of kill between field and laboratory samples, suggesting an incubation delay in the field.