Conidial Powder Research Articles

Entomopathogenic fungi against the dengue vector Aedes aegypti: laboratory and semifield assessment

Aedes aegypti, in addition to its association with arboviruses of significant public health concern, poses a considerable challenge to the scientific community, which is actively working to devise innovative strategies to address this threat. Entomopathogenic fungi (EPF) are important bioagents for insect pest control. This study aimed to evaluate the virulence of EPF against Ae. aegypti larvae and adults under laboratory and semifield conditions. Conidia powder from M. anisopliae CG 153 or B. bassiana CG 479, at concentrations ranging from 1×105 to 1×108 conidia/mL, was tested against larvae (N=30) under laboratory conditions, while conidia suspension was used against adults (N=30) via the impregnated filter paper method. Survival curves were compared using the Log-rank test. Both isolates exhibited virulence against larvae and adults, with survival rates ranging from 0% to 64% and 20% to 76%, respectively. Subsequently, both fungi, at a concentration of 107 conidia/mL, were tested against larvae (N=60) and adults (N=60) under laboratory and semifield conditions. Under semifield conditions, larvae and adults showed survival rates ranging from 12% to 35% and 5% to 20%, respectively. The semifield tests produced promising results in decreasing mosquito survival rates. Consequently, this study concludes that the isolates M. anisopliae CG153 and B. bassiana CG 479 have the potential to serve as eco-friendly insecticides against mosquitoes, thus warranting further exploration in the bioprospecting of EPF-based products.

The Dissemination of Metarhizium brunneum Conidia by Females of the Red Palm Weevil, Rhynchophorus ferrugineus, Suggests a New Mechanism for Prevention Practices.

Direct contact between the conidia of entomopathogenic fungi (EPF) and their host is a prerequisite to successful infection; the host can, therefore, be infected by both direct treatment and by transmission of fungal inoculum from infested surfaces. This unique characteristic makes EPF especially relevant for the control of cryptic insects. In the case of the red palm weevil (RPW) Rhynchophorus ferrugineus, the eggs and larvae are almost inaccessible to direct-contact treatment. The objective of the present study was to investigate the mechanism of conidia transmission from a treated surface to host eggs and larvae. Foam pieces infested with Metarhizium brunneum conidial powder, conidial suspension, or distilled water were used as a laying surface for RPW females. The number of eggs laid was not affected by the EPF treatments and ranged from 2 to 14 eggs per female. However, hatching rate and larval survival were significantly reduced in the conidial powder treatment, resulted in 1.5% hatching and no live larvae. In the conidial suspension treatment, 21% of laid eggs hatched, compared to 72% in the control treatment. In both M. brunneum treatments, females' proboscis, front legs and ovipositor were covered with conidia. The females transferred conidia in both treatments to the laying holes, reaching up to 15 mm in depth. This resulted in reduced egg-hatching rate and significant larval mortality due to fungal infection. The stronger effect on egg and larval survival using dry conidia seemed to result from better conidial adhesion to the female weevil in this formulation. In future studies, this dissemination mechanism will be examined as a prevention strategy in date plantations.

Formulation of Metarhizium pinghaense and Metarhizium robertsii and the infection potential of the formulations against Pseudococcus viburni (Hemiptera: Pseudococcidae), after storage

Formulation of entomopathogens refers to the mixing of various inert ingredients, like clays and mineral oils, with the active ingredients which are the entomopathogens. Successful formulation enhances the survival of the entomopathogen and also eases their transportation, storage, preparation and application. The aim of this study was to develop a formulation to maintain the longevity and pathogenicity of the mass-produced conidia of local Metarhizium pinghaense and M. robertsii, for above-ground future commercial field application against Pseudococcus viburni. The objectives were to develop a cost-effective protocol for formulation of infective propagules and to test their effectiveness under laboratory conditions. The conidia of both isolates were formulated using four different oils (liquid paraffin, coconut, canola and olive oils) as liquid carriers, and diatomaceous earth as a mineral carrier. Conidial viability and pathogenicity were assessed over a period of eight weeks. In the study, it was observed that the conidia formulated in oil carriers maintained a high conidial viability and survival rate of >95 % over a period of eight weeks for both isolates, relative to when formulated in mineral carriers, or when stored as dry conidial powder. The conidia in all the oil formulations were also observed to induce high mortality, ranging between 60 % and 90 % for M. pinghaense, and between 70 % and 90 % for M. robertsii, when used against P. viburni. The ability of conidia of both isolates to maintain viability and pathogenicity, following storage in the oil formulations, increased the likelihood of the local isolates being successfully integrated as biological control agents for management of P. viburni under field conditions.

Laboratory studies assessing the microbial biocontrol potential of diverse strains of Beauveria bassiana isolated from coffee berry borer, with emphasis on strains from Hawai‘i Island and comparisons to commercial strain GHA

A series of experiments investigated genetically diverse strains of Beauveria bassiana (Bb) isolated from coffee berry borer (CBB). Objectives included assessment of their biocontrol potential, particularly in comparison to Bb commercial strain GHA currently applied for CBB control, and identification of various attributes potentially contributing to their comparatively greater epizootic potential in CBB populations. Bioassays identified one strain from Hawai‘i Island and one from Puerto Rico with virulence greater than GHA based on equal weights of unformulated conidial powder (CP); however, the greater potency of the CPs was ultimately explained by their 2.4-fold greater conidial densities (ca. 3.1 vs 1.3 × 1011 viable conidia/g CP). Density was explained, in large part, by conidial size, but not by size alone. Bb-inoculated CBB held on moist filter paper were more susceptible to infection than those held on cooked green coffee bean (CGCB). A Bb strain representative of the most common Hawaiian haplotype produced 2.6x more conidia after death of CGCB-held beetles than GHA (19.1 vs 7.3 x106 conidia/cadaver). Following host death, no difference was observed in time to emergence and initial conidial production by GHA and a selected group of Hawaiian strains; however, mass sporulation was initiated within 2 days by strain GHA compared to 4–5 days by the Hawaiian strains. In a preliminary evaluation of conidial mass-production potential, CP yields of several strains were comparable to GHA on a weight basis and significantly greater than GHA on a conidial basis (1.3–1.6 vs 0.7 × 1013 viable conidia/kg barley substrate).

Evaluation of the compatibility of Isaria fumosorosea (Hypocreales: Cordycipitaceae) IF-1106 with several adjuvants

ABSTRACT The compatibility of Isaria fumosorosea IF-1106 with 12 commercial pesticide adjuvants was evaluated using the predictive parameter SC90 (the adjuvant concentration at which 90% of conidia survived). Based on the SC90 values and the functionalities of the adjuvants used, two conidial wettable powder formulations of IF-1106 were formulated. Our results indicated that SC90 values can be used to evaluate the compatible concentration of adjuvants and Isaria fumosorosea. The wettable powder formulations F1 and F2 formulated on the basis of this research have a conidia germination rate of 92.4% ± 2.5% and 90.6% ± 1.3%, respectively, showing high compatibility, and their main quality control parameters (conidia germination rate, conidia suspension rate, wetting time, etc.) met commercialisation requirements. Our study also verified that IF-1106 is compatible with major surfactant and water-soluble polymer adjuvants in pesticide formulations when the use concentration is less than its SC90. Our research provided a new method for evaluating the compatibility of adjuvants with entomogenous fungi, and formulated two promising mycoinsecticide formulations for sucking insects in greenhouses.

Capsule formulations of Beauveria bassiana (balsamo) vuillemin for the management of pseudostem weevil, Odoiporus longicollis (oliver)

Capsules of Beauveria bassiana (Balsamo) Vuillemin were developed to target exact delivery at the site of infestation. Biocapsules formulated using gelatin coating, conidial powder and chitosan and talc as carriers were tested for their efficacy against pseudostem weevil. Five month old plants of variety Nendran, artificially infested with second instar grubs were used for the study. Capsules were placed in the leaf axils @ four per plant, one each on four sides of the plant. Damage Index (DI) and pest population were recorded two weeks after releasing weevils, in prophylactic control and two weeks after treatment in curative control. Analysis of data revealed efficacy of biocapsules, spore suspension @108 spores mL−1 and chlorpyriphos 20 EC 0.05% at par for prophylactic management of pseudostem weevil, as indicated by a common DI of one. Treatment with the capsules resulted in 91.67% reduction in population, as against 100% with spore suspension and chlorpyriphos. For curative treatment, plants treated with talc based capsules and chlorpyriphos 20 EC 0.05% exhibited 100% reduction in pest count, while that with spore suspension caused 83.33% reduction in weevil population. Both talc based and chitosan based Beauveria capsules were found highly effective for prophylactic treatment.

Investigating the potential of an autodissemination system for managing populations of vine weevil, Otiorhynchus sulcatus (Coleoptera: Curculionidae) with entomopathogenic fungi.

Vine weevil, also known as black vine weevil, (Otiorhynchus sulcatus) is an economically important pest affecting soft fruit and nursery stock in temperate regions. We used laboratory and polytunnel experiments to investigate a novel control system based on autodissemination of spores of an entomopathogenic fungus to populations of adult vine weevils. The fungus was applied as a conidial powder, used on its own or formulated with talc, to a simple plastic refuge for vine weevils. The potential for adult weevils to disseminate the fungus was investigated first in polytunnel experiments using fluorescent powders applied to the refuge in lieu of fungal conidia. In this system, 88% of adult weevils came in contact with the powder within 48 h. When the powder was applied to five adult weevils that were then placed within a population of 35 potential recipients, it was transmitted on average to 75% of the recipient population within 7 days. Three isolates of entomopathogenic fungi (Beauveria bassiana isolate codes 433.99 and 1749.11 and Metarhizium brunneum isolate code 275.86), selected from a laboratory virulence screen. These three isolates were then investigated for efficacy when applied as conidial powders in artificial refuges placed among populations of adult weevils held in experimental boxes in the laboratory at 20 °C. Under this regime, the fungal isolates caused 70-90% mortality of adult weevils over 28 days. A final polytunnel experiment tested the efficacy of conidial powders of M. brunneum 275.86 placed in artificial refuges to increase vine weevil mortality. Overall weevil mortality was relatively low (26-41%) but was significantly higher in cages in which the conidial powders were placed in refuge traps than in cages with control traps. The lower weevil mortality recorded in the polytunnel experiment compared to the laboratory test was most likely a consequence of the greater amounts of inoculum required to kill adult weevils when conditions fluctuate between favourable and unfavourable temperatures e.g. below 15 °C. The potential of an autodissemination system for entomopathogenic fungi as a means of controlling vine weevil as part of an integrated pest management programme is discussed.

Sodium Humate as a Promising Coating Material for Microencapsulation of Beauveria bassiana Conidia Through Spray Drying

Microencapsulation of Beauveria bassiana (Bb) conidia with sodium humate (SH) was undertaken successfully through spray drying at a high inlet air temperature of 175°C with corresponding outlet air temperature of 86.5 ± 1.3°C using 0.2% SH. The obtained product was a free-flowing, dark-brown powder containing microcapsules of Bb conidia coated with sodium humate (Bb-SH). These microcapsules measured 2.47–3.57 µm and possessed an uneven, fluffy surface. The colony-forming units (CFU) of Bb-SH microcapsules spray-dried at 175°C were 21.54 LCFUg−1, on par with 21.59 LCFUg−1 for Bb conidial powder not subjected to spray drying. Bb-SH microcapsules resulted in a high mortality of 93.0% against six-day-old Helicoverpa armigera larvae within five days after treatment. Bb-SH microcapsules readily dispersed in water, releasing sodium humate from the conidial surface. Germination of conidia was not affected by sodium humate as visualized by scanning electron microscopy of the cuticular surface of treated larvae. Bb-SH microcapsules showed good viability (21.11 LCFUg−1) at the end of six months of storage at room temperature (∼30°). Thus, sodium humate is a promising biopolymer for encapsulation of Bb conidia for extended shelf-life at room temperature.

Enhancing the Thermotolerance of Entomopathogenic Isaria fumosorosea SFP-198 Conidial Powder by Controlling the Moisture Content Using Drying and Adjuvants

Entomopathogenic fungi are promising pest-control agents but their industrial applicability is limited by their thermosusceptibility. With an aim to increase the thermotolerance of Isaria fumosorosea SFP-198, moisture absorbents were added to dried conidial powder, and the relationship between its water potential and thermotolerance was investigated. Mycotized rice grains were dried at 10°C, 20°C, 30°C, and 40°C and the drying effect of each temperature for 24, 48, 96, and 140 hr was determined. Drying for 48 hr at 10°C and 20°C reduced the moisture content to < 5% without any significant loss of conidial thermotolerance, but drying at 30°C and 40°C reduced both moisture content and conidial thermotolerance. To maintain thermotolerance during storage, moisture absorbents, such as calcium chloride, silica gel, magnesium sulfate, white carbon, and sodium sulfate were individually added to previously dried-conidial powder at 10% (w/w). These mixtures was then stored at room temperature for 30 days and subjected to 50°C for 2 hr. The white carbon mixture had the highest conidial thermotolerance, followed by silica gel, magnesium sulfate, and then the other absorbents. A significant correlation between the water potential and conidial thermotolerance was observed in all conidia-absorbent mixtures tested in this study (r = −0.945). Conidial thermotolerance in wet conditions was evaluated by adding moisturized white carbon (0~20% H2O) to conidia to mimic wet conditions. Notably, the conidia still maintained their thermotolerance under these conditions. Thus, it is evident that conidial thermotolerance can be maintained by drying mycotized rice grains at low temperatures and adding a moisture absorbent, such as white carbon.

Persistence of Isaria fumosorosea (Hypocreales: Cordycipitaceae) SFP-198 Conidia in Corn Oil-Based Suspension

Long-term persistence of entomopathogenic fungi as biopesticides is a major requirement for successful industrialization. Corn oil carrier was superior in maintaining germination rates of Isaria fumosorosea SFP-198 conidia during exposure to 50°C for 2 h, when compared with other oils, such as soybean oil, cottonseed oil, paraffin oil, and methyl oleate. The corn oil-based conidial suspension (91.6% germination) was also better in this regard than conidial powder (28.4% germination) after 50°C for 8 h. Long-term storage stabilities of corn oil-based conidial suspension and conidial powder at 4 and 25°C for 24 months were investigated, based on the correlation of germination rate with insecticidal activity against greenhouse whiteflies, Trialeurodes vaporariorum. Viability of conidia in corn oil was more than 98.4% for up to 9 months of storage at 25°C, and followed by 23% at 21 months. However, conidial powder had only 34% viability after 3 months of storage at 25°C, after which its viability rapidly decreased. The two conidial preparations stored at 4°C had better viabilities than those at 25°C, showing the same pattern as above. These results indicate that corn oil-based conidial suspension can be used to improve conidial persistence in long-term storage and be further applied to the formulation of other thermo-susceptible biological control agents.

Identification of a Virulent Isolate of the Entomopathogenic Fungus Beauveria bassiana (Balsamo) Vuillemin, its Mass Multiplication and Formulation for Development into a Mycoinsecticide for Management of Helicoverpa armigera (Hubner)

Two promising isolates of Beauveria bassiana - ITCC 4513 and HaBb DOR were multiplied on wheat bran supplemented with molasses and yeast extract in a polythene bag with sponge plugs for aeration. The yield of dry conidial powder per polythene bag was 18.25 ± 1.79 g and 10.03 ± 2.47 g for ITCC 4513 and HaBb DOR isolates, respectively. Laboratory bioassays with these conidial powders against 6 days old Helicoverpa armigera larvae resulted in LC50 values of 1.8 x 108 and 2.41 x 108 conidia ml-1 for the ITCC 4513 and HaBb DOR isolates, respectively, 5 days after treatment. Conidia of both the isolates were formulated as Suspension Concentrates (SC) in groundnut, sunflower and mineral oils. The formulations gave a clear suspension in water and could be sprayed with high volume knapsack sprayers. Performance of both isolates when formulated in oils was superior to unformulated conidia as reflected by the higher mortality of H. armigera larvae in laboratory bioassays and field trials on sunflower. The ITCC 4513 isolate was, however, superior to the HaBb DOR isolate in terms of conidial yield, efficacy as an SC formulation against H. armigera and safety to the egg parasitoid Trichogramma chilonis , thus proving to be an ideal candidate for development into a mycoinsecticide.

Potential of Beauveria bassiana and Metarhizium anisopliae isolates from Benin to control Plutella xylostella L. (Lepidoptera: Plutellidae)

Diamondback moth (DBM), Plutella xylostella L., is the main pest limiting cabbage production in Benin. In the search for biological agents to control the pest, eight isolates of the entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae indigenous to Benin were screened for virulence against larvae of the insect. The B. bassiana isolates tested were Bba14, Bba5644, Bba5645, Bba5653, Bba5654, and Bba5655, and M. anisopliae isolates were Ma178 and Ma182. The isolate Bba5653 caused 94% mortality of DBM larvae, and the mortality was significantly higher than that caused by any of the other isolates. Cabbage yield was 44.1 t/ha for plots treated with water formulation of Bba5653 at 1 kg conidia powder (CP) per hectare and 41.9 t/ha for plots treated with emulsion formulation of Bba5653 at same CP dose. Each of the yields was approximately threefold higher than the yield in plots treated with the insecticide bifenthrin or in untreated plots. In water formulations, 1 kg/ha of the conidia powder of Bba5653 reduced DBM populations at about the same rate as did 0.75 kg and 0.5 kg CP/ha, but significantly more than did 0.25 kg CP/ha.

The effects of some storage conditions on viability of Lecanicillium lecanii conidia to whitefly (Homoptera: Trialeurodes vaporariorum)

A study on the survival of Lecanicillium lecanii conidia in storage at room temperature was carried out. Firstly, drying methods of conidia powder were compared. Vacuum-freeze drying (VFD) was more suitable for drying conidia as compared to vacuum drying (VD) at room temperature. Vacuum-freeze drying for 24-h resulted in a water content of 5.4%, and a viability, determined as germination of conidia in 2% glucose solution after16 h, was 90.3% and the infection in greenhouse whitefly, Trialeurodes vaporariorum was about 94.7% at a dose of 1×108 conidia/mL. Secondly, the factors influencing viability of conidia stored at room temperature were evaluated in the laboratory. Temperature was the most critical factor influencing conidial storage stability, among the tested factors affecting survival of conidia stored at room temperature for 6 months. Both conidial germination and infection of hosts decreased with storage temperature increasing from 15 to 35°C, and at 35°C the survival of stored conidia for 6 months was near zero. The moisture content of the conidial powder was another major factor influencing viability of stored conidia at room temperature. Conidial powder dried to about 5% moisture content showed higher viability than non-dried conidial powder. For the carriers, clay and charcoal were more suitable for storage of L. lecanii conidia at room temperature. At a room temperature of 25°C, L. lecanii conidia which were dried to 5% water content and mixed with clay or charcoal could retain about 50% survival after 6 months’ storage.

Reduction of Feeding by Schistocerca piceifrons piceifrons (Orthoptera: Acrididae), Following Infection by Metarhizium anisopliae Var. acridum

The Central American locust, Schistocerca pi ceifrons ssp. piceifrons (Walker), often becomes a major pest of staple and cash crops in Mexico and Central America (Barrientos-Lozano et al. 2002). In 1993, laboratory and field studies were initi ated to develop a biological control strategy for S. piceifrons. The National Centre for Biological Control (Centro Nacional de Referencia de Con trol Biol?gico-CNRCB) has in its entomopathogen collection 35 isolates of Metarhizium anisopliae var. acridum (M. a. acridum) from S. piceifrons in Mexico. Our laboratory studies have shown that the isolates MaPL32 and MaPL40 are 2 of the most virulent against S. piceifrons (Barrientos Lozano et al. 2002). Field trials with M. a. acridum oil-formulated spores have demonstrated effective control of S. gregaria Forskal in Africa (Langewald et al. 1997), Locusta migratoria (L.) and Chortoicetes ter minifera (Walker) in Australia (Hunter et al. 1999, 2001), Rammatocerus schistocercoides (Rehn) in Brazil (Magalhaes et al. 2001) and S. piceifrons in Mexico (Hern?ndez-Vel?zquez et al. 2003). One of the perceived disadvantages, evident in these tri als, is the length of time (13 to 14 d) that the target insect takes to die after the application. However, in practical terms, successful control of locust is re flected by a reduction in food consumption; a locust that has ceased to feed due to infection is no longer a significant pest (Moore et al. 1992). Studies by Moore et al. (1992) and Seyoum et al. (1994) both reported significant reductions in feeding by S. gregaria following infection with M. a. acridum; similar results were also observed with the grass hopper Zonocerus variegatus (L.) (Thomas et al. 1997). All of these reported studies were carried out using a high dose of the pathogen, in some cases with few insects per treatment, without con trols, and a mixture of instars. The aim of the present work was to examine the effect of a conidia low dose (6 x 104) per S. piceifrons adult on both feeding rate and feces production. First instars of S. piceifrons locusts were col lected in Tizim?n, Yucat?n, Mexico. Locusts were kept in 1 x 1 x 1 m cages inside a controlled envi ronment (CE) room and fed on a diet of leaves of the grass Cynodon dactylon (L.) and rolled oats. The mean daily temperature and relative humid ity (RH) in the CE room was 27?C and 70 ? 5% re spectively, with a photoperiod of 12:12 h (L:D). The fungal isolate was a monospore isolate (EH-502/8) of M. a. acridum MaPL40 from S. pi ceifrons (Hern?ndez-Vel?zquez et al. 1997). Fun gal conidia were produced by a diphasic method. In the first phase, the fungus was cultured in a liquid medium of 2% sucrose and 2% yeast extract (Jenkins & Prior 1993). Fungal biomass was transferred to rice in a plastic bag (250 g/bag) with a cotton filter for further growth and sporu lation. After 14 d the bags were opened in the CE room which allowed the fungus to dry to a mois ture content of approximately 9%. Conidia were separated from the rice by sieving through a 300 um mesh. The resulting conidia powder was then re-sieved through a 90-um mesh to remove any remaining rice-dust particles. Conidial suspensions were formulated in citro line (a mineral oil derived from petroleum for ag ricultural use in Mexico) by mixing 1 g of conidial powder in 100 mL with a magnetic stirrer. It was then adjusted to 3 x 107 conidia/mL with use of a Neubauer haemocytometer. Germination rates were determined by randomly examining 100 conidia per plate with a compound microscope (400x). A conidium was considered to have germi nated if the germ tube was at least as long as the width of the conidium. Germination of conidia was 95-100% immediately after formulation and just before locust infection. Each treatment consisted of 20 adult locusts, 7 d post-fledging, each receiving 2 uL of the formu lation applied on the pronotum via a Hamilton SGE syringe. Control groups received 2 uL of ei ther citroline or sterile distilled water with Tween 80 (0.1%, v/v, Difco ) without conidia. Following treatment, locusts were placed in subgroups of 4 insects in 13 x 10.5 cm plastic containers, covered with muslin. Containers were maintained at 28?C and 70 ? 5% RH. The experiment was replicated 4 times. Mortality was recorded daily for 12 d; dead insects were placed individually in Petri dishes on moist filter paper at 27?C for 4 d to allow growth

Effect of the combined use of Metarhizium anisopliae (Metschinkoff) Sorokin and diatomaceous earth for the control of three stored-product beetle species

Laboratory bioassays were conducted in order to evaluate the use of the entomopathogenic fungus, Metarhizium anisopliae (Metschinkoff) Sorokin (Deuteromycotina: Hyphomycetes), against adults of three stored-grain beetle species, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae). Two fungal preparations were compared, a conidial suspension and a conidial powder. These were applied to wheat, at three dosages, 8×10 6, 8×10 8 and 8×10 10 conidia/kg of wheat, alone, or in combination with the diatomaceous earth (DE) formulation SilicoSec ® (Biofa Gbmh, Germany), applied at 0.5 g/kg of wheat. Adult insects were exposed to treated wheat for 24 h, 48 h, 7 d and 14 d. The mortality of R. dominica adults after 14 d of exposure to the treated substrate was 100% and 96% at the dosages in combination, for the suspension and the powder, respectively. The respective figures without DE were 94.4% and 74.6%. In contrast, against S. oryzae adults, the application of conidial suspension combined with DE was not as effective as the application of DE alone. Adult mortality of S. oryzae increased notably on wheat treated with the conidial powder. Similarly, the conidial suspension, with or without DE, was not as effective against T. confusum as the conidial powder. The progeny production of R. dominica on wheat treated with the highest suspension dosage, with or without DE, was significantly lower than that for the other aqueous fungal dosages. Moreover, significantly less progeny were produced on wheat treated with the highest dosage of powder conidia combined with DE, in comparison with the other treatments. In contrast, S. oryzae progeny production was notably reduced only in wheat treated with the highest dosage of fungal spore powder mixed with DE. No T. confusum progeny were found on wheat treated with the highest dosage of both fungal preparations combined with DE.

Saturated salt solutions for humidity control and the survival of dry powder and oil formulations of Beauveria bassiana conidia

Oil-based formulated conidia sprayed on steel plates and conidia powder (control) of Beauveria bassiana isolate IMI 386243 were stored at temperatures from 10 to 40 °C in desiccators over saturated salt solutions providing relative humidities from 32 to 88%, or in hermetic storage at 40 °C, and moisture contents in equilibrium with 33 or 77% relative humidity. The negative semi-logarithmic relation ( P < 0.005) between conidia longevity (at 40 °C) and equilibrium relative humidity did not differ ( P > 0.25) between formulated conidia and conidia powder. Despite this, certain saturated salts provided consistently greater longevity (NaCl) and others consistently shorter longevity (KCl) for formulated conidia compared to conidia powder. These results, analysis of previous data, and comparison with hermetic storage, indicate that storage of conidia over saturated salt solutions provides inconsistent responses to environment and so may be problematic for bio-pesticide research. In hermetic storage, oil formulation was not deleterious to longevity and in the more moist environment enhanced survival periods.

Field Evaluation of Selected Formulations of Beauveria bassiana for the Management of the Banana Weevil ( Cosmopolites sordidus ) on Plantain ( Musa spp., AAB Group)

Field experiments were undertaken to determine the efficacy of two formulations of Beauveria bassiana isolate IMI331094 against the banana weevil, Cosmopolites sordidus . Oil palm kernel cake-based formulation of conidia (OPKC-C) and conidial powder (CP) were applied to the planting holes and suckers. After artificial weevil release, OPKC-C and CP gave the same high level of weevil mortality (75%) compared with only 1% in the untreated control. Under natural levels of weevil infestation, 42% of weevils collected from suckers treated with OPKC-C died compared with 6% and 3% weevil mortality for CP and the untreated control, respectively. None of the suckers treated with OPKC-C died during the study period (60 days) while 17% and 19% of suckers from the CP treatment and the untreated control respectively, were killed. A study on the spread of fungal conidia using artificially infected and non-infected adult weevils showed a possible dissemination of B. bassiana conidia from infected weevils up to 18 m from the release point. On the basis of these results, the isolate IMI330194 of B. bassiana could clearly play a key role in the management of C. sordidus adults on plantain.

Activity of the Entomopathogenic Fungus Beauveria bassiana (Deuteromycota: Hyphomycetes) Against Three Coleopteran Pests of Stored Grain

A Beauveria bassiana isolate from the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), was evaluated as a conidial powder against 3 coleopteran pests of stored grain: the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae); the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae); and the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). Bioactivity of B. bassiana isolate 22292A was assessed on 3 types of food substrates (red flour beetle media, medium grain brown rice, and long grain rough rice) at 27°C and 60% RH. Adult mortality was 80–100% at the higher dosage levels for all insects tested on all media types at 21 d after treatment. Emergence of adult progeny on brown and rough rice was reduced by 83–99% at the 2 highest dosage level. The abrasive nature of rice hulls on the rough rice may contribute to the accelerated mortality seen on this medium.

The Selection of an Isolate of the Hyphomycete Fungus,Metarhizium anisopliae,for Control of Termites in Australia

Ninety-three isolates ofMetarhizium anisopliae,mostly derived from a survey of termite material, were screened for activity againstNasutitermes exitiosusandCoptotermes frenchiorC. acinaciformisusing a grooming assay technique. Twenty-six of the most promising isolates were further evaluated by bioassay againstN. exitiosusandC. acinaciformis.All isolates were pathogenic withCoptotermesspp. being more susceptible thanN. exitiosus.A group of nine isolates, chosen for their level of pathogenicity for one or other genus of termites and to represent a genetically diverse group, was finally compared in a minicolony test using termite colonies in 1 liter jars. The isolate, code-named FI-610 (derived from nest-mound material ofC. lacteusin SE New South Wales), was one of the most effective isolates against termites from both of the two colonies tested. This isolate also grew relatively well on agar plates at 36°C. FI-610 was thus selected for field trials and was found to be effective in killing colonies ofC. acinaciformiswhen 10 g (=3 × 1011conidia) or more of conidial powder was blown into the center of the large mound colonies.

Aerial spray trials against brown locust ( Locustana pardalina, Walker) nymphs in South Africa using oil-based formulations of Metarhizium flavoviride

A large micro-light aircraft fitted with Micronair AU7000 atomisers was used to apply Metarhizium flavoviride isolate IMI 330189 to brown locust ( Locustana pardalina) populations (mostly Vth instar nymphs) in the Richmond District of the Karoo in South Africa. Dry conidial powder was formulated in a paraffinic oil mixture to apply approximately 2.0 × 10 12 conidia per hectare with volume application rates of 1.0 and 2.5 l/ha. Three different droplet size spectra were produced by setting the pitch of the atomiser turbine blades to 25, 35 and 45 °. A total of ten hopper bands were treated on three separate days. Samples consisted of insects kept in cages under field conditions and sections of hopper bands maintained in open-topped field enclosures. All treated bands showed significantly greater mortality than the controls, with up to 98% mortality in samples maintained in enclosures after 3 weeks. Mortality in caged samples was often faster than with hoppers maintained in field enclosures. The relative efficacy of the various methods of aerial application will need confirmation in further trials; a volume rate of 2.5 l/ha appeared to give more consistent results than 1 l/ha applications. Mortality was probably related to droplet impaction, affected primarily by the wind-speed at the time of spraying.