LABORATORY SUSCEPTIBILITY OF PLUTELLA XYLOSTELLA TO METARHIZIUM ANISOPLIAE AND NOMURAEA RILEYI*

Abstract Five isolates of Metarhizium anisopliae and one isolate of Nomuraea rileyi were bioassayed against larvae of Plutella xylostella. Larvae were treated by exposing cabbage leaf discs previously immersed in conidial suspension, and were then incubated at 25^oC and observed daily. One of M. anisopliae isolates, F11248, originally from Mastotermes darwiniensis was found being most virulent against P. xylostella. The LC₅₀ was estimated as 2.03 times 10⁴conidia/ml with 9 d mortality data, and the LT₅₀ was 4.97 d at concentration of 10⁷conidia/ml. Isolate F163 (N. rileyi) showed virulence to P. xylostella in both tests, but no cadavers sporulated.     

Efficacy of entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae against Thaumetopoea pityocampa Shiff. (Lepidoptera: Thaumatopoeidae)

Abstract

In this study, Metarhizium anisopliae TR 106 and Beauveria bassiana TR 217 was tested against fourth instar larvae of Thaumetopoea pityocampa. The LT₅₀ and LT₉₀ of 1?×?10⁶ concentration of M. anisopliae against T. pityocampa were 3.60 and 4.11 for direct application, while these were 2.87 and 3.60?days, respectively in leaves application. The LT₅₀ and LT₉₀ of the 1?×?10⁸ concentration of the same isolate were 2.50 and 2.95?days for direct application, and 2.98 and 3.74?days for leaves application. The LT₅₀ of insect and leaves application for 1?×?10⁶ of B. bassiana were 3.75 and 3.49?days, respectively. The LT₉₀ of same concentration for insect application was 4.48?days, while LT₉₀ for leaves application was 4.63?days. Similarly, LT₅₀ of insect and leaves application for 1?×?10⁸ of B. bassiana were 3.03 and 3.31?days, while LT₉₀ were 3.68 and 4.29?days, respectively. Approximate 100% mycosis was observed in all treatments.     

Susceptibility of apple clearwing moth larvae,Synanthedon myopaeformis (Lepidoptera: Sesiidae) to Beauveria bassiana and Metarhizium brunneum

Apple clearwing moth larvae, Synanthedon myopaeformis (Lepidoptera: Sesiidae) were found to be susceptible to infection by two entomopathogenic fungi: an indigenous fungus isolated from S. myopaeformis cadavers and identified as Metarhizium brunneum (Petch); and Beauveria bassiana isolate GHA. In laboratory bioassays, larvae exhibited dose related mortality after exposure to both the M. brunneum and Beauveria bassiana with 7 day LC₅₀'s of 2.9×10⁵ and 3.4×10⁵ spores/mL, respectively. Larval mortalities caused by the two isolates at 1×10⁶ spores/mL were not significantly different and 73% of the M. brunneum-treated, and 76% of the B. bassiana-treated larvae were dead 7 days post treatment, with LT₅₀'s of 5.5 and 5.1 days, respectively.     

Isolation and evaluation of South African isolates of Beauveria bassiana (Hypocreales: Cordycipitaceae) on Rhipicephalus microplus (Acari: Ixodidae)

Beauveria bassiana (Hypocreales: Cordycipitaceae) is an entomopathogenic fungus that has shown promising results as a biocontrol agent of ticks. Locally isolated B. bassiana are better acclimatised to the natural conditions of their geographical origin; therefore, they are essential in developing effective biocontrol agents for ticks. The current study aimed to isolate native strains of B. bassiana that are pathogenic to Rhipicephalus microplus ticks. The virulence of the isolates was tested against R. microplus larvae using a formulation containing 15% avocado oil, 0.05% adjuvant and 10⁸ conidia mL^?1. The two best strains were further evaluated for various biological parameters on adult engorged female ticks. Breakthru® or Ballista® (adjuvant) was mixed with the formulation to compare their effect on the isolates' virulence. In total 61 entomopathogenic fungi were isolated from the 360 greater wax moth larvae, Galleria mellonella (Lepidoptera: Pyralidae) used. The virulence test identified Bb-40 and Bb-41 to be the most virulent isolates against R. microplus larvae with mortalities of 91 and 93% and LT₅₀ values of 5.8 and 6.2 days, respectively. Compared to the control, both strains significantly affected all the measured biological parameters. The type of adjuvant also considerably affected the susceptibility of ticks to the fungi. In conclusion, the two isolates combined with adjuvants can be used as a biocontrol agent to control R. microplus.

     

Susceptibility of the tobacco whitefly,Bemisia tabaci (Hemiptera: Aleyrodidae) biotype Q to entomopathogenic fungi

Recently, the Q biotype of tobacco whitefly has been recognized as the most hazardous strain of Bemisia tabaci worldwide because of increased resistance to some insecticide groups requiring alternative strategies for its control. We studied the susceptibility of this biotype of B. tabaci to 21 isolates of Beauveria bassiana, three isolates of Isaria fumosorosea, one isolate of I. cateni, three isolates of Lecanicillium lecanii, one isolate of L. attenuatum, and one isolate of Aschersonia aleyrodis. These isolates were evaluated on pruned eggplant seedlings, at a concentration of 10⁸ conidia/mL (deposited at 6000±586 conidia mm^?2). The mortality based on mycosis varied from 18 to 97% after 6 days. Isaria fumosorosea isolate Pf04, B. bassiana isolates Bb06, Bb12, and L. lecanii L14 were found the most effective. Furthermore, five isolates were chosen for concentration–mortality response assays and compared to B. bassiana GHA as a standard. The numbers of nymphs infected by fungi were correlated with the spore concentration. L. lecanii L14 and I. fumosorosea Pf04 had the shortest LT₅₀ at 3.5 and 3.3 days at 6000±586 conidia mm^?2. Mortality declined and LT₅₀ values were longer as the concentration of conidia was reduced. The LD₅₀ values were calculated as 87, 147, 191, 263, and 269 conidia mm^?2 for isolates L14, GHA, AS1260, Bb13, and Pf04, respectively. These results indicated that the Q biotype of sweetpotato whitefly was susceptible to the five isolates of entomopathogenic fungi and these isolates have potential to be developed as microbial pesticides for whitefly control.     

Pathogenicity of Beauveria bassiana (Deuteromycotina: Hypomycetes) to Larvae of the Small Poplar Longhorn Beetle, Saperda populnea (Coleoptera: Cerambycidae)

The small poplar longhorn beetle, Saperda populnea is an important pest of Lombardy poplars (Populus nigra L.) in Turkey. A survey for natural entomopathogenic fungi of S. populnea larvae was made in Erzurum, Turkey, during the period 2004–2005. Larvae (13.5%) infected with a strain of the fungus Beauveria bassiana were found. The pathogenicity of B. bassiana strain 46 was conducted with different concentrations of conidia (10⁶, 10⁷ and 10⁸ conidia/ml) of this isolate on S. populnea larvae. The lowest concentration (10⁶ conidia/ml) caused about 56% mortality within 6 days. One hundred percent mortality was achieved after median lethal time (LT₅₀) of 4.6 and 4.4 days for 10⁷ and 10⁸ conidia/ml, respectively. There were no significant differences between median lethal times. This is the first record of natural infection of S. populnea larvae by B. bassiana.     

Potential of Metarhizium anisopliae and Beauveria bassiana to control Dinoderus porcellus (Coleoptera: Bostrychidae) infesting yam chips

The beetle Dinoderus porcellus Lesne is a serious storage insect pest that causes important losses by destroying stocks of yam chips. In the aim to found an alternative control method to the use of synthetic insecticides for its management, the virulence of the entomopathogenic fungi Beauveria bassiana (Balsamo) Vuillemin (isolate Bb115) and Metarhizium anisopliae (Metschnikoff) Sorokin (isolate Met 31) against adults of D. porcellus was evaluated under laboratory conditions (25 ± 2 °C and 70 ± 5% RH). Then, the effectiveness of the most virulent entomopathogenic fungus as biological agent against D. porcellus was assessed under farmer storage conditions. For each entomopathogenic fungus isolate, four conidial concentration (0, 10⁵, 10⁷, and 10⁹ conidia/mL) at the dose of 1 µL were inoculated topically on D. porcellus adults (3–5 days old). Observations focused on insect mortality, cadaver sporulation and weight loss of yam chips. Lethal dose and lethal time values were estimated using probit analysis. Both fungal isolates at all conidial dose caused more than 50% mortality on day 7, with the highest mortality (94.44%) achieved using B. bassiana at the 10⁹ conidia/mL. LT₅₀ values for B. bassiana and M. anisopliae isolates were 2.63 and 3.35 days, respectively, while their LT₉₀ values were 6.15 and 9.87 days, respectively. Yielding the lower LD₉₀ values and the highest rates of cadaver sporulation, B. bassiana isolate appeared as the most virulent against D. porcellus. After 3 months of storage, comparatively to the control, the B. bassiana isolate at the highest conidial dose (10⁹ conidia/mL) significantly reduced D. porcellus populations, and weight loss of yam chips. This study revealed the potential of B. bassiana and M. anisoplae isolates as biological control agent against D. porcellus for yam chips protection.     

Evaluation of twenty-eight strains of Heterorhabditis bacteriophora isolated in Azores for biocontrol of the armyworm, Pseudaletia unipuncta (Lepidoptera: Noctuidae)

The armyworm, Pseudaletia unipuncta, is the most important pest in Azorean pastures. Although this pest has some parasitoids and pathogens, additional biological control agents are needed to manage it. Entomopathogenic nematodes, particularly Heterorhaditis bacteriophora, are good candidates because they have been isolated from pastures and crops in almost all islands of the Azorean Archipelago. We tested 28 Azorean isolates of H. bacteriophora in the laboratory against the 6th instar P. unipuncta to determine mortality rates and virulence of each isolate. Plot tests in the field were also conducted to evaluate the best time for application of the selected isolate. All isolates killed the larvae although important differences in the mortality rates were observed. Forty-eight h post exposure (HPE) to the nematode infective juvenile (IJ), insect mortality ranged from 0 to 92.5% and at 96 HPE, mortality ranged from 32.5 to 100%. Based on LC₅₀ and LT₅₀, H. bacteriophora Az29 was the most pathogenic and the remaining 27 isolates were grouped in three classes of virulence. The most virulent class included four isolates with LC₅₀ ranging from 180 to 327 IJs/insect and LT₅₀ from 44 to 62.9 h. These isolates were obtained from three of the nine islands. High intrapopulational variability was detected on isolates in the moderately virulent class suggesting that these isolates are good candidates for genetic improvement. Field tests showed H. bacteriophora Az29 was more effective to control P. unipuncta larvae than Steinernema carpocapsae Az20 and H. bacteriophora Az32, belonging to the less virulent class. These tests also showed that applications performed during May resulted in better control than in July.     

Pathogenicity of the entomogenous,hyphomycete fungus,Metarhizium anisopliae against the chrysomelid beetles Psylliodes chrysocephala and Phaedon cochleariae

Susceptibility of the mustard beetle (Phaedon cochleariae) and the cabbage stem flea beetle (Psylliodes chrysocephala) to six isolates of the entomogenous, hyphomycete fungus Metarhizium anisopliae, was investigated. A farther six isolates were assayed against P. cochleariae only. The isolates originated from hosts of various insect orders. Five of the six isolates tested against P. chrysocephala and P. cochleariae were infective for both species whereas one isolate, V107, was non‐pathogenic to both. The level of virulence of different M. anisopliae isolates for these chrysomelid beetles varied considerably. Isolates V90 and V93 were highly virulent to P. chrysocephala and P. cochleariae respectively but were significantly less virulent against the alternate host species. The LT₅₀ of isolate V90 for P. chrysocephala was 7 days at 4 x 10⁷ conidia/ml and its LC₅₀ value was 16 x 10⁵ conidia/ml. The LT₅₀ of V93 for P. cochleariae was approximately 8 days at 4 X 10⁸ conidia/ml and its LC₅₀ value was 3 x 10⁷ conidia/ml. Following inoculation, germinating conidia of all isolates produced appressoria on the cuticular surface of both hosts suggesting that specificity is determined at later stages of infection.     

Pathogenicity of Beauveria bassiana,Metarhizium anisopliae and Serratia marcescens to the banana weevil Cosmopolites sordidus

Two exotic fungal isolates, one of Beauveria bassiana (268–86) and another of Metarhizium anisopliae (100–82), three local isolates of B. bassiana (isolates I, II, III) and one of the entomogenous bacteria Serratia marcescens, were tested for pathogenicity against the banana weevil Cosmopolites sordidus. All four isolates of B. bassiana and the one of M. anisopliae were found to be pathogenic to third—instar larvae of C. sordidus, causing mortalities of 98–100% by 9 days post—exposure to dry fungal spores. M. anisopliae was the least pathogenic to larvae with LT₅₀ of 4.2 days, compared to 3.5, 3.3, 3.6 and 4.0 respectively for isolates I, II, III and 268–86. B. bassiana was also pathogenic to adult C. sordidus, causing mortalities varying from 63–97% by 35 days post—exposure depending on isolate. As for larvae M. anisopliae exhibited low pathogenicity for the adult C. sordidus. In general, all the fungi tested were less pathogenic to adult weevils (LT₅₀ = 17.5; 12.5; 8.0 and 22.0 days) for isolates I, II, III and 268–86 respectively, while isolate 100–82 failed to kill 50% of adults even by 35 days post—exposure. Incubation of dead weevils in a moist environment led to development of surface mycelia starting from intersegmental junctions. Histopathology revealed extensive destruction of internal organs by hyphae which invaded most of the organs. The LT₅₀ for S. marcescens against C. sordidus larvae was 2.8 days. However, the bacterium did not kill adult C. sordidus even at 10 times the concentration applied on larvae.     

Variability in virulence of Beauveria spp. soil isolates against Ostrinia nubilalis

European corn borer (Ostrinia nubilalis) is an important maize pest which is treated mainly by synthetic pesticides with many negative effects for ecosystem and human health. Soil borne entomopathogenic fungi of species belonging to Beauveria genus may provide an alternative strategy for biological control of this pest. In this article, we report results of virulence testing of 46 soil isolates of Beauveria spp. against O. nubilalis in relation to isolates origin and haplotype. All strains were collected from soil using Galleria mellonella bait method. Conidia suspension with concentration 10⁷ conidia in ml was used for virulence test against 4th instar larvae of O. nubilalis at temperature 25°C. After 14 days, mortality of larvae was in the range 34%–96%. Median lethal time LT50 was estimated to 5.5–21.3 days. Mortality was not in relation to habitat or any other environmental parameter of sites where isolates came from. Differences among species were insignificant. Isolates were divided into 8 genetic lineages and 14 haplotypes using sequencing of ITS and Bloc nuclear regions. None of the lineages showed higher mortality than others. Despite more or less virulent isolates being found in each lineage, the three most virulent isolates belonged to the same lineage Beauveria bassiana A3. The four most virulent isolates were compared to commercial isolate GHA to assess medium lethal concentration. LC50 were estimated in range 7.5 × 10⁴ to 9.5 × 10⁵. Three of the four isolates showed equal or greater efficiency than strain GHA.     

Molecular and Morphological characterization of multiple nucleopolyhedrovirus from Mexico and their insecticidal activity against Spodoptera frugiperda (Lepidoptera: Noctuidae)

The fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera: Noctuidae), is the most important pest of maize in many countries. Entomopathogenic viruses mainly Baculoviruses family are excellent biological control agents and therefore a viable alternative for managing this pest. The aim of this study was to determine the biological activity of eight native nucleopolyhedrovirus (NPVs) against FAW larvae. Additionally, two of the most virulent isolates (SfCH32 and SfCH15) were characterized biologically by bioassays to estimate their median lethal dose (LD₅₀) and median lethal time (LT₅₀), morphologically by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and molecularly by restriction enzymes. Three (SfCH15, SfCH18 and SfCH32) of the eight tested native nucleopolyhedrovirus isolates caused mortalities ˃98% at 168-hr post-inoculation (hpi) with a dose of 9.2 × 10⁴ OBs/larva. SfCH15 and SfCH32 isolates showed occlusion bodies (OBs) of irregular shape and size (1.02–2.24 μm). The SfCH15 and SfCH32 isolates showed similar median lethal dose (5.6 × 10²–6.4 × 10² OBs/larva). The lowest median lethal time (114.5 hpi) was observed with the SfCH15 isolate at the highest concentration (2.5 × 10⁶ OBs/larva). The DNA restriction profiles for SfCH15 and SfCH32 were different, with their genome size being ~128,000 bp and 132,000 bp, respectively. SfCH15 and SfCH32 isolates showed similar morphological characteristics and the highest virulence against fall armyworm. This study showed that native isolates were highly virulent against S. frugiperda larvae, being similar to other reported strains; however, field studies are required to confirm their insecticidal effect.     

Combining vegetable oil and sub-lethal concentrations of Imidacloprid with Beauveria bassiana and Metarhizium anisopliae against adult guava weevil Conotrachelus psidii (Coleoptera: Curculionidae)

Of the insect pests that attack guava fruits, the guava weevil, Conotrachelus psidii Marshall, 1922 (Coleoptera: Curculionidae), is one of the most important in Brazil. In search of alternatives to chemical pesticides, this study was performed to select fungal isolates of Beauveria bassiana and Metarhizium anisopliae as potential candidates for the control of adult C. psidii. Tests were carried out using three products applied with the entomopathogenic fungi: Tween 80, sunflower oil and Imidacloprid (IMI). A sub-lethal concentration of IMI was determined (100 ppm). The results demonstrated that LPP 19 and LPP 114 were the most effective isolates when used in combination with all of the products. The least virulent isolate, ESALQ 818, when applied in Tween 80 caused only 26.6% mortality, however, this isolate showed significantly improved efficiency when applied together with either sunflower oil or IMI, causing 57.3 and 88.6% mortality, respectively. The efficiency of all the isolates tested here improved when applied together with IMI, with LT₅₀ values of 5.3–10.3 days when compared to LT₅₀ values in Tween alone of 9.5–17 days. The isolate that produced the highest number of conidia on the cadavers of adult C. psidii was LPP138, independent of the product used; however, conidial production was slightly reduced when fungi were applied together with IMI. These results are promising for developing new formulations of the isolates to be tested in the field.     

Evaluation of Beauveria bassiana (Hyphomycetes) isolates as potential agents for control of Dendroctonus valens

Abstract The red turpentine beetle (RTB), Dendroctonus valens LeConte, as a destructive invasive pest, has become one of the most economically important forest pest in China. Effective control measures are desperately needed. Entomopathogenic fungi, such as Beauveria bassiana, have shown great potential for the management of some bark beetle species. In this study, 12 isolates of B. bassiana from bark beetle were examined for biological characteristics and virulence, to assess their potential as biocontrol agents for RTB. There were significant differences (at P= 0.05) in colony growth rate, conidial yield, conidial germination, tolerance to UV light and extracellular proteases activity among the tested B. bassiana isolates. Isolates, including Bb1801, Bb1906, Bb789 and Bb773, exhibited the best characteristics, because they have faster hyphal growth rate, higher spore production and faster spore germination, higher UV tolerance and protease (Pr1) production. The results of a pathogenicity test of B. bassiana on RTB larvae showed that most isolates of B. bassiana have demonstrated high efficacy and the highest virulent isolate was Bb1801, which killed 100% of the treated insects and had a median lethal time (LT₅₀) of 4.60 days at a concentration of 1×10⁷ conidia/mL. Therefore, isolate Bb1801 has a great potential for sustainable control of RTB in the forest. The correlation between biological characteristics and virulence of the fungal isolates is discussed and the possibility of combination of entomopathogenic fungi with semiochemicals, as one of the promising strategy for RTB control, is considered.     

Diapause in a tropical species,Cothonaspis boulardi (Parasitic hymenoptera)

Summary The strain of Cothonaspis boulardi originating from a field collection at Guadeloupe (16° lat. N-West Indies) exhibits a facultative diapause that occurs at the final larval instar. The diapause was induced by low temperature (17.5° C) and was inhibited at 25° C. Diapause was independent of photoperiod. The termination of diapause was hastened in about 10 days by exposing larvae to a temperature of 25° C. Although a succession of sufficient cold days for diapause occurs only rarely in the collection area (Petit-Bourg), at higher elevations within 20 km of Petit-Bourg conditions that could induce diapause occur annually.This study is supported by research grant of C.N.R.S. (ATP Ecophysiologie, n^o 51-3571)     

Manifold passages in an assorted infection in a host could improve virulence of Helicoverpa armigera Nucleopolyhedrovirus (HaNPV)

Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) is serious pests of cotton and several other crops. Helicoverpa armigera Nucleopolyhedrovirus (HaNPV) can be important alternative to synthetic insecticides for the management of H. armigera. However, the efficacy of HaNPV can vary in horizontal and vertical transmission. In the current study, we evaluated the efficacy of HaNPV of a virulent strain (vertically transmitted up to six generations) and wild strains (used after isolation from the field infected larvae). Both strains were applied to the 2nd instar larvae of H. armigera @ 1 × 10⁹ polyhedral inclusion bodies (PIB)/ml. There were six replications of each strain (strains). The results indicated higher mortalities in larvae exposed to virulent strains (68.33 ± 6.07%) as compared to wild strain (45 ± 2.24%). Virulent strains killed the larvae quite faster than wild strain. The lethal time (LT₅₀) to kill 50% of the larvae by virulent strain was 7.15 days and for wild strain it was 19.47 days. The results showed that multiple passage of HaNPV through several generations enhances its efficacy to kill H. armigera larvae faster. The results of this study will be helpful to manage H. armigera and other related lepidopoterous pests.     

Entomopathogenic potential of fungi isolated from intertidal environments against the cabbage aphid Brevicoryne brassicae (Hemiptera: aphididae)

The use of biopesticides formulated from entomopathogenic fungi is a strategy utilised in integrated pest management programmes. The microorganisms used in these biopesticides are isolated from terrestrial organisms and ecosystems. However, bioprospecting in marine environments may lead to the discovery of promising fungi for pest control. In this study, marine fungi were identified and evaluated for the control of Brevicoryne brassicae. The effects of the most virulent isolate so identified on the mortality of aphids were compared to the effects of bioinsecticides that were formulated from fungal strains of Beauveria bassiana (Bovemax®) and Metarhizium anisopliae (Methamax®). Moreover, lethal and sublethal effects of this isolate on B. brassicae biological parameters were also examined. The isolates were identified as Aspergillus versicolor, Aspergillus sydowii (isolates 1 and 2), Penicillium dipodomyicola, and Trichoderma harzianum. The fungal strain A. versicolor was the most virulent fungal species, causing 85.9% mortality in B. brassicae at 24 h. The mortality rate caused by A. versicolor was similar to that caused by Bovemax® and Methamax® at concentrations of 10⁵ conidia mL^?1, and superior to that caused by Methamax® at a concentration of 10⁹ conidia mL^?1. The exposure of B. brassicae to CL₂₅ (0.32 × 10³) of A. versicolor did not affect the net reproductive rate (R_o), average generation time (T), intrinsic rate of population growth (r_m), and finite rate of population increase (λ). This is the first study to demonstrate that A. versicolor isolated from a marine environment is a promising candidate for the biological control of agricultural pests.     

The effect ofMetarhizium anisopliae (DAT F-001) concentration and exposure time on the survival of the subterranean pasture pest,Adoryphorus couloni (Col.: Scarabaeidae)

The virulence of the DAT F-001 isolate ofMetarhizium anisopliae forAdoryphorus couloni was tested by exposing final instar larvae (L3) to concentrations of 10¹ to 10⁷ spores/g in a sand-peat mix for up to 112 days at 20°±2°C. All concentrations were pathogenic to L3 larvae and survival was dependent on concentration and correlated with exposure time. The time to kill 50% of the treated larvae (LT₅₀) ranged from 18.9 days (10⁷ spores/g) to 82.7 days (10¹ spores/g). The effect of DAT F-001 on feeding by L3 larvae was determined by comparing the production and weight of frass pellets/larva/day of untreated control larvae with larvae rolled in sporulating cultures ofM. anisopliae DAT F-001 and DAT F-054 (low virulence). Exposure to, and infection byM. anisopliae DAT F-001 had minimal impact on larval feeding. L3 larvae continued to feed at the same rate as both untreated and DAT F-054 treated larvae virtually until they died.

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Résumé La virulence deM. anisopliae DAT F-001 pourA. couloni a été analysée en exposant des larves L3 à des concentrations de 10¹ à 10⁷ spores/g dans un mélange de sable et de tourbe pendant un maximum de 112 jours à une température de 20°±2°C. Toutes les concentrations sont pathogènes pour les larves L3; la survie dépendait de la concentration et est en corrélation avec le temps d'exposition. Les LT₅₀ sont compris entre 18,9 jours (10⁷ spores/g) et 82,7 jours (10¹ spores/g). L'effet de DAT F-001 sur l'alimentation des larves L3 a été évalué en comparant la production et le poids des fèces/larve/jour des larves non-traitées avec des larves roulées dans des cultures sporulées deM. anisopliae DAT F-001 et DAT F-054 (faible virulence). L'exposition àM. anisopliae DAT F-001 suivie de l'infection a peu d'effet sur l'alimentation des larves. Les larves L3 continuent à s'alimenter au même rythme que les larves non-traitées de DAT F-054, quasiment jusqu'à leur mort.

     

Discovery of a North American genetic variant of the entomopathogenic fungus <Emphasis Type="Italic">Metarhizium anisopliae</Emphasis> var. <Emphasis Type="Italic">anisopliae</Emphasis> pathogenic to grasshoppers

A genetic variant of the entomopathogenic fungus Metarhizium anisopliae var. anisopliae, isolated from a soil in Alberta, Canada, from a location with a history of severe grasshopper infestations, was evaluated for pathogenicity in bioassays of living grasshoppers. Mortality in treated individuals drawn from a laboratory colony was 99% (LT₅₀ = 6.7 days, LT₉₀ = 9.6 days) at 12 days post-inoculation compared to 100% (LT₅₀ = 4.1 days, LT₉₀ = 5.8 days) mortality at 8 days in insects exposed to a commercial isolate of M. anisopliae var. acridum (IMI 330189). Experimental infection of field-collected grasshoppers under laboratory conditions with the native isolate of M. anisopliae var. anisopliae resulted in 100% (LT₅₀ = 4.4 days, LT₉₀ = 5.4 days) mortality attained within 7 days compared to 100% (LT₅₀ = 4.7 days, LT₉₀ = 6.3 days) mortality in 9 days in insects treated with M. anisopliae var. acridum. Amplification of fungal genomic DNA from the indigenous isolate with primers for the specific detection of M. anisopliae var. anisopliae produced a product almost 300 bp larger than expected based on previously known isolates. This is the first demonstration of a highly virulent, indigenous non-chemical control agent of grasshoppers in North America. GenBank Accession Nos. DQ342236, DQ342237.     

Influence of Temperature on Virulence of Fungal Isolates of <Emphasis Type="Italic">Metarhizium anisopliae</Emphasis> and <Emphasis Type="Italic">Beauveria bassiana</Emphasis> to the Two-Spotted Spider Mite <Emphasis Type="Italic">Tetranychus urticae</Emphasis>

Twenty-three isolates of Metarhizium anisopliae (Metschnikoff) Sokorin and three isolates of Beauveria bassiana (Balsamo) Vuillemin (Ascomycota: Hypocreales: Clavicipitaceae) were assessed for their virulence against the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). Based on the screening results, nine isolates of M. anisopliae and two isolates of B. bassiana were tested for their virulence against young adult (1- to 2-day-old) female T. urticae at constant temperatures of 20, 25, 30 and 35°C. At all temperatures tested, all the fungal isolates were pathogenic to T. urticae but mortality varied with isolates and temperatures. Fungal isolates were more virulent at 25, 30 and 35°C than at 20°C. The lethal time to 50% mortality (LT₅₀) and lethal time to 90% mortality (LT₉₀) values decreased with increased temperature. There were no significant differences in virulence between fungal isolates at 30 and 35°C; however, significant differences were observed at 20 and 25°C.