Pathogenicity of hyphomycetous fungi against <Emphasis Type="Italic">Cyclocephala signaticollis</Emphasis>

Susceptibility of the white grub Cyclocephala signaticollis Burmeister (Coleoptera: Scarabaeidae: Dynastinae) larvae to seven isolates of Beauveria bassiana (Balsamo) Vuillemin, five of Metarhizium anisopliae (Metschnikoff) Sorokin and two of Paecilomyces lilacinus (Thom) Samson (Deuteromycotina: Hyphomycetes) was investigated. Among 14 fungal isolates screened the most virulent was a B. bassiana isolate (Bb 53) that caused 70% mortality of third instar larvae in 40 days after inoculation at 1 × 10⁸ conida/ml. Strains of M. anisopliae and P. lilacinus showed low efficacy or no virulence to the target host.     

Effect of culture medium on the production and virulence of submerged spores of Metarhizium anisopliae and Beauveria bassiana against larvae and adults of Aedes aegypti (Diptera: Culicidae)

Three Metarhizium anisopliae and three Beauveria bassiana isolates were cultivated in media containing casamino acids, soybean flour or sunflower seed flour and were shaken for three days. M. anisopliae presented similar yields of around 10⁶ submerged spores/ml without significant differences among them, whereas B. bassiana produced yields of around 10⁸ spores/ml, of which GHA strain produced more submerged spores in the casamino acids medium. The other two strains showed no significant difference in the production of submerged spores in the three media used. Differences in mortality on Aedes aegypti larvae were observed with the submerged spores of Metarhizium depending on isolate and medium used. M. anisopliae 2157 caused significantly higher mortality (40%) when cultivated in casamino acids medium. It presented an LC₅₀ of 8.93 × 10⁵ submerged spores/ml water against mosquito larvae five days after application, whereas it caused 27% mortality in Ae. aegypti adults 10 days after application. In conclusion, fungal nutrition affected virulence of some isolates of M. anisopliae against Ae. aegypti larvae while such an effect was not noted for B. bassiana isolates.     

Acid production by Metarhizium anisopliae: Effects on virulence against mosquitoes and on detection of in vitro amylase,protease, and lipase activity

The imperfect fungus Metarhizium anisopliae infects and kills larvae of many insect species, including the mosquito Culex pipiens. Mutants of M. anisopliae selected for enhanced production of amylase have been found to have simultaneously acquired hypervirulence against C. pipiens larvae. In the present work, wild-type and some mutant strains of M. anisopliae were found to excrete an acid or acids which alter the pH of fungal cultures below that permissible for amylase activity. The amylase-enhanced hypervirulence mutants did not excrete acid. Detection of protease and lipase activities was complicated by the acid excretion. When this was taken into account, mutants having altered lipase or protease production were found to have no alteration in virulence against mosquito larvae. The link between acid excretion, amylase activity, and hypervirulence is discussed.     

Isolation and virulence of entomopathogenic fungi against larvae of hazelnut weevil Curculio nucum (Coleoptera,Curculionidae) and the effects of combining Metarhizium anisopliae with entomopathogenic nematodes in the laboratory

An approach to ensure effective pest biocontrol would be to select native isolates of biological control agents (BCAs). A survey to isolate entomopathogenic fungi (EPF) from a hazelnut growing area has been carried out. EPF were recovered from 133 of the 295 soil samples. The main species isolated were Metarhizium anisopliae sensu lato (36%) and Beauveria bassiana sensu lato (42.8%). With regard to controlling abiotic factors, altitude had an effect on the distribution of B. bassiana, but not on M. anisopliae. Cropping system did not have an effect on the occurrence of these EPF, while pH appeared as a predictive variable for both. In addition, we tested the virulence of six of these isolates: three M. anisopliae and three of B. bassiana against larvae of Curculio nucum L. The highest larval mortality (reaching 80%) was due to M. anisopliae (strain 34) when applied in simultaneous combination with four entomopathogenic nematode species: Steinernema carpocapsae (strain B14), Steinernema feltiae (strain D114), Steinernema. sp. (strain D122) and Heterorhabditis bacteriophora (strain DG46). The effect of nematodes was greater and no antagonistic or synergistic effects were observed.     

Comparative laboratory studies on three fungal pathogens of the elm bark beetle Scolytus scolytus: Pathogenicity of Beauveria bassiana,metarhizium anisopliae, and Paecilomyces farinosus to larvae and adults of S. scolytus

The entomogenous fungi Beauveria bassiana (nine isolates), Metarhizium anisopliae (seven isolates), and Paecilomyces farinosus (four isolates) were tested as pathogens of larvae of the elm bark beetle, Scolytus scolytus. Single isolates of B. bassiana and M. anisopliae were also tested against adult beetles. Of the 21 isolates tested as conidial suspensions against larvae, all proved pathogenic. The three most and least virulent isolates were, respectively, isolates of B. bassiana and M. anisopliae. The other isolates fell between these two extremes, with the four P. farinosus isolates all moderately virulent. Spore retention on larvae following inoculation was estimated by washing conidia off the larvae. From the results it was possible to relate larval mortality to the approximate spore dose causing infection at different spore concentrations. Thus, application of spores of the three pathogens at a concentration of 10³ spores/ml resulted in limited mortality. At this concentration, an average of only a single spore was recovered from the inoculated larva. Adult bark beetles also proved susceptible to infection by isolates of B. bassiana and M. anisopliae. They were exposed to discs of elm bark dipped in a conidial suspension. It was estimated that a dose of less than 100 spores could cause infection of beetles following feeding on the elm bark discs.     

Susceptibility of Phyllophaga polyphylla and Anomala cincta larvae to Beauveria bassiana and Metarhizium anisopliae isolates, and the interaction with soil properties

The white grub species Phyllophaga polyphylla and Anomala cincta (Coleoptera: Melolonthidae) are economically important species that affect many crops in Mexico. A series of experiments to study the pathogenic interaction between isolates of Beauveria bassiana and Metarhizium anisopliae and these two insect species were undertaken. First, the susceptibility of third instar P. polyphylla larvae to each of seven isolates representing both species of fungus was evaluated by dipping the insects in 1?×?10⁸ conidia?ml^?1 suspensions. A second study examined the differences in the susceptibility of P. polyphylla and A. cincta larvae to two selected isolates for each of the fungal species. Finally, the susceptibility of A. cincta larvae to one M. anisopliae isolate when incubated in soil collected from four different sites was assessed. No significant differences in proportion of infection of P. polyphylla larvae were observed amongst the fungal isolates tested and mortality due to fungal infection was never greater than 20% after 36?days incubation. Anomala cincta larvae were more susceptible than P. polyphylla larvae, with greater than 90% infection when inoculated with isolates of M. anisopliae whereas mortalities of only 20% where achieved against P. polyphylla larvae. The soil type in which A. cincta were incubated following inoculation with M. anisopliae affected their susceptibility to infection. The results demonstrated that there is a complex interaction amongst entomopathogenic fungi, white grub larvae and soil properties, and points to the need of further investigation of this system in order to optimize the efficacy of entomopathogenic fungi against these insect species.     

Selection of promising fungal biological control agent of the western flower thrips Frankliniella occidentalis (Pergande)

Aims: Larval stages of Frankliniella occidentalis are known to be refractory to fungal infection compared with the adult stage. The objective of this study was to identify promising fungal isolate(s) for the control of larval stages of F. occidentalis. Methods and Results: Ten isolates of Metarhizium anisopliae and eight of Beauveria bassiana were screened for virulence against second‐instar larvae of F. occidentalis. Conidial production and genetic polymorphism were also investigated. Metarhizium anisopliae isolates ICIPE 7, ICIPE 20, ICIPE 69 and ICIPE 665 had the shortest LT₅₀ values of 8·0–8·9 days. ICIPE 69, ICIPE 7 and ICIPE 20 had the lowest LC₅₀ values of 1·1 × 10⁷, 2·0 × 10⁷ and 3·0 × 10⁷ conidia ml^?1, respectively. Metarhizium anisopliae isolate ICIPE 69 produced significantly more conidia than M. anisopliae isolates ICIPE 7 and ICIPE 20. Internally transcribed spacers sequences alignment showed differences in nucleotides composition, which can partly explain differences in virulence. Conclusion: These results coupled with the previous ones on virulence and field efficacy against other species of thrips make M. anisopliae isolate ICIPE 69 a good candidate. Significance and Impact of the Study: Metarhizium anisopliae isolate ICIPE 69 can be suggested for development as fungus‐based biopesticide for thrips management.     

Interaction between entomopathogenic nematodes and entomopathogenic fungi applied to third instar southern masked chafer white grubs,Cyclocephala lurida (Coleoptera: Scarabaeidae), under laboratory and greenhouse conditions

Four entomopathogenic nematode (EPN) species (Heterorhabditis bacteriophora Poinar, Heterorhabditis megidis Poinar, Jackson & Klein, Steinernema feltiae Filipjev and Steinernema riobrave Cabanillas, Poinar & Raulston) were tested for virulence against 3^rd instar southern masked chafer white grubs, Cyclocephala lurida Bland. H. bacteriophora and H. megidis, being the most virulent, were selected to evaluate the interaction with an entomopathogenic fungus (EPF), Beauveria bassiana (Balsamo) Vuillemin strain GHA or Metarhizium anisopliae (Metsch.) Sorokin strain F-52, under laboratory and greenhouse conditions. Nematodes and fungi were either applied alone or in combination, with nematodes added to fungi at different times. When applied alone, B. bassiana and M. anisopliae did not reduce grub numbers. Under laboratory conditions, additive interactions were found between H. megidis and B. bassiana, and between H. bacteriophora and B. bassiana or M. anisopliae in most combinations against chafer grubs; a few treatments showed synergism or antagonism. The combined effect did not differ significantly for nematode and fungal applications made simultaneously or at different times. Nematode infection and infective juveniles (IJs) production in grub carcasses were not significantly affected by the presence of a fungus. Efficacies of H. bacteriophora and M. anisopliae were affected by temperature, with grub mortality increasing at higher temperatures. Under greenhouse conditions, additive or synergistic interaction was found between H. bacteriophora and B. bassiana or M. anisopliae in different formulations in simultaneous applications or when the nematode was applied 4 weeks after the fungi, except between B. bassiana ES and H. bacteriophora. The impact of H. bacteriophora alone or in combination with M. anisopliae or B. bassiana on 3^rd instar C. lurida was comparable to that of an imidacloprid insecticide used as curative applications. More virulent fungal strains or species may be required to achieve a stronger interaction with nematodes in the management of C. lurida.     

Potential of a combination of entomopathogenic fungal strains and a non-ionic surfactant to control the fall armyworm (Spodoptera frugiperda)

The fall armyworm, Spodoptera frugiperda, is an emerging invasive pest in Taiwan that feeds on a wide range of crops and causes serious damage. Herein, an entomopathogenic fungal library (EFLib) was constructed to identify potential microbes to control FAW. Twenty-eight indigenous entomopathogenic fungi (EPF) were isolated and investigated for their potential pathogenicity, with Metarhizium pinghaense (Mp-NCHU-124) and Beauveria bassiana (Bb-NCHU-157) exerting dose-dependent effects on the 4th instar FAW larvae. The non-ionic surfactant Silwet L-77 rapidly killed FAW larvae after spraying at a concentration of 300 mg/kg and the toxic effect of Silwet L-77 on FAW larvae was dose-dependent. When the EPF isolates (10⁶ conidia/mL) were applied to FAW larvae in combination with the non-ionic surfactant Silwet L-77 (30–90 mg/kg), the mortality rate dramatically increased and the LT₅₀ reduced, with increased fungal mycosis (Mp-NCHU-124: 38% to 72% and Bb-NCHU-157: 20 to 62%), indicating the high compatibility of EPF with the non-ionic surfactant. Thus, the Silwet L-77+EPF combined formulation has potential for practical field application for FAW pest control and sustainable agriculture in the future.     

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.     

Biochemical properties of different entomopathogenic fungi and their virulence against Chilo suppressalis (Lepidoptera: Crambidae) larvae

We determined the virulence of Beauveria bassiana, Metarhizium anisopliae, Isaria fumosoroseus and Lecanicilium lecanii against larvae of Chilo suppressalis Walker by bioassay and evaluated several enzymatic and non-enzymatic components. LC₅₀ values of the entomopathogenic fungi revealed 90, 32, 45,000, 4600, 42,000 and 1,540,000 spores/larva for isolates BB1–BB3 of B. bassiana, I. fumosoroseus, M. anisopliae and L. lecanii, respectively. Isolate BB3 and I. fumosoroseus had the highest amounts of total protein and hydrophobin and isolates BB3 and M. anisopliae showed the highest activities of lipases and chitinases. In case of proteases, the highest activities were observed for Pr1 of BB1 and Pr2 of L. lecanii. The highest general esterase activities were obtained in I. fumosoroseus and BB1 when 1-naphtyl acetate and 2-naphtyl acetate were used as substrates. The highest activity of glutathione S-transferase (GST) was observed in I. fumosoroseus by using both reagents but BB1 demonstrated the highest activities of alkaline phosphatase and acid phosphatase. Clustering of the fungi using biochemical enzymes revealed BB2 and BB3 as a separate group of entomopathogenic fungi. In another group, I. fumosoroseus and L. lecanii had the most similarity and were separated from BB1 and M. anisopliae. The fungi exhibited different virulence on larvae of C. suppressalis by producing adhering protein and extracellular enzymes. Overall, results of the bioassays and clustering based on enzymatic activities revealed that isolate BB2 was the most effective fungus against larvae of C. suppressalis.     

Ovicidal effects of entomopathogenic fungal isolates on the invasive Fall armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae)

Maize is a major staple food for over 300 million people in sub‐Saharan Africa. Sustainable productivity of this primary crop has been recently threatened by Fall armyworm (FAW), Spodoptera frugiperda invasion. Due to lack of environmentally safe management strategies, immediate responses by growers and governments to tackle FAW are based on rampant use of pesticides. Looking for efficient biopesticides, twenty entomopathogenic fungal isolates (14 Metarhizium anisopliae and 6 Beauveria bassiana) were screened for their efficacy against eggs and second instar larvae of FAW. A single discriminating concentration of 1 × 10⁸ conidia ml^?1 and four replicates per treatment were used in all experiments. Isolates were assessed for their ability to cause mortality of FAW second instar larvae, eggs and the neonate larvae that emerged from treated eggs. Among the isolates tested, only B. bassiana ICIPE 676 caused moderate mortality of 30% to second instar larvae. Metarhizium anisopliae ICIPE 78, ICIPE 40 and ICIPE 20 caused egg mortalities of 87.0%, 83.0% and 79.5%, respectively, and M. anisopliae ICIPE 41 and ICIPE 7 outperformed all the others by causing 96.5% and 93.7% mortality to the neonate larvae, respectively. The cumulated mortality of eggs and neonates was highest with M. anisopliae ICIPE 41 (97.5%), followed by M. anisopliae ICIPE 7, 655, 40, 20 and 78 with total mortality of 96.0%, 95.0%, 93.5%, 93.0% and 92.0%, respectively. These isolates with high cumulated mortality (≥92%), especially ICIPE 78 and 7, which are already commercialized for spider mites and ticks control respectively, would be good candidates for development as biopesticides for management of FAW in Africa if further evidence of their efficacy is obtained in the field.     

Management of pine wilt disease vectoring Monochamus alternatus adults using spray and soil application of Metarhizium anisopliae JEF isolates

Chemical control is widely used to control the Japanese pine sawyer beetle, Monochamus alternatus, but strong chemical regulations require an environmentally sound management strategy. In this work, we investigated the use of entomopathogenic fungi and their application as a means of practical pest management. Thirty-two diverse species of fungal isolates were assayed against adult pine sawyer beetles using a contact method under laboratory conditions, and four isolates showed over 70% virulence consequently. These isolates, two each of Beauveria bassiana and Metarhizium anisopliae were sprayed on the adult beetles at 1 × 10⁷ conidia/ml in plastic containers, respectively. The M. anisopliae-treated adult beetles showed 67% mortality. M. anisopliae isolates JEF-197 and JEF-279 demonstrated dosage-dependent insecticidal activity. Following the laboratory experiments, semi-field trials were conducted in young pine trees under high (RH 94%) and low (RH 35%) humidity conditions. In the high humidity conditions, most of the adult beetles stayed on the top of the branches. When the two M. anisopliae isolates were sprayed on the beetles, they showed ca. 50–70% insecticidal activity 11 days after application. In contrast, in low humidity conditions, the adult beetles tried to move off the branches and onto the soil. When the beetles reached the JEF-197 and JEF-279-treated soil, we measured >90% insecticidal activity. This work suggests that M. anisopliae was the most virulent entomopathogenic fungus against adult Japanese pine sawyer beetles, and this forest insect could be ecologically controlled by the spray and soil application of the M. anisopliae isolates.     

Successive subculturing alters spore-bound Pr1 activity,germination and virulence of the entomopathogenic fungus,Beauveria bassiana

One of the hurdles in the development of entomopathogenic fungi such as Beauveria bassiana is loss of virulence when successively maintained in vitro. This may result in products of inferior quality in mass production programs. Also, there are many contradicting data and unclear points in this case. Three isolates of B. bassiana were subcultured successively 15 times. Spore-bound Pr1 activity, germination rate, and virulence of conidia against mealworm (Tenebrio molitor L.) larvae were studied. Results showed that isolates normally retained their virulence during 10 subculturings. However, they clearly offered decreased virulence (elevated LT₅₀ values and lower percent mortality). The activity of Pr1 bound to conidia declined as subculturing continued; the lowest spore-bound activity and germination potential of conidia was recorded for the 15th subculture. Virulence data were in agreement with Pr1 activity and germination rate as there was a positive correlation between germination rate and spore-bound Pr1 activity with fungal virulence. This explains that at least a part of attenuation in fungal virulence can be explored in enzymatic activity, especially in the important cuticle-degrading protease, Pr1.     

Attenuation of the entomopathogenic fungus Beauveria bassiana following serial in vitro transfers

Stability of pathogenicity in continuous in vitro cultivation is desirable for the purpose of large-scale production of a mycoinsecticide. Fungal biocontrol agents may lose virulence when maintain on artificial media, resulting in products of commercially inferior quality. In this research, two isolates (DEBI007 and DEBI008) of entomopathogenic fungus Beauveria bassiana were investigated for their stability following fifteen serial in vitro transfers assaying virulence to mealworm larvae, conidiation, and hyphal development on artificial culture as some fungal virulence determinants. Moreover, role of insect cuticle on fungal virulence restoration and protease 1 (Pr1) activity was considered as the most important factor. Although radial hyphal development and colony colour on in vitro culture was not affected following serial transfers, conidiation and Pr1 activity of both fungal isolates were reduced remarkably after fifteen transfers compared with control. Similarly, mean lethal concentration (LC₅₀) values were increased as the number of serial transfers on artificial diet increased, although these increases were not statistically significant in both isolates as the confidential limits of LC₅₀ values were overlapping. Our results revealed that attenuation of entomopathogenic fungi following serial in vitro transfers is a combination of interconnected factors. Other probable components such as pathogenicity determinants in this interaction should be explored in next researches.     

Age of three dipteran hosts as a factor governing the pathogenicity of Beauveria bassiana and Metarrhizium anisopliae

The age of three adult dipteran hosts was tested as a factor governing the virulence of two fungal pathogens. The subjects tested were 1-, 5-, 10-, 15-, 20-, 25-, and 30-day-old animals. The age of the house fly, Musca domestica, the age of the black blowfly, Phormia regina, and the age of the onion fly, Hylemya antiqua, do not significantly affect the virulence of either Beauveria bassiana or Metarrhizium anisopliae. B. bassiana kills M. domestica and P. regina more quickly than does M. anisopliae, but B. bassiana and M. anisopliae kill H. antiqua at the same rate. The ages of all three flies had no significant effect on average death time after inoculation with either pathogen.     

Pathogenicity of Beauveria bassiana and Metarhizium anisopliae to the tobacco spider mite Tetranychus evansi

Seventeen isolates of Metarhizium anisopliae (Metschnikoff) Sorokin and two isolates of Beauveria bassiana (Balsamo) Vuillemin were evaluated for their pathogenicity against the tobacco spider mite, Tetranychus evansi Baker & Pritchard. In the laboratory all the fungal isolates were pathogenic to the adult female mites, causing mortality between 22.1 and 82.6%. Isolates causing more than 70% mortality were subjected to dose–response mortality bioassays. The lethal concentration causing 50% mortality (LC₅₀) values ranged between 0.7×10⁷ and 2.5×10⁷ conidia ml⁻¹. The lethal time to 50% mortality (LT₅₀) values of the most active isolates of B. bassiana and M. anisopliae strains varied between 4.6 and 5.8 days. Potted tomato plants were artificially infested with T. evansi and treated with B. bassiana isolate GPK and M. anisopliae isolate ICIPE78. Both fungal isolates reduced the population density of mites as compared to untreated controls. However, conidia formulated in oil outperformed the ones formulated in water. This study demonstrates the prospects of pathogenic fungi for the management of T. evansi.     

Isolation of entomopathogenic fungi from Northern Thailand and their production in cereal grains

Spore productivity in six entomopathogenic fungal strains isolated from insect cadavers at four locations in Chiang Mai province was evaluated in five cereal grains: white-rice, wheat, rye, corn and sorghum. According to sequence analysis of the internal transcribed spacer regions of these isolates, they were closely related to Beauveria bassiana (2 isolates), Metarhizium flavoviride (1 isolate), Metarhizium anisopliae (1 isolate), Paecilomyces lilacinus (1 isolate) and Isaria tenuipes (1 isolate). Among all fungal isolates, the maximum amount of spores (530.0?×?10⁹ conidia/g) was yielded P. lilacinus CMUCDMT02 on sorghum grain followed by white-rice (399.3?×?10⁹ conidia/g). Moreover, the highest number of spore in M. flavoviride was 102.8?×?10⁹ conidia/g sorghum whereas white-rice yielded the greatest amount of spore for B. bassiana CMUCDMF03 (141.0?×?10⁹ conidia/g) after 60?days incubation. The fungal growth rate was found highest in corn for all strains and rye showed the lowest with the exception of P. lilacinus CMUCDMT02 among the tested grains. Spore viability was over 80?% for all isolates that had been inoculated for 60?days. Fungal conidia suspension of P. lilacinus obtained highest virulence against Bactrocera spp. at a concentration of 1?×?10⁶ spore/ml. The strains isolated, exhibited good production of conidia suggesting a promising strategy for the mass production of inoculum as biocontrol agents with low production cost.     

Virulence,proteolytic and lipolytic activities of Brazilian Beauveria bassiana s.l. isolates (Hypocreales: Clavicipitaceae) to Rhipicephalus microplus ticks (Acari: Ixodidae)

Beauveria bassiana s.l. is a cosmopolitan fungus used in the control of different species of arthropods. The current study explored the virulence for ticks, proteolytic and lipolytic activities of 10 Brazilian B. bassiana s.l. isolates. For this purpose, Rhipicephalus microplus biological parameters was evaluated after immersion of the engorged females in fungal suspension (10⁸ conidia mL^?1) and the enzymatic activities were performed posteriorly the fungal growth in minimal medium. After the biological assays, five isolates changed all parameters analysed with highest efficacy of approximately 61% (CG 206) and 66% (CG 481). However, we observed that the most virulent isolates did not show the highest enzymatic activities. Interestingly, CG 500, considered an isolate of intermediate efficacy, demonstrated higher enzymatic activities than the other isolates in four of five analyses (total protease, Pr1, Pr2 and lipase; p?相似文献   

Selection of virulent isolates of entomopathogenic hyphomycetes against Clavigralla tomentosicollis Stål. and evaluation in cage experiment using three cowpea varieties

The virulence of 8 isolates of entomopathogenic hyphomycetes against adult and 5th instar nymph of Clavigralla tomentosicollis was evaluated in the laboratory at 4 different concentrations of inoculum. At all concentrations, Beauveria bassiana CPD 9 and Metarhizium anisopliae CPD 5 caused the highest mortality in adult bug ranging from 58 to 97% and 53 to 100%, respectively at 7 days post inoculation. The same isolates had the shortest LT₅₀ (3.5 and 4.1 days, respectively) and the lowest LC₅₀ (1.8 × 10⁵ and 9.8 × 10⁴ conidia ml^-1 values in adult insects. In nymphs, M. anisopliae CPD 5 was the most virulent isolate causing mortality of between 43 to 92% with the shortest LT₅₀ of 2.7 days and the lowest LC₅₀of 4.6 × 10⁵ conidia ml^-1 which however did not differ significant from LC₅₀ observed in B. bassiana CPD 9 isolate at 5 days post inoculation. A significant reduction in feeding in both developmental stages treated with fungi was observed at 2 days after treatment with the greatest reduction occurring in insects treated with B. bassiana CPD 9 and M. anisoplia CPD 5. In adult insects treated with these isolates, some bugs ceased feeding 24 h before death. When these two isolates were compared in caged experiment with an untreated control using a susceptible, tolerant and moderately resistant variety of cowpea, percentage pod and seed damage were significantly lower in fungal treated cages than in the control cages on all varieties tested. Grain yield per plant was also significantly higher in fungal treated cages than in the control cages on all varieties. The performance of M. anisopliae CPD 5 was however superior to B. bassiana CPD 9. Application of the fungi on moderately resistant variety of cowpea was found to enhance the performance of the pathogen. This revised version was published online in June 2006 with corrections to the Cover Date.