Evaluation of the Entomopathogenic Potential of Beauveria bassiana, Metarhizium anisopliae and Isaria fumosorosea for Management of Cosmopolites sordidus Germar (Coleoptera: Curculionidae)

The banana weevil (BW), Cosmopolites sordidus, is the main coleopteran pest of banana, causing up to 100% yield loss. In this study, we screened 20 isolates of entomopathogenic fungi (EPF) for the management of BW. In the lab, eight Beauveria bassiana isolates caused >50% mortality of the adult BW, whereas Metarhizium anisopliae and Isaria fumosorosea isolates were less pathogenic. B. bassiana isolates ICIPE 648, ICIPE 660 and ICIPE 273 were the most pathogenic, killing ≥80% of adult BW. B. bassiana isolate ICIPE 622 yielded the highest spores per BW cadaver (1.84 × 108 spores), followed by ICIPE 660, ICIPE 273 and ICIPE 648—1.17 × 108, 3.8 × 107 and 3.6 × 107 spores, respectively. ICIPE 273 had the shortest LT50 (5.3 days) followed by ICIPE 648 (9.8 days) and 660 (11.1 days). Similarly, the LC50 values for the three isolates were 5.18 × 107, 5.49 × 107 and 5.2 × 107 spores mL−1, respectively. In the field, ICIPE 273 and ICIPE 648 had the highest (31.3%) and lowest (20.8%) pathogenicity, respectively. This study indicates that the B. bassiana isolates ICIPE 273, ICIPE 648 and ICIPE 660 are potential candidates for the environmentally sustainable management of BW.

Alkane-priming of Beauveria bassiana strains to improve biocontrol of the redbanded stink bug Piezodorus guildinii and the bronze bug Thaumastocoris peregrinus

Insect Epicuticle hydrocarbons (CHC) are known to be important determinants in the susceptibility degree of insects to fungal entomopathogens. Five Beauveria bassiana isolates were phenotypically analyzed regarding their response to CHC nutrition and their pathogenicity and virulence towards high fungal-susceptible Thaumastocoris peregrinus and low fungal-susceptible Piezodorus guildinii, which are important hemipteran pests in eucalyptus and soybean plantations, respectively. Two of these isolates, resulting the most (ILBB308) and the least (ILBB299) virulent to P. guildinii, were also evaluated at gene expression level after growth on n-pentadecane. B. bassiana most virulent isolate ILBB308 showed the lowest growth on most evaluated CHC media. However, this isolate distinctively induced most of the analyzed genes involved in CHC assimilation, cuticle degradation and stress tolerance. Virulence towards low susceptibility P. guildinii was enhanced in both hypervirulent ILB308 and hypovirulent ILBB299 isolates after growth on n-pentadecane as the sole carbon source, whereas virulence enhancement towards high susceptibility T. peregrinus was not observed in alkane-grown fungi. Virulence enhancement towards P. guildinii could be mostly explained by a priming effect produced by CHC on the induction of some genes related to hydrocarbon assimilation in ILB 205 and ILB 308, such as hydrophobin (Bbhyd2) and cytochrome P450 genes (BbCyp52g11 and BbCyp52x1), and partially by the induction of genes related to cuticle degradation (Bbchit and Bbcdep1) and stress tolerance (Bbsod1) observed only in ILB308.

Efficacy of Entomopathogenic Fungus Beauveria bassiana Isolates against Callosobruchus maculatus (Coleoptera: Chrysomelidae) under Controlled Conditions

Callosobruchus maculatus FaB (Coleoptera: Bruchidae), is a major field-to-store post-harvest pest of in the tropics and worldwide. They cause weight loss, decreased germination potential and reduction in commercial and aesthetic value as a result of physical contamination of grain by insects, eggs and excrement, decreased nutritional value. Entomopathogenic fungi have been employed in control of a number of storage pests and has been demonstrated to have potential in control of C. maculatus in cowpea during storage. Nine B. bassiana isolates were evaluated for effectiveness in controlling C. maculatus in cowpea grain under controlled laboratory conditions. Mortality of the bruchids was evaluated stepwise where the most effective isolate concentrations against C. maculatus were assessed. Initial assessment involved determination of the most effective concentration among the isolates following dilution. The isolates showed significant differences on the mortality of cowpea bruchids at the different concentrations. Isolate J35 had 98.2% mortality at 5 days after application during the first season and 88.3% during the second season, which was only lower to the formulated isolates BBC and BVT. The current study shows the pathogenic effectiveness of B bassiana on C. maculatus.

Establishment of Beauveria bassiana isolates as endophytes in rice cultivars and their biocontrol efficacy against rice stem borer, Sesamia calamistis

Possible endophytic colonisation of rice cultivar parts (leaves, stem and roots) by Beauveria bassiana isolates and their potential as biocontrol agents against Sesamia calamistis Hampson (African pink stem borer) were investigated. Five promising B. bassiana isolates were evaluated for their endophytic colonisation, the effectiveness of the inoculation methods and the efficacy of the isolates as biocontrol agents against S. calamistis. The plant part colonised is often dependent on the inoculation method. Colonisation of plant parts was assessed at 30 and 60 days after seed inoculation and foliar spray. For the pathogenicity activity, third instar larvae of S. calamistis were fed with rice stems that were previously inoculated with endophytic isolates of B. bassiana. Both inoculation methods led to the colonisation of the rice cultivar tissues, but were affected by the interactions of cultivars x isolates x inoculation methods. The colonisation of the cultivar plant parts varied over time (30- and 60-day intervals), and was affected by the inoculation method used. For both inoculation methods, highly significant differences were observed in the roots and the leaves over time (p=0.0001). However, with seed treatment, there was no significant difference in levels of colonisation in stems by the isolates x time (p=0.32). The B. bassiana isolates were pathogenic on the third instar larvae of S. calamistis, causing mortalities of more than 50% at 28 days after treatment. However, the virulence of the isolates varied. According to the isolates and the inoculation methods, B. bassiana formed an endophytic relationship with rice plants, and produced various mortality rates.

Virulence Screen of Beauveria Bassiana Isolates for Australian Carpophilus (Coleoptera: Nitidulidae) Beetle Biocontrol

Carpophilus beetles are serious pests of Australian fruit and nut crops, causing significant damage through adult and larval feeding and vectoring plant diseases. Six strains of the entomopathogenic fungus Beauveria bassiana ((Balsamo) Vuillemin; Hypocreales: Cordycipitaceae), isolated from a range of hosts in Australia, together with one commercial strain, were screened for virulence to adult and larval stages of Carpophilus attacking stone fruits (C. davidsoni (Dobson)) and almonds (C. truncatus (Murray)) under laboratory conditions. The two species differed significantly in their susceptibility to the B. bassiana isolates. In the adult beetle assay, C. truncatus had a maximum Abbott’s control corrected mortality of 19% when treated with the most effective isolate, B54, compared to 52% for C.davidsoni. In larval bioassays, mortality rates for the two species were generally higher than adults: four isolates caused greater than 80% mortality in C. davidsoni; while only one isolate was considered effective against C. truncatus (causing 73% mortality), all other isolates caused less than 40% mortality. The results indicate promising potential for B. bassiana to be applied as a biopesticide as part of an integrated pest management strategy, which might take the form of a soil application against larvae or an autodissemination program using adult beetles.

Entomopathogenic Fungi as Endophytes for Biological Control of Subterranean Termite Pests Attacking Cocoa Seedlings

This study was conducted in the scope of developing a sustainable effective approach against subterranean termite pests using entomopathogenic and endophytic fungus-based biopesticides. Termites, Odontotermes spp. workers, were tested for their susceptibility to 15 entomopathogenic fungal isolates through the direct spraying of conidia suspensions at 1 × 108 conidia/mL. In general, all the isolates screened were pathogenic, with 100% mortality 4–7 days post-inoculation. However, the most virulent isolates were Metarhizium brunneum Cb15-III; the M. anisopliae isolates ICIPE 30 and ICIPE 60; Hypocrea lixii F3ST1; and the Beauveria bassiana isolates ICIPE 279, ICIPE 706 and ICIPE 662. These isolates were further tested for their endophytic colonization of cocoa seedlings using seed soaking, soil drench and foliar spray at 1 × 108 conidia/mL. The colonization of the plant tissues by the fungi was determined using a culture-based technique. Only the B. bassiana isolates ICIPE 706 and ICIPE 279, and H. lixii F3ST1 colonized the cocoa seedlings, with varied colonization rates among isolates and inoculation methods. Three naturally occurring endophytes—Trichoderma asperellum, Fusarium solani and F. redolens—were also isolated from the cocoa seedling tissues. These findings suggest that cocoa seedlings are conducive to endophytic fungal growth either occurring naturally or from artificial inoculation Our findings could possibly lead to an innovative approach to the management of herbivory and subterranean termite pests in cocoa agroforests.

Test of Various Carrier Materials Against Viability and Conidia Density in Some Liquid Biopesticides of Entomopathogenic Fungi

Indonesia is a country that has a large biological diversity but has not been fully utilized for agriculture. The effectiveness of biological agents in controlling pests and plant diseases still needs further investigation, one of which is the use of entomopathogenic fungi as biopesticides. The purpose of this study was to determine the effect of storage on the viability and density of conidia in several entomopathogenic fungi; Beauveria bassiana, Metarhizium anisopliae, Paecilomyces. This study used 5 entomopathogenic fungi isolates, 2 Beauveria bassiana isolates (JBG and JBR), 2 Metarhizium anisopliae isolates (JBG and UST), 1 Paecilomyces. Biopesticide carrier material consisted of 6 carrier materials, namely soybean decoction waste, soy washing waste, Potato Dextrose Agar, tapioca waste, rice waste, rice washing waste and coconut water. Biopesticides have been made one year before and the viability and complexity of the conidia is re-examined one year later. From the observations of conidial density, the best was found in Beauveria bassiana JBG liquid biopesticide of 4.8 x 10 x conidia / ml from the initial density of 3.4 x 10⁸ / ml in the soybean decoction (RK) carrier material. The highest viability was found in JBG Metharizium anisopliae on soybean washing waste material by 14%. Key words: Conidia viability, conidial density, entomopathogenic fungi