Seasonal prevalence of the insect pathogenic fungus Colletotrichum nymphaeae in Brazilian citrus groves under different chemical pesticide regimes (original) (raw)
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Impact of natural epizootics of the fungal pathogen
The tomato red spider mite, Tetranychus evansi (Acari: Tetranychidae) was recently introduced in Africa and Europe, where there is an increasing interest in using natural enemies to control this pest on solanaceous crops. Two promising candidates for the control of T. evansi were identified in South America, the fungal pathogen, Neozygites floridana and the predatory mite Phytoseiulus longipes. In this study, population dynamics of T. evansi and its natural enemies together with the influence of environmental conditions on these organisms were evaluated during four crop cycles in the field and in a protected environment on nightshade and tomato plants with and without application of chemical pesticides. N. floridana was the only natural enemy found associated with T. evansi in the four crop cycles under protected environment but only in the last crop cycle in the field. In the treatments where the fungus appeared, reduction of mite populations was drastic. N. floridana appeared in tomato plants even when the population density of T. evansi was relatively low (less than 10 mites/3.14 cm 2 of leaf area) and even at this low population density, the fungus maintained infection rates greater than 50%. The application of pesticides directly affected the fungus by delaying epizootic initiation and contributing to lower infection rates than unsprayed treatments. Rainfalls did not have an apparent impact on mite populations. These results indicate that the pathogenic fungus, N. floridana can play a significant role in the population dynamics of T. evansi, especially under protected environment, and has the potential to control this pest in classical biological control programs.
2009
The biology of key citrus pests Thaumatotibia leucotreta Meyrick (Lepidoptera: Tortricidae), Ceratitis capitata Wiedemann (Diptera: Tephritidae) and Ceratitis rosa Karsch (Diptera: Tephritidae) includes their dropping from host plants to pupate in the soil below citrus trees. Since most EP fungi are soil-borne microorganisms, the development and formulation of alternative control strategies using these fungi as subterranean control agents, targeted at larvae and pupae in the soil, can potentially benefit existing IPM management of citrus in South Africa. Thus, a survey of occurrence of entomopathogenic fungi was undertaken on soils from citrus orchards and natural vegetation (refugia) on conventionally and organically managed farms in the Eastern Cape Province in South Africa. A method for baiting soil samples with citrus pest T. leucotreta and C. capitata larvae, as well as with the standard bait insect, Galleria mellonella Linnaeus (Lepidoptera: Pyralidae), was implemented. Sixty-two potentially useful entomopathogenic fungal isolates belonging to four genera were collected from 288 soil samples, an occurrence frequency of 21.53%. The most frequently isolated entomopathogenic fungal species was Beauveria bassiana (Balsamo) Vuillemin (15.63%), followed by Metarhizium anisopliae var. anisopliae (Metschnikoff) Sorokin (3.82%). Galleria mellonella was the most effective insect used to isolate fungal species (χ 2 =40.13, df=2, P≤ 0.005), with a total of 45 isolates obtained, followed by C. capitata with 11 isolates, and T. leucotreta with six isolates recovered. There was a significantly (χ 2 =11.65, df=1, P≤ 0.005) higher occurrence of entomopathogenic fungi in soil samples taken from refugia compared to cultivated orchards of both organically and conventionally managed farms. No significant differences were observed in the recovery of fungal isolates when soil samples from both farming systems were compared. The physiological effects and host range of 21 indigenous fungal isolates obtained in the Eastern Cape were investigated in the laboratory to establish whether these isolates could be effectively used as biological control agents against the subterranean life stages of C. rosa, C. capitata and T. leucotreta. When these pests were treated with a fungal concentration of 1 x 10 7 conidia ml-1 , the percentage of T. leucotreta adults which emerged in fungal treated sand ranged from 5 to 60% (F=33.295; df=21; P=0.0001) depending on fungal isolate and the percentage of pupae with visible signs of mycosis ranged from 21 to 93% (F= 96.436; df=21; P=0.0001). Based on fungal isolates, the percentage adult survival in C. rosa and C. capitata ranged from 30 to 90% and 55 to 86% respectively. The percentage of C. rosa and C. capitata puparia with visible signs of i ii ii i mycosis ranged from 1 to 14% and 1 to 11% respectively. Deferred mortality due to mycosis in C. rosa and C. capitata adult flies ranged from 1 to 58% and 1 to 33% respectively, depending on fungal isolate. Entomopathogenic fungal isolates had a significantly greater effect on the adults of C. rosa and C. capitata than they did on the puparia of these two fruit fly species. Further, C. rosa and C. capitata did not differ significantly in their response to entomopathogenic fungi when adult survival or adult and pupal mycosis were considered. The relative potency of the four most virulent Beauveria isolates as well as the commercially available Beauveria bassiana product, Bb Plus ® (Biological Control Products, South Africa), were compared against one another as log-probit regressions of mortality against C. rosa, C. capitata and T. leucotreta which all exhibited a dose-dependent response. Against fruit flies the estimated LC 50 values of all five Beauveria isolates ranged from 5.5 x 10 11 to 2.8 x 10 12 conidia/ml-1. There were no significant differences between the relative potencies of these five fungal isolates. When T. leucotreta was considered, isolates: G Moss R10 and G 14 2 B5 and Bb Plus ® were significantly more pathogenic than G B Ar 23 B3 and FCM 10 13 L1. The estimated LC 50 values of the three most pathogenic isolates ranged from 6.8 x 10 5 to 2.1 x 10 6 conidia/ml-1 , while those of the least pathogenic ranged from 1.6 x 10 7 to 3.7 x 10 7 conidia/ml-1. Thaumatotibia leucotreta final instar larvae were exposed to two conidial concentrations, at four different exposure times (12, 48, 72 and 96 hrs) and showed an exposure time-dependant relationship (F=5.43; df=3; P=0.001). At 1 x 10 7 conidia/ml-1 two Beauveria isolates: G Moss R10 and G 14 2 B5 were able to elicit a response in 50% of test insects at 72 hrs (3 days) exposure. Although a limited amount of mycosis was observed in the puparia of both fruit fly species, deferred adult mortality due to mycosis was high. The increased incidence of adult mortality suggests that post emergence mycosis in adult fruit flies may play a more significant role in field suppression than the control of fruit flies at the pupal stage. The increased incidence of pupal mortality, as well as the relatively low concentrations of conidia required to elicit meaningful responses in T. leucotreta pupae may suggest that pre-emergent control of false codling moth will play a more significant role in field suppression than the control of adult life stages using indigenous isolates of entomopathogenic fungi. Various entomopathogenic fungal application techniques targeted at key insect pests within integrated pest management (IPM) systems of citrus are discussed. i iv v To my parents, Clive and Jen Thank you both for your incredible love of nature and your incredible nature of love v v Declaration The following thesis has not been submitted to any university other than Rhodes University, Grahamstown, South Africa. The work presented here is that of the author.
International Journal of Tropical Insect Science, 2020
Panonychus citri (citrus red mite) is a devastating pest of citrus orchards. The conventional chemical acaricides have been strongly forbidden for the management of agricultural insect pests in China. Therefore, we evaluated the susceptibility of adult and nymphs P. citri in laboratory against eight isolates of four fungal species, Akanthomyces lecanii, Metarhizium anisopliae, Beauveria bassiana and Aschersonia aleyrodis. Each citrus seedling having 40 adults (2-d-old) and nymphs (on separate plants) were sprayed with isolates at the concentration of 10 4~1 0 8 conidia mLˉ1 whereas controlled seedlings were sprayed with 0.02% Tween-80. After 9 days of fungal exposure, the four fungal isolates caused more than 50% mortality of mites, such as; 85.6%, 87.9%, 64.6% and 79.7% by A. lecanii (V3450), B. bassiana (BFZ0409), M. anisopliae (MFZ0706) and A. aleyrodis (AsG0910), respectively. The nymphal mites were less susceptible to applied fungi compared to adults. The LC 50 s of the tested isolates were determined by the fitted time-concentration-mortality relationships, which declined over days after spray. LT 50 s were decreased with a high concentration of isolates. After the 9-d inoculation, two isolates of B. bassiana (BFZ0409 and D1344) and one isolate of A. lecanii (V3450) were highly effective at the minimal dose of LC 50 of 10 4 conidia mLˉ1 and are promising candidates to control mites, as compared to other tested fungal isolates.
Observations on the entomopathogenic fungus
2012
A two-year field study was conducted in an orange grove in the United States (Florida) to characterize the phenology of the entomopathogen Hirsutella citriformis Speare infecting adults of the Asian citrus psyllid, Diaphorina citri Kuwayama. On the average, 23% of adults observed on mature leaves were killed by H. citriformis. These dead psyllids were characterized as being mummified and covered to various extents by synnemata produced by the fungus.
The objectives of this research were: to evaluate, in laboratory, the pathogenicity of fungi isolates and nematodes in the control of fruit fly prepupae and adults in the laboratory and the application of these entomopathogens in the greenhouse. Different Beauveria bassiana (Bals.) Vuill. and Metarhizium anisopliae (Metsch.) Sorok. concentrations were tested on Ceratitis capitata (Wied.) prepupae in sterilized and natural soil under laboratory conditions. The efficiency of six B. bassiana and M. anisopliae isolates was evaluated on C. capitata prepupae with application this selected isolates at a concentration of 5×108 conidia/mL in soil pots containing citrus seedlings in the greenhouse. In addition, the pathogenicity of the entomopathogenic nematode Heterorhabditis sp. (isolate IBCBn 05) was evaluated by applying 200 infective juveniles (JI)/ prepupae with the same methodology used for the fungi. Transmission of the above fungi in C. capitata adults was also studied under laboratory conditions. It was verified that the fungi B. bassiana and M. anisopliae were pathogenic to C. capitata prepupae, with the isolates IBCB 66 and IBCB 425, respectively, were the most virulent. Heterorhabditis sp. was also pathogenic at the concentration applied. In the greenhouse, the B. bassiana fungus reached a prepupal control efficiency of 66.6%. The fungi were transmitted among the C. capitata adult population even when only 10% of the population was initially contaminated.
Agricultural Bioinformatics, 2014
Insect pathogenic fungi have a huge potential as microbial components of biopesticides which serve as benign components in plant protection. The infection cycle of these fungi is well known. Realising their potential and scope to improve their utility in phytomedicine, extensive work on the molecular biology of pathogenesis has been done in the past decade. Wet bench techniques like gene isolation, cloning and characterisation and gene knockout experiments to transcriptomics techniques like cDNA-AFLP, microarray, qPCR, cDNA, EST and SSH library construction, as well as whole genome sequencing and analysis of data with a suite of bioinformatic tools and pipelines integrated with several biological databases, were done to understand the process/processes involved at each stage of the infection cycle of the insect pathogenic fungi. These are in particular adherence of spores to the insect cuticle, factors that aid in coping with the physical stress conditions in the surrounding environment, formation of an infection peg, penetrance into the insect, factors that abet in overcoming insect defence systems and growth in the insect, production of toxic secondary metabolites that lead to insect death and surfacing out from the insect cadaver as well as sporulating to iterate the infection cycle on yet another insect. The picture that emerged is detailed in this chapter. The genes/proteins involved and the analyses that aided in their identification are described. Environmental genomics through multitag 454 pyrosequencing of rRNA sequence reads in deciphering the effect of the
Use of the entomopathogenic fungi Metarhizium anisopliae, Cordyceps bassianaand Isaria
The Asian citrus psyllid Diaphorina citri Kuwayama is a destructive insect pest in citriculture, because it is an efficient vector of the proteobacteria ‘Candidatus Liberibacter asiaticus’ (Las), ‘Ca. L. africanus’ (Laf) and ‘Ca. L. americanus’ (Lam). These bacteria cause the ‘huanglongbing’ disease or ‘greening’ or ‘yellow dragon’ disease. The disease kills the plant and reduces fruit production. This insect pest is susceptible to entomopathogenic fungi, and we report the use of different strains of Metarhizium anisopliae, Cordyceps bassiana and Isaria fumosorosea against the nymphs and adults of D. citri under field conditions. The fungi were applied four times using a concentration of 2 £ 1013 conidia/ha with a time interval of 15 days between applications. The percentage of control of Cb 108, Ma 65, Ma 14 and Ifr 4 was 60, 50, 40 and 35% in nymphs, and 50, 50, 42 and 22% in adults, respectively. Metarhizium anisopliae, C. bassiana and I. fumosorosea applied on Persian lime groves are more effective in reducing higher density of nymphs than adults of D. citri.
Entomopathogenic Fungi as a Biological Pest Management Option: A Review
International Journal of Research Studies in Agricultural Sciences
myco-biocontrol agents depend on the susceptibility of the insect and also virulence of the fungus. Virulence of the fungus depends on the selection of the stable strain with specific efficacy for the Abstract: Entomopathogenic fungi are myco-biocontrol, potentially the most versatile biological control agents with a wide host range and are an environmentally sound and effective means of reducing insect-pests. The use of microbial control agents particularly entomopathogenic fungi, have been investigated for the control of a wide range of orchard and field crop pests and are a widespread component of most terrestrial ecosystems. Entomopathogenic fungi are a major component of integrated pest management techniques as biological control agents against insect pests and other arthropods in horticulture, forestry and agriculture and are found in the divisions of Zygomycota, Ascomycota, Deuteromycota, Chytridiomycota and Oomycota, which were previously classified within fungi. Insect control using entomopathogenic fungi is achieved when sufficient infective propagules, conidia contact a susceptible host and conditions are suitable for a lethal mycosis to develop. A wide range of fungi occur in the soil environment and they have various ecological functions. Most of these fungi, along with a range of bacteria, can grow on artificial media in vitro. Several methods have been used to describe the variation within a species of entomopathogenic and mycoparasitic fungi including morphological characteristics of spores and colonies, extracellular protein profiles, pathogenecity, growth and nutrient requirements. Furthermore, immune taxonomic and chemotaxonomic methods have been used, though only with limited success. Taxonomic procedures are becoming more and more complex and it is generally accepted that some forms of molecular identification techniques are needed in addition to the traditional morphological characteristics formally used to classify fungal species. During the last four decades, over 80 companies worldwide have developed 171 mycoinsecticides and myco-acaricides. Use of mycoinsecticdes is likely to rise if research is focus on; improving its performance under challenging environmental conditions, formulations that will increase persistence, longer shelf life, ease of application, pathogen virulence and wider spectrum of action.