Teaching in the Discipline of Plant Pathology at the University of Kwazulu-Natal, Pietermaritzburg, from April 2002 to August 2005. Staff members and students of the Discipline of Plant Pathology at the University of Kwazulu-Natal, Pietermaritzburg, for their help and sound advice on topics that related to the study.
Appendix 78
CHAPTERS
Problems associated with fungal biological controL 94
Fungal biological control of agricultural pests 94
Future considerations and research needs 97
CHAPTERl
General introduction
Biological control
A classic example of this would be the development and use of Green Muscle™ to control locust populations (Kooyman, 1999; Bateman, 2003). Other microbes have proven effective and have been registered as control products, such as Beauveria bassiana and f3acillus thuringiensis.
Entomopathogens
- Fungal-host interactions
Once the hyphae detach from the inner procuticle, they enter the body cavity of the host. The death of the insect puts an end to the parasitic development of the fungus (Tanada & Kaya, 1993).
Insect pests
- Fungal biological control
- Grapevine mealybug, Planococcus ficus (Signoid)
- Control
However, the use of insecticides has a negative impact on the mealybugs' natural enemies. In many cases, having sufficient natural enemies results in effective control of the pest population.
General problems with fungal biological control
The only common natural enemy in all regions of Africa is the entomopathogenic fungus Beauveria bassiana. However, little research has been conducted on the potential use of entomopathogenic fungi in the control of this pest.
General discussion
Research has shown that Aschersoniasp., which are specific to whiteflies, have great potential for effective biological control of whiteflies. However, the positive results appear to outweigh the negative and therefore there is potential for biological control of whiteflies within these three genera. The literature clearly shows that there is potential for the fungal biological control of S.
After extensive literature research, it became clear that no research has been done into the fungal biological control of mealybugs on vines. A future possibility would be an integrated control system in which natural enemies, entomopathogenic fungal control, and biodegradable insecticides can work together and complement each other in the control of harmful agricultural pests.
Selective isolation of the entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae from artificial potting medium. Biocontrol of the sugarcane borer Eldana saccharina by expression of Bacillus thuringiensis crylAc7 and Serratia marcescens chiA genes in sugarcane-associated bacteria. Acute and sublethal activity of the entomopathogenic fungus Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes) on Aphelinus asychis adults.
Activity of the entomopathogenic fungus Beauveria bassiana (Deuteromycota: Hyphomycetes) against three coleopteran pests of stored grain. Evaluation of the entomopathogenic fungi Beauveria bassiana and Paecilomyces fumosoroseus for microbial control of the silver-leaved whitefly, Bemisia argentifolii.J.
Introduction
Materials and methods
- Maintaining whitefly cultures
- Laboratory culturing
- Insect netting tanks
- Ventilated rearing chambers
The laboratory was maintained at a constant temperature of 23 °C (± 2 °C) and was illuminated by standard fluorescent bulbs with a 12/12-h light-dark cycle. trade name: Gadra) were grown in 250 ml Styrofoam jars with holes in the bottom, six of which were inserted into 21 plastic containers. Trade name: Grada) plants were placed in each tank and inoculated with 40 whiteflies collected from the surrounding area. The wet wall cooling system in the greenhouse was replaced with an industrial air conditioning system towards the end of 2002, and the wet wall was sealed with silage plastic to prevent air flow through the greenhouse (Figure 2.5).
Excess water was piped away from the drainage points and directed down the drain to prevent excess water in the greenhouse and to try to lower humidity levels. Each Hobo was placed in the center of an individual greenhouse and covered with a Stevenson screen.
Results
On average, the humidity rose above 90% for Ilhr d-I in the glasshouse and 16 h d-I in the rearing rooms. The removal of the wet wall cooling system and the installation of the alr conditioning system resulted in a reduction in humidity and an accurate temperature control with fewer fluctuations. The average temperature over the 9th period in the air conditioned glasshouse and wet wall cooled glasshouse was 19.9°C and 23.8°C, at the end of the 200212003 season.
The use of the ventilated rearing cages in the air-conditioned greenhouse produced healthy insect cultures. Sufficient numbers of adult whiteflies were reared and the cultures remained relatively disease free throughout the study period.
Discussion
The insects in the glass breeding tanks were found to be exposed to temperatures ranging from 10oC to 43.9°C. This prolonged period of high humidity combined with an average temperature of 19.9°C in the greenhouse and 22.6°C in the glass growth chambers resulted in optimal conditions for both fungal and insect pathogens (Appendix 2.1). The ventilated growth chamber had increased ventilation, which reduced the humidity in the insect culture and therefore resulted in little to no pathogens being present.
In order to breed insects adequately, the temperature and humidity in the breeding environment must be controlled. With the installation of air conditioning, this problem was largely overcome and clean whitefly cultures were obtained through better ventilation in the growth chambers.
Appendix 2.1
Sitophilus oryzae, Trialeurodes vaporariorum, Planococcus ficus and Eldana saccharina are four of the most important agricultural pests occurring in southern Africa. Beauveria bassiana Isolates Bl and PPRI 6690 caused >70% mortality and did not differ significantly from PPRI 6864 and PPRI 7062.
Introduction
The germination capacity of the spore suspensions was assessed by spraying 1 ml of spore suspension (standardized to 1 x 10 5 spores/ml) onto water agar plates using a handheld atomizer. The development of the egg to second and third instar larvae took approximately 14 - 16 days under greenhouse conditions. The fungi were re-isolated from the infected insects to confirm the identification of the fungus and to maintain isolation virulence.
Three ml of the 2 x 10 6 conidia/ml suspension were applied to the fungi at an air flow rate of SI/min. Carcasses showing external hyphal growth resembling the characteristics of the fungal entomopathogen were recorded as infected and included in the mortality analysis.
Results
Conidial growth on carcasses showed that all isolates resulted in fungal mortality (Figure 3.1). Based on the results from the first phase bioassay, isolates B1, PPRI 6690, PPRI 6864 and PPRI 7062 were selected for further testing. The results showed little or no infection at lower conidial concentrations of 1 x 103 and 1 x 104 conidia mr!, as above, mortality of S.
Treatments with BI and PPRI 6690 had the highest mortality at 1 x 106 conidia mr! produced, both leading to 68% mortality of the population after 2d , LTso's were calculated at 6.8 and 5.9d, respectively (Table 3.5). In the study, five fungal isolates were tested against second and third stage larvae, three of which resulted in mortality.
Discussion
Based on the results of the second phase bioassay treatments, Bland PPRI 6690 can be considered as potential biocontrol agents of S. oryzae and warrant further investigation. Research into mass production, yields, and specificity should be considered before recommending any of the isolates as potential biological control agents. Progress still needs to be made to improve the reliability and effectiveness of biological control agents before using entomopathogenic fungi as a control method for storage grain pests.
Further testing of different fungal strains and application methods will explore the use of entomopathogenic fungi as biological control agents against P. Conlong (1994) discussed the interactions between Eldana and various parasitoids and their potential as biological control agents.
Conclusion
Field propagation of cork bark, blotch, leaf spot and Shiraz reduces diseases and associated viruses in South African grapevines. Trials of Beauveria bassiana, Paecilomyces fumosoroseus and imidacloprid for the management of Trialeurodes vaporariorum (Homoptera: Aleyrodidiae) in greenhouse-grown lettuce. Activity of the entomopathogenic fungus Beauveria bassiana (Deuteromycotl;t.: Hyphomycetes) against three coleopteran pests of stored cereals.
Effect of air humidity on the infection potential of hypomycetous fungi as mycoinsecticides for Trialeurodes vaporariorum.
Appendix 3.1
Effect of temperature and humidity on the susceptibility of Sitophilus oryzae (L.) (Coleoptera: Curculionidae) to four entomopathogenic fungi. The effect of temperature and relative humidity on the pathogenicity of four entomopathogenic isolates for the rice beetle Sitophilus oryzae was investigated. Mortality rates decreased as temperatures decreased, but no mortality was recorded for all four isolates at 30°C.
Both temperature and relative humidity were found to significantly affect the infection potential of the isolates. Considering both the temperature and humidity results, Isolates BI and PPRI 6690 showed the most potential for further development as biological control agents of S.
Introduction
- Temperature bioassay
- Statistics
Twenty adult fungi were randomly selected from the sieves and placed in Petri dishes containing filter paper (9 cm diameter). Petri dishes containing the anesthetized scrapings were placed in a Burgerjon spray tower constructed by UKZN, Pietermaritzburg, in accordance with the plans of Burgerjon (1956). Sterilized shoots were placed on wet filter paper in sterile Petri dishes and kept in an incubator at 25°C for 7 days.
Dead insects were removed from the Petri dishes 3d, 5d, 7d, 14d and 21d after inoculation by sifting the grain and identifying the dead individuals. The data were analyzed using Probit analysis and for the different treatments the lethal times for 50% (LT50) of the weevils that had to be killed were obtained.
Discussion
Mortality rates for the experiment were low compared to those reported in Chapter 3 and can be explained by considering the overall germination rate. This could not be explained since the same experimental procedures were followed as in Chapter 3. By extending the experiment to 21d, there would have been less extrapolation of the data sets, resulting in more accurate results.
The mortality results obtained in this study at 25°C are similar to those reported by Dal Bello et al. Considering both the temperature and humidity, isolates Bl and PPRI 6690 showed the most potential for further development as biological control agents of S.
Activity of the entomopathogenic fungus Beauveria bassiana (Deuteromycota: Hyphomycetes) against three coleopteran pests of stored grain. Efficacy of Beauveria bassiana for the control of the rice weevil Sitophilus oryzae (L.)(Coleoptera: . Curculionidae).
Thesis overview
- Introduction
- Problems associated with fungal biological control
- Fungal biological control of agricultural pests
- Future considerations and research needs
- References
The conditions typically found in a greenhouse make the use of biological control fungi a viable proposition. The rice borer Sitophilus oryzae is considered one of the most serious pests of raw cereals worldwide. Bland PPRI 6690 isolates showed the most potential for further development as agents for biological control of S.
However, unless formulations are developed that will reduce the dependence of entomopathogenic fungi on high moisture levels, the potential of biological control of fungi will not be realized. Laboratory evaluation of chemical-biological control of rice fungus (Sitophilus oryzae L.) in stored grains. J Stored Prod.
