Biopesticides; fresh hope for the future

Gavin J. Ash, B.A. Wilson, J.A. Pattemore, K. Crampton and A. Wang.,

Graham Centre for Agricultural Innovation, Charles Sturt University

Take home messages

• Biopesticides have been commercialised in Australia.
• They offer another avenue for managing recalcitrant insects, diseases and insects.
• Success with biopesticides depends on choosing the right target as well as the right agent.
• There are a large number of potential biopesticide agents but their commercial success depends on long term industry investment.

Introduction

Biopesticides offer an innovative approach to the management of pests in farming systems using formulated microbial agents as the active ingredient. Microbes that have been used in this approach include fungi, bacteria, viruses and nematodes. Biopesticides are a viable adjunct to synthetic pesticides in a number of crops. The development of microbial biopesticides relies on agent discovery and selection, development of methods to culture the pathogen, creation of formulations that protect the organism in storage as well as aid in its delivery, studies of field efficacy, and methods of storage. Each microbial biopesticide is unique, in that not only will the organism vary but so too will the host, the environment in which it is being applied, and economics of production and control.

There are a large number of commercial products now available in most regions of the world, where biopesticides are being incorporated into farming systems. It has been projected that the market potential for these so-called “green products” could triple by 2020 and be worth over $4 billion (USD) (Bayer, 2013). The most successful examples of biopesticides include Dipel (a formulation of Bacillus thuringenesis - Bt), Gemstar (containing a nucleopolyhedrovirus – NPV) and T22 (Trichoderma harzianum). The development of biopesticides is being driven by market opportunities such as pesticide resistance, changing consumer demands and the difficulty and cost of finding new synthetic pesticides. In Australia there are registrations for products based on Bt, NPV, Trichoderma, Metarhizium and Beauvaria.  However, the number of registrations are relatively small when compared to the synthetic pesticides.

The use of biopesticides as a strategy in pest management can be applied to both native and introduced pests. However, the success of this type of biocontrol revolves around the costs of production, the quality of the inoculum and, most importantly, the field efficacy of the product. Biopesticides are usually developed through collaboration with commercial companies with an expectation that they will recoup their costs and make a profit through the sale of the product.

Currently, in the Graham Centre at Charles Sturt University, there are a number of projects, at various stages of development, examining biological control of disease, insects, molluscs and nematodes affecting broad acre crops. These projects are variously funded by GRDC and CSU and have some level of commercial involvement.

Biocontrol of diseases

Blackleg disease of canola is a fungal disease of global importance. It is difficult to control by the use of chemicals and to date the best control measures are the use of genetically resistant canola cultivars and good farming practices. These cultivars display incomplete resistance to the disease and resistance breakdown has occurred in Australia.

Recent studies in other crops like radish and cucumber have identified a plant mechanism known as induced systemic resistance (ISR). This mechanism involves the use of naturally occurring beneficial soil bacteria, which switch on and activate the plant’s defence system. The bacteria act somewhat like a vaccination to trigger the plants immune system. Such bacteria grow adjacent to and colonise a plant root system, this zone is high in nutrients released by the root system and consequently is heavily colonised by bacteria and fungi. The beneficial effects of rhizosphere bacteria have most often been based on increased plant growth, better seed germination and seedling emergence. These types of bacteria are now commonly called plant growth-promoting rhizobacteria (PGPR). PGPR use different mechanisms to suppress plant pathogens which include competition (nutrients and space), antibiosis production and inducing a plant’s resistance mechanisms. This defence affects treated areas but also extends into non-treated areas and often even into newly developing plant parts. Systemic protection does not confer absolute immunity against disease but may reduce the severity by reducing lesion number, size and the extent of sporulation. Disease can be reduced by up to 90%. The potential of such bacteria is enormous for the reduction of disease and may be developed as seed coatings, drenches and powder applications depending upon the target pathogens, crop and the type of bacteria involved.

At Charles Sturt University we have isolated bacteria from the roots of canola and wheat in the southern cropping area. Some of these bacteria were from the rhizosphere and others were endophytic. They have been characterised in terms of their effect on growth of both wheat and canola, their ability to produce antibiotics active against the fungus that causes blackleg, numerous biochemical tests as indicators of their ability to suppress root pathogens and their ability to induce systemic resistance in canola against blackleg. Their ability to suppress disease in the glasshouse and in the field has also been assessed. Selected bacteria have been shown to reduce blackleg by induced systemic resistance in both sterile and non-sterile situations. The bacteria have then been ranked on desirable characteristics and the top 14 isolates have been identified using fatty acid analysis. This group includes endophytes and rhizobacteria, Bacillus and some Pseudomonads and all are plant growth promoters. Initial field results indicate that these bacteria are having positive effects on growth in the field. Furthermore, other species of bacteria have been isolated which have effects on other canola diseases and are comparable in efficacy to synthetic fungicides in field applications.

Biocontrol of molluscs

Four introduced Mediterranean snail species; Cernuella virgata, Theba pisana, Cochicella barbara and Cochicella acuta have become serious pests for the Australian grain industry in recent years. These pest snails cause heavy economic loss to farmers and the whole grain industry by contaminating the grain (wheat, barley, canola, lentil etc.), clogging harvesting equipment and downgrading the quality of grain. The lack of natural enemies of these pests in their distribution areas (most in SA, particularly in the Yorke Peninsula, some in VIC, TAS, WA and NSW) allow populations of these pest snails to increase rapidly.

This project was designed to investigate the possibility of developing a nematode based bioagent to control these pest snails in Australia. Nematodes have been successfully used for the management of slugs in over 14 European countries, and entomopathogenic nematode (EPN)-based bioinsecticides have been widely applied for the control of insect pests in Forestry, Horticulture and the turf industries.

In this project, a survey from south eastern Australia was used to isolate hundreds of indigenous potential EPNs from soil. From this collection, five nematode species with molluscicidal activities were selected and identified. The bacteria found associated with the nematodes were also isolated and identified. One of the bacteria, a strain of Bt molluscicidal activity (Bacillus thuringiensis DAR 81934), was found to be highly effective by itself and in combination with the nematode in killing the target snails. The complete genome of the Bacillus was sequenced and is a resource for further research. The nematodes were also found to be effective against slugs in the laboratory.

To be able to apply these organisms in the field, commercially available systems were used to produce the nematodes in Australia and internationally. Different systems were successful for different nematode species, allowing the production of concentrated nematode suspensions to be used in field trials conducted in South Australia over a number of years. It was found that the nematodes were best applied in the field in spring when the snails were laying eggs and moving on the soil surface. Unformulated nematodes caused up to 65% mortality in the field. However, synthetic snail baits provided up to 92% control.

This research has been discontinued as the cost of production of the nematodes was found to be too high for the use of the organism in broad acre agriculture in Australia.

Biocontrol of insects

Sucking insects like aphids can cause significant yield losses in agriculture due to the direct effects of feeding and the indirect effects associated with the spread of viruses. Current control of sucking insects relies on the use of chemical insecticides; however, these encourage the development of chemical resistance and suppress natural predator populations. Integrated Pest Management (IPM) programs that reduce the reliance on chemical pesticide therefore are likely to provide better management strategies for the future. As part of an IPM strategy GRDC have funded research into the discovery of biopesticides for the management of aphids in cereals and canola in Australia. The aim of the project was to develop pre commercialisation data for the registration of a biopesticide based on the fungus M. anisopliae.  

A number of isolates of the fungus from Queensland and New South Wales have been isolated and cultured, with a number of the strains found to be highly pathogenic to a wide variety of aphid species common in Australia. Bioassays have been used to establish application concentrations and production efficacy of the strains is being established in the laboratory. All isolates are being compared to commercially available standards. Initial indications are that the Australian fungi are as efficacious as the internationally sourced commercial strains and are amenable to large scale manufacture.

Biocontrol of nematodes

At least four species of root lesion nematodes (RLN) in the genus Pratylenchus are considered serious pests of grain crops in Australia. Pratylenchus neglectus and P. thornei were chosen as the initial target species for this research project because of their prevalence and economic importance (recent estimates suggest losses due to RLN exceed $102M p.a. in Australia). Average incidence for both species across regions in Australia is 67-72% but with higher incidences recorded in the Northern and Southern regions (78-89%) compared to the Western region (43%). P. neglectus is more prevalent than P. thornei in the Western region but elsewhere the incidence levels are similar. It is important that the grains industry has robust control measures available to minimise the current and future losses from these nematode pests. Currently, there are no nematicides registered for use in Australian cereal crops although some degree of management is possible with the use of resistant and/or tolerant crop cultivars, rotations incorporating poor host crops, manipulation of sowing time, provision of adequate nutrition and weed control within/between cropping phases. The cost of current control measures is estimated at $31OM p.a. for wheat and $81 M p.a. for barley.

The aim of this research project is to develop a bionematicide with activity against RLN on cereals. This strategy is based on the isolation and identification of naturally occurring beneficial microbes which are able to suppress the activity of the disease causing nematodes. The development of a new biological control product that is compatible with standard cereal cropping practices will provide growers with a wider range of disease management options for RLN and will add significant value to the grains industry.

The project has three initial research targets: the identification and evaluation of existing commercial biopesticides with potential suitability for this crop/pathogen system, the development of a Trichoderma-based bionematicide for cereal root lesion nematodes and the identification of indigenous strains of selected microbe groups that may have potential as bionematicides.

From initial surveys, a number of species of Trichoderma not previously recorded from Australia have been identified and their interaction with the organism responsible for crown rot and RLN are being evaluated in laboratory and glasshouse trials. A large screen of potential bacterial and fungal isolates have indicated that there are some which have potential as biological controls when compared with commercially available biopesticide formulations. Field trials in 2014 will establish whether these isolates can be used to manage nematodes in the field.

Conclusion

There are a number of advantages of the use of biopesticides over the use of conventional pesticides, including the minimal residue levels, control of pests already showing resistance to conventional pesticides, host specificity, and the reduced chance of resistance to biopesticides. This indicates an emerging, strong role for biopesticides in any integrated pest management strategy and an important involvement in sustainable farming production systems in the future. The main constraints to the production and use of biopesticides in Australia are the existence of facilities capable of producing the organisms economically and the systems for distribution and marketing of the products. These rely on the continued involvement of large corporations in the funding and development of these new management options.

Contact details

Gavin Ash

Graham Centre for Agricultural Innovation, Charles Sturt University, Locked Bag 588, Wagga Wagga 2678, NSW, Australia. 

02 69332765

gash@csu.edu.au