In addition to conservation biological control (relying on and protecting the natural enemies which are locally present, as explained above), other approaches include for instance classical biological control(importing natural enemies from elsewhere and establishing them in farmers fields) and augmentative biological control (supplementing the numbers of naturally-occurring natural enemies with releases of natural enemies reared in labs or collected in the field; they can be released in large quantities – these are called inundative releases, or beginning with small quantities– these are called inoculative releases).
In Latin America Trichogramma spp., in particular T. pretiosum and T. atopovirilia, are commonly mass-reared on alternative hosts in local mass production units, and commercialized for inundative field releases against the FAW. Release rates totalling circa 100 000 wasps/ha performed in 3 introductions spaced each by 3 days, is a recommended release scheme. In Brazil, control levels are reported as good in conjunction with the use of pheromone traps to monitor thresholds. However a number of constraints such as production technique, susceptibility to weather conditions, threshold adjustment for interventions, transportation to release site, the need for repetitive releases, compatibility with other interventions etc. are limiting a wide application.
As explained above, a number of parasitoids of FAW have already been identified in Africa. Before introductions of the FAW co-evolved parasitoids from the Americas are contemplated, or complex rearing and release efforts of local NEs envisaged, a thorough inventory work and impact assessment of the native guild of natural enemies is necessary.
Biopesticides
Biopesticides can be instrumental as part of an IPM approach against the FAW. The term biopesticide comes from”bio”, a root word derived from Greek which means “life” while “pesticide” includes all substances or mixture of substances that are intended to suppress pests and prevent the damage or loss that they cause. Biopesticide is a generic term generally applied to a substance derived from nature, such as a microorganism or botanical or semiochemical, that may be formulated and applied in a manner similar to a conventional chemical pesticide and that is normally used for short-term pest control.2 Thus, biopesticides are “living formulations” that are derived from natural materials originating from plants, animals (including parasitoids and predators), or microorganisms, are often cultured to increase amounts in order to exploit their characteristics of controlling pests.
- Broadly, biopesticides may belong to several classes:
- Microbial pesticides or microorganisms – including bacteria, algae, protozoa viruses or fungi
- Pheromones and other semiochemicals; these are chemicals produced by plants and animals (and synthetic analogues of such substances) that influence the behaviour of individuals of the same or other species
- Plant extracts and botanicals and
- Invertebrate Biological Control Agents, or macrobials – including insects, mites and nematodes that are natural enemies, antagonists or competitors of a pest. This class is sometimes not considered as a “biopesticide” per se.
Compared to broad spectrum conventional pesticides, biopesticides are usually more target-specific and inherently less toxic, and this limits their impact on non-target species, such as other insects, birds and mammals. They usually are biodegradable in the natural environment, thus reducing exposure and environmental pollution as well as reducing chances of pests developing resistance to them.
Microbial biopesticides are particularly relevant for the management of FAW. In this category of biopesticides, the active ingredient is typically the microorganisms themselves or the spores that they produce which are pathogenic to the target pest. For a description of the naturally occurring entomopathogens of FAW, see section A.3.5.1. on Biological control. They may be bacteria, fungi, algae, viruses or protozoans that suppress the target pests, either by producing toxic metabolites that are relatively specific to the target insect pest or closely related species, causing disease and are thus entomopathogenic.
Promotion of biopesticides to manage the Fall Armyworm
Biopesticides, such as those based on the bacteria Bacillus thuringiensis (Bt), fungi (such as Beauveria bassiana) and Baculoviruses have proven to be effective in the management of FAW.
Biopesticides – like any other pesticide – should be registered in the country before use. FAO has developed Guidelines3 on the registration of microbial, botanical and semiochemical substances for both plant protection and public health uses.
Some of the biopesticides that have been registered to control FAW
Other biopesticides registered for control of Lepidoptera are currently being tested for Fall Armyworm. In addition, certain botanical pesticides, such as those based on neem have also shown positive results.
Some of these naturally occurring diseases have been harnessed to produce commercial biopesticide products, such as Bt spray; but their availability in Africa is currently limited.
Substantial success has been recorded worldwide in using specific entomopathogens to control lepidoperan pests such as stem borers, a number of armyworm species as well as Helicoverpa.
Key limitations in the use of biopesticides in general include their delayed knockdown effect on pests compared to synthetic pesticides which is more immediate; lack of awareness of their existence; lack of standard recommendations for their use; improper storage conditions impacting the product efficacy; most of them usually have a short life; process of their official registration is often costly and time consuming; and the slow development of research in this area.
Furthermore, utilization of microbial pesticides in IPM of FAW requires scientific studies such as systematic surveys and larval collections and rearing, investigations on their properties as well as modes of action on the targeted insect pest and pathogenicity. The starting point for the scientific studies is local identification of their existence and impact.
Participants in FFS can conduct their own pilot exploration of locally available microbial pesticides which can be incorporated as one of the key tools for the IPM of FAW. It is recommended that trainers develop collaboration with national research centres for further support in the characterization of microbes that will be encountered.
Farmers should be aware that most biological pesticides do not kill pests immediately; but they reduce feeding, which is essential, while insects/larvae die normally in a few days time.
Botanical pesticides for Fall Armyworm management
The use of plant-derived pesticides (commonly called “botanicals”) in pest management is a cultural practice of most African farmers. It could provide a potential arsenal against the Fall armyworm in Africa.
The mode of action of botanical pesticides is broad and ranges from: repellency, knock-down, larvicidal to anti-feedant, moulting inhibitors and growth regulation.
They have a broad-spectrum activity with generally little or no mammalian toxicity; however some botanical pesticides are highly toxic not only for pests but also for natural enemies and for mammals including humans, for instance tobacco extracts. Pyrethroids will also affect natural enemies.
Farmers generally extract bioactive compounds as a concoction after grinding plant materials using water. Essential oils from bioactive rich plants and powdered forms are also used to some extent.
There are comparative advantages associated with the use of botanicals:
- X they are biodegradable and do not accumulate in the environment
- X generally less harmful to farmers and consumers (though there are some exceptions); and
- X they often are less toxic to natural enemies (predators and parasitoids), hence not disrupting ecosystem services delivered by these natural enemies.
Several plants extracts have been reported to have insecticidal properties against stemborers in cereals. These include Neem, Azadirachta indica; Persian Lilac, Melia azadirach; Pyrethrum, Tanacetum cinerariifolium; Acacia, Acacia sp; Fish-poison Bean, Tephrosia vogelii; Wild marigold, Tagetes minuta; wild sage, Lantana camara; West African peppar, Piper guineense; Jatropha, Jatropha curcas; Chillies, Capsicum spp; onion, Allium sativum, Allium cepa; Lemon grass, Cymbopogon citratus; Tobacco, Nicotina spp; Chysanthemum, Chrysanthemum sp; Wild Sunflower, Tithonia diversifolia. etc. (Ogendo et al., 2013; Mugisha-Kamatenesi et al., 2008; Stevenson et al., 2009, 2017).
Preliminary evidence indicates that seeds or leaves of plants of the Meliaceae family (Azadirachta indica, i.e. neem and Melia) and Asteraceae family (Pyrethrum) and other plants such as Tephrosia vogelii orThevetia neriifolia are showing effecacy in the management of armyworms.
This needs to be investigated in further detail against FAW. Potent botanical pesticides need to be further researched. It is critical to further research promising plants, their plant parts (leaf, stem, root or seeds), to optimize extraction methods and to evaluate their efficacy (mortality and repellence).
The capacities of smallholders should be strengthened through to promote preparation, utilization, testing, and adoption of botanical pesticides for FAW management as appropriate.
It is also important to assess the compatibility of botanical pesticides with other pest management options such as pheromones and entomopathogens, in order to optimize low-cost and effective pest management strategies for FAW.
Integration of botanical pesticides with management options such as Push-pull/ intercropping; pheromones, and less toxic synthetic pesticides as a last resort, is critical to achieve effective management of FAW.
Note that trainers and farmers should not assume that botanical pesticides are always harmless to humans and animals. Some can be highly toxic (such as tobacco leaf extract, containing nicotine). Farmers should rely on traditional knowledge about plant toxicity, and take precautions to reduce risks when preparing and using local botanicals especially in first instances.
See special topic on preparation of botanical pesticides in section B.6.10.
Botanicals are one category of biopesticides and as such, like any other pesticide, their registration in the country should be promoted. For more information on how to deal with botanical registration issues, please refer to the FAO “Guidelines4 on the registration of microbial, botanical and semiochemical substances for both plant protection and public health uses”.