In this category you find natural enemies that kill one or several individuals of FAW during their life time either as larvae or adults. In this case, eggs, caterpillars, pupae or adult FAW are considered as preys. Usually predators are non-selective or generalists, thus they feed opportunistically on more than one host species, sometimes even on their own kind. The following insects belong to generalist predators:
Earwigs (Dermaptera: Forficulidae, Carcinophoridae)
Two species are currently recognized to play a significant role as FAW egg predator in maize crops: Doru luteipes (Scudder) and Euborellia annulipes (Lucas).
Ladybird beetles (Coleoptera: Coccinellidae)
Both adults and larvae of ladybugs feed on various phytophagous insects such as mites, aphids, scales, mealybugs, eggs and young larvae of Lepidoptera including the Fall Armyworm. Coleomegilla maculata DeGeer, Cycloneda sanguinea (Linnaeus), Hippodamia convergens Guérin MenevilIe, Eriopis connexa Mulsant, Olla v-nigrum Mulsant, Harmonia axyridis (Pallas) and Neda conjugata (Mulsant) are species commonly found in maize fields in the Americas.
Ground beetles (Coleoptera: Carabidae)
Many carabid beetle species occurring in maize cropping are known for their predatory habits both as larvae or adults. Calosoma granulatum Perty has been observed to feed on young FAW caterpillars.
Assassin and flower bugs (Hemiptera: Reduviidae, Pentatomidae, Geocoridae, Nabidae, Anthocoridae)
There are several species of bugs that have been observed to feed on immatures of the FAW. The best known of this category belong to the genera Zelus (Reduviidae), Podisus (Pentatomidae), Nabis (Nabidae), Geocoris (Lygaeidae), Orius and Anthocoris (Anthocoridae).
Bottom, from left to right: Podisus sp. (Pentatomidae), Orius insidiosus Say (Anthocoridae), Geocoris punctipes (Say )(Lygaeidae), (© I. Cruz, Embrapa).
Eusocial, solitary and other predatory wasps (Hymenoptera: Vespoidea) Spiders (Arachnida: Araneae)
Ants (Hymenoptera: Formicidae)
Ants are often among the most important predators of FAW larvae and pupae. Perfecto (1980) studied the interactions among ants, FAW and pesticides in maize systems in Nicaragua. She found that ants are very important predators of FAW in maize in Nicaragua and that pesticides dramatically reduced the presence and effectiveness of ants a natural biological control of FAW. She placed FAW pupae in the soil in maize fields and found that 92 percent of the pupae were removed within 4 days in fields without insecticide treatments, compared with only 4 percent in fields with insecticidal treatments.
Ants have already been seen attacking and killing FAW larvae in maize fields in Africa.
Some farmers have begun trying to apply lard or fish soup on their maize plants, to see if they can attract ants to their maize fields, so that they will then eat the FAW larvae present.
Birds and bats
Birds and bats have been observed to prey on FAW larvae. Studies in Central America have demonstrated significant impacts of birds on infestation levels of the FAW. Presence of trees or bird perches in or near fields will help attract birds who can prey on the FAW and help control their population.
Despite their importance as natural antagonists, a thorough assessment for predatory wasps, ants and spiders is often neglected because of the difficulty to establish a methodology to accurately assess their impact.
In Africa, though generalist predators such as ladybug beetles, earwigs, predatory bugs, eusocial- solitary- and other predatory wasps, ants and spiders are regularly observed in maize fields, a list of these natural enemies is yet not available.
It is expected that for these major functional groups, forthcoming assessments will reveal many parallels between the pest’s area of origin and the newly invaded continent.
How to favour the presence of natural enemies in fields?
Farmers can take many actions to protect and favour populations of natural enemies in their fields (this is called “conservation biological control”). Measures include avoiding overuse of synthetic insectides that can have detrimental effects on natural enemies; ensuring diverse boundaries around fields including open flowers and shrubs as habitat or food for natural enemies; trees or bird perches in or near fields; if pesticides are considered necessary, selecting products that are compatible with biological control such as Bt and botanicals based formulations, and more.
Entomopathogens
Pathogens (microorganisms that can cause disease) are everywhere. In agriculture, plant pathogens (e.g. fungi, bacteria, viruses, nematodes) affect plants, reducing yield or quality. Also very important, but less perceived by farmers, are entomopathogens – those pathogens that affect insects (‘entomo-‘).
The Fall Armyworm is naturally affected by several different types of pathogens:
- Viruses, in particular Nuclear Polyhedrosis Virus (NPVs) such as the Spodoptera Frugiperda Multicapsid Nucleopolyhedrovirus (SfMNPV)
- Fungi, in particular
- Metarhizium anisopliaey
- Metarhizium rileyi
- Beauveria bassian
- Bacteria, such as the Bacillus surigensis(Bt)
- Protozoa
- Nematodes
The host-specificity of these pathogens is quite high, usually restricted to a few closely-related insect species. These pathogens do not affect other groups of insects (natural enemies), plants, animals or humans.
FAW larvae naturally killed by viruses and fungi are easily identified in the field. Virus-killed larvae become soft and many hang from leaves, eventually oozing viroid particles and fluids (photo 2). Fungal- killed larvae turn rigid and appear “frozen” on the leaves, eventually turning white or light green, as the fungal spores mature (photo 1). These are the two most common groups of entomopathogens naturally killing FAW larvae in the field.
Virus infected larvae of the African Armyworm (© Ken Wilson).
Farmers can learn to recognize these ‘farmer-friendly’ pathogens in the field. They can also multiply them locally. Farmers in the Americas sometimes collect the dead and dying larvae, full of viroid particles of fungal spores (the infective stages of the pathogens), grind them up in kitchen blenders. Then they strain the larval body parts out, mix the concentrated filtrate of virus or fungus with water, and spray them back out into the field, especially directly into maize plants currently infested with FAW.
Entomopathogens can play a very important role in natural regulation of FAW populations in the field. Farmers should learn how to identify the different organisms, understand their biology and ecology, and begin to experiment with them! They are truly farmers’ friends!