Bioinsecticide product types and key considerations

Discover the main bioinsecticide groups and why products require careful integration in crop protection programmes.

Globally, there is a variety of bioinsecticide options for various cropping situations.

Some bioinsecticide products are already authorised for use in UK horticultural systems, where high-value crops support innovation.

There is potential to extend some advances to cereal and oilseed crops, but it is important to understand how they work, in advance of products coming to market.

Bioinsecticides are a type of biopesticide and are regulated as plant protection products.

Insecticides, including bioinsecticides, have been classified into several mode of action groups by the Insecticide Resistance Action Committee (IRAC).

These organisms interfere with the target insect’s ability or desire to feed.

They may:

• Land on or be consumed by the target insect
• Infect the insect through the cuticle or digestive system
• Damage the insect gut, causing rapid cessation of feeding

Ultimately, microbial insecticides can cause starvation, impaired development and death.

They include a well-known example: Bacillus thuringiensis, Bt.

Classified within the BM 11a mode of action group, the Bt bacterium produces toxic insecticidal proteins that disrupt insect gut membranes and feeding.

There are several Bt sub-species that produce different Bt proteins with efficacy on various pests.

The toxins tend to target larval stages.

Although Bt has been formulated for sprays, the Bt genes, which code the toxic proteins, have been used in some genetically modified crops.

There are many other microbial insecticides, including those with unknown or uncertain modes of action:

• Non-Bt bacterial agents, in the UNB mode of action group
• Fungal agents, in the UNF mode of action group

Examples of the latter are:

• Beauveria bassiana – used to control whiteflies, for example
• Metarhizium anisopliae – used to control whiteflies, thrips and mites, for example

Viruses are also known to regulate some insect populations, which are classified within mode of action group 31.

These products disrupt normal insect behaviour and growth, rather than killing a pest immediately.

They may:

• Repel insects and deter feeding
• Restrict egg laying, eventually reducing pest pressure
• Interfere with moulting and development, reducing survival of juveniles

Once again, the group includes those with unknown or uncertain modes of action, such as some botanical essences from the UNE group.

An example is azadirachtin – an extract from the neem oil, which is found in the seeds of the neem tree.

Although it may affect a pest’s hormonal system and disrupt moulting, it may also smother and desiccate insects.

Another example is d-limonene, which is the main constituent of orange oil.

It has a strong citrus smell that can repel insects.

These biologically derived compounds can interfere with insect nerve signalling.

They may:

• Affect movement and coordination
• Cause paralysis
• Prevent feeding and kill the pest

Spinosad, from mode of action group 5, is an example.

It is based on chemical compounds found in the bacterial species Saccharopolyspora spinosa.

It primarily targets binding sites on nicotinic acetylcholine receptors of the insect nervous system.

It is highly active, by both contact and ingestion, and has been used to control a variety of insect pests globally.

In general, parasites do not kill their hosts quickly, as they often gain from keeping the host alive. For example, to ensure a continuous supply of food.

They may:

• Actively locate prey, such as in soil or other habitats
• Enter through natural openings during susceptible insect stages
• Reproduce within the dead insect before moving on to find new hosts

Some parasites are classified as macrobials, which are another type of biological control.

Based on living invertebrate biocontrol agents (IBCAs), they are not regulated as plant protection products and do not have a mode of action grouping.

Macrobials cover small animals, such as beneficial insects, nematodes, and mites, which control pests by direct consumption or infection.

Entomopathogenic nematodes are well-known examples, which include Steinernema species and Heterorhabditis species.

These microscopic ‘worms’ actively seek and penetrate hosts, where they release pathogenic bacteria that kill the insect.

The nematodes then feed on the dead tissues.

Macrobials often use specialist release methods to distribute adults throughout the crop.

However, nematodes are often applied in spray formulations.

The UK Plant Health Risk Register provides information on IBCAs in England, including non-native species that require a licence for release.

Do not expect bioinsecticides to perform in the same way as conventional insecticides.

In general, bioinsecticides do not deliver an immediate ‘knockdown’ effect, which is often associated with conventional synthetic insecticides.

They tend to and act slower as the often rely on ingestion, infection or interference with pest development.

It may take several days to see the full impact.

Bioinsecticide performance is also often influenced by environmental conditions, pest life stage and application timing.

They are not necessarily direct replacements for conventional chemistry.

The best results are usually achieved when used alongside other integrated pest management (IPM) approaches.