Baculoviruses and codling moth control using Madex® Top

Baculoviruses and codling moth control using Madex® Top

What are baculoviruses?

Baculoviruses are naturally occurring insect specific viruses. These natural pathogens are often very specific and often only target one particular species of insect. The insect becomes infected with the baculovirus after ingestion of the virus particles. Once ingested, baculoviruses replicate inside host cells causing the insect to become sick and die.

Baculoviruses are classified as microbial biological control agents. In the UK they are regulated on an individual strain level under pesticide legislation (EC 1107/2009). 


Types of baculoviruses

There are two main classes of baculoviruses, nucleopolyhedroviruses (NPVs) and granuloviruses (GVs). The main difference between the two is the number of virions, also known as the number of virus particles. Nucleopolyhedroviruses contain several virions, whereas granuloviruses contain a single virion.


What are the benefits to using a baculovirus?

Baculoviruses are naturally occurring insect specific pathogens that can be used for controlling certain types of insect pests. Baculoviruses are usually very specific and often control only one species of insect, meaning that they are safe to non-target organisms, including humans, beneficial insects, mammals, other arthropods and pollinators.

Baculoviruses that are used as biological control agents in the UK have to be registered as plant protection products under 1107/2009, meaning that baculoviruses have to undergo the same stringent evaluations to demonstrate their safety and efficacy as the conventional chemical insecticides. Baculoviruses with approval for use can be used in integrated pest management programmes and on organically produced crops. They can be used alongside other forms of biological control, including macro biologicals, microbial products, mating disruption, pheromones and also in programmes with other plant protection products. Baculoviruses have a unique mode of action, belonging to IRAC group 31, meaning that using them as part of plant protection programme is an excellent way to help prevent resistance developing to plant protection products and active ingredients.


Mode of action of baculoviruses

Baculoviruses contain high concentrations of virus particles, also known as virions. Each virus particle is surrounded by a protein matrix called the occlusion body which helps protect the virus from environmental conditions, such as UV. The occlusion bodies containing the virus particles are sprayed onto the leaves where the virus particles must be ingested by the larvae of the target insect in order to be effective. Baculoviruses have no direct effects on adults, eggs or pupae.

Once ingested, the occlusion bodies that surround the virus particles dissolve due to the highly alkaline environment in the larva’s midgut. The infective part of the virus called the occlusion derived virus (ODV) is responsible for the primary infection in the midgut cells. Replication takes place in the nuclei of the midgut cells. Following the primary infection, cell to cell transmission occurs by the budded virus (BV). This is how the virus spreads throughout the insect’s body. Towards the end of the infection cycle, larval host cells produce new occlusion bodies to help protect the virus once it gets released back into the environment when the insect dies. Once released from the insect, these occlusion bodies can then be ingested by other larvae which will lead to another virus infection.

Figure 1. Diagram showing the mode of action of baculoviruses


How do baculoviruses provide population control?

As well as being able to cause a direct effect on larvae when baculoviruses are ingested, baculoviruses can also provide population control. Population control can occur due to either the horizontal effect, the fitness effect or the vertical effect.

The horizonal effect takes place after an infected larva ingests a lethal dose of the virus and dies and the virus is released back into the field environment, where other larvae feed on the virus particles that have been released from the dying insect, leading to further insect mortality.

Baculoviruses can also cause a fitness effect. This is when an insect ingests a sublethal quantity of baculovirus. The insect may not have enough virus to be controlled after ingestion at the larval stage, but the level of virus can lead to a reduction in pupation or egg hatching of the next generation.

Finally, baculoviruses can also spread via the vertical effect. Again, this can happen when a sublethal quantity of virus is ingested by the larva. The infected larva may not die from the virus, however the virus can get passed onto the insect’s offspring. The next generation can carry the virus infection which can cause an outbreak after activation due to stress factors e.g. heat and disease etc.

All three of these effects; horizonal, fitness and the vertical effect ultimately provide population control of codling moth.


Figure 2. Diagram illustrating how baculoviruses can provide population control


Timing of baculoviruses

The two main factors determining the time taken for larvae to die after becoming infected by baculoviruses are the dosage of virus ingested and larval stage of the insect. A higher dose of the baculovirus will ensure that the larvae will ingest a higher viral load, ultimately leading to quicker death of the larvae. The other factor that will influence mortality rate is the larval stage of the insect. Younger/smaller larvae will be controlled more quickly than older/larger larvae as the smaller larvae are more susceptible to the baculovirus. Quicker mortality helps reduce the amount of damage caused by the pest.


Examples of baculoviruses

In the UK, Andermatt sell Madex® Top and Tutavir® which are both examples of registered baculoviruses. Madex® Top is a baculovirus used for the control of codling moth (Cydia pomonella) and Tutavir® is a baculovirus for the control of the tomato leafminer (Tuta absoluta).


What is Madex® Top?

Madex® Top is a baculovirus that contains the Cydia pomonella granulovirus (CpGV). It is a registered plant protection product that can be used to control codling moth (Cydia pomonella).


Codling moth (Cydia pomonella)

Codling moth is one of the most significant issues that UK apple and pear growers face. When the larvae hatch, they feed and burrow right to the core, causing serious damage to the fruit. Infected and damaged fruit will often fall from the trees or be graded out at harvest. If damaged fruit makes it into stores, it can become infected with storage rot disease, and this can spread to other fruit in the store.

In the UK there tends to be one full generation, followed by a partial generation of codling moth per year. However, depending on temperatures, codling moth can complete two full lifecycles in a year.

In the past, growers have been able to rely on the use of conventional chemical insecticides to protect their fruit. However, with the ongoing loss of and restrictions placed on conventional chemical pesticides, growers are having to find alternative methods for codling moth control.


Why use Andermatt’s Madex® Top?

Andermatt are global leaders in baculovirus production, with over 35 years of experience in their development, formulation and production. Madex® Top was the first ever baculovirus produced and registered for the control of codling moth and was developed by Dr Martin Andermatt and Dr Isabel Andermatt, founders of the Andermatt Group.

Madex® Top is a highly concentrated product used for both the damage control and population control of codling moth. Madex® Top has an IRAC code of 31, making it an excellent resistant management tool for using in codling moth control programme. Madex® Top has good compatibility with other products and can be used in integrated pest management programmes for controlling codling moth. Due to the nature of baculoviruses, Madex® Top is very species specific, meaning it has no negative effects on non-target organisms including beneficial insects and pollinators. Madex® Top is also non-toxic to mammals, birds and other arthropod species.

Madex® Top has no Maximum residue limit (MRL) or no Re-entry interval (REI) meaning that it can be used right up until harvest and that no restrictions are needed regarding workers re-entering a treated area. Madex® Top take 3 to 4 hours to dry after application and has good rainfastness once dried.

Madex® Top is manufactured in Switzerland where Andermatt have excellent inhouse research and development facilities, routinely carrying out quality control bioassays to ensure performance.


When to apply Madex® Top?

It is very important that Madex® Top is applied just prior to egg hatch. Madex® Top works best on young larvae and relies on ingestion, so needs to be ingested by the larvae before they enter the fruit.

To know when eggs hatch, growers and advisors can use models such as RIMPRO, which take local weather data into account to help predict when egg laying and egg hatch is likely to occur. Alternatively, degree days can be calculated manually. Adult codling moths hatch in spring and start mating when evening temperatures (21.00) reach 18°C. From this point they will start to lay their eggs. Eggs take 90 degree days to hatch and so it is advised to apply Madex® Top at 85 degree days, just prior to egg hatch.

For effective control, Madex® Top should be applied every 8 to 14 days throughout the codling moth hatching period. It is important to follow an 8 day interval between applications during periods of bright sunshine. However, during cloudy days, where UV levels are lower, it is possible to extend the application interval up to 14 days. Please note 1 day of full sunshine equates to 2 days of half sunshine. 

For more information on Madex® Top and Madex® Top application please see the product page here.

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