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11 Aug 2021

Can biopesticides beat the beetle?

As featured in Arable Farming Magazine

Can biopesticides beat the beetle?

by Arable Farming

As plant protection products benefit from innovation and move with the times, more biological products that fit the bill for being less harmful to the environment are emerging. Alice Dyer finds out what biopesticides could offer oilseed rape growers.

Cultural controls, varietal vigour, companion cropping and boosting beneficials are all non-chemical methods of attack showing merit in tackling cabbage stem flea beetle (CSFB).

But use of novel biopesticides to complement these is something the industry is expecting to see more of as chemical solutions become fewer Harper Adams University PhD student Claire Hoarau is conducting a number of experiments to determine the scope for biopesticides in CSFB control, including the first lab studies to evaluate the effect of nematodes on adult CSFB mortality.

She is also exploring the potential for entomopathogenic fungi, bacteria and natural products, such as botanical insecticides.

Four species of nematodes in commercial formulations were screened in the lab against adult CSFB steinernema feltiae, steinernema carpocapsae, steinernema kraussei and heterorhabditis bacteriophora and cumulative mortality was recorded every two days, until eight days post-inoculation.

Mortality Ms Hoarau says: The species heterorhabditis bacteriophora worked the best with more than 75% mortality after six days at the middle dose.

Others were good but slower to kill, reaching high mortality after four days.

The species that did not work so well was steinernema kraussei, but it was still better than the control, so these are encouraging results.

Nematodes work by entering the beetles body and releasing a fatal bacteria.

The nematodes then feed on the beetle and multiply.

Ms Hoaraus next steps will be to test the product in the field during flea beetle migration.

The nematodes come as a paste to be dissolved in water and they would be applied by spraying with the same equipment as other pesticides.

Biocontrols However, with biocontrols we have to maximise their effect by applying them at the correct moment.

Biopesticides based on entomopathogens are living organisms, so when applied in the field theyre exposed to the environment, so the sun, UV radiation, temperature, humidity and all these factors can be detrimental to these biopesticides.

I am going to spray in the evenings because nematodes are sensitive to UV and humidity.

Beetles are nocturnal and feed mostly at night.

How long the nematodes last depends on humidity if its dry they might just last 24 hours.

Im planning to apply them several times, with at least four applications every seven days.

However, not all results were as promising.

Several lab bioassays were carried out with the entomopathogenic bacteria bacillus thuringiensis tenebrionis, which infects the host insects by ingestion and causes them to die of septicaemia within a few days.

Formulations Three formulations were tested at field rate and mortality of adult beetles was monitored for 12 days post-treatment.

However, no mortality above 40% after 12 days was seen in any of the treatments and Ms Hoarau decided not to investigate entomopathogenic bacteria any further.

The plant-based compound azadirachtin, which is derived from the neem tree and currently used in horticulture as an insecticide, also did not have high mortality in the lab, but studies in the USA where it is combined with entomopathogens (microorganisms pathogenic to insects) showed significant results.

It sounded like azadirachtin enhanced the effect of the entomopathogen so Im going to try this combined with a fungi.

The fungi would be applied by dissolving spores in water and spraying.

Its a contact pesticide, so spores will germinate on the beetles cuticle and theyll produce toxins and break into the insect and grow into it.

Usually after a few days you can see the fungi developing on the beetle.

It can also contaminate other CSFB. It would take a few days to take effect from application, but being a living organism too, it is going to depend on the temperature and humidity. says Ms Hoarau.

Products competing with chemistry

Already used in UK veg production, the novel bioinsecticide Flipper is based on extracts from olive oil but claims to have multiple modes of action, including immediate paralysis or knock-down of the target species as a result of interactions with the nervous system, while still being relatively benign to beneficial insects and pollinators.

As part of her studies, Claire Hoarau investigated the bioinsecticides potential for flea beetle control in oilseed rape at half, double and the regular field rate.

She says: This worked very well in the lab.

After just 24 hours it had killed 85% of my beetles, which is a very good result.At double the field rate it had killed 100%.

The beetle must come in direct contact with the product, which attacks lipids in the insects cuticle, interfering with feeding activity and resulting in mortality.

Dr Julian Little, spokesman for AlphaBio Control, the company which developed Flipper, says the product is particularly interesting because, despite having organic accreditation, it is being widely adopted in conventional farming.

Innovation Unusually for a biopesticide, it is not just being adopted in organic sectors, showing its clearly able to stand up to the rigours of conventional farming in a way that most biologicals dont. I think thats a massive step forward for bioinsecticides.

In April, Flipper, which has undergone the same rigorous regulatory tests as any chemical pesticide, was awarded the Queens Award for Enterprise in the innovation category.

Dr Little says: Its not a given that a bioproduct is bound to be safer or have less impact on the environment, but Flipper has a very low environmental impact and no residue issues for example, which is particularly important in fresh produce.

Were well aware of the potential for use of these products in oilseed rape, but the trick will always be whether it works compared to standard products currently being used.

Viability The next steps of the project for Ms Hoarau will be to test Flipper and other products on oilseed rape in the field and to examine viability in terms of cost-effective pest control in broadacre arable scenarios.

This is not a living organism so its less sensitive to the environment, Ms Hoarau adds.

However, lab results are very controlled, so we need to wait until we have field results.

The cost also needs to be considered and if its going to be affordable for farmers.

Im convinced that just one solution is not going to be enough and biopesticides will need to be paired with what other researchers are doing as part of an integrated pest management programme.

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