The quest for a ‘super nematode’
Among the many nematodes that exist in the wild, there are several that are able to attack beetles of the genus Diabrotica.
The larvae of these beetles are known as the infamous western corn rootworm. ‘At e-nema, we have been breeding and selecting the nematodes that attack these harmful insects. Using classical genetic tools we have also been able to select strains of nematodes that are less susceptible to heat stress or desiccation during transport’, professor Ralf-Udo Ehlers of e-nema says. ‘In this quest for a “super nematode” we need to cross these strains. That is where the partnerships in BIOCOMES are of crucial importance.’
Nematodes as players in IPM
Originating from North- and Central America, the western corn rootworm is one of the most devastating pests that can hit a corn plantation. So far, this pest is mostly controlled by agents from the class of neonicotinoïds, but these products are under increasing pressure in Europe, because of their effects on non-target insects. Nematodes are a possible biological alternative that could be included in Integrated Pest Management against rootworms.
Breeding nematodes in vitro
Whereas the nematodes normally reproduce inside the bodies of insects, e-nema developed techniques to grow these little animals in vitro. ‘After reproduction, we can expose the nematodes to e.g. heat shock. This way we are able to select the ones that are more resistant to heat, and then continue breeding with those individuals. We breed them as if they were normal domesticated livestock’, Ehlers jokingly says.
Crossing improved strains
One of the problems with this strategy is that never one single strain is good in all beneficial traits. Ehlers: ‘We need to cross several strains to produce a “mighty nematode”. After crossing, we would have to start again with the selection process. To make this easier we are now trying to identify the genes behind the beneficial traits. The genetic information will provide us with DNA sequence data, which can be used as markers to identify whether the hybrids carry the beneficial trait. That is why we are cooperating within BIOCOMES with the Israeli Volcani Center. They are developing genetic markers to identify the specific characteristics that we are breeding in our nematodes.’
Increase the virulence
Apart from breeding for higher resistance against heat and drought, Ehlers and his colleagues try to increase the virulence of the nematodes as well. ‘We cooperate with another partner within BIOCOMES, the Universidade dos Acores. They are trying to identify the genetics behind specific proteins that help the nematodes to penetrate the larvae of the beetles. Knowing these proteins may enable us to select for them as well.’
Less nematodes for the same effect
By increasing the virulence of the nematodes, Ehlers hopes to be able to decrease the dosage of nematodes that is needed to protect the corn from the beetles. ‘So far, a farmer needs to treat his crops with no less than two billion nematodes per hectare for effective protection. That makes our environmentally friendly strategy twice as expensive as the chemical option. Of course it is in our benefit that Europe is limiting the use of neonicotinoids. But it would also be in the farmers benefit if we could increase the virulence of the nematodes in such a manner that only one billion nematodes would be enough. This year we hope to start the first trials with a new hybrid strain, to see if we can achieve that goal.’
Read more about the BIOCOMES research on entomopathogenic nematodes
Industrial production of entomopathogenic nematodes at e-nema is done in large fermentation tanks. (Picture: e-nema)