MothStop
Mothstop
- Wood ants can help improve organic apple production
Danish fruit is in short supply. Among other things, this is due to the fact that organic fruit growers have a battle against pests and diseases that are hard to fight without the use of pesticides. Therefore, the result is a more unstable production in organic farming than in conventional.
If it is possible for MothStop to find new organic methods for pest control, it will improve and stabilize the organic outcomes from growers, and thereby improve the competitiveness of organic fruit production.
More fruits without pesticide residues will then be available for the Danish supermarkets and the production method is more environmentally friendly than the conventional.
Purpose of the project
In organic apple production, the winter moth and apple scab are hard to fight with existing methods.
The winter moth larvae hatches in early spring and begin to gnaw the new leaves and flowers of the apple trees. In early spring, the larvae’s enemies are still in hibernation - therefore, the larvae can keep on eating without any interruptions by predators.
Wood ants are known as effective exterminators, and they will happily eat larvae. The ants are also active in the early spring, but they normally live in the woods. In MothStop, ants will be moved from the woods into the apple orchards. MothStop expects the ants to establish in the orchards and eat the larvae so that the outcome of apples can be increased.
Due to the fact that ants live in dense societies, where disease transmission is a hazard to them, they have developed the ability to produce antibiotics, which may fight fungal diseases - for instance apple scab.
In this way, the ants may also help making the organic apples’ quality go up.
MothStop runs in the period 2016-2018.
Findings
- MothStop has shown that it is surprisingly easy to move ants from woods and into the orchards. Fragments of large anthills that were moved from woods to an apple orchard quickly established themselves and survived in the orchard for several years (until the finalization of the project) and resulted in high ant activity in the apple trees. However, if we did not supply the ants with sugar, they slowly deteriorated during about a year. The anthills remained at their original locations and did not spread, which made it easy to remove them again. In another project, we reached the same results when the ants were moved to Christmas tree plantations. The conclusion is that wood ants in all probability can be artificially established in most types of plantations.
- The ants started patrolling apple trees in early spring (from the beginning of May prior to flushing), where we saw them catch wintermoth larvae in the trees. This resulted in significantly fewer larvae in the ant trees compared to control trees without ants.
- In the first half of May, there were more than four times less larvae in the ant trees. However, ant activity also led to an increase of aphids (green apple aphid) nursed by the ants. In August, the share of aphid-infected shoots was 2.5 times higher in the ant trees than in control trees.
- The increase of aphids in ant trees reached an unacceptable level for apple farmers, for which reason the ant technology is not yet applicable to apple orchards. In the long term, the aphid problem may, however, be solved if we can develop sugar solutions that are more enticing than the sugary honeydew produced by aphids. In this case, the ants no longer need the aphids and will stop nursing them.
- When we compared the quality of apples from ant and control trees, we saw that the proportion of apples infected with respectively apple rot (Monilia fructigena) and scab (Venturia inaequalis) was lower in the ant trees than in neighbouring trees without ants. Regarding apple rot, ants reduced the proportion of infected apples by 24 and 84%, respectively, in Alkmene and Collina, which was statistically significant for Collina. With regard to scab, the reduction in ant trees was respectively, 5, 19, 91 and -16% for Alkmene, Collina, Holsteiner Cox and Resista (which is partially resistant to scab). In this case, the difference in Holsteiner Cox was statistically significant. The apples were assessed to have scab if they had more than three spots.
- To test whether ant activity led to fertilizing the trees, we measured the content of 11 different macro and micro nutrients in the trees’ leaves and, again, compared trees with and without ants. For ten of the substances, we found no significant differences, but the Mg content in the leaves of the ant trees was significantly 5% higher than in control trees.
Conclusions and recommendations
The ants had a positive impact on combating insects and diseases as well as enriching the nutrient Mg, while simultaneously having a negative impact due to the propagation of aphids. The overall effect in the project year was neutral, as we did not find a significant difference in the yield of apples between the two types of trees.
The Dutch company BioBest is already working with developing of commercial sugar dispensers for farmers with the aim of destroying the collaboration between ants and aphids. If they succeed, the wood ant may become an important tool in the ecological apple farmers’ battle against pests.
Apart from the aphid problem, ants had a positive effect on the trees in the orchard. Thus, wood ants may potentially be used to control pests in crops not susceptible to aphids nursed by ants.
Alternatively, one could imagine that the ants could be used as a type of ambulance service, where they are applied during intense pest outbreaks and then removed once the problem has been solved before a harmful aphid population has been established. This is a possible, as the anthills are easy to move.
Project leader
Joachim Offenberg, Department of Bioscience,
Aarhus University.
E-mail: joaf@bios.au.dk
Phone: + 45 25 58 06 80
Discussion
The ants’ ability to reduce plant diseases is particularly interesting, as it is a service that has not previously been described in an IPM context.
Is the effect powerful enough to be profitable in highly affected crops, e.g. in plums where Monilia is a much bigger problem than in apples? Does it work on other plant diseases? And what is the mechanism? Prospects are high if ants not only are able to eradicate insects, but also plant diseases that often causes greater problems than the insects.
By further developing the technology, in the long term the wood ant may become a weapon against the enemies or organic famers. A sustainable weapon that, at the same time, can increase and stabilize yields. This may make organic farming more attractive and result in increased market shares benefitting consumers, who are increasingly demanding organic fruit.