Insects such as ladybugs or predatory wasps act as natural enemies against pests and as effective plant protectors. They are good for the environment and help cutting costs – but their habitats are under threat from pesticide use.
In agriculture, beneficial insects are the natural enemies of pests. Beneficial organisms can also be tiny organisms such as bacteria or fungi including miniscule filamentous fungi of the genus Trichoderma, which are naturally found in soil everywhere. Trichoderma are used as pest control in agriculture on pathogenic fungi due to their ability to parasitize them. Studies found that Trichoderma are also capable of controlling insect pests directly through the production of insecticidal metabolites; as well as indirectly through the activation of systemic plant defensive responses, attracting natural enemies or the parasitism of symbiotic microorganisms. But not only fungi also mites, insects, spiders or birds can protect crops. In Israel and the US, barn owls are introduced in agricultural areas to successfully reduce mouse populations in fields. To be able to reduce the use of pesticides in agriculture, the development of new efficient and safe alternatives are required – and smaller organisms are of particular importance. They either eat the pests directly – or parasitize them by laying their own eggs into the pests.
There are diverse types of beneficial insects: Some specialize in controlling specific pest species, while others eat many different species. Aphids, for example, can be successfully controlled by lacewings, hover flies, or earwigs. Ladybugs are probably the most well-known beneficial insects used against insect pests. Their larvae are voracious predators and will feed on aphids and other small insects like cereal chafers, canola gloss beetles, whiteflies, and Colorado potato beetles. A single ladybug can eat about 50 aphids a day – and about 40,000 aphids in its entire life. There are various species of such bugs or flies preying on parasitic pests. The green lacewing larva for example eats up to 500 aphids in its two to three-week life span.
Currently, there are various options to buy commercially bred native beneficial insects. In open fields, in greenhouses, or in storage, customers can use them as a biological alternative to pesticides. For example, ichneumon wasps can be deployed against greenhouse whiteflies infesting vegetable plants such as beans, cucumbers and tomatoes. In grain storage, wheat weevils in particular are a major problem. Starting from a small initial infestation with a few beetles, uncounted offspring can develop within a short time that destroys the grain – ichneumon wasps are particularly suitable for their control.
However, it is not enough to just apply beneficial insects in the fields themselves. They must also find good living conditions throughout the agricultural landscape. Hedges and trees, cairns or dry stone walls provide space to breed and survive the winter. Fallows, strips of old grass, or flowering areas are also effective refuges. A study from England shows that flowering understoreys below apple trees support significantly more natural enemies like spiders and earwigs as well as fewer aphid colonies, fewer aphid-damaged fruits, and higher pollinator visitation – compared to those above mown understories early in the season. As a result, aphid colonies can be reduced naturally and apple crops are protected in an ecological manner. In order to ensure a good living environment for beneficial insects, fields should not be too large, but should be interspersed with hedges or flower strips, and bordered by varied field margins. This can provide an effective population of beneficial insects on crop land.
Significant presence of beneficial insects can reduce the need for expensive pesticides and working hours for farmers. Scientists estimate that the annual value of natural enemies of insect pests contribute to crop protection in the United States to the tune of 4,5 billion US dollars. Large-scale ecological enhancement of agricultural landscapes would make it possible to naturally reduce the number of pests and secure yields. However, currently beneficial insects are having a challenging time in most agricultural areas. A form of agriculture has long since emerged that is largely decoupled from natural regulation: Large-scale cultivation of only a few crop species in hardly varied crop rotations leads to increasing pesticide use to the detriment of natural helpers of pest control. This creates a vicious cycle: A decreasing number of beneficial insects results in increasing pesticide use, which further reduces beneficial insects, which in turn increases pesticide use. Policymakers on all levels are called upon to create economic incentives for organic farming and to define an ecological damage threshold. This damage threshold should take into account not only the economic but also the ecological follow-up costs of pesticide use – such as the damage to beneficial insects. Civil society organizations, science and environmental authorities are calling for agricultural landscapes and land management to be designed in such a way that native beneficial insects find sufficient and safe habitat.