Olive growing is facing a crucial challenge: the progressive disappearance of organophosphorus insecticides, as the chlorpyrifos, dimethoate e phosmet, once fundamental for the control of phytophagous insects that nested under the bark of olive trees. These products possessed gasifying and cytotropic properties, allowing them to penetrate plant tissues and attack hidden insects.
However, their toxicity has led to the revocation of their registration in the European Union, paving the way for the search for safer and more sustainable biological solutions with entomopathogenic nematodes.
A biological solution for the control of olive tree pests
Nematodes are worm-like organisms belonging to the phylum Nematoda, present in numerous natural environments. Some live freely in the soil, while others have developed parasitic capabilities, infesting plants and animals. Among these, entomopathogenic nematodes they have evolved as natural tools for the biological control of harmful insects, exploiting a particular symbiosis with bacteria that are lethal to the host.
Symbiosis with bacteria: an effective evolutionary strategy
Entomopathogenic nematodes live in symbiosis with specific bacteria (of the genera Xenorhabdus e Photorhabdus). This relationship is critical to their survival and ability to rapidly kill host insects through a complex process of colonization and decomposition.
The symbiosis between nematodes and bacteria is a mutual benefit for both species:
– for bacteria, nematodes act as vectors that transport them to the host insects, protecting them from the external environment; without nematodes, bacteria would not be able to reach insects effectively;
– For nematodes, the bacteria produce lethal toxins that kill the host and break down its tissues, creating a nutrient-rich environment that encourages their growth and reproduction.
How do you introduce bacteria into nematodes?
When a nematode develops in the carcass of a dead insect, it absorbs the bacteria present in the corpse. These are incorporated into the intestinal vesicle of new generations of nematodes, creating a stable population of symbionts that will be passed on to the next generation when the nematodes disperse in search of new hosts.
How does the nematode release bacteria?
After penetrating the body of an insect larva through spiracles, anus or mouth, the nematode heads towards the internal cavity of the host (hemolymph) and releases the bacteria through a precise mechanism:
1. environmental stimulus – The nematode senses the physiological conditions of the host and triggers the release of bacteria;
2. active expulsion – The bacteria are expelled from the nematode's intestinal vesicle and spread into the insect's hemolymph;
3. bacterial proliferation – The bacteria multiply rapidly and produce lethal toxins, causing death of the host within 24 to 72 hours.
Application in biological control of olive
Thanks to this predation system, entomopathogenic nematodes are used in the biological control of various agricultural pests. In the case of olive trees, they are used against:
a) Oziorinco (Otiorhynchus spp.) – land applications.
b) Margaronia (Palpita unionalis) – applications to the hair.
c) Bark-sucking Lepidoptera (Euzophera pinguis) – applications to the foliage.
Products available on the market and their use
Capirel® / Larvanem® (Koppert): contain Heterorhabditis bacteriophora
Entonem®: contains Steinernema feltiae
Nemastar®: contains Steinernema carpocapsae
These products should be used according to the manufacturer's instructions, taking care to consider that, as it is a "live" product, it should always be purchased fresh and applied by spraying. The temperature of the water tank should not exceed 25°C.
A practical example of a possible seasonal strategy with entomopathogenic nematodes for olive trees for biological control is reported.
General technical precautions
- do not use fungicidal or insecticidal pesticides in the 48 hours before and after;
- avoid applications on windy, too hot or dry days;
- constantly stir the mixture to avoid sedimentation of the nematodes;
- check that the pump nozzles have a hole ≥ 0,8 mm;
- Apply in the evening or on cloudy days to reduce exposure to UV rays.
The applications of entomopathogenic nematodes on the soil are carried out by spraying. Entomopathogenic nematodes seek out and infest the larvae of parasitic insects; in the case of olive trees, they attack the larvae of Otiorhynchus spp. (vine weevil), which are going through the developmental stages in the soil and in contact with the roots.
Conclusion
With the progressive elimination of organophosphate insecticides, the future of olive pest control depends on safe and effective biological solutions. Entomopathogenic nematodes represent a valid alternative to protect olive orchards, with applications that continue to be studied and refined, especially for difficult-to-reach pests such as Lepidoptera barksucker, vine weevil, and Margaronia.
AIPO Director
Interregional Association
Olive producers
