Flea beetle is an annoying parasitic insect often found in our crops, particularly in beets and cruciferous vegetables, among others. To minimize its damage, it is crucial to recognize it early and intervene with appropriate organic cultivation methods. If you notice many vegetables’ leaves being unusually holey, rest assured that it is the primary culprit. Let’s get to know this polyphagous insect better, which can cause significant damage to our domestic crops.
Now, let’s explore the main species of flea beetles present in our territory and how we can defend against them naturally without the use of chemical pesticides.
The different species of flea beetles
Flea beetles, in general, are polyphagous insects, specifically belonging to the large family of Chrysomelidae.
However, we are interested in only two species: the beet flea beetle and the crucifer flea beetle. Let’s learn more about each of them.
Beet flea beetle
The most well-known species is probably the beet flea beetle (or Chaetocnema tibialis). The small beetle measures approximately 12 mm in its adult stage. Its metallic coloration, typical of beetles, tends towards greenish-blue.
The crucifer flea beetle
Another widespread species in our country, relevant to domestic vegetable crops, is the crucifer flea beetle, or cabbage flea beetle, belonging to the species Phyllotreta nemorum.
This species is even smaller than the previous one, with dimensions ranging from 3 to 4 mm. The lower part of its body is completely black, while the upper part, the elytra, is marked by two evident lateral yellow stripes.
Biological cycle of flea beetles
The biological cycle of both the beet flea beetle and the crucifer flea beetle is similar, especially concerning their behavior.
Depending on the climatic zones and the season, with the arrival of cold winter, the adult specimens hibernate in the soil or at the base of wild plants they find available. In spring, they emerge and start their polyphagous activity, feeding on the plants that hosted them.
After a while, the mating and oviposition phase begins.
The flea beetle lays its eggs directly in the soil, where the young larvae remain without causing damage. When they emerge, they are already in their adult stage.
Depending on the climatic zones, the flea beetle can generate two generations a year, prolonging its trophic activity.
Damage to crops
The flea beetle can cause various damages to our domestic crops. As implied by the colloquial names of these beetles, different species have preferences regarding the plants they attack. Therefore, they primarily target beets and cruciferous vegetables like cauliflower, as well as brassicaceae such as turnip tops and rocket salad.
The severity of the damage depends on the type of crop and the insect’s developmental stage. As mentioned earlier, for instance, the larvae do not cause damage, while the adult specimens do.
The damage to the plants is particularly evident in the aerial parts, especially in young leaves; the powerful mandibular apparatus of the adult beetle creates irregular, roundish erosions on the lower surface of the affected plant’s leaves. The upper part is initially left intact but later gets punctured in multiple spots due to necrosis.
If the attack occurs during the initial growth phase of the plant, the damage can be severe enough to lead to its death.
On crops like beets or rocket salad, even if the damage occurs after overcoming the initial growth stage, the quality and edibility of the produce are compromised due to them being leafy vegetables.
Another consideration to evaluate the extent of the damage caused by the beet and crucifer flea beetles is the insect population’s size. If the specimens are few and can keep themselves under control, the damage to the crops may be negligible. However, if this is not the case, we need to seriously address the situation and find ways to protect our plants organically.
Biological defense strategies against beet and crucifer flea beetles
Biological defense against the beet and crucifer flea beetles can be quite complex and requires various precautions and techniques.
Even identifying the presence of the flea beetle on plants is not easy. This insect is extremely mobile, and that’s why it is also called the ‘garden flea’. When it feels threatened, it makes long jumps that make it difficult to detect. Thus, it is easier to locate it by observing the plants’ vegetation. Unusual perforations are an alarming signal.
Here’s what you can do:
A good agronomic practice like using natural mulch or jute sheets limits the flea beetle’s ability to emerge from the soil and reach our plants.
Using trap crops that the flea beetle is highly attracted to can be a good solution. For example, if you are growing cabbages and want to protect them, you can sow some rocket salad among the rows, as flea beetles cannot resist it. By defending the main crops, you are sacrificing spy plants. This technique is also excellent for monitoring the situation.
Good results can be achieved with other crops such as Indian mustard (Brassica juncea) and horseradish.
Neem oil and nettle macerate
Two organic remedies to keep the beet and crucifer flea beetles away from the garden are neem oil (available here) and nettle macerate. Both products act as protective barriers for the plants. The strong and pungent odor of both neem oil and nettle macerate serves as an effective repellent against this garden flea. Naturally, these two natural products should be used preventively, if possible. Once an infestation is underway, their repellent effect weakens.
Formulations based on azadirachtin are perhaps the most effective biological remedy against both beet and crucifer flea beetles. When applied to the early stages of their development, the active ingredient’s mechanism of action blocks their growth. Within a week, this will lead to the insect’s death. In essence, the young flea beetle stops feeding and halts its trophic activity.
The treatment should be done during the cooler hours of the day to allow more time for the active ingredient to work. An appropriate pressure sprayer can be used for the treatment.
Azadirachtin, while being an active ingredient allowed in organic agriculture, should only be used in severe infestations and when other preventive remedies we have proposed are insufficient to limit the flea beetles’ damage.
- PubMed – “Jumping of flea beetles onto inclined platforms.” This study explores the jumping behavior of flea beetles on inclined platforms.
- PubMed – “Epitrix flea beetles: new threats to potato production in Europe.” This article discusses the threat posed by Epitrix flea beetles to potato production in Europe.
- ResearchGate – “Integrated management of flea beetle and thrips on mungbean in coastal habitat.” This study explores the integrated management of flea beetle and thrips on mungbean in coastal habitat.
- ResearchGate – “A flea beetle can stick a perfect landing.” This research investigates the landing capabilities of flea beetles.
- ResearchGate – “Jumping of flea beetles onto inclined platforms.” This study examines the jumping behavior of flea beetles on inclined platforms.
- University of Minnesota Extension – “Flea beetles.” This comprehensive guide provides information on flea beetles, their identification, life cycle, the damage they cause, and management strategies.
- The Old Farmer’s Almanac – “Flea Beetles.” This article provides an overview of flea beetles and offers tips on how to prevent and get rid of them.
- The Spruce – “How to Prevent and Get Rid of Flea Beetles.” This guide provides practical advice on how to deal with flea beetles in your garden.
- SDSU Extension – “Dealing With Flea Beetles.” This article from South Dakota State University Extension provides information on how to manage flea beetles.