Wireworm - Click beetle
The larvae freshly hatched from the eggs are initially only 1.5 mm long and whitish in color. Within a few days, the cuticle of the wireworms hardens and takes on the golden yellow color typical of Agriotes species. Depending on the species, wireworms go through eight to 14 molts and grow up to two centimeters long before they pupate and develop into beetles.
The beetles are usually inconspicuous in color and have an elongated body shape. They are named after their ability to use their jumping apparatus to catapult themselves from the dorsal position into the air in order to land back on their little legs.
The female beetles lay their translucent eggs shallowly in the soil. The eggs are laid in foci and not evenly distributed over the field. Densely overgrown areas are preferred over bare field soil. Larvae hatch after about four weeks. The larvae need several years for their development, depending on the environmental conditions they pass through different numbers of larval stages. They repeatedly go through longer resting phases during which no feeding takes place.
To feed, digestive fluid is released and the resulting food mush is absorbed. The larvae cover only short distances in the soil, but are able to move to deeper soil layers if environmental conditions require it.
In individual years, damage of varying severity was reported, with dry-hot years being more likely to cause damage. The severity of the damage caused depends on the plant part infested, the time of infestation, and the number of older wireworms in the soil.
In the case of pure root damage, seedlings such as corn are most severely affected, while wireworms in cereals play a lesser role or are often not even noticed. Damage is most severe when crops themselves are infested, as in potato, carrot, onion, asparagus or radish.
Prevention and control
- Information on the currently approved plant protection products in Austria against wireworms can be found in the list of plant protection products approved in Austria.
- Crop rotation measures have so far proven to have only limited success, since wireworms are very polyphagous and can live on a wide variety of host plants. The only consensus is that there is a particularly high risk for the following crop after grassland has been turned over - this also applies to a lesser extent to fallow land.
- Intensive tillage reduces infestation, but harms soil life and promotes soil erosion. Shallow tillage, on the other hand, which targets the sensitive stages in the life cycle of wireworms and must therefore be carried out at an optimized time, is considered a possible sustainable measure against the pest. Sensitive developmental stages are egg clutches and young larvae, but also beetle pupae, which remain in the soil until the adult beetles swarm out.
- The use of the insect pathogenic fungus Metarhizuim anisopliae is in the experimental stage.
- Experiments on resistance of potato varieties to wireworms showed that resistance was related to the content of glycoalkaloids (solanine), which, however, are classified as toxic to humans. In practice, however, cultivar differences in susceptibility to wireworm damage in potatoes are also consistently observed and appear to be independent of the solanine content of the tubers. The causes of these differences have not yet been adequately investigated.
At soil depths greater than 20 cm, wireworms are well protected from control measures. Damage increases from the next year after egg laying. More accurate information on the flight of individual species is provided by the use of pheromone traps for the most common Agriotes species. Monitoring to survey the flight times of the damaging species occurring in Austria has been carried out since 2019. The collected data can be seen on the page of the Austrian Plant Protection Warning Service under "Wireworm monitoring in potato".
Several research studies have found naturally occurring antagonists such as ground beetles and various insect pathogenic fungi(Metarhizium brunneum, Entomophthora elateridiphaga,...), but it is still unclear whether they are sufficiently effective against the pest. Work on biological control with the fungus Metarhizium brunneum is being done at some institutions. Preliminary results indicate some potential of the fungus against wireworms. In contrast, previous results with insect pathogenic nematodes or with the fungus Beauveria sp. have not been promising.
Project "Wireworm Control
Last updated: 17.11.2021