The relationship between humans and cockchafer larvae has always been fraught with conflict. Until the larvae transform into flying harbingers of spring, they attract the displeasure of gardeners and farmers as voracious grubs. This guide highlights ecological control measures, gives tips for effective prevention and takes a look at the development of a cockchafer.

Cockchafer larvae are not particularly popular in the garden

Table of Contents

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  1. the essentials in brief
  2. Pest or Beneficial?
  3. Combat with beneficial insects
  4. Prevent instead of fight
  5. Cockchafer larva wanted poster
  6. frequently asked Questions

    7. the essentials in brief

    • The cockchafer larva is considered harmful because its diet consists of plant roots.
    • Mass occurrences with devastating damage are a thing of the past.
    • Nematodes fight local infestations with cockchafer grubs without poison. Ecological garden care is the best prevention.

    Cockchafer larva - pest or beneficial?

    May beetle larvae owe their bad reputation to their diet. An essential part of the diet of cockchafer grubs are plant roots of all kinds. A grub spends between three and five years of its development deep in the ground and feeds on roots. The cockchafer larva owes its status as a pest to this unfortunate diet. Dramatic harvest losses or serious forest damage can only be complained about in mass occurrence with a population of 100 to 200 larvae per square meter.

    The days of devastating damage caused by cockchafer larvae are of course long gone. In many places, only the grandparents have witnessed a plague of cockchafers. Up until the 1960s there was even a so-called cockchafer year, so that the children could collect beetles and larvae. Today, children and young adults may still know the beetle from Wilhelm Busch's “Max and Moritz” or as Sumseman from “Peterchens Mondfahrt”.

    Local infestation cannot be ruled out

    Locally, cockchafer larvae cause the hobby gardener a headache when nests form in the bed or under the lawn with a dense swarm of grubs. An infestation can be recognized by the stunted growth of perennials, shrubs and trees. Yellow spots appear in the lawn, which gradually enlarge and dry up. Against this background, it is of little consolation for the affected gardeners that lady beetles particularly prefer garden soils that are cultivated in an ecologically exemplary manner as a nursery.

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    Combat cockchafer larvae with beneficial insects - this is how it works

    Have you found a single cockchafer larva? Then this is an occasion to search the bed or the lawn thoroughly for other specimens. If you find large numbers of grubs or unearth entire nests under the lawn, control measures are an option. So that the infestation does not spread to a plague, it is not necessary to resort to chemical poison. Instead, you fall back on the powerful protection of roundworms of the genus Heterorhabditis. How to fight cockchafer larvae with beneficial insects:

    1. The best time to fight is 6-8 weeks after flight
    2. Buy fresh nematodes (e.g. 12 million for 24 m²) as well as watering bars for spreading with the watering can
    3. Dissolve nematodes in clay granules in water according to supplier's instructions
    4. sprinkle infested area with nematode water
    5. keep treated soil constantly slightly moist for 6 to 8 weeks
    6. Do not lime the bed or lawn before or after (fertilizing does not bother nematodes)

    The approximately 1 mm small nematodes actively search for cockchafer larvae and penetrate the body. There, the beneficial insects release a bacterium that is poisonous to the grubs. The larvae are destroyed within 2 to 3 days. The threadworms have their sights set on grubs of cockchafers and June beetles alike. Pupated larvae and adult beetles are not part of the nematode prey scheme.

    Only with emergency approval - soil fungus kills cockchafer larvae

    Fungal infections kill cockchafers in agony

    In their search for alternatives to DDT and other toxins against cockchafer larvae, the scientists struck gold with soil fungi. Beauveria brongniartii has been useful in the fight against masses of grubs and cockchafers for more than 100 years. The fungus infects its host with spores, which neither larvae nor adult beetles survive.

    The control agent is applied in the form of cereal grains that are overgrown with the fungus. The spores form at a depth of 5 to 10 centimeters and infect existing cockchafer larvae. In Germany, the use of the agent still requires emergency approval. In Austria, the preparation is available upon presentation of a plant protection card. Switzerland has approved the agent for use in small and house gardens.

    digression

    Rose beetle larva or cockchafer larva?

    With their shiny metallic green wings, rose beetles are a feast for the eyes. The decorative appearance makes the identification of the noble beetle child's play, even for the layperson. The distinction between rose beetle larvae and cockchafer larvae is more problematic. Both species belong to the scarab beetle family and look confusingly similar at first glance. This resemblance ends tragically for the protected grubs of the rose chafer. The location gives an important indication of which larva you have discovered in the garden. The rose beetle larvae prefer to live in the compost because only dead, decomposing plant parts are on their menu. May beetle larvae colonize the soil under beds and lawns in order to nibble on the roots of bushes, trees, perennials, grasses and vegetables.

    Prevention is the best fight

    Hedgehogs love grubs and grubs

    Targeted prevention can successfully avoid direct confrontation with cockchafer larvae. A wide range of effective methods is available for this purpose, so that female cockchafers do not lay their eggs in the bed or lawn in the first place. How to do it:

    insect protection nets

    After the last frost, May beetles start their main flight season. Now the finished beetles leave their pupal shell, in the protection of which they spent the winter. Males and females do not hesitate to start a family. Within a short time, the winged females have mated and are looking for a place to lay their eggs. By covering the garden with insect protection nets, you thwart the beetle ladies. In the course of global warming, the preventive measure should already be noted in the diary for the beginning/mid-April.

    Attract natural enemies

    The declared enemies of cockchafer grubs include moles, hedgehogs, badgers, starlings and crows. Numerous other biological opponents like to eat the succulent larvae. In order for the predators to find their way into the garden and hunt down the cockchafer larvae, the right framework conditions are advantageous. The following tips & tricks may inspire you for a natural garden in which harmful cockchafer larvae and other grubs have a bad hand:

    • consistent avoidance of pesticides
    • Garden design with wild corners, piles of leaves, rotten tree trunks as retreats
    • Create mixed and Benjes hedges as hiding places for beneficial insects

    Keeping chickens and ducks is one of the most effective control methods in a natural garden. Pecking hens and busy runner ducks discover every little cockchafer egg and every grub in no time. A positive side effect, running ducks thwart the plans of voracious slugs to attack flowers, perennials and vegetables.

    scarify the lawn

    Regular scarifying hides an infestation by grubs

    The lawn is a popular spot for female cockchafers to lay their eggs. However, a well-groomed green area with dense turf is not popular with the beetle ladies. Regular scarifying is one of the smart preventive measures against grubs, especially since the best time is when the eggs are laid. The scarifier (€84.00) not only combs out thatch and makes room for strong noble grasses. Cockchafer eggs that have already been laid are also destroyed.

    lawn protection fabric

    If you are laying out a new lawn, it is worth investing in a protective fabric between the coarse subgrade and the fine subgrade. The precaution is always advisable if you or your neighbors have already had to contend with an increased number of cockchafers. Admittedly, this preventive measure has its price. In return, you not only fend off cockchafer larvae. Other uninvited guests, such as moles, also stay away from your lawn carpet.

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    Mass emergence every 30 to 45 years

    Scientists have found that mass infestations of cockchafer larvae occur every 30 to 45 years. If the larvae with a population of 200 grubs per square meter cavort in the forest floor and nibble on tree roots, the affected trees die off across the board. However, May beetle plagues are mostly local, as in 2010 in a southern Hessian district. There, those responsible resorted to a chemical insecticide to combat the pests. This triggered nationwide protests by nature conservation groups. As early as 2006, the NABU (Nature Conservation Union Germany) pointed out in a much-noticed position paper that natural regulatory mechanisms solve the problem just as quickly as toxic chemicals.

    There are no more cockchafers… Maybe their departure frightens me and maybe I conclude from this that the cockchafers are just a little bit ahead of us (Reinhard May)

    May beetle larvae in portrait - profile to get to know each other

    Cockchafer larvae grow up to 5cm in size

    The development of a cockchafer larva begins as a tiny, 3 mm long, yellowish colored egg. When the larva hatches from the egg after 4 to 6 weeks, the parents have long since passed away. Male cockchafers die immediately after mating. Females carefully choose different locations to lay 15 to 100 eggs about 10 cm deep in the ground. With this work, female cockchafers have fulfilled their purpose in life and die as well. The following profile summarizes important characteristics of grubs:

    cockchafer larva
    insect family Scarab Beetle (Scarabaeidae)
    genus Cockchafer (Melolontha)
    size 3-5 cm
    body shape cylindrical, curved
    extremities 3 pairs of legs in front
    coloring light to cream with brown head
    development 3 to 5 years
    slip and excursion from the end of April/beginning of May
    habitat ground to a depth of 100 cm
    food plant roots

    Immediately after hatching from the egg, cockchafer larvae begin to feed. In the first few days, the grubs mainly eat mulm and very delicate roots. In proportion to their growth, the larvae feed on thicker roots, which they locate using root exudates. A powerful mouth tool allows the insatiable larvae to lay hands on almost all plant roots in the ground. When it is dry, grubs look for deeper soil layers with a higher moisture content. Humid weather lures them into higher layers, but not until daylight.

    tips

    The grubs of the rhinoceros beetle are of a completely different caliber than the cockchafer larvae. With a body length of up to 12 centimetres, rhinoceros beetle larvae are among the giants among the beetle offspring. The privilege of seeing a rhinoceros beetle larva or an adult beetle is usually reserved for organic gardeners with their own compost heap.

    frequently asked Questions

    Are cockchafer larvae poisonous?

    Hobby gardeners and forest owners chalk the cockchafer larvae to the fact that plant roots are at the top of the menu. Depending on the population in the garden or forest, the insatiable grubs cause damage to shrubs and shrubs of all kinds. While herbaceous plants and deciduous trees can recover after adult cockchafers have eaten them above ground, cockchafer grubs deprive the plants of their livelihood with no prospect of regeneration. The harmful effect is based on the insatiable appetite. May beetle larvae do not release toxic substances into the plants or the soil.

    There is a cockchafer larva in our garden. How long does it take to develop from a grub to a finished cockchafer?

    A cockchafer larva spends three to five years in the ground. On average, the development from the newly hatched grub to the winged cockchafer takes four years. During this time, the diet consists exclusively of roots of flowers, perennials and woody plants. Under favorable conditions, a cockchafer larva overwinters twice, pupates in August of the third year, hibernates in the pupal cradle, and flies out of the ground as a mature beetle in April or May of the fourth year.

    Are there manual control methods against a local infestation with cockchafer larvae in flower beds and perennial beds?

    If you suspect that May beetle larvae are romping about in the bed, dig up the affected plants together with the root balls. Hand gather any grubs you spot in the root system. You cannot be sure that you have got hold of all May beetle larvae. For this reason, we recommend replanting the plants in a spacious pot with fresh substrate. Hidden specimens cannot spread further in the garden in this way.

    We are struggling in the garden with a high incidence of cockchafer larvae. Shouldn't we just mill the contaminated soil?

    Only when all control methods fail should the use of a tiller against May beetle larvae be considered. The tiller plows through the earth to a depth of 10 centimeters and destroys all grubs. Further control agents are no longer required. However, all other soil creatures also have to pay for the radical tillage with their lives. Furthermore, the soil structure is completely destroyed. Subsequent regeneration takes a long time.

    tips

    The fight against a gigantic population of billions of cockchafers in Avignon, France, was unsuccessful. In 1320 the vermin were ordered by court order to "retire within three days to a field marked by signs where there was sufficient food for them." Violators would be treated as outlaws and exterminated, it said. Although the announcement shows the first signs of an ecological attitude, the measure came to nothing.

Category:

Animals in the garden