Colorado beetle larvae »Look, control and more

the essentials in brief

• A Colorado potato beetle larva is 2-10 mm long, bright red, later reddish-yellow, has 6 short legs, a black head and a black neck plate.
• A special feature are 2 rows of black dots on each side of the elongated, cylindrical body.
• Biological control methods are: collect, shake off, organic sprays (neem, vegetable stock, rock flour) and household remedies (coffee grounds, moon amine, wood ash).

Recognize Colorado beetle larva.

Colorado beetle larvae hardly look like their parents

The appearance of a Colorado potato beetle larva is far removed from the yellow and black striped warning look of adult potato beetles. At the same time, specific features shape the appearance, even for the inexperienced eye enable reliable identification. The first appearance of the pests can be expected from the end of May / beginning of June. At this time, the Colorado beetle larva hatches from its orange-yellow egg, which its mother placed two weeks earlier on the underside of the leaf of a young potato plant. The larva cannot complain about loneliness, because the eggs are laid in packets in numerous clutches of around 20 eggs each. Within three to four weeks, a Colorado potato beetle larva goes through four larval stages (L1-L4) and changes size and color in the process:

• Larval stages L1 and L2: 1-3 mm long, bright red to red-brown
• Larval stages L3 and L4: 4-10 mm, reddish yellow
• Appearance L1 to L4: 6 black legs, black head, black neck plate
• Special distinguishing feature: 2 rows of black dots on each side of the elongated cylindrical body

By far the greatest damage is caused by a Colorado beetle larva in the fourth instar (L4). At this stage it is not uncommon for potato plants to be deflated. After the four-week feast in the potato bed, the fully eaten larvae drop to the ground, bury themselves and pupate. Two weeks later, finished young beetles in yellow and black stripes crawl out of the earth and start procreating the second generation. The pictures below show the development of a Colorado potato beetle larva from L1 to L4.

Fighting Colorado beetle larvae - an overview of organic methods.

When natural hobby gardeners cross the blades with voracious Colorado potato beetle larvae, biological methods have priority. What commercial farmers spray tons of pesticide in the potato field is not allowed in the private allotment garden and is not permitted anyway. Ecologically ambitious allotment gardeners do not throw in the towel straight away. In fact, the arsenal is well stocked with natural anti-Colorado beetle weapons, as the following table shows at a glance:

The ultimate remedy for Colorado beetle larvae has yet to be invented. Indeed, Colorado beetles are masters of adaptation. Since the introduction at the beginning of the 20th Century, the pests quickly develop resistance to arsenic, DDT and other toxins. Modern pesticides such as pyrethroids are increasingly losing their effectiveness in commercial potato cultivation. Hobby gardeners who are close to nature transfer this knowledge to the use of natural control agents against Colorado beetle larvae. The effectiveness of biological methods is based on a well thought-out combination and alternating use so that the beasts do not have time to adjust to them.

In the following video, Professor Dr. Kühne, an expert in the field of Colorado beetle control. Accompany the experts on a short journey through time, which shows why Colorado beetles and their larvae are so difficult to get hold of.

Fight Colorado beetle larva manually - this is how it works.

Manual methods undermine the ingenious adaptability of Colorado beetle larvae. When collecting and shaking off, you target the pests one at a time.

• Best time: From mid / end of April every few days until August
• Half fill the empty PET bottle with water
• In the morning, collect larvae and beetles from the leaves and throw them into the water bottle
• Alternatively, spread out a foil, shake the plant and collect any pests that have fallen off

At the end of the day, please carefully check all the undersides of the leaves. Discover orange-yellow eggs here, remove the clutch by hand or with kitchen paper.

Digression

Preventing Colorado beetles - tips & tricks

Organic spray against Colorado potato beetle larva.

As a biological spray against the destructive Colorado potato beetle larvae, an extract from neem seeds is certified as being extremely effective. Hobby gardeners who are close to nature swear by plant stock as a liquid and Rock flour(€ 12.33 at Amazon *) as a dry spray against the eaten larvae. The following brief instructions explain the details:

Neem versus Colorado potato beetle larva

Neem supplements stop feeding and multiplying

The biological insecticide organic pest-free neem from Naturen is a liquid azadirachtin extract from neem kernels. Applied to the young potato plants, the agent stops feeding within a few hours. In addition, the entire reproduction process comes to a standstill. The preparation is bee-friendly, biodegradable and also approved for use in home and allotment gardens.

Plant stock

If you spray potato plants regularly with plant stock, Colorado beetle larvae will lose their lust for balding and females who want to reproduce will turn away in disgust as soon as they approach them. Various herbs can be used as ingredients for the bio-spray. Production and application are very easy in the home garden. How to do it right:

1. Collect 1000 grams of leaves from nettles, mint, bracken or thuja (green needled shoot tips)
2. Place green groupage in a large cauldron
3. Pour 10 liters of water over and bring to the boil
4. Simmer gently for 20 to 30 minutes, stirring occasionally
5. Take the pot off the fire and set aside
6. Let it steep for 24-48 hours
7. Sieve the plant stock and pour it into a spray bottle or one Pressure sprayer to fill
8. Spray potato plants and other nightshade plants every 3 to 4 days (please do not forget the underside of the leaves)

The natural remedy is optimally effective before and during oviposition (beginning / middle of April) and shortly after the first larvae hatch (L1).

Rock flour

Rock flour prevents Colorado beetles from laying eggs

Grazing in the house garden mildew or other fungal infections, liquid pesticides are unsuitable. Permanently moist leaves offer fungal spores ideal living conditions. That doesn't mean you have to give up Colorado beetle larvae. With a wafer-thin layer of rock flour, you can prevent the laying of eggs and spoil the appetite of larvae that are already present. You can also sprinkle the remedy by hand. It is better to use a powder syringe.

Home remedies combat Colorado beetle larvae.

Home remedies are not a panacea for Colorado beetle larvae. At least they can increase the effectiveness of other biological methods. How to do it right:

• Coffee grounds: Sprinkle the dried coffee grounds every 4 weeks in the bed, spread thinly on the plant leaves
• Mondamin: use as an inexpensive alternative to rock flour
• Wood ash: Apply pure ash (without toxic combustion residues) using a powder spray on the top and bottom of the leaves

These home remedies with plant stock achieve a powerful synergy effect. If the potato leaves are still slightly damp from the organic spray, sprinkle with coffee grounds, moon amine or wood ash.

frequently asked Questions

What do adult Colorado beetles look like?

Adult Colorado potato beetles are orange-yellow with black stripes

Adult Colorado beetles have a distinctive appearance. The round-oval body is 7 to 15 mm long and striped black and yellow. Each of the light yellow, shiny cover wings are adorned with 5 black vertical stripes. Characteristic are black blemishes on the yellow-orange pronotum. There are no special features on the red-brown underside of an adult Colorado beetle. Black feelers and 6 thin legs complete the visual appearance.

Is the Colorado potato beetle larva only harmful to potato plants?

No, unfortunately the food spectrum of Colorado beetle larvae extends over numerous nightshade plants. Tomato plants, peppers, chilli, aubergines and even tobacco plants are also eaten with great appetite. Not growing potatoes in your own garden is therefore no guarantee that you will be spared from a Colorado potato beetle plague.

Can Colorado beetle larvae bite?

Like most beetles, Colorado beetles and their larvae also have chewing and biting tools for ingesting food. This mouth tool is of course only sufficient to feed on delicate plant leaves. The so-called mandibles are far too weak to bite into human skin.

Are there any beneficial insects against Colorado beetle larvae?

The Colorado beetle is an introduced pest from North America. This fact plays into the hands of the invaders because there are no predators in Europe. Birds, ground beetles, Predatory bugs and other beneficial insects spurn both the adult beetles and the reddish larvae. Whether in the course of evolution, parasites such as lacewings or Parasitic wasps,(€ 69.90 at Amazon *) recognize the Colorado beetle larva as potential prey remains to be seen.

Tips

The high expectations of the biocide Novodor FC as a control agent against Colorado beetles have not been met. The non-toxic bacilli contained in the agent called Bacillus thuringiensis subspecies tenebrionis should stop the Colorado beetle larvae from feeding immediately. At the request of the authorization holder, the authorization as a plant protection product was granted on the 30th April 2019 revoked. This does not apply to Bacillus thuringiensis israelensis. This strain of bacilli is still available for combating Mosquito larvae.