Adult Colorado beetle
The Colorado beetle is a beetle of American origin, once it arrived in Europe it did not find natural enemies and has therefore spread, becoming a problem for crops. In the garden it attacks in particular the plants of the Solanaceae family, such as potatoes and aubergines.
This insect has several metamorphoses: from eggs it passes to the larval state until it becomes an adult. To overwinter it takes refuge underground, it comes out when the ground stably exceeds 10-12 degrees, we usually find it in May in search of food.
An adult Colorado beetle guided by the smell is able to travel up to 300 meters to reach the solanaceous plants of which it is greedy, after eating it begins to fly, mates and lays its eggs on the low side of the leaves of a healthy plant.
Recognize larvae and adults
Colorado beetle is an insect that it is easily recognized:
- The larva is very easy to spot on potato leaves: these are insects between red and orange, with swollen bellies, with black heads and tubercles. Its dimensions are approximately 1.5 cm in length. Colorado beetle larvae are most often found on the underside of the leaf, but being quite large it is not difficult to identify them by checking the plant, also because they usually meet in groups.
- The adult is slightly smaller than its progeny, generally around one centimeter in length, and is characterized by a yellow body lined with black, the shape is that of a typical beetle. Being flying it is more difficult to see the adults but they are yellow and black insects that are really easy to identify.
- The small yellow eggs can be found stuck to the leaves, like the larvae on the underside.
Damage brought by the Colorado beetle
Colorado beetle larvae
This phytophagous beetle damages the solanaceous plants, turning in particular its attention to the potatoes, its favorite plant, and secondly to the aubergines and tomatoes.
Both the adult Colorado beetle and the insect in the larval stage feed on leaves, if they are allowed to proliferate in the garden they can compromise the vitality of the infested plant and quickly defoliate the other solanaceae present. When the insect is an adult it can easily move between plants and even from one field to another.
The insect cycle reaches two or three generations a year, the greatest damage is usually found in May, with the first birth of larvae.
Prevent insect attacks
The only prevention system of Colorado beetle is crop rotation. On the size of a small family garden, however, this method cannot give many results: if you move the potatoes a few meters, the adult beetle reaches them without difficulty. For crops on a larger scale, it is important not to repeat solanaceous plants on the same soil, so as not to attract Colorado beetles.
The biological fight against Colorado beetle
Manual control. The fight against Colorado beetle in a small organic garden is done primarily with manual checks, this very simple method works very well on the larvae, the important thing is to catch the infestation early. If you carefully inspect the plants during the month of May, you can intercept the first generation of newborn beetles and remove them, keeping the insect under control without doing any treatment.
The voracious turkey. Turkeys are fond of Colorado beetles and can help the horticulturist who has a small herd in cleaning up the crops from these beetles.
The bait method. A good way to bring out the Colorado beetles in the area is to force the early growth of a potato plant, which must be kept sheltered in the heat, so that at the beginning of May it is already formed and can be taken to the garden. . The Colorado beetles will be attracted to this "first fruits" and will infest the plant, which acts as a bait to allow us to find and eliminate the beetles.
Insecticides. As insecticides in organic farming against Colorado beetle, it is possible to use pyrethrum, bacillus thuringensis, and neem oil. All three treatments can kill Colorado beetle and are allowed in natural crops. The pyrethrum has the defect of acting only by contact, it is not easy to find and hit adults, moreover it is a product that although of natural origin has a toxicity and can also kill bees and ladybirds. Neem oil, like pyrethrum, strikes by contact, is less effective but also less toxic for the ecosystem. The bacillus, on the other hand, is only suitable for killing the larvae, on these it is very effective in blocking their digestive system causing their death, while it has no effect on adult specimens. There are several strains of bacillus thuringiensis, the best for fighting Colorado beetle is the tenebrionis variety, but the more common kurstaki can also be used. It is a beetle that adapts well to insecticides, creating increasingly resistant offspring. This makes manual elimination in May still the best way to protect potatoes and other crops from Colorado beetle.
Methods of biological control. There are also two methods of struggle that involve the insertion into the environment of natural agents hostile to the beetle: theBeauveria bassiana, antagonist fungus capable of killing the insect, and the hymenoptera Edovum puttleri, which feeds on the Colorado beetle eggs and is therefore useful in stopping the proliferation.