The moth is the generic name of a butterfly (lepidoptera), of the family of noctuids, which counts about 25000 species in the world, and 750 in metropolitan France. The caterpillar, the larva of the moth, is a major pest of a large number of annual and perennial plants.
The moth and its caterpillar
The moth is a stocky moth with a dull, gray-brown body. Its wings form a roof at rest, and have a wingspan of 40 to 50 millimeters. There are sedentary species, which overwinter in the form of an egg, caterpillar or pupa, and migratory species which, naturally in their adult state, fly south (sometimes as far as Africa) from the very first cold. The caterpillar is generally plump, glabrous or not very hairy, and 35 to 50 millimeters long. She is very voracious, which favors her grinding oral appliance. The color varies according to the species, but most frequently, the caterpillar is green or gray, with black spots on each segment. If touched, it immediately coils in a spiral, typically.
The life cycle of the moth and its harmful effect
In spring, two situations arise, either some moths come out of their hibernation state (egg, caterpillar or pupa), or others, in the form of adult butterflies, return from migration. The adult female lays up to 1,500 eggs, from June, either on the leaves or at the base of the plants. The egg incubates for about two weeks. The larva, a small caterpillar, feeds on plants and moults several times before reaching the size of about 5 centimeters. So it pupates into a pupa, before transformation into a very different adult insect, it is complete metamorphosis. If the season conditions are favorable, there may be one or two other generations. Imagine the proliferation of caterpillars on a crop, it's quickly a disaster!
Damage to nocturnal caterpillars
The nocturnal caterpillars are truly polyphagous, that is to say that they feed on a very large number of plants. It is rare that one or the other of them is subservient to a single plant. The species and the nature of its pest behavior made it possible to classify the noctuids in two groups, that of the defoliating caterpillars, and that of the ground caterpillars, the latter better known to gardeners under the name of "cutworms". The action of all these caterpillars is essentially nocturnal. You should also know that these larvae come from both sedentary and migrating butterflies.
Victims of defoliating caterpillars
Defoliatory caterpillars eat away at the aerial parts of plants, especially the leaves, which are perforated or even eaten up to the main vein (corn, fodder grasses, sunflower, celery, cabbage, cauliflower, spinach, lettuce, pelargonium). In the artichoke, it is the stem and the flower bud that are attacked. On fruit trees like apple and apricot, caterpillars nibble on buds, flowers, and even young fruits.
Victims of earthworms or cutworms
Ground crawlers, as their name suggests, act at ground level. They feed at night and hide in the earth during the day. They gnaw and cut the roots near the collar. Damage is noticed on each plant and follows the row. Gradually, the subjects are withered and lying on the ground. Young plantations are particularly vulnerable. These cutworms attack beets, leeks, potatoes, carrots, parsley, strawberries and many other species.
Preventive measures are important because it is difficult to predict attacks. First, let act natural enemies, birds, blackbirds and crows among others, moles, auxiliary insects such as lacewings, bedbugs and some hymenoptera. Bats are also devourers of these moths. The elimination of weeds, regular hoeing on the surface, mulching and watering the soil will be unfavorable to the laying of certain moths. It is still possible to monitor thefts by trapping with sex pheromones, and thus eliminate the males on sticky plates. If a treatment against the caterpillars proves necessary, it is important to act on the larvae which are still small, more sensitive to phytosanitary products than the older ones. Treatments are to be carried out at dusk, due to the nocturnal activity of the caterpillars. Biological control is possible by spraying the foliage of the Thuringian bacillus, a bacterium that kills only the young caterpillars that ingest it, and which has no action on the auxiliaries, enemies of noctuids. In case of heavy infestation, spray an insecticide product (consult the phytosanitary index). If the vegetable plants are close to harvest, obviously use a product with a short persistence. By Claire Schutz Croué