The European corn borer ( Ostrinia nubilalis ) is a Insecte of the order of the Lépidoptère S, in the past of pyralidés now placed in the crambidés . The Larve S of the bee moth tackle mainly the cultures of Maïs, of which it is the principal ravageur, and also of others Plante S cultivated like the Tournesol, the Houblon, the Chanvre, the Chrysanthème S… The fight against the European corn borer calls upon methods of biological Lutte by using in particular the Trichogramme S, of the methods of chemical fight (currently the most used) and also with corn transgenic (Maïs LT).

Description and biological cycle

The European corn borer is a butterfly of night manners, from 25 to 30 mm of scale. The males have wings ocher dark with fine dark stripes while the females are clearer. The female lays its eggs by groups of 15 to 20, with the armpit of the corn in May sheets - June. The young caterpillars, hatched at the end of 15 days, devour initially the Parenchyme sheets, then dig galleries in the marrow of the stem, weakening the seedlings considerably. The larvae, resistant cold, pass the autumn and the winter in the stems and transform themselves into nymphs next spring.

The annual number of generations of the ravageur depends on the climate. In France, there are one or two generations per annum according to whether one is in north or the south. Certain areas of the United States see following one another three to four generations per annum.

Damage

The symptoms of a infestation of Bee moth in corn plantation are the presence of small perforations on the sheets (symptom of first generation on young corn at the stage horn), the breakage of the stem under the panicle (male flowers) or on the level of the foot on developed corn, with presence of galleries and generally deposit of a sawdust. The larvae can also directly attack the ears which then carry signs of perforation and sawdust on the level of silks.

While feeding from the marrow of the stems, the larvae weaken the seedlings which become more sensitive to the Verse, disturb their development and support the infestation by mushrooms the such Fusarium .

The damage is thus direct (reduction of the output, harvests more difficult because of pours) and indirect (stronger incidence of the fusarioses they even responsible for the presence of Mycotoxine S).

On the other types of cultures, the symptoms remain the presence of stems broken with galleries and sawdust cluster. On sweet pepper, frequently attacked, the larvae are introduced into the fruits, making them unsuitable with marketing.

Means of fight

The recourse to means of fight against the European corn borer is not systematic and depends in particular:

  • of the pressure of the ravageur, variable for example according to the number of generations of the ravageur which the culture will have to undergo.
  • of economic constraints associated with the type of culture and the options of fight. Thus the decision of treatment on corn with low added-value (corn intended for the animal feeds for example) is justified only seldom whereas for corn of strong added value (corn seeds, corn intended for the human consumption), the treatments are quickly profitable and thus more frequent.

The techniques of fights are varied. One distinguishes mainly:

  • farming techniques, consisting to crush and hide the crop waste products to prevent the wintering of the larvae.

  • the chemical fight, founded on the Insecticidal use of S of synthesis, especially of the Pyrethrenoïde S.

  • the biological Fight, founded on the use of micro-organisms pathogenic or parasites/predatory. In the first category bacteria (Bacillus thuringiensis) are, mushrooms (Beauveria bassiana) and Nématodes which are marketed under various names. The application of these treatments differs little from the application of the traditional chemical treatments.

In the second category, mainly a tiny insect parasoïde, the Trichogramme is, about the Hyménoptères. The female trichogrammes lay in eggs of bee moth and their larvae develop inside by killing their host. The technique thus consists in hanging capsules releasing of great adult quantities of trichogrammes to kill " in the œuf" the generation to come from the ravageur. This technique developped at the point in the years 1970-80 gives results as satisfactory today as the chemical treatments in term of effectiveness; it remains however more constraining for the application.

  • the bio-technologique fight. Recent in the arsenal against the ravageur, this technique consists in using varieties of corn genetically modified to resist the ravageur. In the actual position, these genetic modifications are limited to incorporation in the genome of the plant of genetic information of bacterial origin, inducing the production by the plant of a toxic protein for the insect.

Varieties of corn transgenic resistant to the bee moth were developed by private firms, and are authorized and cultivated with the the United States since 1995. The February 8th 1998, France authorized the cultures of Maïs LT and this variety was registered, a first for a GMO, with the official catalog of the species and varieties, reverted decision temporarily in September of the same year by the Council of State, then restored in October 2000.

In France, the rejection of such varieties of corn by the consumer makes that this technique of fight remains little used by the farmers.

It also seems that the bee moth can develop resistances to the GMO in the long term, following the example other Insects. The American regulation thus recommends to mix seeds GMO with traditional seeds (20%) or to alternate morsels of corn conventional with morsels of corn LT. These recommendations take again the principles of a strategy known as " high amount/zone refuge" formulated to avoid or delay the recessive gene diffusion of resistance. This strategy is founded on the postulate that in a situation of proximity of the sensitive populations (bee moths resulting from the zones refuges consisted conventional corn not LT) and of the resistant populations (possibly resulting from corn LT) the rare resistant individuals have a high probability to couple themselves with sensitive individuals. In this case, the hybrid descent is of significant phenotype because of the recessive character of resistance and thus will be eliminated if it tries to develop on corn LT.

However, of recent work of the INRA showed that the adults of bee moth move little during the period previous the coupling. These data call in question this method of fight against resistance in the case of the Bee moth since the physical proximity of the pieces LT and not LT would not be a sufficient guarantee of genetic mixing between sensitive and resistant individuals.

It is also advisable to stress that the surface dedicated to the zone refuge - 25% of entire surface and any treatment applied - does not correspond to the recommendations which had been provided by the consulted scientific organizations but to an American administrative decision; which at summer retranscribed in Europe.

The pledges of confidence provided by the seed-bearer companies and the European and national administrations are thus to consider with prudence.

Internal bond

  • List of the ravageurs of the crop plants

External bonds

  • Management of resistances to '' LT '': The device of the zones refuges for corn LT in the United States
  • the biological fight using Trichogrammes

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