1. Method for controlling a population of social insects such as ants, wasps or cockroaches characterized in that an effective amount of a insecticide composition comprising a bait and a compound of formula (I):   in which: R1 is a halogen atom, CN or methyl; R2 is S(O)nR3; R3 is alkyl or haloalkyl; R4 represents a hydrogen or halogen atom; or a radical NR5R6, S(O)mR7, C(O)R7 or C(O)O-R7, alkyl, haloalkyl or OR8 or a radical -N=C(R9)(R10); R5 and R6 independently represent a hydrogen atom or an alkyl, haloalkyl, C(O)alkyl, S(O)rCF3; or R5 and R6 may together form a divalent alkylene radical which may be interrupted by one or two divalent hetero atoms, such as oxygen or sulphur; R7 represents an alkyl or haloalkyl radical; R8 represents an alkyl or haloalkyl radical or a hydrogen atom; R9 represents an alkyl radical or a hydrogen atom; R10 represents a phenyl or heteroaryl group optionally substituted with one or more halogen atoms or groups such as OH, -O-alkyl, -S-alkyl, cyano or alkyl; R11 and R12 represent, independently of each other, a hydrogen or hafogen atom; R13 represents a halogen atom or a haloalkyl, haloalkoxy, S(O)qCF3 or SF3 group; m, n, q and r represent, independently of each other, an integer equal to 0, 1 or 2; X represents a trivalent nitrogen atom or a radical C-R12 the other three valency positions of the carbon atom forming part of the aromatic ring; with the proviso that when R1 is methyl, then R3 is haloalkyl, R4 is NH2, R11 is Cl, R13 is CF3 and X is N, characterised in that it is applied to a minor fraction of said population, and wherein said effective amount is such that the dose is equal to the dose required to destroy at least 90% of the minor fraction of the population of social insects to which said composition is applied, in a time between 2 and 30 days. 2. Method according to claim 1, characterized in that the controlled population of social insects is a population of ants. 3. Method according to claim 1, characterized in that the controlled population of social insects is a population of cockroaches. 4. Method according to claim 1, characterized in that  the treatment is conducted with dose equal to 0,0001 - 20g per 100m<2> of one or more frequented by, or assumed to be frequented by, the said social insects, the said area being outside the place of the said common dwelling but being a place in which the cockroaches circulate or are assumed to circulate. 5. Method according to any one of the preceding claims, characterized in that the anthill is treated with the dose of in between 0.05 and 50 mg per anthill, preferably in between 0.1 and 20 mg 6. Method according to any one of the preceding claims, characterized in that the bait employed is chosen from animal and/or plant proteins, or from fats, also of animal and/or plant origin, or from mono-, oligo- or polyorganosaccharides, in particular, sucrose, lactose, fructose, dextrose, glucose, molasses or honey. 7. Method according to any one of the preceding claims, characterized in that the compound of formula (I) used is 5-amino-3-cyano-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl)sulphinyl]-1H-pyrazole. 8. Method according to any one of the preceding claims, characterized in that the composition is applied to a fraction of the population which is between 1 and 40% of the total population, preferably between 2 to 20%. 9. Method according to any one of the preceding claims, characterized in that the controlled population of ants is a population of ants living in the same anthill. 10. Method according to Claim 9, characterized in that the minor fraction of the population to which the composition is applied consists of harvester workers from the anthill. 11. Method according to any one of the preceding claims, characterized in that the dose of compound of formula (I) in the composition is between 0.0005 and 0.5%, preferably between 0.001 and 0.2%. 12. Method according to any one of the preceding claims, characterized in that the dose of bait in the composition is between 1 and 99%, preferably between 30 and 99%. 13. Method according to any one of the preceding claims, characterized in that the composition is applied by placing it in a closed bait-carrier box containing openings which are reserved, on account of their size, for the exclusive use of ants or cockroaches, in an area where these are likely to be found. 14. Method according to Claim 13, characterized in that the area is in a public or private place, such as a living area, or alternatively on a balcony, a patio, in a garden or in a field.