wherein r1 represents an optionally substituted 5 - 6 membered aromatic hetero ring containing nitrogen atom , except a non - substituted 2 - pyridyl ; r2 represents a hydrogen , a carbamoyl , a mono or di c1 - 5 alkyl carbamoyl , a thiocarbamoyl , a mono or di c1 - 5 alkylthiocarbamoyl , a sulfamoyl , a mono or di c1 - 5 alkylsulfamoyl , an optionally substituted c1 - 5 alkyl , an optionally substituted c2 - 5 alkenyl , an optionally substituted c2 - 5 alkynyl , an optionally substituted c3 - 8 cycloalkyl , an optionally substituted c3 - 8 cycloalkenyl , an optionally substituted aryl or - y - r5 ; r5 represents a hydrogen , an optionally substituted c1 - 5 alkyl , an optionally substituted c2 - 5 alkenyl , an optionally substituted c2 - 5 alkynyl , an optionally substituted c3 - 8 cycloalkenyl or an optionally substituted aryl ; r3 represents a hydrogen , an optionally substituted c1 - 5 alkyl , an optionally substituted c2 - 5 alkenyl , an optionally substituted c2 - 5 alkynyl , an optionally substituted c3 - 8 cycloalkyl or an optionally substituted c3 - 8 cycloalkenyl ; the present invention provides a method of protecting a crop by combatting eggs of insects susceptible to damage the said crop whereby an effective amount of a compound of formula ( i ), or a salt thereof , is applied at a locus where there are eggs or where eggs are expected to be present or where eggs are expected to be going to be present . according to the invention it has also been found ovicidal compositions which comprise an effective amount of a compound of formula ( i ) or a salt thereof . the present invention provides a method of protecting a crop by combatting eggs of insects susceptible to damage the said crop whereby an effective amount of an ovicidal composition as already defined is applied at a locus where there are eggs or where eggs are expected to be present or where eggs are expected to be going to be present . another feature of the present invention is that an ovicidal composition is applied at a locus where a crop is growing , especially a plantation crop , more especially cotton . the method of the invention is particularly appropriate to kill or control the following insects at the egg stage : tobacco budworm ( heliothis virescens ), mexican bean beetle ( epilachna varivestis ), colorado potato beetle ( leptinotarsa decemlineata ). the method of the invention is especially advantageous to kill tobacco budworms , at the egg stage , which are resistant to pyrethroids . the method of the invention is particularly appropriate to protect cotton crop from tobacco budworm or pyrethroid resistant tobacco budworm , beans and soybean from mexican bean beetle , potato crop from colorado potato beetle . preferred active ingredients which may be used in the invention are those wherein : the preparation of compounds of formula ( i ), or a salt thereof , may be made according to any process described in patent application wo 91 / 04965 , or other process according to the knowledge of a man skilled in the art of chemical synthesis . the disclosure of wo 91 - 4075 is in toto incorporated herein by reference . by the term &# 34 ; eggs &# 34 ; as used in this specification , it is to be understood eggs which are in their simple state laid upon the soil or on the plant or eggs which are inside pregnant insect . most of the eggs which are to be killed according to the present invention are eggs upon leaves , so that the method whereby an active ingredient of formula ( i ), or a salt thereof , is applied is also a treatment of leaves of crops . the invention enables compounds of formula ( i ), or salts thereof , to combat insects , especially the tobacco budworm , at the egg stage before they reach the damaging later stages . thus , compounds of formula ( i ), or salts thereof , are applied to the locus to be treated before substantial infestation with tobacco budworm larvae occurs . for instance , on cotton plants , an ovicidal composition comprising a compound of formula ( i ), or a salt thereof , should be applied to eggs before applying it to the larval stage , preferably 4 to 7 days before one would first apply such a composition to the larval stage of tobacco budworm . the ovicidal compositions of the invention may be applied once , or more than once . thus , for some crops one may apply the ovicidal compositions periodically through the insects season . usually ovicidal compositions according to the invention are applied to the crop area at a rate of 0 . 04 to 2 kg / ha of active ingriedent , preferably 0 . 1 to 1 kg / ha . ovicidal compositions according to the invention may be applied in a manner which is safe for the crop . the ovicidal concentrated compositions according to the invention may be in the form of a solid , e . g . dusts or granules or wettable powders , or , preferably , in the form of a liquid , such as an emulsifiable concentrate or a true solution . the concentrated compositions are the compositions which are commercialized or transported or stored . for application to plant they are normally diluted in water and applied in such a diluted form . the diluted form are part of the invention as well as the concentrated forms . the concentrated ovicidal compositions of the inventions contain generally from 0 . 001 to 90 % of active ingredient of formula ( i ), or a salt thereof . a concentrate may contain from 5 to 90 % of active ingredient . parts and percentages in this specification are by weight unless otherwise indicated . the ovicidal compositions may also contain all kind of compatible surface active agent and / or carrier . the agriculturally acceptable carrier may be solid or liquid . the composition may further contain a fertilizer . the compounds of formula ( i ), or a salt thereof , may be used in sequence or admixture , particularly admixtures with another pesticide e . g . an insecticide , acaricide or fungicide . ( 6 - cl pyrid 3 - yl )- ch2 - n ( ch3 )- c ( ch3 )═ n - cn was dispersed in a mixture of acetone / surfactant / dimethylformamide and then diluted in water . strips of cheese cloth which contained about 30 to 40 one day old eggs of tobacco budworm were used . they were eggs of tobacco budworm non resistant to pyrethroids . the aqueous dispersion of active ingredient was sprayed upon the eggs . the application condition were such that a 1000 ppm concentration corresponds to an application rate of 188 g / ha on the crop . the observation of the obtained results was made three days after spraying . the dead eggs are brown and do not hatch ( they normally hatch about 3 to 4 days after being laid down ). a lethal dose killing 90 % of the eggs was found at 1000 ppm . a lethal dose killing 50 % of the eggs was found at 230 ppm . example 1 was repeated , except that eggs of pyrethroids resistant tobacco budworm were used . a lethal dose killing 64 % of the eggs was found at 250 ppm ( 6 - cl pyrid 3 - yl )- ch2 - n ( ch3 )- c ( ch3 )═ n - cn was dispersed in a mixture of acetone / surfactant / dimethylformamide and then diluted in water . strips of bean plant leaves bearing about 65 one day old eggs of mexican bean beetle were used . the aqueous dispersion of active ingredient was sprayed upon the eggs , the application condition were such that a 1000 ppm concentration corresponds to an application rate of 188 g / ha on the crop . the observation of the obtained results was made three days after spraying , the dead eggs are brown and do not hatch ( they normally hatch about 7 days after being laid down ). a lethal dose killing 100 % of the eggs was found at 250 ppm . ( 6 - cl pyrid 3 - yl )- ch2 - n ( ch3 )- c ( ch3 )═ n - cn was dispersed in a mixture of acetone / surfactant / dimethylformamide and then diluted in water . strips of egg plant leaves bearing about 20 one day old eggs of colorado potato beetle were used . eggs of beetles resistant as well as non resistant to pyrethroids were used . the aqueous dispersion of active ingredient was sprayed upon the eggs . the application condition were such that a 1000 ppm concentration corresponds to an application rate of 188 g / ha on the crop . the observation of the obtained results was made three days after spraying . the dead eggs are brown and do not hatch ( they normally hatch about 5 days after being laid down ). a lethal dose killing 100 % of the eggs of both type of beetles was found at 250 ppm .
a method has been found for protecting a crop by killing eggs of insects , or insects at the egg stage wherein the insects are detrimental to the crop . this method comprises applying to a locus where the eggs of insects are located or are expected to be located an effective amount of a compound of formula , or a salt thereof , r1 - x - n - c ═ z - r4 wherein r1 represents an optionally substituted aromatic hetero ring containing nitrogen atom ; x represents an optionally substituted alkylene or alkylidene ; r2 and r3 represent hydrogen or optionally substituted alkyl ; r4 represents a cyano or a nitro , and z represents ch or n . the insect eggs which can be killed include tobacco budworms , pyrethroid resistant tobacco budworm , mexican bean beetle or colorado potato beetle .