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Ten 4,7-methanoisobenzofuran-1(3H)-ones were synthesized and their insecticidal activities against the insect pest Diaphania hyalinata were evaluated. The most active substances have been selected from the initial screening to find the dose to kill 50 (LD50) and 90% (LD90) of the melonworm. Time-mortality curves of the three selected formulations at the LD90 concentration have been made against D. hyalinata. From the time-mortality curves we found that the formulation (3aR,4R,5S,6S,7S,7aS)- and (3aS,4S,5R,6R,7R,7aR)-5,6-dichlorohexahydro-4,7-methanoisobenzofuran-1(3H)-one + (3aR,4R,5R,6R,7S,7aS)- and (3aS,4S,5S,6S,7R,7aR)-5,6-dichlorohexahydro-4,7-methanoisobenzofuran-1(3H)-one has killed 50% of the melonworm after 2 h, presenting the best knockdown effect. Bioassays against Solenopsis saevissima and Tetragonisca angustula were carried out for the lactones selected in the initial screening against D. hyalinata. The formulation (3aS,4R,5S,6S,7S,7aR)- and (3aR,4S,5R,6R,7R,7aS)-5,6-dibromohexahydro-4,7-methanoisobenzofuran-1(3H)-one + (3aS,4R,5R,6R,7S,7aR)- and (3aR,4S,5S,6S,7R,7aS)-5,6-dibromohexahydro-4,7-methanoisobenzofuran-1(3H)-one has killed 31.25 and 68.30% of the pest natural enemy and the pollinator bee, respectively. At the same concentration this formulation killed 90% of D. hyalinata. The selectivity in favor of the non-target organisms has rendered this formulation a position as a promising agrochemical.