A formulation for the biological control of pests comprises a cohort of infective juvenile insect-parasitic nematodes from at least three species, wherein at least two of the species are of a first genus, and at least one of the species is from a second genus, and the species number from the first genus is greater than the species number from the second genus. The cohort of nematodes consists essentially of two species from the first genus and one species from the second genus and comprises at least one ambusher foraging species of nematode from a first genera and at least two cruiser foraging species of nematode from a different genera, or at least two ambusher foraging species of nematode from the same genera and at least one cruiser foraging species of nematode from a different genera. The first and second genus are selected from the group comprising: Steinernematidae and Heterorhapditidae.
