ABSTRACT.1Larval gypsy mothLymantria dispar(L.) mortality depends upon the number and type of plant species consumed as well as the sequence in which they are consumed.2When a two‐species diet is composed of a favourable and an unfavourable species, larval mortality is higher on the two‐species diet than on the diet of the favourable species alone.3When a two species diet is composed of a favourable and unfavourable coniferous species, larval mortality is higher on the single conifer species diet than on the two‐species diet.4Two‐species diets, in which one species is a conifer, produce individuals with a greater fecundity than diets of either species alone.5The influence of diets composed of two favourable species, on development, size and fecundity, depends both on the relative quality of each of the two plant species and which of the two is consumed by older