A cause and effect relationship was demonstrated between cotton leafworm,Alabama argillacea(Hübner), larval crowding, and increased parasitism by the pupal parasiteBrachymeria ovata(Say). In overcrowded conditions the larvae exhibited a conspecific-destructive reaction by resorting to eating the leaf covering from the pupae of their own species, thus destroying needed protection from natural enemies. The minimum larval density required before larvae consumed pupal leaf covers and exposed the pupae was l8.4/m of row, with a larval density of 142.l/m of row resulting in almost complete defoliation and consumption of most pupal covers. Parasitism of covered pupae byB. ovatawas 1.0 ± 0.6 to 4.9 ± 1.7%, whereas 30.3 ± 9.7 to 46.6 ± 6.2% of the exposed pupae produced under crowded conditions were parasitized. Intraspecific competition between the cotton leafworm larvae and pupae is unequal because the larvae have a marked effect on pupal survival, but there is no detectable, reciprocal effect on the larvae. In most cases of intraspecific competition, the relatively successful individuals are those that begin and complete development first. However, in the case of the cotton leafwonn, the opposite may be true.