The hormetic influence on silkworm, Bombyx mori L. (Lepidoptera: Bombycidae) of the juvenile hormone mimic ω-formyl longifolene oxime propargyl ether (NL13) was assayed. Emulsions containing 2.5, 5.0 and 10.0 ppm of the compound were administered topically as a single dose, to two popular commercial silkworm hybrids, viz. KA × NB4D2 and PM × NB4D2, at 24,48, 72 and 96 h into the 5th instar, and economic characters of the larvae and resultant cocoons measured. A medium and absolute control were maintained in parallel. It was found that administration of 5 ppm of NL13 to 48-h-old 5th instars resulted in the maximum improvement in commercial traits. The possible role of exogenous JH-like compounds in eliciting this response in silkworm is discussed.