Technical Abstract: Although mated females of the western tarnished plant bug, Lygus hesperus, are known to produce more eggs than virgins, the nature of the inducing stimuli and the specific changes occuring in the female required additional elucidation. Compared to virgin females isolated from males, those exposed to male precopulatory behaviours produced similar numbers of eggs, while inseminated females produced 50% more. Although the quantity of seminal fluids recieved by a female did not influence egg mating more than twice during the same period did not exhibit additonal benefits. Because virgin females were found to contain more chorionated eggs than were oviposited, mating appeared to enhance the rate of deposition. However, to achieve a sustained increase in fecundity, an augmented rate of oocyte maturation would also be required. Male-derived spermatophores were found to lack substantive quantities of nutrients that might otherwise have enhanced female fecundity. The macro and micrinutrients transferred by yhe male are insufficient for producing even a single egg, and the female has already produced a large number of chorionated oocytes before she mates. Collectively, the data sugges that seminal fluid contains an activational molecule, such as peptide, which triggers and increas in egg deposition. A prolonged increase in oviposition rate may be achieved through multiple matings to ensure a supply of sperm or to offset the degradation of the putative activational factor.