(1) This paper reports (a) the differential extinction and persistence of 3-liter mass populations following the addition of 10 ppm of 6 derivatives of biodegradable carbamate and organophosphorus pesticides, (b) the reproductive performance of Artemia pairs removed from the 6 treated populations after 24 hours, and (c) reproduction tests of pairs from the populations surviving an overwintering evaporation cycle. (2) Life span was decreased to some degree for adults treated with any of the 6 tested derivatives of "degradable" pesticide. A concomitant decrease in life time totals of offspring can explain the results for 3 of the compounds. (3) The reproductive performance is further curtailed by cytogenetic destructive action of naphthalene and carbamate types of compounds on gametes and zygotes. The implied mode of action is on dividing cells. Furthermore, related naphthalene compounds are spindle poisons. (4) An adequate "standing crop" of adults is no assurance of survival of the population. More significant is the presence of either live larvae or viable cycts. The latter are especially important if the culture is subjected to periodic evaporation as is typical of many natural salterns. (5) Appreciable improvement in the components of reproductive fitness was observed for surviving populations a year after the initial treatment.