The ecological success of the desert pocket mouse (Perognathus penicillatus Woodhouse) as influenced by methyl parathion

Abstract

An 18 month field and laboratory study was conducted on the behavioral effects of methyl parathion (MP), an organophosphorus insecticide, on the desert pocket mouse (Perognathus penicillatus). The study was conducted in the northern Chihuahuan desert at and near Presidio, Texas. Applications of three pints/acre (ten or eleven per season) of MP caused no noticeable effects on natural history parameters in the field. Intense air and soil temperatures and ultraviolet radiation probably shortened the persistence of the compound. Little MP accumulated in environmental components including the desert pocket mouse. Population densities were similar between a population exposed to MP and one not exposed. Both populations fluctuated seasonally. Production of young began in March and continued through October. Females produced an average of 3.8 young per litter and probably two litters per year. Availability of seeds fluctuated seasonally. Large amounts were available during the summer but only small quantities were available during the winter. Availability of food was reflected in most of the behavioral parameters investigated. The field results were corroborated in the laboratory. Caged mice assimilated 1.9 g (12.9% of the body weight) of seeds per day. This was an exposure rate of 0.29 ppm (parts per million) MP per day. Little accumulation occurred at this rate. Higher concentrations resulted in higher accumulations. These higher exposures resulted in decrements in exploration, caching of food, agonistic behavior, and burrowing. Field exposures had no significant effects. The dependence upon stereotyped behavior patterns by desert pocket mice was elucidated. I concluded that MP, applied at recommended rates, in the Chihuahuan desert does not persist and poses little danger to primary consumers in a desert situation.