The Effects of Food Quality on the Life History Tactics of the American Cockroach, Periplaneta americana

Abstract

The American cockroach, Periplaneta americana, is an abundant and globally distributed species. Much of its success is attributed to its remarkable ability to alter rates and utilization efficiencies of behavioural and physiological processes so as to maintain growth and reproduction within nutritionally variable environments. This study utilized artificial diets diluted with cellulose to investigate the impact of food quality on the life history tactics of this species and the compensatory mechanisms involved in offsetting these impacts. To investigate the impact of diet quality on the life history tactics of the American cockroach, seven dietary regimes were implemented. The control condition consisted of an unaltered 100% quality diet. The remaining six treatments were diluted with cellulose resulting in diet qualities of 50%, 25%, 10%, 5%, 2.5%, and 0%. The parameters examined included mortality, longevity, instar number, instar durations, growth, maturation dates, maturation sizes, dry mass budgets, and reproduction. The dry mass budgets involved observations of growth rate, feeding rate, assimilation rate, respiration rate, assimilation efficiency, efficiency of conversion of ingested food into biomass, and efficiency of conversion of digested food into biomass. Reproductive studies entailed observations of oothecal production, oviposition intervals, inter-oviposition intervals, mass of oothecae, oothecal dimensions, egg number, oothecal cannibalism, and hatching dates. Strongly canalized development was achieved by resilient compensatory responses indicative of altered physiological and behavioural features. Cockroaches developed and reproduced adequately even when nutrient concentration was reduced to 25% of the controls. The declines in various key parameters were considerably less than expected from the degree of dietary dilution. In addition, elevated consumption and enhanced conversion efficiencies strongly suggest that cockroaches normally function at submaximal levels. The applied relevance of this research entails possible ramifications into the regulation and control of cockroaches. Furthermore, such knowledge enhances our understanding of not only diverse lifestyles but also the degree of variability to which insects may modify life history features in response to resource supply.