Respiration Rates of Resproductively Active and Diapausing Boll Weevils
Low metabolism is a primary index of diapause in insects. Thus. rates of oxygen (O2) consumption and carbon dioxide (CO2) production are lower in diapausing than reproductive insects. To test this hypothesis, a respirometer was used to examine the age-, sex-, and food-dependent respiration rates of reproductive and diapausing boll weevils. CO2 rates of 97 females and 81 males were measured individually every second over 6-min periods at different ages up to 44 days. Weevils were held at about 275°C and fed squares or bolls. Observations indicated that respiration rates of reproductive females declined from about 1.74 to 1.05 µl/mg/hr between day 2 and 44. This decline was attributed to age-related changes in reproductive rates or metabolism. Rates of reproductive males declined in a similar fashion (from 1.50 to 0.76 µl/mg/hr), but reached a lower asymptote (extension of a line approaching a minimum) than females. In contrast, age-dependent rates of diapausing females and males were nearly identical, declining from about 1.73 µl/mg/hr on day 1 to an asymptote of about 0.38 µl/mg/hr. Thus, rates declined more sharply and to a lower asymptote in diapausing than reproductive weevils; e.g., 61% and 54% lower for diapausing than reproductive females and males, respectively. Using 95% confidence intervals to determine the age of separation between reproductive and diapausiag adult. respiration rates, divergence first appeared on day 3 for females and day 10 for males. The delay in separation for males was due to suppressed respiration rates of reproductive males compared to females. Respiration was more variable in reproductive than diapausing adults probably hecause of differences in reproductive rates among individuals and a greater capacity for these adults to respond to changing environments. Adult feeding on squares or bolls did not influence respiration.