The capacity for increase at a low temperature of some Australian populations of the granary weevil, Sitophilus granarius (L.)

The capacity for increase (rc) of one laboratory and seven field populations of young adult S. granarius from different sites in Australia was determined over thirty‐two weeks at 15°C in wheat of 14% moisture content. The mean value of rc was 0.0704 ±0.0016 and the populations differed significantly with respect to this parameter. Variation in the net reproductive rate (R0), which averaged 25.4± 1.29, had a greater effect on the value of Ic than did variation in the cohort generation time (Tc), which averaged 45.7±0.37 weeks. The populations did not differ significantly in terms of adult survivorship and 94% of females were still alive at thirty‐two weeks. The maximum rate of oviposition, about ten eggs per female per week, was achieved in the eighteen‐twenty week age‐interval. About 41% of the immature stages survived to adulthood. Estimates of rc over a twenty‐four week period were only slightly lower than those over thirty‐two weeks. The capacity for increase at 15°C of a given population was shown to be correlated with its fertility at 29°C, an optimal temperature, and with its body weight rather than with its cold tolerance, as indicated by its chill‐coma temperature, or its previous temperature‐history. The temperature experienced by the immature stages had a marked influence on rc in that weevils reared at 15°C and 27°C had respective values of 0.0654 and 0.0786 when subsequently held at 15°C. The differences in the survivorship and fertility of S. granarius and S. oryzae (L.) when both species were reared at 15°C are considered.