The effect of humidity on the development and survival of the immature stages of strains of Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae) at constant temperatures

The influence of humidity on the development and survival of a large, an intermediate and a small strain of Oryzaephilus surinamensis (L.) on kibbled wheat was studied. Three humidities, 30, 50 and 70% r.h., were used, over the temperature range of 17.5–35°C. At 17.5°C, eggs of the large and intermediate strains hatched at each humidity whereas the eggs of the small strain failed to hatch at humidities below 70% r.h. Larvae of all three strains died at 17.5°C, 30% r.h. At 17.5°C, 50 and 70% r.h., as well as at 20 and 35°C at 30% r.h., larval survival was higher for the large than for the two smaller strains. At 17.5°C, 50 and 70% r.h., pupae of all strains died as did those of the intermediate and small strains at 20°C, 30% r.h. Pupal survival was relatively high for the large strain over the range 22.5–35°C at 30% r.h. The pupal survival of each strain decreased with decreasing humidity even at temperatures favourable for development.