Effect of temperature and relative humidity on the development and fecundity of Chilo partellus (Swinhoe) (Lepidoptera: Crambidae)

The spotted stemborer, Chilo partellus (Swinhoe) (Lepidoptera: Crambidae), is one of the most important insect pests attacking maize and sorghum in Ethiopia. Recent studies have indicated that the pest is spreading to new locations where it was not reported before. In the current study, laboratory investigations were carried out to determine the combined effect of different levels of relative humidity and temperature regimes on the development and fecundity of C. partellus, as these physical factors are known to play an important role in the life cycle of insects and adaptability to local climate. Developmental time, longevity, potential fecundity and realized fecundity of C. partellus were measured under controlled conditions. Three temperature regimes (22 degrees C, 26 degrees C and 30 degrees C) and three relative humidity levels (40%, 60% and 80%) were tested. It was found that temperature, relative humidity (RH) and their interaction significantly affected the developmental time, adult longevity, potential fecundity and realized fecundity of the pest. Developmental time was inversely related to temperature. Mean duration of C. partellus life cycle was 70.2 days at 22 degrees C and 80% RH, whereas it took only 26.5 days to complete its life cycle at 30 degrees C and 40% RH. Male and female longevity were similar in most cases. The adult life span ranged between 6.9-11.1 days at 22 degrees C and 3.1-7.2 days at 30 degrees C for different levels of relative humidity. The most suitable conditions for C. partellus development and fecundity were 26-30 degrees C temperatures regimes and 60-80% RH levels.