Effect of Temperature on the Synchrony of Stem Borer Pests and their Associated Larval Parasitoids

Abstract

This study was undertaken to establish the effect of temperature on the development and survival of B. fusca, S. calamistis and C. partellus and their larval parasitoids The stem borers and the larval parasitoids were reared at 200C, 250C, 280C and 300C and their development time, survival, fecundity and longevity were recorded. These parameters were subjected to analysis of variance (ANOVA) in General Linear Model (GLM). Results showed that development of stem borer larvae varied among different temperature regimes (F3,367=105.3; P<0.0001), B. fusca (F3,451=66.43; P<0.0001), S. calamistis(F3,540=887.8; P<0.0001).C. partellus. Development time of B. fusca larvae decreased with increase in temperature with the longest and shortest time recorded at 200C (78.30 days) and 300C (36.8 days) respectively. In S. calamistis larvae, the development time reduced with increase in temperature with mean larval duration ranging between 34.6 days (300C) to 48.1 days (200C). In C. partellus there was a decrease in larval development time (days) as the temperature increased. The longest development time, 57.4 days, was observed at 200C while the shortest, 22.2 days, was recorded at 300C. There was a significant influence of temperature on the development of C. sesamiae Kitale (F3,139=125.6; P<0.001), C. Sesamiae Mombasa (F3,148=246.1; P<0.001) and C. flavipes (F3,187=719.7; P<0.001). Among C. sesamiae Kitale, mean total development time ranged between 17.8 days (280C) to 29.7 days (200C), while among C. sesamiae Mombasa, the highest and lowest mean total development time varied between 29.4 days (200C) and 17.0 days (280C) respectively. In C. flavipes, mean total development time varied between 15.0 days (300C) and 31.4 days (200C). Temperature affected the host-parasitoid synchrony between stem borers and their associated larval parasitoids as reflected in the variations in respective life table parameters. Biological control of B. fusca, S. calamistis and C. partellus is likely to be affected by changes in temperature. Due to the increased development rate and survival of the stem borers coupled with reduced survival rates of the parasitoids associated with increase in temperature, biological control is likely to be less effective in areas with higher temperatures ranging between 250C to 280C.