The effect of temperature on the development and reproduction of Busseola fusca (Lepidoptera: Noctuidae)
Busseola fusca is an indigenous lepidopteran pest species in tropical Africa, attacking several grain crops. Crop loss caused by this pest can be as high as 100% depending on conditions. Despite it being a major pest in Africa, occurring in contrasting climatic zones, only a few studies have been published on its developmental biology. The effect of temperature on the development of B. fusca was studied at five different temperature regimes namely 15, 18, 20, 26 and 30 ± 1 °C and 70 ± 30 % relative humidity (RH) with 14L: 10D photoperiod. The number of instars for B. fusca was also determined. The most favourable temperature as well as the upper threshold temperature for larval development was found to be between 26 and 30 °C. Total development period was 152.6 to 52.6 days, respectively, at 15°C, and 26 - 30°C. The thermal constants for B. fusca was 99.50, 536.48, 246.25 and 893.66°D and lower temperature threshold was 10.36, 8.14, 8.99 and 8.84°C, for completion of the egg, larval, pupal, and egg-to-adult stages, respectively. The number of larval instars was determined by using head capsule widths that ranged from 0.31 - 2.68 mm. Clear distinctions of head capsule widths could be made from instar 1 to 3, yet overlapping occurred from instar 4 to 6. No distinction could be made between instars 7 and 8 in terms of head capsule width. All successive instars, except for instar eight, increased in size according to Dyar’s ratio. The effect of temperature on reproduction of B. fusca was studied at 15, 20, 26 and 30 ± 1°C, 70 ± 30% RH with 14L: 10D photoperiod. Oviposition occurred at all the temperatures evaluated, but no fertility was recorded at 30°C. The total number of eggs laid by B. fusca females was 300 - 400 eggs and the optimum temperature for oviposition and fertility was determined to be between 20 and 26°C. Results from this study on the thermal constants and lower and upper threshold temperatures of B. fusca can be used to predict the impact of climate change on the distribution and population growth of this pest.