Effect of temperature on the phenology of Chilo partellus (Swinhoe) (Lepidoptera, Crambidae); simulation and visualization of the potential future distribution of C. partellus in Africa under warmer temperatures through the development of life-table parameters (plus corrigendum)

Maize (Zea mays) is a major staple food in Africa. However, maize production is severely reduced by damage caused by feeding lepidopteran pests. In East and Southern Africa, Chilo partellus is one of the most damaging cereal stem borers mainly found in the warmer lowland areas. In this study, it was hypothesized that the future distribution and abundance of C. partellus may be affected greatly by the current global warming. The temperature-dependent population growth potential of C. partellus was studied on artificial diet under laboratory conditions at six constant temperatures (15, 18, 20, 25, 28, 30, 32 and 35 degrees C), relative humidity of 75 +/- 5% and a photoperiod of L12:L12 h. Several non-linear models were fitted to the data to model development time, mortality and reproduction of the insect species. Cohort updating algorithm and rate summation approach were stochastically used for simulating age and stage structure populations and generate life-table parameters. For spatial analysis of the pest risk, three generic risk indices (index of establishment, generation number and activity index) were visualized in the geographical information system component of the advanced Insect Life Cycle modeling (ILCYM) software. To predict the future distribution of C. partellus we used the climate change scenario A1B obtained from WorldClim and CCAFS databases. The maps were compared with available data on the current distribution of C. partellus in Kenya. The results show that the development times of the different stages decreased with increasing temperatures ranging from 18 to 35 degrees C; at the extreme temperatures, 15 and 38 degrees C, no egg could hatch and no larvae completed development. The study concludes that C. partellus may potentially expands its range into higher altitude areas, highland tropics and moist transitional regions, with the highest maize potential where the species has not been recorded yet. This has serious implication in terms of food security since these areas produce approximately 80% of the total maize in East Africa

Effect of temperature on the life history parameters of noctuid lepidopteran stem borers, Busseola fusca and Sesamia calamistis

The influence of temperature on the development, mortality, fecundity and life table parameters of two important noctuid African cereal pests, Busseola fusca and Sesamia calamistis was investigated under laboratory conditions. Experiments were carried out with larvae reared on artificial diet under eight constant temperatures (12 degrees C, 15 degrees C, 18 degrees C, 20 degrees C, 25 degrees C, 28 degrees C, 30 degrees C and 35 degrees C) and a 12L:12D photoperiod. Life table parameters were calculated using Insect Life Cycle Modelling (ILCYM) software. At 12 degrees C and 35 degrees C insects failed to develop. Mean development time for both species decreased with increasing temperature for all stages. Between 15 degrees C and 30 degrees C, mean larvae development time is divided by four for both species and adult mean longevity is divided by 1.5 and 2.5, for both sexes of S. calamistis and B. fusca, respectively. Fecundity varied according to temperature; the highest was estimated at 22 degrees C and 24 degrees C for B. fusca and S. calamistis, respectively. The lower thermal threshold for B. fusca and S. calamistis was, respectively, 6 degrees C and 9 degrees C, while the upper thermal threshold was 31 degrees C and 32 degrees C, respectively. The highest intrinsic rate of natural increase for B. fusca was obtained at 25 degrees C while for S. calamistis it was obtained at 28 degrees C. The highest net reproduction was obtained at 25 degrees C for both species, but it was higher for S. calamistis than for B. fusca. The shortest population doubling time was observed at 25 degrees C for B. fusca and at 28 degrees C for S. calamistis. The optimum temperature range for development of both species was 25-28 degrees C. The lower lower thermal threshold found for B. fusca than for S. calamistis and the higher upper thermal threshold found for S. calamistis than for B. fusca explain in part the observed distribution of both species in sub-Saharan Africa with S. calamistis occurring in all the agro-ecological zones but being usually more common than B. fusca in savannah lowland and B. fusca reported mainly from mid and high altitude areas