Since the appearance of the stem borer Chilo partellus (Swinhoe) on
the African continent in 1932, it has continuously expanded its distribution in
the warm, low-altitude regions of eastern and southern Africa. The current study
revealed that C. partellus is expanding its distribution into the high
elevations of the eastern Highveld region of South Africa. The only stem borer
already found there (elevation 1,600 m) is Busseola fusca (Fuller). C.
partellus, having invaded the region, rapidly increased its share of the
total borer population every year. On maize, it reached 32% of the total borer
population within 6 years and on grain sorghum 59% within 7 years. The most
rapid population increase by C. partellus occurred on the ratoon grain
sorghum crop. Within 2 years it became the predominant borer, constituting ± 90%
of the total stem borer population.
Chilo partellus has proven to be a very efficient colonizer, and it
seems to be displacing the indigenous B. fusca. C. partellus survives
the dry winters (with subzero temperatures) of the Highveld region in South
Africa by diapausing low in the dry stalks, often beneath the soil. Hibernating
larval populations of C. partellus terminate diapause and emerge as
moths ± 1 month earlier than B. fusca. This enables C.
partellus to infest the grain sorghum ratoon crop before B. fusca,
thus becoming the predominant borer in this niche. The life cycle of C.
partellus is 3 weeks shorter than that of B. fusca, which gives it
a further competitive advantage because of its higher potential rate of
increase.
For more detail see:
Kfir, R. 1997. Competitive
Displacement of Busseola fusca (Lepidoptera: Noctuidae) by Chilo
partellus (Lepidoptera: Pyralidae). Annals of the Entomological Society of
America 90: 619-624
