Abstract
Habitat modification and fragmentation are considered as some of the factors that drive organism distribution and host use diversification. Indigenous African stem borer pests are thought to have diversified their host ranges to include maize [Zea mays L.] and sorghum [Sorghum bicolor (L.) Moench] in response to their increased availability through extensive cultivation. However, management efforts have been geared towards reducing pest populations in the cultivated fields with few attempts to understand possible evolution of "new" pest species. Recovery and growing persistence of Busseola segeta Bowden on maize (Zea mays L.) in Kakamega called for studies on the role of wild host plants on the invasion of crops by wild borer species. A two-year survey was carried out in a small agricultural landscape along the edge of Kakamega forest (Kenya) to assess host range and population genetic structure of B. segeta. The larvae of B. segeta were found on nine different plant species with the majority occurring on maize and sorghum. Of forty cytochrome b haplotypes identified, twenty-three occurred in both wild and cultivated habitats. The moths appear to fly long distances across the habitats with genetic analyses revealing weak differentiation between hosts in different habitats (FST = 0.016; p = 0.015). However, there was strong evidence of variation in genetic composition between growing seasons in the wild habitat (FST = 0.060; p < 0.001) with emergence or disappearance of haplotypes between habitats. Busseola segeta is an example of a phytophagous insect that utilizes plants with a human induced distribution range, maize, but does not show evidence of host race formation or reduction of gene flow among populations using different hosts. However, B. segeta is capable of becoming an important pest in the area and the current low densities may be attributed to the general low infestation levels and presence of a wide range of alternative hosts in the area.
Highlights
Natural ecosystems provide important habitats for a wide range of organisms
Though trade-offs associated with host use diversification have been evaluated in different contexts and applied in stem borer pest management, this study focused on the effects of fine scale host use diversification on genetic structure of a native phytophagous stem borer sub-species, Busseola segeta
Though the density of this moth is lower than economically important pest species in the area [25], the B. segeta moths did not exhibit genetic variation in terms of host use
Summary
Natural ecosystems provide important habitats for a wide range of organisms These habitats have been subjected to diverse forms of modifications over the past half century resulting in significant loss and fragmentation of natural ecosystems [1±4]. Organisms exposed to these modifications, phytophagous insects, exhibit a wide range of responses varying from host range expansion to local species extinction [5±8]. The ability of insects to utilize different host plants has been suggested to be a dynamic and transient phase [9]. During or after this phase, species can shift to novel host plants or re-specialize on ancestral ones.
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