Diversity and abundance of wild host plants of lepidopteran stem borers in two agro-ecological zones of Kenya

Abstract

A survey was carried out between 2005 and 2006 in two ecologically different localities, Suam and Mtito Andei, to assess diversity and abundance of wild host plants of lepidopteran stem borers during the cropping and non-cropping seasons. Suam in western Kenya is situated in the moist high tropics and is characterised by an Afromontane vegetation mosaic, while Mtito Andei is located in the dry mid-altitudes characterised by a Somalia Masai vegetation mosaic. In Suam, wild host plants and maize covered 11 and 50%, respectively, of the surveyed area. In Mtito Andei, 27% of the surveyed area was under maize during the cropping season, while wild host plant species covered 13% and 8% during the cropping and non-cropping seasons, respectively. There was no significant variation in the relative abundance and diversity of the wild grasses between the two seasons in either location. The abundance of host plants of B. fusca and C. partellus is low in natural habitats surrounding cereal crops. The abundance of C. partellus was low in its wild host plants and B. fusca was absent. Therefore, the role of wild vegetation surrounding cultivated areas in the carry-over of these pests during the non-cropping season is limited.

Factors Affecting Stem Borer Parasitoid Species Diversity and Parasitism in Cultivated and Natural Habitats

“…In line with the resource concentration hypothesis (Root 1973) and previous results by Ndemah et al (2007) and Matama-Kauma et al (2008), stem borer density was generally low in natural habitats. Low stem borer host abundance in this study coupled with a high density of nonhost plant species in natural habitats existing in the same localities (Otieno et al 2006(Otieno et al , 2008 suggests host Þnding difÞculty of parasitoids in such habitats (Chabi-Olaye et al 2005). Moreover, parasitoids exhibit low Þtness and high mortality on wild host plants, as a consequence of low nutrition (Sé tamou et al 2005) and/or toxic phytochemicals or secondary plant compounds (Ode 2006).…”

“…Suam is a major production region, where 50% of the area is under cereal cultivation at commercial scale, mainly with an average Þeld size of 3.4 ha. The area under natural habitats was 50%, of which the total relative cover of all potential wild host plants of stem borers was 11.2 and 10.9% during the rainy and dry seasons, respectively (Otieno et al 2008). Human settlement was clearly separated from cultivated areas, with very few wild grass patches found mainly along Þeld edges and road sides.…”

“…Area under cereal cultivation was 27.3%, with an average Þeld size of 0.37 ha mainly found surrounding sparsely populated and distant homesteads. The area of natural habitats was 72.7%, of which the total relative cover of all potential wild host plants of stem borers was 13.0 and 8.0% during the rainy and dry seasons, respectively (Otieno et al 2008). Wild grass patches were generally small and few, mainly existing in water trenches bordering crop Þelds or in swamps and along irrigation canals.…”

Species richness and nest dispersion of some tropical meliponine bees (Apidae: Meliponinae) in six habitat types in the Kakamega forest, western Kenya

“…In each studied habitat (homestead, forest type and grassland), a 30 ha area was surveyed using continuous line transect methods (Krebs, 1999;Jongjitvimol et al, 2005;Otieno et al, 2008). Thirty line transects, 500 m long and 20 m apart, were followed in each habitat during the search for stingless bee nests.…”

Do Larvae of Species in Macrolepidopteran Assemblages Share Traits That Influence Susceptibility to Parasitism?

“…Suam is a major production region, where 50% of the area is under cereal cultivation at commercial scale mainly with an average field size of 3.4 ha. The area under natural habitats was 50%, of which the total relative cover of all potential wild host plants of stem borers were 11.2% and 10.9% during the rainy and dry seasons, respectively (Otieno et al 2008 Area under cereal cultivation was 27.3%, with an average field size of 0.37 ha mainly found surrounding sparsely populated and distant homesteads. The area of natural habitats was 72.7%, of which the total relative cover of all potential wild host plants of stem borers were 13.0% and 8.0% during the rainy and dry seasons, respectively (Otieno et al 2008).…”