Abundance of insect pests and their effects on biomass yields of single vs. multi-species planted fallows

Abstract

Indigenous and exotic leguminous shrubs that are promising for planted fallow for soil fertility replenishment in east and southern Africa have been found to harbour many herbivorous insects, giving suspicion that widespread adoption of fallow systems may aggravate insect pests. Studies were conducted on farms in western Kenya from 1999 to 2001 to monitor the abundance of herbivorous insects and assess their effects on biomass yields of pure and mixed fallows. The treatments tested were single and two-species mixtures of Tephrosia vogelii, Sesbania sesban and Crotalaria grahamiana and a natural fallow in a split plot design, with the fallow systems in the main plots and protection vs. no protection against insects in sub-plots spread over six farms. Eighteen insect species belonging to seven orders and 14 families were identified as pests of the fallows with varied abundance and infestation level across the sites. While Hilda patruelis and Amphicallia pactolicus were most damaging to C. grahamiana, Mesoplatys ochroptera was detrimental to S. sesban. T. vogelii hosted fewer insects than others. Nevertheless the pest infestation did not cause significant biomass yield reduction during the study period. Pest attack was generally greater in villages that had been testing the planted fallows for some years compared with villages that took up the fallows recently. This indicates the potential for increased pest infestation with increased adoption of the system by farmers. Multi-species fallows did not indicate any advantage over single species fallows in terms of either reduced pest incidence or increased biomass production.

Potential of improved fallows to increase household and regional fuelwood supply: evidence from western Kenya

“…The consistent superior performance of T. candida across these two regions that contrast sufficiently well in their agro-ecologial conditions indicates its robustness and potential to meet expected fuelwood production levels. The fuelwood yield from 12 month-old T. vogelli and C. grahamiana fallow observed in our study were, somewhat surprisingly, higher than those reported by Girma et al (2006) in the same study area but under researcher management. In part, these differences could be explained by the higher stand densities used by the farmers (see section on 'stand density').…”

“…More research, however, is needed to establish and better predict the most appropriate fallow stand density for different species and ages. In addition, there is a need to further explore the potential of mixing species, since this may reduce the risk of loss of a single species stand due to pests and diseases (Girma et al 2006) or the risk of a single species failing to establish well (Gathumbi et al 2004). Sub-national fuelwood supply potential…”

The Role of Trees in Agroecology and Sustainable Agriculture in the Tropics

“…However, there has been concern that some leguminous shrubs also harbor insect herbivores. However, when pure and mixed-species legume fallows were tested there was no evidence of serious biomass loss due to herbivory (41). Tephrosia fallows had the lowest population densities of 18 species recognized as pests of fallows.…”

Effects of crop species richness on pest-natural enemy systems based on an experimental model system using a microlandscape

“…Fortunately, biomass analysis, a method that mainly considers material recycling and energy flow, provides an effective method which can be used to study predator-prey interactions related to agricultural plants, associated pest species and the natural enemy species of agricultural pests. Thus, we can place all species in one trophic level into a group and analyze the tri-trophic interactions (plant, pest, and natural enemy) [13,14].…”