Yield Losses Caused by the Stem-/Pod-Borer Complex Within Maize-Cowpea-Sorghum Intercropping Systems in Kenya
The present article considers quantitative assessment of crop losses in relation to attack by three trophic levels of insect pests on maize, cowpea and sorghum intercropping systems. The trophic levels considered are (i) specialist feeders subsisting only on one crop within the intercropping systems, e.g. Maruca testulalis (Geyer) on cowpea, and Atherigona soccata (Rondani) on sorghum; (ii) the relative specialist feeders subsisting on two out of the three crops e.g. Busseola fusca (Fuller), Chilo partellus (Swinh.) Sesamia calamistis (Hmps.) and Eldana saccharina (Wlk.) feeding on maize and sorghum cereal plants; and (iii) the generalist feeders e.g. Heliothis armigera (Hbn.) which feeds on all three plant species. Tests for loss assessment were done under natural field conditions within maize, cowpea, sorghum monocropping patterns; maize-cowpea, maize-sorghum, sorghum-cowpea dicropping patterns; and the maize-cowpea-sorghum tricrop intercropping patterns. The authors discuss in detail their modified analytical methods based on the comparison of yield of sets of plants growing under identical conditions except that one set is unattacked by the stem-/pod-borers and the other set attacked, to generate economic losses. The comparative advantages of the planting systems on crop turnover is further discussed. The biomass and plant population fluctuations caused by pest attacks and ‘dead hearts’ at differential time scales in indices of yield have also been discussed. Yield per unit area of monocrop and intercropping patterns have been contrasted using the yield turnover of monocrop plant equivalence as the baseline for comparisons. Maize-cowpea-sorghum mixed intercrop of 1.45 land equivalent ratio (LER), and that for the sorghum-cowpea dicrop with 1.3 LER are considered the most advantageous cropping patterns. Yield losses significantly higher (P < 0.05) within maize-sorghum intercropping combinations with 0.89 LER further suggests that stem-borer colonisation which occurs at an earlier stage of crop establishment resulting in ‘dead hearts’ and significant reduction on plant population per unit area within the two cereal combinations contribute significantly to the overall reduction in crop turnover within such mixtures.
Key WordsYield losses stem-borers pod-borers maize cowpea sorghum intercropping Kenya economic losses
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