| dc.description.abstract | The Mount Elgon coffee farmlands exist in mosaical patterns with banana, annual crops, and semi natural vegetation with a hierarchy of bio-physical characteristics conferred by altitudinal positioning and cropping intensity. Insect pests are one of the key challenges in coffee production, further exacerbated by the rising temperatures that are known to favor the coffee berry borer (Hypothenemus hampei), a key pest. It is not yet clear to what extent such abiotic factors, which drive insect pests’ dynamics are influenced by the existent farming systems, altitudinal positioning, and dynamics of associated natural biological control agents.
The objectives of this study were to: i) To determine the effect of altitude and farming system, on the occurrence of the parasitoid complex of the coffee berry borer in the mount Elgon Region (MER), ii) To determine the effect of farming system and altitude on occurrence and distribution of the predatory Carabidae, and the association to the coffee aphids (Toxoptera aurantii) in the MER, and iii) To determine the most suitable farming system for high coffee foliage and coffee bean yield performance at the different altitudes in the MER.
The study was set up in Kapchorwa and Sironko, districts of the MER. The selected coffee fields in the study were delineated by two factors: altitude at three levels: lower (1400-1499 m.a.s.l); mid (1500-1679); and high (1680-2100); and coffee farming system at four levels: Coffee monocrop; Coffee+annual crop; Coffee+banana; and Coffee+banana+shade trees with three replications of each farming system. A total of 72 coffee fields were sampled in the longitudinal study for two years.
With regard to the key natural enemies (parasitoids) of the coffee berry borer, results revealed highly significant interactions between altitude and farming system in influencing H. hampei field infestation (Fdf 6; 2146 =20.39; P<0.001) and the abundance of the four parasitoids recorded namely: Phymastichus coffea (Fdf 6; 130 =11.48; P<0.001); Cephalonomia stephanoderis (Fdf 6; 130 =0.96; P<0.001); Prorops nasuta (Fdf 6; 130 =5.67; P<0.001) and Heterospilus coffeicola (Fdf 6; 130 =3.6; P=0.002). Highest level of P. nasuta emergence from the reared berries was at high altitude within the Coffee + banana system (78±7.1); C. stephanoderis emergence (73±3.5) was highest in the mid altitudes within Coffee + banana+shade tree system; P. coffea (58.3±3) in the mid altitudes within the Coffee+banana farming system; and H. coffeicola (13.0±0.9) in the high altitudes within the Coffee+annual crop.
Microclimate and semi natural vegetations had specific and significant relationships with the abundance of parasitoids. Of the four parasitoids, C. stephanoderis had a positive relationship to semi-natural vegetation species counts (t=2.778, SE= 0.093, P=0.006); P. coffea had a negative relationship with temperature (t= -4.209, SE=0. 015, P<0.000); P. nasuta had a negative relationship with temperature (t= -2.620, SE=0.013, P=0.010); H. coffeicola had a positive relationship to light intensity (t= 2.389, SE=0.000, P=0.018) and a negative relationship to temperature (t= -2.707, SE=0.011, P=0.008). These relationships contrasted that of H. hampei, which was positively related to temperature (t=5.503, SE=0 .057, P<0.000); negatively related to light intensity (t= -1.984, SE=0.001, P=0.049) but with no significant relationship to vegetative species counts. P. coffea caused the highest parasitism rates for the coffee berry borer in the Coffee + banana farming system (54%); C. stephanoderis (52%) achieved highest parasitism at mid altitude in the Coffee + banana system+ shade trees systems.
The predatory Carabidae beetles revealed highly significant interactive effects of altitude and farming systems on the occurrence of three genera: Anisodactylus, Chlaenius, and Harpalus. The abundance of Harpalus spp. were highest at lower altitudes in Coffee monocropped farming systems (165±4); Anisodactylus spp. were more abundant at higher altitudes in Coffee+annual crop systems (144±2); while Chlaenius spp. were highest in the Coffee+banana+shade tree system at mid altitudes (22±0.5). Anisodactylus spp. had a significant positive relationship to soil moisture (t= 2.58**, SE= 1.5); Harpalus spp. had a significant positive relationship to soil EC (t= 5.30***, SE= 1.27) while Chlaenius spp. had a significant negative relationship to soil pH (t= -2.19*, SE= 0.133). It was only Chlaenius spp. which had a significant positive relationship with the semi natural vegetation (t=2.37*, SE= 0.176). In the predator-pest relationship with the coffee aphid Toxoptera aurantii, a biplot showed that the aphid correlated highly and negatively to all the three Carabidae (Anisodactylus spp. Chlaenius spp. and Harpalus spp.).
For the effect of farming system on coffee foliage and coffee bean yield performance, the highest number of coffee leaves/branch were on farms with Coffee+annual cropping. Coffee bean yields were highest in the Coffee+banana+shade trees, specifically at low altitude. PCA results revealed a strong relationship of temperature, and relative humidity with the clean coffee bean yield and leaves per branch.
This study recommends that: i) to reduce infestation of the coffee berry borer and promote the occurrence of the Hymenopteran parasitoids that regulate the pest, growers should embrace the Coffee+banana+shade trees system farming systems that buffer rising temperatures. This is especially relevant for farmers in the range of 1400-1499 m.a.s.l; ii) to promote the generalist predatory Carabidae beetles especially Anisodactylus, Harpalus and Chlaenius species, which regulate the coffee aphid and other hemipteran pests on coffee, growers should adopt practices that enhance soil moisture retention through maintaining good ground cover and/or inclusion of shade trees+banana in their fields; and iii) Growers are urged to embrace innovative ways of introducing semi natural vegetation in their coffee fields/proximity to promote biological control agents like the Carabidae beetles and the parasitic wasps so as to increase the unit productivity/yields of coffee farms. Semi natural vegetation can be incorporated in form of diverse hedges, borders, road reserves, and if possible, by letting adjacent plots to fallow in some periods. | en_US |
