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 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 (Far 6; 2146 =20.39; P<0.001) and the abundance of the four parasitoids recorded
namely: Phymastichus coffea (Far6; 130 = 1 1.48; P<0.001); Cephalonomia stephanoderis (Far6; bo
=0.96; P<0.001); Prorops nasuta (Fare; 130 =5.67; P<0.00l) and Heterospilus coffeicola (Far6; 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 Coffce+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 (1=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 (l= -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
diverse hedges, borders, road reserves, and if possible, by letting adjacent plots to fallow in some
periods.