The Antestia Bug Complex in Africa and Asia 477
dropped from March to May. Recent studies in Burundi reported lower densities, although using the
same assessment technique (Leblanc 1993, Bouyjou et al. 1999).
10.3.5.2 Spatial Distribution in Plantations
Some studies have addressed the spatial distribution of Antestia bug populations in coffee plantations
in order to recommend reliable sampling procedures for accurate infestation estimations. For instance
in Burundi, Cilas et al. (1998) showed that Antestiopsis thunbergii ghesquierei populations were aggre-
gated in coffee plantations, meaning that some coffee trees sheltered several insects whereas others
were totally free from insects. Moreover, the study showed that A. thunbergii adults usually were more
aggregated than nymphs and the authors suggested that this may have been due to reproductive behavior
and may have involved communication with semiochemicals. The study also showed that population
distributions were not structured spatially; in other words, infested coffee trees were not grouped but
randomly distributed in the plantation. The above authors suggested that, while laying eggs, females
could move through the plantation and detect more attractive coffee trees, ultimately more favorable for
their offspring.
However, a recent study conducted in a plantation in Rwanda found that the population of Antestiopsis
thunbergii ghesquierei was distributed mainly on the coffee plants in the border of the plantation (85.5%),
whereas a small percentage of the population (14.5%) was on coffee plants in the middle of the field.
Moreover, the study showed that 63% of the population was on coffee trees with berries, whereas only
37% was on trees without berries (N. D. T. M. Rukazambuga, unpublished data).
10.3.5.3 Factors Involved in Population Dynamics
Most authors agree that, in the absence of control practices, Arabica coffee plantations offer conditions
for the survival of Antestia bug populations throughout the year (Le Pelley 1968). However, as shown
above, populations varied significantly in time and space in coffee plantations, and this may be linked to
different agroecological factors affecting pest behaviour and development. Although the feeding habits
of the bugs (see Section 10.3.2, Feeding Habits) suggest that wild Rubiaceae present in close association
with plantations may encourage infestation, coffee tree phenology also is an important factor because
these bugs show a preference for some parts of the tree over others, particularly green berries and shoots.
Thus, Foucart and Brion (1959) suggested that the low number of berries on coffee trees as well as the
dry weather were factors affecting the annual population decrease in Rwanda and Burundi. Microclimate
May051015Bug p^20er tree
253035404550JunJul AugSeptOct Nov DecJan Feb Mar AprMayFIGURE 10.4 Seasonal variation of Antestiopsis thunbergii ghesquierei populations in Rwanda-Burundi from May 1954
to May 1955 (from Foucart and Brion 1959). Densities were obtained using the “pyrethrum test,” a knock-down technique
using pyrethrum insecticide.