480 Invasive Stink Bugs and Related Species (Pentatomoidea)
10.5.3 Coffee Potato Taste Defect and Possible Causing Mechanisms
Potato taste defect (PTD), also known as “peasy off-flavour,” is a flavor defect characterized as a potato-
like taste in coffee, which diminishes coffee quality and, thus, makes coffee undesirable (Jackels et al.
2014). Current research is designed to elucidate the role of Antestia bugs in PTD transmission with the
hypotheses that PTD is caused by Antestia-derived chemicals originating from the bugs feeding on ber-
ries or from Antestia-vectored pathogens or Antestia-borne microorganisms such as symbiotic bacteria
(Matsuura et al. 2014).
Bouyjou et al. (1993, 1999) reported that PTD flavor was produced by an Enterobacteriaceae bacte-
rium, and they hypothesized the linkage of Antestia bugs, bacteria, and PTD. The bacterium recently
was identified as Pantoea coffeiphila (Gueule et al. 2015). The compounds responsible for PTD first
were identified as 3-isopropyl-2-methoxypyrazine (= 2-isopropyl-3-methoxypyrazine, IPMP) and
2-isobutyl-3-methoxypyrazine (IBMP) (Becker et al. 1988). The recent study of Jackels et al. (2014)
revealed that IPMP is produced inside the beans but not deposited on the bean surface by a bacte-
rial growth because they found IPMP only in interior volatiles of PTD coffee, not in surface vola-
tiles. Also, in the PTD coffee surface volatile, as well as on desiccated Antestiopsis thunbergii, they
found three major alkanes including tridecane, using Gas Chromatography–Mass Spectrometry. Their
results supported the hypothesis of Bouyjou et al. (1993). In addition, links between bacterial symbi-
onts of Antestia bugs in the development of potato taste defect in coffee may be worth investigating
(Matsuura et al. 2014).
10.6 Management and Control
10.6.1 Economic Impact
Antestia bugs are major pests of Arabica coffee in Africa everywhere it is grown on the continent.
They cause significant losses both in yield and quality of coffee. Globally, production loss due to all
the pests of the group is estimated between 20 and 35%, but in East Africa crop losses up to 45%
are reported. In Ethiopia, a strong correlation between berry drop and the presence of Antestiopsis
intricata in coffee plantations was noted and the crop loss due to berry drop was assessed at 9%
(Tadesse et al. 1993). Studies in the same country also showed that Antestia bugs caused ≈48% dark-
ened coffee beans (Abebe 1988; IAR 1996a, b). A study by Chichaybelu (2008) using artificial infesta-
tion with Antestia bugs showed that four pairs of the pest on a branch caused 54% berry drop and 90%
damaged berries.
In Ethiopia, Antestia bugs, in general, are a more serious problem in large plantations compared
to coffee home gardens and coffee forest production systems. In Kenya, a study showed that 2 to 4
Antestia bugs per tree caused a crop loss between 15 and 27% in total bean weight (Wanjala 1980),
whereas in Uganda, 20, 36, and 51% yield losses were attributed to densities of 0.5, 1, and 2 bugs per
coffee bush, respectively (McNutt 1979). In Rwanda, density of 5 bugs per tree was shown to cause
≈20% damaged berries, and ≈7% total crop loss. The same study showed that with high density at 30
bugs per tree, crop loss was more than 30% (Foucart and Brion 1959). Following a large sampling
effort in washing stations of various coffee growing areas in Rwanda in the 1960s and 1970s, Leblanc
(1993) reported rates of damaged berries between 2 and 40% and total crop losses between 1 and
32%.
The Great Lakes region in Africa also is strongly affected by PTD, with a presence centered in the
western Rift Valley areas of Rwanda, Burundi, Eastern DRC, and Western Uganda. In Rwanda, for
instance, the presence of PTD with other quality defects disqualifies up to 80% of the high quality green
coffee that initially was qualified to be specialty coffee grade as opposed to standard grade. This effect
has great negative impacts on revenue from coffee as the standard grade has a much lower price than
specialty coffee (N. D. T. M. Rukazambuga, unpublished data).