May Harbor Its Weakest Link
By Sharon Durham
December 7, 2001
Bacteria named Wolbachia may
be the key to discovering why the coffee berry borer (CBB) is such a
destructive insect pest of the coffee bean, causing an estimated $500 million
in annual losses worldwide. Agricultural Research Service scientist Fernando
Vega in the Insect
Biocontrol Laboratory in Beltsville, Md., is studying the relationship
between the bacteria and CBB.
Adult females enter the coffee berry and deposit their eggs; larvae feed on
the coffee bean, lowering its quality or causing the entire berry to fall off.
A skewed, 10-to-1 sex ratio favoring females ensures high reproduction and
greater berry damage. Adult females emerge from the berry already inseminated,
taking less than one day to enter another berry and start depositing eggs. This
life cycle makes the insect an extremely difficult candidate for integrated
pest management programs.
But why are there so many females? Research suggests that Wolbachia
might play a role in sex determination. This bacterium has been widely reported
to affect insect sex ratios; skewed sex ratio is observed in CBBs throughout
the world. No other bacterium is known to have such an effect on sex ratio.
Researchers collected CBBs from 16 countries: Benin, Brazil, Cameroon,
Colombia, the Dominican Republic, Ecuador, El Salvador, Honduras, India,
Indonesia, Jamaica, Kenya, Mexico, Nicaragua, Uganda and Peru. Genetic analysis
done in collaboration with Pablo Benavides and Jeff Stuart of
Purdue University and Scott ONeill
of the University of Queensland, Australia,
indicates Wolbachia is present in CBBs originating from 11 of the
countries. Wolbachia was not detected in CBBs from five of these
countries, but a genetic variation may make it undetectable using current
Additional studies confirming the elimination of the female-biased sex ratio
in the offspring of CBB females treated with antibiotics would support the
hypothesis that Wolbachia is indeed involved in sex determination.
Understanding the relationship between the CBB and Wolbachia may provide
insight into the basic biology of the insect, perhaps leading to possible
ARS is the chief scientific research agency of the
U.S. Department of Agriculture.