Walnut husk fly, Rhagoletis completa (Diptera: Tephritidae), invades Europe: invasion potential and control strategies

Rhagoletis completa Cresson (Diptera: Tephritidae)
is native to North America and invaded Western
Europe in the late 1980s, causing important damage to its
principal host, walnut (Juglans spp.). In this review, we
summarize the important elements of R. completa’s biology,
phytosanitary status and methods used in Europe for
its control, and then present the main conclusions associated
with a completed risk analysis performed in 2014 to
evaluate the dispersion and establishment potential of R.
completa in Europe. The walnut husk fly was initially identified
in Switzerland (1988) and Italy (1991), from where
it spread to at least seven additional countries: France,
Spain, Germany, Austria, Croatia, Slovenia and Hungary.
R. completa has not reached the limits of its potential distribution.
The main dissemination pathways within Europe
include: (1) natural adult dissemination; (2) adult hitchhiker
behaviour; and, to a lesser extent, (3) transportation
of larvae in fresh fruits. R. completa host plants are widely distributed in Europe, either as isolated wild trees or in
orchards, favouring the probability of fly establishment in
currently fly-free areas. In addition, the European territories
where Juglans species are present share biogeographic
similarities. In orchards where R. completa is present and
uncontrolled, 100% of walnut trees can be infested, causing
losses in walnut yields of up to 80%. The negative
effect is low (<10% yield loss) under phytosanitary control,
although additional costs must also be considered to support
specific monitoring for R. completa. The information
presented here underlines a strong need for better walnut
husk fly monitoring across European countries, as well as
for increasing efforts to develop biological methods to control
this emerging pest.