View - ResearchGate

406
D. Babendreier
pods, agents released for weed control indeed generally have a better safety
record,although in some cases non-target effects have materialized.One of the
hotly debated cases is the flower head weevil Rhinocyllus conicus which was
introduced to North America already in 1969, and later also into other countries
for control of weedy thistles. This decision was taken at that time by the
national authorities despite host range tests indicating that some non-target
thistles may be attacked as well to some degree. In fact, feeding on the seeds of
some non-target Cirsium spp.did occur shortly after introduction,and there is
evidence from field experiments that populations of these thistles are decreasing
due to lower seed production (Louda 2000; Louda et al. 2003). In addition,
Louda (2000) showed that populations of a native floral-feeding tephritid
decreased simultaneously, indicating that also indirect effects are associated
with the introduced beetle. This case reflects the former lack of concern over
non-target effects on non-economic species.More generally,it reflects a different
perception of risks and benefits of the authorities at that time, as the predicted
feeding on several non-economic plants was disregarded in light of the
high pest pressure and the probability of solving this problem.
Another interesting case is the Argentine pyralid moth Cactoblastis cactorum.
In 1926, this moth was introduced against Opuntia spp. in Australia
where it is clearly one of the major success stories. In 1957, it was introduced
into the Caribbean islands and also reduced populations of the target species.
It was considered for introduction into the US but this was not permitted
because feeding on native Opuntia spp. was suspected. However, C. cactorum
did accidentally arrive in Florida by the end of the 1960s, and the moth was
indeed found to feed on non-target Opuntia spp. Included in its diet were several
endangered species, which led to increasing efforts to prevent these from
going extinct. The most important conclusion here is that even a successful
biological control agent with a narrow host range can cause serious non-target
effects in specific geographical areas. The case further suggests to include
adjacent regions within potential dispersal distance in pre-release risk assessments
(Louda and Stiling 2004).
23.3.2 Arthropod Biological Control
In contrast to weed biological control, the potential risks for non-target
organisms have only recently received attention and, consequently, most of
the relevant studies have been published only within the last 10–15 years
(Babendreier et al. 2005). In an attempt to quantify the number of cases where
non-target effects have occurred and also the relevance of these effects, Lynch
et al. (2001) screened the BIOCAT database. Of the 5,279 classical introductions
of insects listed in BIOCAT, 80 were associated with one or more such
non-target effect records. However, this includes all kinds of smaller effects
such as low parasitism of a non-target species at a single location – indeed,