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D. Babendreier
strated that parasitism of non-target species under field conditions is zero or
restricted to a few meters from the release field (Orr et al. 2000; Babendreier
et al. 2003a, 2003b). All these studies concluded that non-target effects of the
biological control agent have been negligible, which is remarkable in light of
the fact that such effects were presumed in these cases.Although still no comprehensive
answer is possible on whether we have missed many non-target
effects, evidence is increasing from the abovementioned studies and others
that at least the more serious effects would have been detected.
23.4 Harmonia axyridis, a Case Study
Already in the section above it was mentioned that especially the polyphagous
predators have the potential to cause serious non-target effects if introduced
into foreign countries. The multicoloured Asian ladybeetle, Harmonia axyridis,
is native to large parts of Asia and definitely is a polyphagous predator.
It is a voracious feeder, preying mostly on aphids but also on immature stages
of various other insects – psyllids, butterflies and aphid predators, including
other ladybeetles. Moreover, cannibalism is often observed in adults and larvae
of H. axyridis, which consume conspecific eggs and sometimes smaller
larvae. Due to its effects on native coccinellids in the US and its recent invasion
in Europe, H. axyridis has attracted quite some attention. Many studies
have already been conducted and, thus, H. axyridis may serve as a case study
to be examined in greater detail.
Since H. axyridis feeds voraciously on aphids and has strong dispersal
capacities, it was released as a classical biological control agent in the United
States already in 1916. However, these early introductions failed and periodic
releases continued until the 1980s. First established populations were documented
only in 1988 and, subsequently, the beetle spread rapidly across North
America. Currently, H. axyridis occurs throughout much of the continental
United States and also in southern Canada. The ability of H. axyridis to feed
on many non-target herbivores, intraguild prey and conspecifics may contribute
to its success to invade new ecosystems but also to control aphid numbers.
After the introduction in North America, it provided control of pests in
several systems. For instance, H. axyridis provides effective biological control
of Aphis spiraecola in apple orchards (Brown 2004), and the biological control
of several citrus pests may also be benefiting from the establishment of H.
axyridis (Michaud 2002a). Harmonia axyridis has also been utilized successfully
in augmentative biological control in Asia, Europe and North America. In
Europe, releases were first undertaken in 1982, i.e. before the negative impact
had emerged, but continued until only a few years ago.
However, the same attributes responsible for the effectiveness of H.
axyridis against aphids may also cause less desirable effects. A number of