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Pros and Cons of Biological Control 409
recent studies indicated that the establishment of exotic ladybeetles may
have adverse affects on native coccinellids. In South Dakota, the abundance
of Coccinella transversoguttata richardsoni and Adalia bipunctata was
approximately 20 times lower after the establishment of an exotic coccinellid,
C. septempunctata (Elliott et al. 1996). Evidence is building to indicate
that H. axyridis may be having similar adverse effects on native Coccinellidae.
Over a 13-year period, Brown and Miller (1998) monitored the
abundance of various coccinellid species in apple orchards. The abundance
of native coccinellids decreased after the establishment and rapid rise to
dominance of the exotics, C. septempunctata and H. axyridis (Brown and
Miller 1998). A 9-year study of the abundance of various Coccinellidae in an
agricultural landscape showed a decrease in the abundance of Brachiacantha
ursina, Cycloneda munda and Chilocorus stigma after the establishment
of H. axyridis (Colunga-Garcia and Gage 1998). Similarly, a field study conducted
in the major citrus-producing regions of Florida over 5 years showed
that the introduced H. axyridis has increased in abundance while the formerly
dominant ladybeetle Cycloneda sanguinea has declined (Michaud
2002b). The author concluded that competitive displacement of C. sanguinea
by H. axyridis may be in progress in this citrus ecosystem in Florida.
Recently, a study conducted on the coccinellid community inhabiting potato
crops in northern Maine over 31 years showed dramatic changes. Prior to
the arrival of the exotic species, ladybeetle communities were comprised
almost exclusively of the two native ladybeetles, Coccinella transversoguttata
and Hippodamia tredecimpunctata. Starting 1980, the exotic C. septempunctata
became permanently established and quickly began to dominate the
ladybeetle community (Alyokhin and Sewell 2004). Two other exotic species,
H. axyridis and Propylea quatuordecimpunctata, became prominent members
of the ladybeetle community in 1995 and 1996. Altogether, these studies
conducted in the US demonstrate the profound effects that the exotic natural
enemy H. axyridis may have on the abundance of native coccinellid
species.
To date, research has concentrated on the effect of common natural enemies
of agricultural crops because of fears regarding the loss of biocontrol
function. As a consequence, there is a paucity of studies on the potential
adverse effects of H. axyridis on coccinellids in non-agricultural settings or
generally on less common coccinellids. In addition, few studies have been
conducted on other non-target insects. In one of those few studies, Koch et al.
(2003) recently identified H. axyridis as a potential hazard to immature
Monarch butterflies, Danaus plexippus. In laboratory and field-cage studies,
eggs and larvae of D. plexippus incurred significant predation by H. axyridis
adults and larvae.A follow-up study showed that this effect is mediated by the
presence of aphids, the preferred prey of H. axyridis. However, although predation
on the monarch decreased in the presence of aphids, some monarch
larvae were nevertheless consumed (Koch et al. 2005).