Ecological and Geographic Range Expansion of the Introduced Predator Anthocoris nemoralis (Heteroptera: Anthocoridae) in North America: Potential for Nontarget Effects?

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Anthocoris nemoralis (F.) (Heteroptera: Anthocoridae) is native to the western Palearctic region and is among the most widespread geographically of all Anthocoris species in Europe. The predator originally established in North America as a consequence of at least one unintentional introduction occurring sometime before 1960 and an intentional introduction made in the early 1960s to control a non-native psyllid pest in pear orchards. Recent collecting efforts suggest that A . nemoralis has expanded its geographic range and host plant range. It is now found in western North America from southern California north into British Columbia. An eastern population located on the Niagara peninsula was reported in the late 1950s and was collected from that location at least until the late 1970s. Old and New World populations of A . nemoralis appear to prefer plant species that host psyllid prey. In North America, A . nemoralis has been recorded from 13 plant genera, of which 11 host psyllids. This percentage is much higher than the percentage of tree and shrub genera that host psyllids, suggesting that A . nemoralis in North America has preferentially colonized plants that host psyllids, including plants that do not occur naturally in the native Old World range of A . nemoralis . Several of the plant genera are hosts to newly arrived psyllids from South America and Australia. Concerns have been expressed that the introduced predator in North America may adversely affect native anthocorids, particularly species that occur in pear orchards: A. antevolens White, A . tomentosus Péricart, and A . musculus (Say). Overlap in plant genera used by four native anthocorids and the introduced A . nemoralis was highest between A . nemoralis and two mostly western species, A . antevolens and A . tomentosus . Detailed surveys of native tree and shrub species in North America that host psyllids should be done to determine actual extent of range expansion (geographical and ecological) by A . nemoralis , and to provide more information about competition between native anthocorids and A . nemoralis .