Insects Colonizing Eucalypts in California

Abstract

The Mediterranean climate zone in North America is restricted to the states of California in the USA and parts of Baha California Norte in Mexico. As described in other chapters in this volume, the climate is characterized by cool wet winters and hot dry summer conditions. The greatest amount of precipitation falls in the late fall and winter months. The remainder of the year is dry. Eucalypts were introduced from Australia as seed in the mid nineteenth century and have been widely planted in California. Although there have been a few rare reports of occasional host use, no native insect species have undergone a host shift onto the trees. Until the mid 1980s there were only two exotic insects that feed on eucalypts introduced from Australia to California. In a 20 year period beginning in 1984, 16 exotic insects from four feeding guilds established in the state. Three of these insects are under complete biological control [the blue gum psyllid (Ctenerytinae eucalypti (Maskell)), the eucalyptys longhorned borer (Phoracantha semipunctata F), and the eucalyptus snout weevil (Gonipterus scutellatus Gyll.)] are under complete biological control. Several more [the red gum lerp psyllid (Glycaspsis brimblecombei Moore), the lemon gum psyllid (Cryptoneossa triangular Taylor), the spotted gum psyllid (Eucalytolyma maideni Froggatt), and, possibly, a second longhorned borer (Phoracantha recurva Newman)] are under partial biological control. The introductions have continued since 2004, but at a much slower pace than the previous 20 years. Although there have been differences in the patterns of introductions of insects that feed on eucalypts in different Mediterranean climates zones, the community of insects is becoming homogenized as movement of people and goods continues to spread the insects into new areas. The management approaches developed in one part of the Mediterranean world will find broader applications in other parts of that world as the movement of invasive arthropods continues.