Some organisms, including insects, are referred to as exotic, invasive species, or sometimes as alien species. Put simply, these organisms were introduced, intentionally or accidentally, into an ecosystem outside their own and managed to thrive. Exotic, invasive species can tip the balance in an ecosystem, sometimes with serious environmental and economic consequences.
How Exotic, Invasive Insect Species Are Introduced:
Accidental escapes - Sometimes an entomologist or naturalist makes his mark on history by letting one of his collected specimens escape. Etienne Leopold Trouvelot, a Frenchman living in Massachusetts in the 1800's, unleashed a Lepidopteran beast in his own backyard. An amateur naturalist fascinated with silkworms, he brought some gypsy moth egg masses back from his native country. Some larvae escaped, and by the 1880's the caterpillars were defoliating his neighborhood. Today, over a century later, they feed on forests throughout the eastern U.S. and cost millions of dollars just to contain.
Imported goods - Most exotic insect invaders make their way to foreign regions by stowing away in imported goods or other transported items. In the 1800's, California farmers imported citrus trees from Australia. Along with the trees came another organism from down under - the cottony cushion scale. The scale insects enjoyed decades of prosperity as they infested orchards with no natural enemies in the U.S. Other infamous aliens, like the wood-boring Asian longhorned beetle, hid in wooden shipping pallets to make the overseas journey to America.
Intentional releases - Entomologists made a smart move in the case of the cottony cushion scale, searching for another Australian insect that would prey naturally on the scale. In 1889, Vedalia beetles from Australia were released in the orchards, and the citrus crops were soon free of scale. The Vedalia beetle continues to be a front-line weapon for citrus farmers, with no devastating impact on the ecosystem. Biological controls introduce alien insect species to new ecosystems, but when done correctly do not become invasive pests.
Other intentional introductions yield less success, and may be disastrous. The Asian multicolored lady beetle was first introduced as a biological control in California in 1916; subsequent releases occurred in other U.S. regions for years after. The beetle is a voracious eater of soft-bodied insects like aphids, and went to work immediately. Unfortunately, the alien lady beetle out-competes our native lady beetle species, making their survival more challenging. In addition, the Asian lady beetles have a nasty habit of aggregating in homes and buildings during winter months, something our native species does not do.