Invasion

Abstract

Analysis To determine the origin and biological characteristics of vegetable pests, I reviewed the original scientific literature of over 330 pests known to feed on vegetable crops (Capinera 2001 and references therein), and compiled data on pest origin, period of introduction, host range, portion of plant damaged, and damage frequency. In most cases the literature contains reference to the likely source of these pests (126 of 135 invaders). However, for some cosmopolitan pests or poorly studied organisms the source is unknown or uncertain. Similarly, the period of detection in the United States and Canada varies from precise to unknown, with knowledge of the period of establishment (detection) limited to 87 of the 135 invading pests. Lack of data stems mostly from the early period of settlement, but invasions since 1900 are fairly well documented. The host range of the vegetable pests is quite well documented in the literature, although there is a tendency for species that are better studied to have longer lists of hosts. Also, during periods of great abundance (outbreak), pests often use hosts that they will not normally accept. Thus, outbreak species probably have inflated host ranges. For the purposes of this analysis, I have defined a narrow host range to consist of consumption of vegetable plants from a single botanical family. A moderate host range consists of consumption of vegetable plants from two to five families, and a wide host range is defined as consumption of greater than five families of vegetable crops. Damage frequency is based on the literature for each pest, as described elsewhere (Capinera 2001), and considers damage to both home gardens and commercial vegetable production. Damage frequency is designated as rare when there are few reports of serious injury in the literature. Damage frequency is considered periodic when there is general recognition that the organism is capable of The successful e s t a b l i s h m e n t in North America of invading pests is not a new phenomenon. Since the earliest arrival of European explorers and colonists, pests of plants have accompanied movement of people, food, and plant materials to the “ N e w World.” The long sea voyage during the initial stages of colonization likely inhibited extensive transport of many short-lived pests. Up until 1800, only about 36 species of insects invaded the United States (Simberloff 1986). However, by the late 1800s not only was the speed of transport greatly increased, but transport of living plant material (and associated pests) was commonplace. Sailer (1978, 1983) analyzed the invasion of the United States by arthropods. He reported that initially the invaders (immigrants) consisted mostly of Coleoptera, which arrived principally in ship ballast. The dominance by beetles decreased as more Lepidoptera and then Homoptera invaded, often in association with living plant material. The rate of invasion increased greatly after the 1860s as international commerce expanded. Sailer also noted that there was a slight reduction in the rate of invasion commencing in the 1920s as the Plant Quarantine Act of 1912 was implemented. Invasion by high-profile and damaging species in recent years has increased the awareness and concern by the scientific community, government, and the general public over invading species (U.S. Congress 1993, Simberloff et al. 1997, Sakai et al. 2001). The pattern of invasion is poorly documented, despite heightened concern, and many questions remain. Has the increase in international commerce and tourism in recent years resulted in higher rates of invasion and establishment of pests? Are we at greater risk from certain types of pests, or from certain sources? Are certain taxa of pests more likely to invade and establish successfully, and are all crops equally at risk? Here I address these questions and present a comparative analysis of indigenous (naIncreased concern over invasion by high-profile and damaging insects requires the answers to questions about the origin of pests, period of invasion, taxa, feeding behavior, damage frequency, and the influence of crop characteristics on pest species richness.