Andrei Alyokhin1, Maxim Udalov2 and Galina Benkovskaya2

1School of Biology and Ecology, University of Maine, Orono, ME, USA

2Institute of Biochemistry and Genetics, Russian Academy of Science, Ufa, Russian Federation

Introduction

The Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae), is one of the most notorious insect pests of potatoes. Since becoming a problem in the mid-19th century, this insect has received enormous attention from the scientific community. A comprehensive Colorado potato beetle bibliography (Dill and Storch 1992) contains 3537 references. A more recent on-line bibliography limited to peer-reviewed journal articles written in English (Alyokhin 2011) has over 700 entries. Despite this, the beetle remains a formidable threat to the potato industry in already-colonized potato-growing areas, and it continues to expand its geographic range into new regions of the world. A diverse and flexible life history, combined with a remarkable adaptability to a variety of stressors, makes the Colorado potato beetle a very challenging pest to control.

Taxonomic Position and Morphological Description

The Colorado potato beetle belongs to the family Chrysomelidae, or leaf beetles. With 35,000 species described worldwide, it is the third largest family in the order Coleoptera. Members of this family feed on plants, both as larvae and as adults, with both life stages consuming the same or related plant species. Many species are host-specific (Arnett 2000).

The Colorado potato beetle was first described by Thomas Say in 1824 as a member of the genus Chrysomela (Say 1824). Based on morphological characteristics, it was then moved to the genus Doryphora (Suffrian 1858). Finally, Stål (1865) included this species in a newly described genus, Leptinotarsa, where it remains at the present moment. Jacques (1988) listed a total of 41 species in this genus, of which 9 occur in the United States, 9 in Central and South America, and 27 in Mexico. However, Bechyne (1952) argued that L. porosa Baly and L. paraguensis Jacoby belong to the genus Cryptostetha.

Leptinotarsa is considered to be an evolutionarily recent genus that is still in the process of active speciation, with Southern Mexico most likely being its center of origin (Tower 1906, Medvedev 1981). Host plants are known for 20 Leptinotarsa species (Hsiao and Hsiao 1983). All of them are specialized feeders, with 10 species (including the Colorado potato beetle) feeding on plants in the family Solanaceae, 9 in the family Compositae, and 1 in the family Zygophyllaceae.

The Colorado potato beetle is the most notorious member of Leptinotarsa. The adult beetles are oval in shape and are approximately 10 mm long by 7 mm wide. They are pale yellow in color, with five black stripes along the entire length of each elytron and black spots on the head and pronotum. The eggs are about 1.5 mm long, and their color changes from yellow right after oviposition to orange for mature eggs that are ready to hatch. The larvae are eruciform, red to orange in color, with black head and legs and two rows of black dots on each side. Four instars are completed before pupation.

Based on morphological characteristics, in particular on spot patterns and coloration of the head, pronotum, and elytra, Tower (1906) originally subdivided what is currently known as L. decemlineata into four species and nine varieties. However, later experiments showed that all of those were fully capable of interbreeding (Tower 1918, Hsiao 1985). Furthermore, analysis of male genitalia did not reveal any noticeable differences. As a result, Jacques (1972) merged them into a single species – an approach currently followed by most scientists. However, Jacobson and Hsiao (1983) found distinct differences in isozyme frequencies in the Colorado potato beetle population from southern Mexico and populations from the United States, Canada, and Europe. The difference was large enough to regard the two as separate subspecies. Morphological analyses of spot patterns on the adult pronotae (Fasulati 1985, 1993, 2002, 2007) (Fig. 2.1) also supported the existence of several (American, European-Siberian, and Central Asian) subspecies of the Colorado potato beetle. Interestingly, there were considerable changes in spot patterns within the same populations over several decades (Zeleev 2002, Benkovskaya et al. 2004, Kalinina and Nikolaeva 2007). These may indicate active microevolutionary processes within the species. Alternatively, they could be attributed to genetic bottlenecks due to insecticide applications (see Chapter 19 for more details).

Origins and History of Spread

The Colorado potato beetle is native to the central highlands of Mexico. Wild populations feed mostly on buffalobur, Solanum rostratum, which is considered to be its original ancestral host (Tower 1906, Hsiao 1981, Casagrande 1987). Both buffalobur and the beetles might have been brought into the southern and central plains of the United States by early Spanish settlers moving northwards (Gauthier et al. 1981, Casagrande 1987, Hare 1990). The Colorado potato beetle was first collected in the United States in 1811 by Thomas Nuttall. Subsequently, additional collections were made in 1819–1820 near the Iowa-Nebraska border by Thomas Say, who later described it for science (Casagrande 1985, Jacques 1988).

The first major Colorado potato beetle outbreak in cultivated potatoes was reported in 1859, when severe damage was observed on fields about 100 miles west of Omaha, Nebraska (Jacques 1988). Feeding on potatoes represented a host range expansion for this species, which is described in detail in Chapter 19. Following the initial outbreak, eastward expansion of the beetles’ geographic range was very rapid, with beetles reaching the Atlantic coast of the US and Canada in 15 years (Casagrande 1987). The beetles crossed the Mississippi river in 1865, reached Ohio in 1869, and arrived at Maine in 1872 (Jacques 1988). They then proceeded to the southern provinces of Canada, which were colonized by 1901 (Ivanschik and Izhevsky 1981).

Westward expansion was somewhat slower, limited in part by scarcity of potatoes (Riley 1877). The first serious damage to potatoes in Colorado was reported in 1874 (Riley 1875). However, 10 years earlier, Walsh (1865) saw a considerable beetle population feeding on S. rostratum in Colorado. That observation eventually resulted in the name of that state being incorporated into the generally accepted common name of this species (Jacques 1988). All in all, the beetle’s range between 1860 and 1880 expanded by more than 4 million square kilometers (Trouvelot 1936). Colonization of North America was completed in 1919, when the beetles were found in British Columbia (Ivanschik and Izhevsky 1981).

The first European population of Colorado potato beetles was discovered in England in 1875; the beetle then invaded continental Europe via Germany in 1877. Another infestation was discovered 1 year later in Poland. All those populations were successfully eradicated soon after being discovered (Feytaud 1950, Wegorek 1955, Jacques 1988). Quarantine measures and eradication campaigns were largely successful in keeping the pest out of Europe until 1922, when self-propagating populations were finally established in France (Feytaud 1950). After that, the beetle steadily spread throughout Western and Central Europe, reaching the border of Poland by the mid-1940s (Ivanschik and Izhevsky 1981). Beetle dispersal was greatly facilitated by relaxed quarantine regulations and large-scale movements of military cargo during World War II. In 1949, Colorado potato beetles crossed the border of the Soviet Union but were quickly eradicated. Strict quarantine, combined with field monitoring and eradication programs, kept beetles away for the following 9 years. However, in 1958, warm spring temperatures and strong western winds resulted in massive invasions from the Carpathian Mountains to the Baltic Sea. This led to the establishment of reproducing populations, which have continued their eastward spread ever since (Ivanschik and Izhevsky 1981).

Presently, the Colorado potato beetle damages potato crops all over Europe, Asia Minor, Iran, Central Asia, and western China (Jolivet 1991, Weber 2003). Its current range covers about 16 million square kilometers in North America, Europe, and Asia, and continues to expand (Weber 2003). Potentially, the beetle could spread to temperate areas of East Asia, the Indian subcontinent, South America, Africa, New Zealand, and Australia (Vlasova 1978, Worner 1988, Jolivet 1991, Weber 2003).

Although the Colorado potato beetle is a highly mobile species that is capable of flying over long distances, especially with prevailing winds (Boiteau et al. 2003), its rapid dispersal had been greatly facilitated by human movement. Potato is a common and ubiquitous crop, which is often moved over considerable distances after harvest....