Colorado Potato Beetle
(https://en.wikipedia.org/wiki/File:Colorado_potato_beetle.jpg) Colorado potato beetle (Leptinotarsa decemlineata) is the most important insect defoliator of potatoes. It also causes significant damage to tomato and eggplant. One beetle consumes approximately 40 cm2 of potato leaves at a larval stage, and up to additional 9.65 cm2 of foliage per day as an adult (Ferro et al., 1985). In addition to impressive feeding rates, Colorado potato beetle is also characterized by high fecundity, with one female laying 300-800 eggs (Harcourt, 1971). Furthermore, the beetle has a remarkable ability to develop resistance to virtually every chemical that has ever been used against it.
Since Colorado potato beetle shifted from its original wild hosts in southwestern North America, it has spread throughout the rest of the continent and has invaded Europe and Asia. Currently its distribution covers about 8 million km2 in North America (Hsiao, 1985) and about 6 million km2 in Europe and Asia (Jolivet, 1991). It has appeared recently in western China and Iran. Potentially the Colorado potato beetle can occupy much larger areas in China and Asia Minor, spread to Korea, Japan, Russian Siberia, certain areas of the Indian subcontinent, parts of North Africa, and the temperate Southern Hemisphere (Vlasova, 1978; Worner, 1988; Jolivet, 1991).
The Colorado potato beetle has a complicated and diverse life history. The beetles overwinter in the soil as adults, with the majority aggregating in woody areas adjacent to fields where they have spent the previous summer (Weber and Ferro, 1993). The emergence of post-diapause beetles is more or less synchronized with potatoes. If fields are not rotated, they are colonized by overwintered adults that walk to the field from their overwintering sites or emerge from the soil within the field (Voss and Ferro, 1990). If fields are rotated, the beetles are able to fly up to several kilometers to find a new host habitat (Ferro et al., 1991; 1999). Once they have colonized the field, the overwintered beetles first feed and then oviposit within 5-6 days depending on temperature (Ferro et al., 1985; Ferro et al., 1991).
Eggs are usually laid on the underside of potato leaves. Upon hatching, larvae may move over short distances within potato canopy and start feeding within 24 hours of eclosion. Development from the time of oviposition to adult eclosion for pupae takes between 14-56 days (de Wilde, 1948; Walgenback and Wyman, 1984; Logan et al., 1985; Ferro et al., 1985). The optimal temperatures range between 25-32ºC and appear to differ among populations of different geographic origins. The larvae are capable of behavioral thermoregulation via moving within plant canopies (May, 1981; Lactin and Holliday, 1994), thus optimizing their body temperature compared to the ambient temperature. Pupation takes place in the soil near the plants where the larval development has been completed.
Diapause is facultative, and the beetles can have between one and three overlapping generations per year. It takes a few days for the newly emerged adults to develop their reproductive system and flight muscles (Alyokhin and Ferro, 1999). After development has been completed, the beetles mate and start laying eggs. The reproduction continues until diapause is induced by the short-day photoperiod, then the beetles migrate to overwintering sites (mainly by flying), and enter the soil to diapause. Those beetles that emerge under short-day photoperiod do not develop their reproductive system and flight muscles that season. They feed actively for several weeks and then either walk to the overwintering sites or burrow into the soil directly in the field (Voss, 1989).
Colorado potato beetle's diverse and flexible life history is well-suited to unstable agricultural environments, and makes it a complex and challenging pest to control. Flight migrations closely connected with diapause, feeding and reproduction allow the Colorado potato beetle to employ "bet-hedging" reproductive strategies, distributing its offspring in both space (within and between fields) and time (within and between years). Such strategies minimize the risk of catastrophic losses of offspring, otherwise quite possible in unstable agricultural ecosystems (Solbreck, 1978; Voss and Ferro, 1990).