Pests

Leptinotarsa decemlineata Say - Colorado Potato Beetle.

Systematic position.

Class Insecta, order Coleoptera, family Chrysomelidae, subfamily Chrysomelinae, tribe Doryphorini, genus Leptinotarsa.

Biological group.

Oligophagous pest of solanaceous cultures.

Morphology and biology.

Body of beetle is oval, convex, shiny, 8-12 mm in length. Elytra are light yellow, each one with 5 black longitudinal stripes. Other parts of body are brown-yellow or red-orange with black spots. Eggs are oval, shiny, about 1.5 mm in length; their number in a batch may reach 100, though it is usually 30-40 eggs. The coloration of eggs and pupae varies from yellow to brick-red and does not change over the course of their development. Body of larva is shortened, convex dorsally, up to 15-16 mm in length. Head and legs of larva are black; abdomen is red-brown during I-III instars and pink-orange or yellow at the end of IV instar (before pupation). The length of pupa is 8-12 mm; the weight is 50-170 mg. Beetles and larvae live openly on plants; they feed on leaves, eating them completely. If the leaves are absent, the imagoes eat any plant part, including non-harvested tubers. Females lay eggs on lower leaf surfaces. The fertility of female is usually 400-1000, maximum 5000 eggs. Larvae pupate in soil at a depth of 5-10 cm. Depending on the temperature, eggs develop over 5-17 days, larvae on optimal food plants over 10-30 days, and pre-pupae and pupae both over 8-20 days. Young beetles of a new generation emerge from soil and feed intensively over 6-20 days, forming a fat body. Later, they either diapause and bury themselves in the soil, or they couple and lay eggs of the next generation before diapause. Only imagoes are capable of wintering; they usually hibernate in soil at a depth of 20-50 cm. Longevity of imagoes is 1-4 years due to the diversity of diapause types in this species.

Distribution.

The species.s native land is the Rocky Mountains in the Southwestern USA. Now the pest lives in Northern America (USA, Mexico, and southern Canada), in Europe (everywhere except in Great Britain, Ireland, Iceland, and Scandinavia), in Southwestern Asia (Turkey, Syria, Iraq, Iran), and in ex-USSR countries: in Moldova, Ukraine, Belarus, Lithuania, Latvia, everywhere in Estonia, Georgia, Armenia, everywhere in Azerbaijan except the high-mountain districts, Kazakhstan, Uzbekistan, Tajikistan, and Kyrgyzstan in intensively developed populous districts, everywhere in the Russian Federation in steppe, forest-steppe, and mixed-forest zones, and in some regions of the boreal coniferous forest (taiga) zone of the European part, Ural, and Western Siberia. The pest distribution area in Eurasia is continuously expanding northward and eastward, successively spreading all over the zones of potato production due to the wide limits of adaptive variability of this species and due to climate warming.

Ecology.

L. decemlineata is a polycyclic species with a long-day photoperiodic reaction. The number of generations per year is as follows: in forest and forest-steppe zones of Europe and Asia, there is 1 complete and (often) an incomplete second generation; in steppe and subtropical zones of Europe and of the Caucasus, there are 2-3; in Middle Asia, up to 4 generations. The overwintered beetles emerge from soil at soil temperatures of +13-14°C or as potato shoots appear in fields, i.e., in March-June, depending on the climatic zone. The emergence of overwintered adults and their reproductive activity are often prolonged, reaching 1.5 to 2 months due to non-synchronic soil warming at different depths of the beetles' hibernation area. Females can lay eggs after their diapause without repeated copulation if they have been fertilized before hibernation. Imagoes are active in daylight. The optimum temperature for development of all stages is +20-32°C; the temperature thresholds for development are as follows: for eggs +11.5°C; for larvae and pupae +9-11°C. The developmental degree days (for each stage and in total) is inconstant and depends on average environmental temperature. The frost-resistance threshold for imagoes of different populations varies from -7 to -13°C. The Colorado Potato Beetle feeds on plant species related to the family Solanaceae, such as the genera Solanum (potatoes, eggplant, etc.) and Lycopersicon (tomato). The size of the pest population in a field depends on local climate, on seasonal weather conditions, on the characteristics of the host plant species and varieties, and on the activity of natural enemies, entomophages and pathogens. The specialized entomophages of the Colorado Potato Beetle live in North America only. In Eurasia, some polyphagous predatory insect species are known among beetles (Coleoptera: Carabidae, Coccinellidae), bugs (Heteroptera: Pentatomidae, Miridae, Nabidae), and chrysopids (Neuroptera: Chrysopidae).

Economic significance.

L. decemlineata highly damages potato and eggplant, damaging tomato to a lesser extent. The pest is potentially dangerous for red sweet and hot pepper, strawberry, tobacco, and some other solanaceous cultures. On potato, the pest is especially dangerous during budding and flowering periods; on eggplant, it is harmful during the entire period of plant vegetation. Yield losses of potato tubers are often higher than 30%. In connection with the insect.s rapid adaptation to a wide range of ecological conditions, high pest population density and its harmfulness are now observed every year in all places of beetle distribution and often even in localities near the northeastern frontier of the species distribution area. Preventive and protective measurements are as follows: growing of resistant potato and eggplant varieties; maintenance of crop rotation in conjunction with territorial isolation of potato (eggplant, tomato, etc.) plantations and their growing in the same place not more than 1 out of every 4 years; planting of solanaceous crops near forests, groves, meadows, and pastures that harbor natural enemies of the beetle; defoliation of potato before harvesting and thorough removal of all tubers from field; and preventive planting of trap potato. If the pest population size is higher than economic threshold, treatments on plantations should include the application of bio-preparations and insecticides of different chemical classes in order to prevent development of resistance within pest populations.

Related references:

Amirkhanov, D.V. 1995. Toxicological substantiation of improvement of chemical potato protection from Colorado Potato Beetle in Southern Ural. Doct. Dissert. Abstr. Saint-Petersburg: VIZR, 48 p. (in Russian).
Fasulati, S.R. 2004. Spreading of Colorado Beetle and ecological problems of potato protection in northern regions of Russia. In: 3rd Cyril & Methodius Readings. Proc. Intern. Scient. Confer. - Saint-Petersburg: Saint-Petersburg State Polytechnic Univ., p. 70-75 (in Russian).
Fasulati, S.R., Vilkova, N.A. 2000. Adaptive microevolution of Colorado Beetle and its intraspecific structure in area nowadays. In: Skryabin, K.G. & Novozhilov, K.V., eds. Genetic Engineering and Ecology. Moscow: "Bioengineering" Centre of Russ. Acad. Sci., vol. 1, p. 19-25 (in Russian).
Glyoz, V.M., Cherkashin, V.I. 2002. Colorado Beetle. Zashchita i karantin rastenii 5 (Suppl.), p. 67(3)-90(26) (in Russian).
Kryzhanovskii, O.L., ed. 1974. Insects and mites - pests of agricultural plants, V. 2. Coleoptera. Leningrad: Nauka. 335 p. (in Russian).
Shapiro, I.D. 1985. Immunity of Field Crops to Insects and Mites. Leningrad: Zool. Inst. Acad. Sci. USSR, 321 p. (in Russian).
Ushatinskaya, R.S., ed. 1981. Colorado Potato Beetle. Moscow: Nauka, 377 p. (in Russian).
Vilkova, N.A., Asyakin, B.P., Nefedova, L.I., Fasulati, S.R., Konarev, A.V., Yusupov, T.M. 2004. Research-based parameters of designing pest-resistant agricultural crops. Saint-Petersburg: VIZR, 75 p. (in Russian).
Vilkova, N.A., Fasulati, S.R., Kandybin, N.V., Koval', A.G. 2001. Bioecological factors of Colorado Potato Beetle expansion. Zashchita i karantin rastenii 2: 19-23 (in Russian).
Vilkova, N.A., Sukhoruchenko, G.I., Fasulati, S.R. 2002. Resistant varieties and means of plant protection as inductors of micro-evolutionary processes in phytophagous insects. Inform. Bull. EPRS IOBP 32: 194-204 (in Russian).
Zhuraev, M.Zh. 2000. The biological peculiarities of Colorado Beetle (Leptinotarsa decemlineata Say) development in Uzbekistan conditions and its control. Cand. Dissert. Abstr. Tashkent: Uzbek NIIZR, 24 p. (in Russian).

© Fasulati S.R.